Cruising Air fuel ratios.

[riche]

I appreciate yalls help with timing, and have made some progress. But I have a question about air fuel ratios.
In Holey's software you can set the air/fuel ratio table. Then it has a base fuel and a learn table. The air/fuel table then compares the O2 readings to the air/ fuel table. That in-turn applies an adjustment value to a learn table. Then the learn table modifies the base fuel table all in real time. For the most part it works really well with a few exceptions I learned about the hard way.
Just wanted to ask a few questions about cruising air/fuel ratio. I have been playing around with it leaning it out and was hopping to get some opinions of what is too lean foe a early model small block with vortec heads.
I leaned it out to 15.2:1 (in the "cruise" area of my table) and it seems like the temp is jumping up to 195 degrees cruising down the interstate. Just wondering if that is too much.

[steveo]

although 15.2 isnt so bad (if it actually IS 15.2, are you usign a wideband?)... i wouldn't be pushing it past stoich if i were you, not unless it has provisions for proper lean cruse that engages and disengages with very tight thresholds.

leaning it out seems to be one of those things where it gets way worse before it gets better. you can go super lean, and suddenly the combustion temperature drops again. but if you put any load on the engine while it's at that AFR, things go sideways really quickly.

[riche]

Ok. I appreciate the advice.
Yes it is a wide band O2. I did notice with the plugs that My o2 appears to be on the rich bank. So I added a few points across my table.
Then I started thinking about what you mentioned in my previous post about my cam and vacuum. I am wondering if I really can't get to a low load condition b/c of the weight/aerodynamics of my truck and the cam in my motor. I.E. if a car has my same motor and a better cam it could get to a lower area of the map at a certain mph lets just say that is 45 kpa @ 65 mph and my truck with it's cam and weight is 65 kpa @ 65 mph. So do I assume that my truck shouldn't go as lean and I shouldn't advance my timing as much as I would in a light car with a better cam and aerodynamics?

[trippyjoey]

I would agree with Steveo don't lean it out unless it has a Hiway lean cruise mode. I've gone down that path before leaned it out and my BLM's were in the high 130's low 140's it seemed to get better mileage but the engine temps were rising and the engine was always running at 80kpa map. I richened it up so my BLM's dropped to 126-128 and my fuel economy increased and my engine is now running at 50's Kpa map so the engine is under much less load now that it is making enough power to easily move my big Yukon.

[Fast355]

I would agree with Steveo don't lean it out unless it has a Hiway lean cruise mode. I've gone down that path before leaned it out and my BLM's were in the high 130's low 140's it seemed to get better mileage but the engine temps were rising and the engine was always running at 80kpa map. I richened it up so my BLM's dropped to 126-128 and my fuel economy increased and my engine is now running at 50's Kpa map so the engine is under much less load now that it is making enough power to easily move my big Yukon.

I religiously use lean cruise, even with the 305 I had pushing my 700r4, 3.08 geared G20 van back in the day. 1,800 rpm @ 70 mph, running about 65-70 KPA. As long as your air/fuel mixture richens as the MAP increases, it works well. At 30-50 KP I would run about 17:1, 50-70 KPA about 15:1, and 70-100 KPA tapered up to 14:1, then PE active would bring it down to 12.6:1. With E10 fuel knock .75 off those values.

[RobertISaar]

i love lean cruise....

with a light enough load, you're only really limited to how little fuel you can inject and not have a misfire. how well the air/fuel mixture actually mixes will play a large part in that, which will be RPM and presumably MAP specific.

there is a really noticable bell curve when it comes to AFR and combustion temps, in theory you'll get max burn temps at 14.7:1, but in practice it will be leaner than that. how much leaner will be engine dependant(mixing is big here too). i wouldn't want to operate in lean cruise right on that crest.... might be a bit more heat than what the headgasket or piston crown will allow. leaner than that though, to bring it down to where the 14.7:1 AFR mix produces temps at or leaner, that is where i would look. EGT probes are great for this.

there are some fairly conventional(not direct injected) gas engines that run some incredibly lean AFRs(22:1 for mid 90s honda lean-burn engines), but they are specifically built to do so. most take advantage of only operating 1 of 2 intake valves or only supplying fuel to 1 of 2 intake valves, all kinds of tricks that may or may not be usable depending on the engine you're playing with.

[riche]

Thanks for the replies, Is the best way to find were you get to a lean cruise sweet spot is with EGT?

At 30-50 KP I would run about 17:1, 50-70 KPA about 15:1, and 70-100 KPA tapered up to 14:1,

This is what I am wondering. I cant really get below 65 KPA cruising... I am assuming that is b/c my cam does not make enough vacuum. At idle out of gear I am in the same range.

[delcowizzid]

i run cams with 60-70kpa at idle and once cruising at 14.7:1 and up on the cam they cruise at 30-40kpa.if your driving everywhere down low in the rpm out of where the cam starts beginning to smooth out andwork and getting some efficiency in cylinder fill expect cruise vacuam to be bad.spark makes a big difference to cruise vacuam .i add spark at steady state cruise and watch tps % and map or my driver for tuning missions knows to tell me if hes needing to lift off the pedal to maintain speed. as TPS goes down vacuam goes up.less throttle opening and lower map readings equals less fuel injected equals economy.i leave the lean cruise turned off on performance engines i dont want to go out of lean cruise straight to WOT to overtake at pace on the off chance theres a glowing sparkplug electrode or a hot spot in a chamber from cruising lean.fuel vapour is also a boundary layer in the engine.it sits against the piston crown and cylinder walls and is quite an insulator of heat.when you expereince pre ignition (not detonation theres a difference)this boundary layer is broken and thats when you get a hole melted in the centre of a piston from the heat actually getting to the alloy surface real lean and bad timing could melt shit faster than you realise.hondas run lean burn but with chambers that suit and other mystical tricks.when i do use lean cruise the easy way to tell if its too lean is you will feel lean cruise activate from the loss of torque time to add more fuel.

[Fast355]

i run cams with 60-70kpa at idle and once cruising at 14.7:1 and up on the cam they cruise at 30-40kpa.if your driving everywhere down low in the rpm out of where the cam starts beginning to smooth out andwork and getting some efficiency in cylinder fill expect cruise vacuam to be bad.spark makes a big difference to cruise vacuam .i add spark at steady state cruise and watch tps % and map or my driver for tuning missions knows to tell me if hes needing to lift off the pedal to maintain speed. as TPS goes down vacuam goes up.less throttle opening and lower map readings equals less fuel injected equals economy.i leave the lean cruise turned off on performance engines i dont want to go out of lean cruise straight to WOT to overtake at pace on the off chance theres a glowing sparkplug electrode or a hot spot in a chamber from cruising lean.fuel vapour is also a boundary layer in the engine.it sits against the piston crown and cylinder walls and is quite an insulator of heat.when you expereince pre ignition (not detonation theres a difference)this boundary layer is broken and thats when you get a hole melted in the centre of a piston from the heat actually getting to the alloy surface real lean and bad timing could melt shit faster than you realise.hondas run lean burn but with chambers that suit and other mystical tricks.when i do use lean cruise the easy way to tell if its too lean is you will feel lean cruise activate from the loss of torque time to add more fuel.

The purpose of lean cruise is to LOSE torque!!! When you reduce the torque, you increase the angle on the throttle plate to compensate and decrease pumping losses, increasing MPG. EGR and Multiple Displacement Systems aka Modulated Displacement or DOD systems also do this. Keep an eye on EGT and Oil Temp and you will generally be ok in lean cruise. That being said the transition to lean cruise should be fairly smooth and non-noticeable other than the fact it takes a little more pedal to keep you going down the highway compared to a richer mixture. When you taper the fuel mixture correctly you will have plenty of torque with the throttle open and as you start to enter cruise throttle position it will not be noticeable.

I just tuned an EBL setup on vortec head 350 in an early 90s C1500. Had a small XR269HR cam in it and flat tops. He had enabled open loop and it was running so lean down the highway it would start misfiring at cruise. After tuning it with the numbers above it was getting 19-21 mpg highway.

[suffolkauto01]

I use lean cruise up to 16.2 but cruise make sure when on gas clears out I do this on all cars i tune with hp tuners. (on N/A cars) 14.7 driving 13-12.7wot 15-16.2the most lean cruise meaning 55mph+less then 25% throttle under 2700rpm

]

[Fast355]

Thanks for the replies, Is the best way to find were you get to a lean cruise sweet spot is with EGT?

This is what I am wondering. I cant really get below 65 KPA cruising... I am assuming that is b/c my cam does not make enough vacuum. At idle out of gear I am in the same range.

I logged my 5.7 Vortec with a 215/220 cam in it today. 55 mph @ 1,500 rpm with 13% throttle and 45-50 kpa on flat land. 70 mph @ 2,175 and 22% throttle at 45-55 kpa. Cruise timing was 32-39* btdc. 32* @ 1500 rpm and 39* @ 2,150. It wants more but distributor limitations prevent it. 41+ gives misfiring. Stock 0411 van tune only allows 35*BTDC.

[delcowizzid]

I logged my 5.7 Vortec with a 215/220 cam in it today. 55 mph @ 1,500 rpm with 13% throttle and 45-50 kpa on flat land. 70 mph @ 2,175 and 22% throttle at 45-55 kpa. Cruise timing was 32-39* btdc. 32* @ 1500 rpm and 39* @ 2,150. It wants more but distributor limitations prevent it. 41+ gives misfiring. Stock 0411 van tune only allows 35*BTDC.

how is the rotor phased you can probably get more in it if you clocked it round so its firing closer to the correct cylinder post in the cap

[Fast355]

how is the rotor phased you can probably get more in it if you clocked it round so its firing closer to the correct cylinder post in the cap

Its phased to spec of 0, it will throw a P1345 if i get it too far off.

[delcowizzid]

that is if you move the whole dizzy a tooth or clocked the case round and put the cam and crank triggers to far out of sync but if you move only the rotor on its shaft like an adjustable msd rotor it wont know its moved just the rotor will line up better at full timing and youll get more timing in the tune before you start sparking either to nowhere or to the previous distributer post in the firing order.if its phased with the rotor pointing directly at the post at TDC its going to be 20 degrees round from the post at 40 degrees advance.you can also do it with a rotor with a long outer edge and trim off either end of the contact to cover the post in a decient arc of movement but chop it short enough o stop it crossfiring to the next post

[Fast355]

that is if you move the whole dizzy a tooth or clocked the case round and put the cam and crank triggers to far out of sync but if you move only the rotor on its shaft like an adjustable msd rotor it wont know its moved just the rotor will line up better at full timing and youll get more timing in the tune before you start sparking either to nowhere or to the previous distributer post in the firing order.if its phased with the rotor pointing directly at the post at TDC its going to be 20 degrees round from the post at 40 degrees advance.you can also do it with a rotor with a long outer edge and trim off either end of the contact to cover the post in a decient arc of movement but chop it short enough o stop it crossfiring to the next post

Honestly its more trouble than I am looking to go into at the moment as the only time I pull those kind of numbers are steady speed, flat road, with no headwind, the only time it really needs much more than 39* of timing is downhill, overrun. When I put gears in it, I may look more into it. However my longer term plans are 24x or 58x and CNP ignition. Might also convert to DBW and someday a GM 6L80E.