Add Highway mode to LT1

[space387]

Over the past few days I have been looking through the features and decoded options for my LT1 Firebird and L98 Corvette. While sifting through the L98 tune (7277 ecu) I found it has a highway mode. Set it and sure enough the car runs leaner as advertised. Now I looked for a way to replicate it in my LT1 ecu but its nowhere is sight and if you leave closed loop enabled, its locked to the stoich afr constant. Has anyone seen a way to run a table for closed loop afr similar to the older highway mode? I'm not sure if this is how it works but would it be possible to take the 4 points of the stoich afr table and make them seek out a value from another table? You could set the table to reference map vs rpm like a VE table.

[steveo]

i started writing a highway lean cruise type thing a long time ago. i found space for the code and figured some thresholds and constants based on some other similar patch. it never got into testing as i ended up running open loop on that car.

i might have the patch around somewhere but i bet its nowhere near working as my assembly code isn’t awesome

[NomakeWan]

I have not tried this, but I have given this some thought before. You could tune the car in open loop to run 14.7 in every cell, then find the cell that gets hit at your intended highway cruise RPM/airflow and adjust it to be leaner. Then use Power Enrichment to add fuel when you have more load than cruise to drop AFRs down around 13.2 or so when it kicks in. This way you should have 'safe' stoich on almost all of the VE/MAF, super lean cruise for a specific range of RPM/airflow, and richer mixture for heavy throttle application. It's not perfect because you give up closed-loop O2 feedback, but it works in theory.

A similar thing was done on an LS: https://www.youtube.com/watch?v=keGz_1BwcdQ

Technically there is space available in the computer to put a table of some sort and some arbitrary code, but you'd have to figure out how to create the appropriate jump commands to make the PCM use it. Creating custom code for the PCM is above my pay grade, though.

EDIT: Damn, steveo beat me to it. Super cool that you were working on a lean cruise patch. If you ever want to add that back to your pile of things to develop, sign me up to test it out! I've got some Corvettes here that would make great testbeds. :thumbsup:

[space387]

Thats the video that got me looking into this again.

Steveo I am not familiar with writing patches but if you want a tester I am all yours to try it. The engine is mildly ported and cammed with a raise in Compression ratio and its bolted to an M6. I also daily the car so it would be nice to see some improvement in milage when I'm not romping on it.

[space387]

Another option is if we can figure out how to limit the Closed loop mode to upper limits like exceed a MAF or TPS value. Does anyone know if you remain in closed loop if you enter PE mode?

[steveo]

its in closed loop but not updating trims. so it uses your stored blm data to trim fuel in pe. most people use the blm locker patch so that doesn’t happen

[space387]

ok, today I tested out today by setting the CL constant to 15.3 and once warmed up it was defaulting to the new AFR. When I exceeded the PE threshold it dropped to 12.5:1 for a target. I'm about to run through the logs to see if it actually did this or just showed the target in EEhack.

So further investigation its just a display number, but, the EGO sensor did show it ran richer. To be safe I will be applying the BLM locker on my next flash. Just to be clear its only during Pe it locks the BLM to 128 correct?

[steveo]

yeah the blm locker in EEX is only for power enrichment...

....but wait .. wait what are you doing?

i don't understand.

dont run your car at 15.3:1 all the time..... that'd be dumb.

you have to realize that "highway lean cruise" isn't the same as "leaning it out all the time during cruise". it's supposed to be lean during very specific and non-damaging conditions. there's a reason GM never put this code in the LT1, you know.

[steveo]

you also can't achieve that AFR in closed loop, it'll just 'target' it, and your CL trims will pull it back to an actual value of stoich,

[spfautsch]

steveo speaks the truth. You can't make your LT-1 run richer or leaner in closed loop by changing the CL afr target. The oxygen sensors will detect lean combustion and add fuel to your BLMs to correct it back to whatever stoichiometry is for the fuel you're burning. If that happens to be an ethanol blend it's probably closer to 14.3-14.4 to 1. What you're doing is equivalent to trying to herd cats.

For a properly functioning lean cruise you have to jump out of closed loop in lower load regions, and ideally make the PCM use a separate AFR target table. Also some additional spark advance may be beneficial to compensate for lost torque that results from leaner (and slower) combustion.

I tried summoning kur4o to this thread because this is something he could probably whip out in a couple days (a real lean cruise strategy for $ee).

I would be very interested in a true lean cruise solution for the $ee mask. Unfortunately I have several other projects to complete before I would be able to do any testing, and the weather has taken a massive dump on my joy-riding schedule for the forseeable future.

[dfarr67]

Maybe look into what the australian's had in that model. PCM hack.com might have something. Convert to 411?

[Fast355]

Maybe look into what the australian's had in that model. PCM hack.com might have something. Convert to 411?

Australia did not use the LT1 based engine. They had their own Holden 308 based engine that ran $12P coding in a 808 ECM (Basically 165')

[Fast355]

Maybe look into what the australian's had in that model. PCM hack.com might have something. Convert to 411?

I second an 0411 swap with EFI Connection 24x

[NomakeWan]

Swapping to another computer and ignition system for a four-figure cost seems like a cop-out answer when there is still plenty of potential left in $EE. I wouldn’t personally give up yet, not when the platform is being actively developed.

[Fast355]

Swapping to another computer and ignition system for a four-figure cost seems like a cop-out answer when there is still plenty of potential left in $EE. I wouldn’t personally give up yet, not when the platform is being actively developed.

My 5.7 Vortec gained about 15-20 ft/lbs across the whole RPM range with the 24x ignition. The prior 0411 swap also gave it much better driveability. With the 24x swap I went to the newer 1 meg PCM from a DBC van. That added the ability to run E85 which added even more power.

[NomakeWan]

Cool. Not everyone is looking for that. For ignition there are DIY solutions currently under active development which cost the user $200 or less to go to coil-per-cylinder, and the computer system in $EE is far from inferior. In addition as pointed out in the video I linked at the beginning of this thread the 0411 PCM doesn’t have this function built in either. The way you can do it with an 0411 is the same way you would do it with $EE. And if steveo, kur4o, or any other entrepreneuring individual wished there is the distinct possibility of patching that feature into $EE.

I’m glad you had such good results with your swap. Me personally, I enjoy having invested less than $300 total into tuning two Corvettes. ;)

[Fast355]

Cool. Not everyone is looking for that. For ignition there are DIY solutions currently under active development which cost the user $200 or less to go to coil-per-cylinder, and the computer system in $EE is far from inferior. In addition as pointed out in the video I linked at the beginning of this thread the 0411 PCM doesn’t have this function built in either. The way you can do it with an 0411 is the same way you would do it with $EE. And if steveo, kur4o, or any other entrepreneuring individual wished there is the distinct possibility of patching that feature into $EE.

I’m glad you had such good results with your swap. Me personally, I enjoy having invested less than $300 total into tuning two Corvettes. ;)

Its built into the 0411. It only has to be enabled. I enabled it with HP Tuners. Its also built into the later 2003 1-meg PCM I am running. It was also in the 05 6.0L truck PCM my friend has in his Chevelle.

Just have to change the platform designation to Holden, copy the system options to the Holden line, adjust the lean cruise settings and flash the PCM. I use Write Entire just to make sure the changes are correctly made to the calibration. No custom code work needed. Its already there.

Once it is enabled, the vehicle will command a leaner air/fuel mixture when the parameters are met to enter lean cruise.

[spfautsch]

Its built into the 0411.

That's all well and good, and I've been there and done that on a 0411 equipped vehicle back when gas was $4.50 a gallon. NomakeWan's point is the entry fee to put a 24x based ecu in a gen 2 LT-1 is about $800-$1200 if you're really creative. Considerably more if you want to click the "buy now" button, bolt stuff on and go. To quote facetious Bill Gates from the Simpon's season 8, episode 14, "I didn't get rich by writing a lot of checks".

[steveo]

its weird to pollute a thread about hacking an lt1 with 'just get a better ecm' especially in a forum full of TBI tuners.

isn't this an ecm tuning and hacking forum?

i fully object. beating up old ECMs to do what we want is what we do here.

i call BS that massive torque gains come from an ECM swap. one ECM was just better tuned than the other, that's all that happened there.

[Fast355]

its weird to pollute a thread about hacking an lt1 with 'just get a better ecm' especially in a forum full of TBI tuners.

isn't this an ecm tuning and hacking forum?

i fully object. beating up old ECMs to do what we want is what we do here.

i call BS that massive torque gains come from an ECM swap. one ECM was just better tuned than the other, that's all that happened there.

It was not the PCM swap that gave the gains. It was the coil per cylinder ignition and hotter spark from the D585 coils. The way I had to mount the D585 coils, I even retained the high performance L31 wires. It had Davis Unified stuff on it prior as well. The Davis Unified Ignition stuff had small gains across most of the powerband compared to the stock stuff as well. I put the Davis Unified Ignition stuff on the 305 in my 99 Tahoe after and it ran better as well. With the DUI stuff on the Vortec you can run a 0.060" plug gap vs the 0.035" GM has revised as the spec for the stock ignition. There is a GM TSB stating to close the gap because they found the Vortec engines often misfired with the wider gap. Closing the gap was worth 10 hp on my Express van with the stock ignition.

The newer PCM just operates more quickly and performs more calculations in the same amount of time.

Both the black box and 0411 had good tunes in them. The same timing map and held the same air/fuel ratio. The 0411 had better driveability. They both got the job done. The engine ran and made good power. The 0411 just flat ran better. Adding 8 ignition coils gave the ignition system a boost, resulting in more cylinder pressure and more power. Like starting a fire with a match vs a torch. At higher rpm you get more dwell time to recharge the spark which means hotter spark. Where the single coil drops off, 8 individual coils are still working perfectly. The L31 uses the same coil and module as the later LT1.

[steveo]

oh yeah coil per cylinder is great. im glad you did that for yourself

now lets talk about highway lean cruise on the lt1 again

[Fast355]

oh yeah coil per cylinder is great. im glad you did that for yourself

now lets talk about highway lean cruise on the lt1 again

I am sure some code could be written to easily do it.

However that hotter ignition system I mentioned does wonders in lean cruise. You can run the engine leaner before it starts to misfire. 17:1 air/fuel ratio is misfire free with a hot ignition system. The stock system starts to really struggle around 16:1. You will get alot of misfires and even more partial misfires. Which is why I brought it up in the first place. With the distributor you are also limited in how much timing advance you can run. In lean cruise my engine wants 52° of timing at 2,800 rpm. You are not able to get within 10° of that with a LT1 or L31 distributor because the spark will jump to the wrong cylinder because of rotor phasing. If you cannot compensate for the slower burn you will be losing torque and be shooting yourself in the foot trying to run that lean because you will have more airflow which means more fuel.

[steveo]

theres nothing easy about fundamental fuel system patching. lots can go wrong

just like the tbi engines with lean cruise handle it within reason

by your logic you should swap to direct injection engine that can go even leaner. things have come a very long way since the lt1 came out

i prefer challenging myself with what i have

this guy does too im sure

should he throw a modern ecm on his l98 too?

why dont we all throw our ecms in the garbages and get 0411s?

although you are correct that individual coils are superior to a distributor, you have no idea why we do what we do here, and you aren’t helping this thread at all.

[Fast355]

theres nothing easy about fundamental fuel system patching. lots can go wrong

just like the tbi engines with lean cruise handle it within reason

by your logic you should swap to direct injection engine that can go even leaner. things have come a very long way since the lt1 came out

i prefer challenging myself with what i have

this guy does too im sure

should he throw a modern ecm on his l98 too?

why dont we all throw our ecms in the garbages and get 0411s?

although you are correct that individual coils are superior to a distributor, you have no idea why we do what we do here, and you aren’t helping this thread at all.

I do know what your are doing. I have done code work on TBI ECMs and a little in the TBI PCM as well. I wrote flex fuel code for my TPI years ago. Then ended up swapping it to an 0411.

I also like a challenge. Hence why my Express van did not have a LS but had all the LS management including drive by wire. To add in an even bigger challenge was to base the engine off a L31 and still make head/cam LS power from it.

[Fast355]

Its just hard to ignore the benifits. I tuned a F-car a year or so ago that was 1 meg PCM EFI Connection swapped. We built a custom 4" air induction with a 100mm MAF. The car had a 58mm throttle body and ported intake manifold. Upgraded the springs and put 1.7 rockers on it with guide plates and hardened pushrods. Mid-length headers and a catback. On E85 it made 330 rwhp through a T56 and drove like a new car. With lean cruise on E85 it was still getting 25 mpg.

By that point...Why stop with a direct injected V8. Swap in the new Silverado turbo 4 and that 8 speed automatic. It runs on 2 cylinders on the highway and has good power. It is just begging for a good tune to wake it up too. The turbo 4 cylinder Camaros and Mustangs are out running big block race cars these days.

Even the shared port head 3.6 V6 in the Camaro and Challenger are begging for twin turbos. Single exhaust port heads would be stupid easy to turbo.

Just making a point.

[Fast355]

If you could somehow advance the optispark you could run more ignition advance FWIW. The TPI Corvettes used 6° initial to get to 48° total advance on the aluminum head engines. Distributor is limited to 42° advance.

[kur4o]

Blackbox and 0411 pcm runs the same processors and use almost identical strategies in spark and fuel calculations. So the only difference will be coil on plug and fine tunning with the later code.
Better spark can always increase fuel economy and power.

Lean cruise can be patched easily from the 94 v6 pcm as a template, but I have no interest in doing it.
I don`t see any real gains in fuel economy vs perfectly tuned lt1 engine in closed loop. The most efficient combustion is at stoich where engine makes best power. Leaning the mixture reduce engine power and the map jumps, leading to least efficient engine and you have crap running engine with less power and worse fuel economy.

Not to mention the extra heat produced that put enormous stress on the engine components. Burned valves is usual and not that hard to get a melted catalyst.

I made alot of experiments with a 3.4 camaro running lean cruise. I couldn`t measure any better fuel economy. The overheating catalyst alarm was always on, moving the afr down to 12 to cool down the mixture.

The most important place to tune for fuel economy is the spark advance around on / off idle conditions. The transition must be perfectly dialed.
The other place is the maf pumpshot scalar.
General rule is to tune for higher engine vacuum. More vacuum equals less fuel needed and more power being made.

[Fast355]

Blackbox and 0411 pcm runs the same processors and use almost identical strategies in spark and fuel calculations. So the only difference will be coil on plug and fine tunning with the later code.
Better spark can always increase fuel economy and power.

Lean cruise can be patched easily from the 94 v6 pcm as a template, but I have no interest in doing it.
I don`t see any real gains in fuel economy vs perfectly tuned lt1 engine in closed loop. The most efficient combustion is at stoich where engine makes best power. Leaning the mixture reduce engine power and the map jumps, leading to least efficient engine and you have crap running engine with less power and worse fuel economy.

Not to mention the extra heat produced that put enormous stress on the engine components. Burned valves is usual and not that hard to get a melted catalyst.

I made alot of experiments with a 3.4 camaro running lean cruise. I couldn`t measure any better fuel economy. The overheating catalyst alarm was always on, moving the afr down to 12 to cool down the mixture.

The most important place to tune for fuel economy is the spark advance around on / off idle conditions. The transition must be perfectly dialed.
The other place is the maf pumpshot scalar.
General rule is to tune for higher engine vacuum. More vacuum equals less fuel needed and more power being made.

You do realize that stoich burns at the highest combustion temps. Once you get leaner the EGTs drop. The oil temps and engine temps actually drop as well. In air cooled air plane engines running 50°F lean of peak EGT results in slightly less power, much cooler cylinder temps and several gallons per hour fuel burn reduction. It also generates less carbon. Valves and pistons are not harmed at all. My Express van gets 2 MPG better in lean cruise. My friends 6.0L Chevelle went from 25 to 29 mpg highway and thats with a 4L80E and 4.10s.

[NomakeWan]

Indeed. Lean of peak you should be burning cooler, though ignition advance is certainly a factor to look out for. Fortunately swapping to coils fulfills that, but even stock being able to get a little more out of the engine MPG-wise should be great. We’re only talking about maintaining a fixed speed at fixed load, so we need a fraction of the power the engine could otherwise make. It’s not like we want lean cruise to affect acceleration.

Also I looked into HPTuners; a $300 piece of hardware you need to buy credits for in order to tune with? Yet more unnecessary cost. steveo already put it very well, but let me drill it home with numbers. I bought a $70 cable and am using free-as-in-beer software. For coils I spent $150 total, plus less than $50 for the controller and its associated parts. That is under $300 to be able to do whatever I want with the LT1, plus convert to coil-near-plug. 24X and 0411 and HPTuners is a very expensive proposition to a much simpler problem than you realize.

[LeMarky Dissod]

LT1 Swap to LS 411 pcm (https://www.youtube.com/watch?v=nk3pvxJtYyU)

Although the video is 32min long for some reason, the gist of it is:
he converted his OBD1 LT1 into an OBD2 LT1 with a 96/97 front timing cover and added wiring for the OBD2 crank sensor
he repinned his harness into an 0411 pcm
he basically runs his OBD2 LT1 as an OBD2 L31

Of note, both the L31 & the LT1 both need only one coil to run.

In terms of inputs and outputs between the pcm and either engine, the distinctions between an OBD2 L31 and an OBD2 LT1 lack any meaningful differences.

Can't think of a cheaper way to use an 0411 pcm to run an LT1 - even though I'm not as imaginative and resourceful as y'all.

That said, if an OBD1 LT1 pcm can be coerced into reliably exceeding 29 highway MpG in an LT1 Caprice Roadmaster or Fleetwood without hypermiling, I'll be impressed regardless of how it's achieved, in inverse proportion to the cost, and not just because it would be novel.

[NomakeWan]

LT1 Swap to LS 411 pcm (https://www.youtube.com/watch?v=nk3pvxJtYyU)

Although the video is 32min long for some reason, the gist of it is:
he converted his OBD1 LT1 into an OBD2 LT1 with a 96/97 front timing cover and added wiring for the OBD2 crank sensor
he repinned his harness into an 0411 pcm
he basically runs his OBD2 LT1 as an OBD2 L31

Of note, both the L31 & the LT1 both need only one coil to run.

In terms of inputs and outputs between the pcm and either engine, the distinctions between an OBD2 L31 and an OBD2 LT1 lack any meaningful differences.

Can't think of a cheaper way to use an 0411 pcm to run an LT1 - even though I'm not as imaginative and resourceful as y'all.

That said, if an OBD1 LT1 pcm can be coerced into reliably exceeding 29 highway MpG in an LT1 Caprice Roadmaster or Fleetwood without hypermiling, I'll be impressed regardless of how it's achieved, in inverse proportion to the cost, and not just because it would be novel.
It's neat, but it runs batch ignition, and you still need OBD2 interface software and hardware to mess with it. The hardware you could just make with parts if you had to (though personally, my attempt to do so with the OBD1 didn't go well, thus my $70 cable), and while flashing software that is free-as-in-beer is finally starting to materialize as of this year, it's very much prototype stuff and they warn you about that up front. Once that materializes, it'll make the OBD2 PCMs much more attractive.

That all said, yeah. It's still worth looking at the OBDI PCM. I wouldn't count it out so fast.

[space387]

Hey guys, the author here. So I see we have run off topic hard here. Let's start with why I am looking for this feature, it's my daily driver. I started looking at options when I enabled it on my L98 corvette and noticed a 2mpg increase in combination driving.

Stevo you asked about me just settings g the afr to 15.3. Yes I did to see if there would be any gains, there where not. The car starts up drives down my road and its highway speeds all the way to work so this was just a test.

For those recommending the LS style ecu, forget it. I have a MS3 unit sitting on a shelf I can throw in for pennies. I was just trying to see what can you get from a stock ecu.

Stevo if you decide to pursue a highway cruise patch I'm more than willing to test it for you.

Kuro if you have any tips for increasing my mpg I'm all ears from the more experienced.

Thanks everyone for the input.

[Fast355]

Hey guys, the author here. So I see we have run off topic hard here. Let's start with why I am looking for this feature, it's my daily driver. I started looking at options when I enabled it on my L98 corvette and noticed a 2mpg increase in combination driving.

Stevo you asked about me just settings g the afr to 15.3. Yes I did to see if there would be any gains, there where not. The car starts up drives down my road and its highway speeds all the way to work so this was just a test.

For those recommending the LS style ecu, forget it. I have a MS3 unit sitting on a shelf I can throw in for pennies. I was just trying to see what can you get from a stock ecu.

Stevo if you decide to pursue a highway cruise patch I'm more than willing to test it for you.

Kuro if you have any tips for increasing my mpg I'm all ears from the more experienced.

Thanks everyone for the input.

Have you altered the 02 sensor target volate in the area you are trying to acheive 15.3:1. At low loads above idle I am running at 15:1 in closed loop. Stoich value on the fuel is 14.1. Instead of the stock 0.450 volt target I am down around 0.325 volts.

[space387]

Have you altered the 02 sensor target volate in the area you are trying to acheive 15.3:1. At low loads above idle I am running at 15:1 in closed loop. Stoich value on the fuel is 14.1. Instead of the stock 0.450 volt target I am down around 0.325 volts.

No I have not. That realization came last night and with my work schedule I have not had time to alter the tune.

[steveo]

i wouldn't really change the switch point in EE, i don't think you'll gain much except an unstable closed loop.

'leaner is better fuel economy' is only true in narrow operating bands like extremely light loads

outside those bands removing fuel can reduce your power enough that you negate the gain.

the point of highway lean cruise is to find the conditions where load is light and having optimal torque isn't helping....then lean it out. that's the 'highway' and 'cruise' part of 'highway lean cruise'. running leaner all the time isn't really highway lean cruise, it's just lean, and that's just bad tuning.

on my own cars i'd tend towards a hair more fuel than stoich in most cruse conditions above coasting. pennies a day for a smoother running engine is worth it.

[Fast355]

i wouldn't really change the switch point in EE, i don't think you'll gain much except an unstable closed loop.

'leaner is better fuel economy' is only true in narrow operating bands like extremely light loads

outside those bands removing fuel can reduce your power enough that you negate the gain.

the point of highway lean cruise is to find the conditions where load is light and having optimal torque isn't helping....then lean it out. that's the 'highway' and 'cruise' part of 'highway lean cruise'. running leaner all the time isn't really highway lean cruise, it's just lean, and that's just bad tuning.

on my own cars i'd tend towards a hair more fuel than stoich in most cruse conditions above coasting. pennies a day for a smoother running engine is worth it.

With an over powered V8 anything the engine is more efficient with less intake vacuum. Meaning the throttle plate is more open. If you have adequate torque even during light throttle acceleration leaner will give better mileage. The OEMs are doing it these days with cylinder deactivation. Hence the turbo 4 cylinder silerado that runs on 2 cylinders.

My 11:1 383 runs and accelerates smoothly at 16.5:1. I pulled the plugs at 5K to read them. They are carbon amd deposit free. Much cleaner than anything running at stoich.

I am getting 14 in town and 18 on the highway in a 6,200 lbs Express van with a near 500 hp 383, 1-ton running gear, a 4L85E and 5.13 gears on LT265/75R16s

If you drive as much as I do it is more than pennies a day. My round trip is 120 miles. Going from 16 mpg to 18 is a BIG difference at the end of the week.

Then again my 4 cylinder/6speed 2014 Nissan Sentra went from 35 mpg to 40+ when I tuned it. It is usually the vehicle of choice.

[NomakeWan]

I don't think you're really getting it...or maybe both of you are actually making the same point but for different reasons.

It was actually touched upon in the video series linked all the way back in the beginning of the thread. There is a specific amount of power required for maintaining steady-state speed of any vehicle. As long as you remain at or above that power, you're golden. So if you don't need any more fuel to hit that power level, you can lean it out and be just fine and dandy. Likewise, you can remove cylinders from the equation and be fine and dandy (what OEMs realized recently). Leaning things out above that load, however, not so fine and dandy (which is why OEMs reenable cylinders once you exceed a specific load value). There are lots of factors involved, and no engine is the same since each is going to have different dynamic compression, peak torque values, control systems, etc. But at the end of the day, if you only need 50 HP to cruise at 65 MPH, you don't need 300 HP worth of fuel.

[space387]

So I have decided to attack this a little more scientifically than just lean it out until I see improvements. So I recorded the car driving down a strait road with stock settings and recorded the engine telemetry. There are 2 factors to watch to directly show if you have achieved tangible improvements, MAP or MAF and injector pulse width. If you can lean the engine out without increasing the MAP or MAF readings then it is not taking more volume to maintain the same speed. You can then show a decrease in fuel use by the injector pulse width. If all this is done at the same RPM and along the same stretch of road the results should show some improvements.

[Fast355]

So I have decided to attack this a little more scientifically than just lean it out until I see improvements. So I recorded the car driving down a strait road with stock settings and recorded the engine telemetry. There are 2 factors to watch to directly show if you have achieved tangible improvements, MAP or MAF and injector pulse width. If you can lean the engine out without increasing the MAP or MAF readings then it is not taking more volume to maintain the same speed. You can then show a decrease in fuel use by the injector pulse width. If all this is done at the same RPM and along the same stretch of road the results should show some improvements.

Actually you want the MAP and MAF to increase. You just want less pulsewidth. More throttle, More Airflow, Less fuel, Less Torque production, Less pumping loss and more MPG.

[kur4o]

For fuel economy thera are 3 parameters that are related, pulse width, rpm and mph. PW and rpm must be as low as possible and mph as high as possible.
We are still missing that INS.Fuel .Economy in eehack. I hope steveo will add it on the next release. If we have that available in the datastream, high end experiments will prove what is needed.

If the engine torque is not efficiently transformed to rolling movement, due to high gears for example, there is a waste of fuel for sure. So lets say the engine makes 100% power and only 70% of the power is used to drive the vehicle, the other 30% are wasted.
One way of improvement will be to lower the gears so the load the engine make can be utilized 100% to movement. Increasing the speed while maintaining the same load on the engine.
It will get alot of trial and errors to get the best combo of gears, weight and engine torque curve.

The other way of improvement will be to lean the mixture so the engine makes less power but enough to be used 100% for vehicle movement.
With really high gears, low weight vehicles going to 18-19:1 even 22:1 AFR can be beneficial.

To sum up lean cruise will work best on high torque, high gears vehicles.

To get a better fuel economy a general engine tune up can be performed.
Full revision of ignition system.
Internal engine cleaning of carbon deposits. A fine water mist method works good and can wake up poorely maintained engines.
Checking injectors for leaks and clogs.
Switching all oils to full syntetic like redline.

[Fast355]

For fuel economy thera are 3 parameters that are related, pulse width, rpm and mph. PW and rpm must be as low as possible and mph as high as possible.
We are still missing that INS.Fuel .Economy in eehack. I hope steveo will add it on the next release. If we have that available in the datastream, high end experiments will prove what is needed.

If the engine torque is not efficiently transformed to rolling movement, due to high gears for example, there is a waste of fuel for sure. So lets say the engine makes 100% power and only 70% of the power is used to drive the vehicle, the other 30% are wasted.
One way of improvement will be to lower the gears so the load the engine make can be utilized 100% to movement. Increasing the speed while maintaining the same load on the engine.
It will get alot of trial and errors to get the best combo of gears, weight and engine torque curve.

The other way of improvement will be to lean the mixture so the engine makes less power but enough to be used 100% for vehicle movement.
With really high gears, low weight vehicles going to 18-19:1 even 22:1 AFR can be beneficial.

To sum up lean cruise will work best on high torque, high gears vehicles.

To get a better fuel economy a general engine tune up can be performed.
Full revision of ignition system.
Internal engine cleaning of carbon deposits. A fine water mist method works good and can wake up poorely maintained engines.
Checking injectors for leaks and clogs.
Switching all oils to full syntetic like redline.

I was assuming same RPM and Speed. Lower pulse width equals more MPG. Less vacuum means the engine is using less of the power it makes just to pull the pistons down against the vacuum. More throttle for the same power is giving it more volumetric efficiency.

I had a Ram that had 3.55 gears and a MDS Hemi in it. When I put 4.56 gears the fuel mileage improved. The truck spent much more time shut down to 4 cylinders. When I put a cam and converter in it stayed in 4 even more. When I opened up the exhaust and intake it almost always ran in 4. The PCM judged when to go into MDS mode by monitoring vehicle speed, rpm and load via the MAP sensor. Over idle, over 20 mph and under X vacuum amount it went to 4 cylinder. With the small cam it made more torque. With the gears and converter the engine ran and accelerated with less load. It would pull into 4 cylinder mode accelerating up an on-ramp.

FWIW an internal combustion engine is only about 30% efficient and even less efficient at part-throttle.

[spfautsch]

More throttle for the same power is giving it more volumetric efficiency.

As much as I hate to agree with Fast355, he is correct. My daily driver regularly gets 49+ mpg because it's a diesel and has no throttle plate, which causes far less pumping loss than an equivalent 1.9L gasser.

The trick with lean cruise strategy is proper tuning. You can't run at 15.4:1 (or equivalent adjusted for fuel stoich) all the time - not even "a lot" of the time. But maintaining speed while going down a hill at 75mph takes a much smaller amount of power than doing the same going up said hill. Coupled with well-tuned DFCO and perfectly tuned stoich combustion with MBT spark, I believe impressive numbers can be made with an over-powered V8 in a light and aerodynamic car.

"Hypermiling" isn't an evil word. Waste not, want not. I look at it this way - I'm all too happy to bank my unused hydrocarbons while driving conservatively so I can gluttonously consume them in the six or eight times a year I get to exit my favorite hard right corner with tires smoking at 80+ mph in 3rd.

[Fast355]

As much as I hate to agree with Fast355, he is correct. My daily driver regularly gets 49+ mpg because it's a diesel and has no throttle plate, which causes far less pumping loss than an equivalent 1.9L gasser.

The trick with lean cruise strategy is proper tuning. You can't run at 15.4:1 (or equivalent adjusted for fuel stoich) all the time - not even "a lot" of the time. But maintaining speed while going down a hill at 75mph takes a much smaller amount of power than doing the same going up said hill. Coupled with well-tuned DFCO and perfectly tuned stoich combustion with MBT spark, I believe impressive numbers can be made with an over-powered V8 in a light and aerodynamic car.

"Hypermiling" isn't an evil word. Waste not, want not. I look at it this way - I'm all too happy to bank my unused hydrocarbons while driving conservatively so I can gluttonously consume them in the six or eight times a year I get to exit my favorite hard right corner with tires smoking at 80+ mph in 3rd.

I run leaner than 16:1 ALOT of the time. Even light throttle acceleration.

In WW2 it became common for planes like the P38 to run with the propellor pitch at maximum advance, a lean cruise mixture and moderate manifold pressure. Basically low rpm, lean and higher load. When a brilliant pikot aka Charles Lindberg first attempted it the ground crew thought he was nuts. They examined the engines after 500 hours and determined their were no ill effects.

On a LS I run as lean as 16.9:1. On the older SBC I run 16.5:1
I run my 8.1 in my Tahoe at 16.5:1 as well. The chamber design better on the LS.

[Fast355]

Here is the basic run down of the P38 story.

For some real world, historical reference here is an excerpt from an article about Lindberg 's briefings about P-38 long range cruise power settings. *Interesting reading.....

"Two missions later, on 3 July, the group covered sixteen heavies on a strike against Jefman Island. Lindbergh led Hades Squadron's White Flight as they wove back and forth above the lumbering B-25s. After the attack the Lightnings went barge hunting.

First one, then two pilots reported dwindling fuel and broke off for home. MacDonald ordered the squadron back but because Lindbergh had nursed his fuel, he asked for and received permission to continue the hunt with his wingman. After a few more strafing runs, Lindbergh noticed the other Lightning circling overhead. Nervously the pilot told Lindbergh that he had only 175 gallons of fuel left. The civilian told him to reduce engine rpms, lean out his fuel mixture, and throttle back. When they landed, the 431st driver had seventy gallons left, Lindbergh had 260. They had started the mission with equal amounts of gas.

Lindbergh talked with MacDonald. The colonel then asked the group's pilots to assemble at the recreation hall that evening. The hall was that in name only, packed dirt floors staring up at a palm thatched roof, one ping pong table and some decks of cards completing the decor. Under the glare of unshaded bulbs, MacDonald got down to business. "Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightnings: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight. When he concluded his talk half an hour later, the room was silent.

The men mulled over several thoughts in the wake of their guest's presentation. The notion of a nine-hour flight literally did not sit well with them, "bum-busters" thought some. Seven hours in a cramped Lightning cockpit, sitting on a parachute, an emergency raft, and an oar was bad, nine hours was inconceivable. They were right. Later, on 14 October 1944, a 432nd pilot celebrated his twenty-fourth birthday with an eight-hour escort to Balikpapan, Borneo. On touching down, he was so cramped his crew chief had to climb up and help him get out of the cockpit.

The group’s chief concern surfaced quickly, that such procedures would foul sparkplugs and scorch cylinders. Lindbergh methodically gave the answer.*The Lightning's technical manual provided all the figures necessary to prove his point; they had been there all along. Nonetheless the 475th remained skeptical. A single factor scotched their reticence.

During their brief encounter, MacDonald had come to respect Lindbergh. Both men pushed hard and had achieved. Both were perfectionists never leaving things half done. And both had inquisitive minds. John Loisel, commanding officer the 432nd, remembered the two men talking for long periods over a multitude of topics beyond aviation. If, as MacDonald had informed his pilots, better aircraft performance meant a shorter war, then increasing the Lightning's range was worth investigating. Lindbergh provided the idea, but it was MacDonald's endorsement, backed by the enormous respect accorded him by the group, that saw the experiment to fruition. The next day, the Fourth of July, Lindbergh accompanied the 433rd on a six-hour, forty-minute flight led by Captain "Parky" Parkansky. Upon landing, the lowest fuel level recorded was 160 gallons. In his journal entry Lindbergh felt ". . . that the talk last night was worthwhile. " The 475th had lengthened its stride."

[steveo]

what works for one engine won’t necessarily work for another. comparing this airplane engine to an lt1 highlights the total absurdity of your generalizations both here and elsewhere. combustion chambers flame fronts and air fuel charge dynamics are an insanely complex thing with so many inputs and outputs and that’s why tuning is required in the first place. lots of engines melt down when lean, and lots can run 25:1+. lots of factors involved.

[Fast355]

what works for one engine won’t necessarily work for another. comparing this airplane engine to an lt1 highlights the total absurdity of your generalizations both here and elsewhere. combustion chambers flame fronts and air fuel charge dynamics are an insanely complex thing with so many inputs and outputs and that’s why tuning is required in the first place. lots of engines melt down when lean, and lots can run 25:1+. lots of factors involved.

A V8 engine is not going to melt down making the 40-50 hp it takes to cruise. Even at 80-100 hp its not going to melt down. I don't care if you were to run it lean enough to cause misfire. You will melt the cats from misfiring before you hurt the valves or pistons. The only way you will melt it down is to run it lean at high rpm and high throttle. You are actually more likely to destroy it at long periods of stoichiometric air/fuel at WOT as the combustion temps are hottest.

Its actually not absurd at all. It was also a proof of concept not execution. The principle does work and I have applied it to Chevy V8s. Keep in mind that engine was running at a lower rpm than most of our vehicles and also running at about 30 in/hg manifold pressure. That is WOT for a non supercharged car at sea level.

Also having a couple of EGT probes and a gauge that monitors both has taught me a thing or two. Under sustained WOT with an air/fuel ratio of around 12.5:1 my EGTs will rise to about 1,350°F. In stoich cruise at 70 mph the EGTs run around 850. In lean cruise they drop to 775. The excess air is cooling the combustion process. The oil temps also drop. With both EGT and Oil Temps lower that means the pistons are running cooler and so are the valves.

[Fast355]

One other observation from a carb to TBI swap years ago. I swapped a 305 with a bone stock Q-Jet to TBI. I had the VE table tuned to a BLM of near 128 across the board. I had the same exact ignition advance curve I had in the mechanical HEI. My highway fuel mileage tanked. Went from 18 mpg to 15 mpg. I had a spreadbore intake still on the thing with a big block TBI unit and a GM TBI to Q-Jet adapter plate off an early 454. I ended up pulling the TBI off, and putting the Q-jet back on. I left the TBI distributor in place. Next highway trip I was up to exactly 18 mpg. I datalogged the fuel trims with the Q-Jet in place. The BLM values were all pegged out in the 160 range. The narrowband was burried at near 0 volts. I ended up turning on lean cruise in the 7747 ECM. I put the TBI back on. I set the air/fuel ratio in lean cruise at 16.5:1. I was instantly back up to 17.5 mpg. The factory Q-Jet was running in the 17:1 range at highway speeds.

[steveo]

nobody is questioning that richer AFRs are necessary at high load and RPM.

the fact a carb'd iron headed 305 ran 17:1 ratios at highway speeds from the factory isn't useful data for tuning any sort of lean cruise for an LT1, which has a totally different spark control, fuel atomization, combustion chambers, and cooling system.

do you happen to have any parameters useful for the LT1 specifically?

i do, at least for the aluminum headed version of it. at dead coast i ran 16:1 without issues. above that, it was never smooth enough for my taste when leaner than stoich. on the highway with some momentum it wasn't a huge problem (lean cruise patch would probably be alright there) but in slow moving traffic you could feel it didn't like it at all. fiddling the timing around to try to smooth it out was eventually successful but it just felt better, had good power, and reasonable fuel economy with a bit more gas.

[kur4o]

Untuned individual trims for lt1 is number reason for crap running engine at light load. At idle they are relative easy to dial but off idle is totally different thing. Untill the airflow equalize at off idle you might need dynamically changed trims based on rpm, map and airflow. Real nigtmare to tune. Now if you lean the mixture enough some cylinders might get just too lean, other might be just right and the unbalanced power cylinder to cylinder will lead to weird feelings.

Once I tried running closed loop at idle.
Upon switching from open loop with slightly richer mixture I noticed immediate rise in map, around 5kp.
So closed loop was running leaner but consumed more air due to rise in map, leading to more fuel needed.
In reallity it is possible to run leaner all the time with higher map readings and poorer fuel economy.

Considering combustion temperature, the extra duration of the burning process with lean mixture[Lean mixture is known to burn much slower] can lead to more heat being accumulated in the engine, especially the valves. You are off peak temp for sure but other factors need to be taken into account. All pcm strategies for cat overtemp are tied to lean running under certain load and airflow, You can hit cat overheat threshold under 1 min of runnig 16.5:1. Also when the cat overheat is on, the pcm commands 11:1 mixture to cool down the cat, negating any gains.
Less fuel also mean hotter intake mixture which further reduce power. When fuel evaporates it cools the intake temperature, increasing efficiency. So you get less cooling on the intake valve and longer burning process that hits the valves.
The temperatures produced at burning gasoline is also constant, like all other burning fluids. I suspect the different temps are from the different quantity of the fuel used at different AFRs and the overall heat dissipation the engine makes.
So with leaner mixture the heat is distributed unevenly in the engine. Cooler cylinders but hotter valves and piston top.

[space387]

So I am curious how are you guys ( Steveo and Kur4o) picking apart and writing patches for these ecu's. I am curious to look deeper at the Highway mode on my C4 so see what if anything I can inject to the LT tune.

Side note: Those modeling theory on the P38 experiment remember the differences in the Allison V-1710 vs our SBC engines. The allison has a bore of 5.5 inches we are using about 4 inches, this promotes a longer burn and better controlled flame front. They also show a CR of only 6.65:1 I am at 11:1, the difference here should be self explanatory. Finally they use an outdated version of Avgas with a much higher octane rating than we have, no ethanol AND lead. It is very unlikely any of us can go as extreme in our cars with a consistently varying load as they did on an aircraft engine that is set and left for 4 or so hours at a time.

[Fast355]

Actually with lead in the avgas they have to vary the power setting every 30 minutes or so to keep from fouling the plugs.

Forgetting the P38, I run 16.5:1 just fine on an 11:1 4.030 x 3.75" aluminum head small block that does not have the LT1s reverse cooling in a heavy, unaerodynamic vehicle. That is also on 10% Ethanol. I would shoot for about 17:1 on non ethanol laced gas. Did I also mention I am doing this on 87 octane. Runs knock free at 52° of timing at 2,850 rpm @ 70 mph.

[NomakeWan]

Give me your tune.

Not even joking. My stock LT1 on 91 (E10, winter formulated) knocks at only 38 degrees of timing under load. If you’re saying you have a tune that makes the LT1 knock-free on 87 at coil-near-plug advance levels, let’s see it.

[space387]

I think you need a new knock sensor.

[NomakeWan]

{delete, replied to wrong post}

[space387]

forgot to quote Fast, he needs the new knock sensor/ module

[PlayingWithTBI]

Knock sensors work just fine, and frankly in the ESC system it's the module that has the most say, not the sensors. I can easily replicate the exact pattern on the knock map by messing with timing step by step. Pulling the advance back to stock resolved the issue. Better fuel would too, but that's not an option here in Commiefornia unless I wanna pay $10/gallon for 100-octane, which I don't.

Stock '95: https://i.imgur.com/llQvpOa.jpg
Advanced 37~39 degrees: https://i.imgur.com/lVb5hRn.jpg

Also this is still a thread about Highway Lean Cruise for the LT1 PCM. So I'm still interested in that magical tune Fast355 is talking about, or a patch to add this type of function to the PCM. Don't want to drag stuff too far off topic.
Since you're from Californicate (I was too) I don't think you'll be able to run HLC anyway. FWIR you won't pass smog with it enabled, that's why GM disabled it in the 7747 ECM back in '87. Although I'm definitely interested in what you save and what dangers you risk with it enabled. I'm running it with my EBL Flash2 on an 88 5.7L aluminum heads, 42* w/91 Octane @16.5:1 and haven't seen a lot of benefit from it, but I don't do a lot of cruising, LOL.

[Fast355]

forgot to quote Fast, he needs the new knock sensor/ module

Knock sensors work perfectly. New Delco sensors that went on the engine 6 months ago. I know they work because I occasionally see 1-2° of retard on throttle tip-in.

[NomakeWan]

Since you're from Californicate (I was too) I don't think you'll be able to run HLC anyway. FWIR you won't pass smog with it enabled, that's why GM disabled it in the 7747 ECM back in '87. Although I'm definitely interested in what you save and what dangers you risk with it enabled. I'm running it with my EBL Flash2 on an 88 5.7L aluminum heads, 42* w/91 Octane @16.5:1 and haven't seen a lot of benefit from it, but I don't do a lot of cruising, LOL.
Easy enough to just disable it before a smog test. :P Even easier if it's a patch that allows for an external trigger pin.


Knock sensors work perfectly. New Delco sensors that went on the engine 6 months ago. I know they work because I occasionally see 1-2° of retard on throttle tip-in.
...isn't that just the burst knock feature built into the PCM that works independent of the sensors and module...?

[Fast355]

Easy enough to just disable it before a smog test. :P Even easier if it's a patch that allows for an external trigger pin.


...isn't that just the burst knock feature built into the PCM that works independent of the sensors and module...?

Burst knock retard does not show up as actual knock retard.

You won't get more than about 40° advance into a distributor that has the base timing at 0.

The aluminum head L98 Corvettes ran up to 48° in their timing maps. They had horrible quench as well.

[NomakeWan]

We’ll cross that bridge if we get there. I have an ignition controller for D514A coils waiting for me to toss it together and throw it on the car.

So, your tune, maestro?

[space387]

Burst knock retard does not show up as actual knock retard.

You won't get more than about 40° advance into a distributor that has the base timing at 0.

The aluminum head L98 Corvettes ran up to 48° in their timing maps. They had horrible quench as well.

The L98 corvette table maxes at 46* with a programmed limit of 41.84* to override the table. Stock the distributor is set to 6* advance and the computer is designed to account for this. Now lets go so far as to say the computer is not factoring it out and the hard limit is not actually there, Highest you will see is 52* at 2000-7000rpm with a MAP of 40. The only way to get to this point is with the throttle plate closed so coasting/ decelerating. For Loaded situations the table shows closer to 42* under normal cruising conditions but remember the hard limit and the factored advance.

[steveo]

Burst knock retard does not show up as actual knock retard.

You won't get more than about 40° advance into a distributor that has the base timing at 0.

The aluminum head L98 Corvettes ran up to 48° in their timing maps. They had horrible quench as well.

huh? the opti doesn’t have any problems up to 50 degrees of advance. its a huge cap.

[kur4o]

Stock lt1 software limit is 46 degrees. I have no idea if it is software limitation or hardware opti limitation. Someone have to guinea pig the setting to 52* and see if the pcm freaks out.
It is not good idea to compare lt1 with 96-00 vortec engine. They have different intake and suppose different chamber and dynamic flow characteristics.

Lt1 have unique intake manifold that brings all kind of nightmare tuning situations. It also doesn`t like too much advance at low loads on cammed cars. I had terrible knock at 25-35 kp range and had to lower stock settings. Than found that lt4 also had less advance at that range.

I forgot to mention that freeing up the exhaust can reduce map and fuel consumption. Confirmed with logs on bad muffler replacement with free flowing one.

[space387]

Stock lt1 software limit is 46 degrees. I have no idea if it is software limitation or hardware opti limitation. Someone have to guinea pig the setting to 52* and see if the pcm freaks out.
It is not good idea to compare lt1 with 96-00 vortec engine. They have different intake and suppose different chamber and dynamic flow characteristics.

Lt1 have unique intake manifold that brings all kind of nightmare tuning situations. It also doesn`t like too much advance at low loads on cammed cars. I had terrible knock at 25-35 kp range and had to lower stock settings. Than found that lt4 also had less advance at that range.

I forgot to mention that freeing up the exhaust can reduce map and fuel consumption. Confirmed with logs on bad muffler replacement with free flowing one.

I'll test it out in the next few days. First will be just overriding to add the 6* over the table with EEhack then if it doesn't freak out I'll add it to my table.

[space387]

So I was able to run as much as +10* spark advance without knock or malfunction during cruise. Hotter coolant temp and less throttle used so a win I guess. Fwiw there is a programed 46* spark limit that can be changed. I know I had it maxed for a significant time.

[kur4o]

So I was able to run as much as +10* spark advance without knock or malfunction during cruise. Hotter coolant temp and less throttle used so a win I guess. Fwiw there is a programed 46* spark limit that can be changed. I know I had it maxed for a significant time.


Did you change the spark limit scalar before testing? Set it higher before the test or the advance will be capped at 46* no matter how much you command in eehack.

Be careful, more advance than the optimal will destroy crank bearings in no time. The map change can be used as a guide.


I am thinking to add a 4cylinder mode as a patch and controlled with external switch. Will it be any beneficial to fuel economy is still unknown. There will be a forced open loop needed to prevent blms from wacking.

[space387]

Did you change the spark limit scalar before testing? Set it higher before the test or the advance will be capped at 46* no matter how much you command in eehack.

Be careful, more advance than the optimal will destroy crank bearings in no time. The map change can be used as a guide.


I am thinking to add a 4cylinder mode as a patch and controlled with external switch. Will it be any beneficial to fuel economy is still unknown. There will be a forced open loop needed to prevent blms from wacking.

No I found the spark limit of 46 doing this and looked further into the tune for confirmation. The issue with running the car in 4cyl mode and not disabling the valves too is you will still burn almost as much fuel and end up with a higher parasitic draw from the non firing cylinders still making compression. Its wort a try but I wouldn't expect much in the way of gains.

[LeMarky Dissod]

The issue with running the car in 4cyl mode and not disabling the valves too is you will still burn almost as much fuel and end up with a higher parasitic draw from the non firing cylinders still making compression.
It's worth a try but I wouldn't expect much in the way of gains.1stly, yes, what space387 said; if all 8 cylinders are inhaling and compressing but only 4 are actually making power, those four will use MUCH MORE FUEL - except maybe during non-DFCO coastdowns.
I wish every 0%TPS deceleration would DFCO, but many do not, and the O2 sensors are always aiming @ 14.7 AFR.

NorthStar V8s use a 4cylinder contingency mode when coolant temps hit 266°F / 130°C. https://www.youtube.com/watch?v=0YWOf6u1sb8
[266°F / 130°C is WAY too late for an all-aluminum engine; 239°F / 115°C would be more sensible. (I'm nuts enough to activate OverHeat Enrichment as early as 221°F / 105°C on my all-iron LT1).]

[space387]

well it finally happened. I bricked the PCM trying to flash a new tune. As a temporary I am going back to megasquirt as it is already tuned for this car just not great. After the holidays I plan to try and resurrect the bricked pcm.

So I have a moates Burn 2, can i use that with an adapter to flash a new chip to get the ecu talking? Also what is everyone using for a USB adapter, I diy'ed my own but I think it was not up to the task. Would like to make another one just need the proper chip.

[spfautsch]

I am thinking to add a 4cylinder mode as a patch and controlled with external switch.

That's not really going to very beneficial to economy because you'll still be using energy pumping air through the engine. What GM is doing on the late model stuff works as well as it does because it collapses both intake and exhaust lifters at BDC of each de-activated cylinder and then leaves them closed throughout the reduced displacement mode. This causes a minimum amount of pumping loss because the compressed air acts to push the piston back down the bore after TDC. It also introduces no oxygen into the exhaust until it reverts back to normal displacement, so the ecu only has to disable BLM learning for the one engine revolution it takes to re-activate the collapsed lifters.

Disclaimer - "as well as it does" is highly subjective. By itself, the increase in efficiency isn't very significant unless it's coupled with other fuel saving techniques. You're still losing energy moving the pistons, just not as much as if you were pumping air through the engine.

Edit: Another consideration to a 4 cylinder mode without cyinder de-activation is catalyst flare / overheating.