Dual quad tbi setup? Start from mid 80's cross-fire ecu?

[Keithnh]

New to fuel injection performance modifications and just trying to get my bearings really. Printed out the "TBI Conversion" article on homepage and was glad to have clear pictures and explanations of basic idea of parts. I would like my first application to be a dual quad (2tbi unit) intake on a custom Pontiac 444ci/400 block with a flat tappet cam. Looking for a very strong high compression 6500rpm maximum operating range in a street driven car. Im not sure this is possible with tbi, have read that tbi is very strong in lower and midrange with 300hp attainable easily with a single on a 350 small block. The rpm limiting factor not being electrical or injector capabilities but flow of tbi unit, heads and intake. I will have ported heads and a dual quad manifold with very straight runners "Offy Equa-Flow" and was thinking 2 sbc 500cfm? tbi's might be just the ticket to have an abundant fuel supply with a self-regulating mechanism(computer) to keep from wasting fuel. Never knew there was such a deal from the factory but recently heard in the mid 80's there was a "Cross-fire" tbi setup used with little success, maybe too much for small block?? I would be running an electric fuel pump and tunable fuel pressure adjuster as well as possibly high performance manifold plates. Think there has been enough aftermarket advancement this may be possible by now and work pretty nice. Just ordered a book on Chevrolet Fuel injection so have some reading to do.

[Byron]

CFM Technologies has the 4bbl - TBI adapters for spread bore and square bore.
Crossfire was 2 single barrel throttle bodies.

[Byron]

Big block TBI's are also bigger with 2" throats with small block TBI's being 1 11/16 bore

[lionelhutz]

The crossfire is too old to bother with. It was only 2 injectors and any newer TBI computer is also capable of firing 2 injectors.

You could do the http://www.dynamicefi.com/ conversion as well as the adder option to run 2 TBI's with the computer. You'd also get the extra features their system offers.

But then, one of the computers from factory that was used for both TBI and multi-port might have V8 TBI code and be capable of driving 4 TBI injectors. Possibly it will require a little modification. Hopefully, someone else who knows more will chime in.

[1project2many]

Hello, and welcome to the forum.

It's neat to see non-Chevy engines getting EFI. I have a friend with an early Poncho fullsize convertible and 455 that's done an EFI swap using a 4bbl manifold with PFI. It's a very cool project.

I'd like to meet the person or people who convinced you the Crossfire system was no good. Usually a poorly working system wasn't the system's fault. But it's not built for what you want to do. It's two single throttle bodies that flow as much as the stock smallblock Chevy TBI.

http://www.grumpysperformance.com/1984c2.jpg

You can see some pictures of what folks do to the stock manifolds here (http://www.technovelocity.com/chevyhackers/tech_articles/port_polish/port_polish.html). It's hard pressed to support over 300hp.

Dual TBI as a first TBI swap project is a big step. There are some challenges in making sure the fuel system will supply both TB's properly and in building a proper throttle linkage which can be synchronized for matching throttle angle. And there's distribution issues in the manifold but those may be secondary if you have a proven manifold. There's wiring but it's not that much worse than a single TBI retrofit. PCM choice could be critical to making this work. Electrically the ecm / pcm must be modified to work with four TBI injectors and of course there's the actual work of tuning this combination so I'd choose the 16197427 or contact Dynamic EFI for an EBL ecm. It's not impossible but it is going to be more work than a single TBI swap.

2bbl TB air flow is measured at higher vacuum than a 4bbl carburetor so the flow numbers you find are not directly comparable. As mentioned, the large bore 454 TB's are the ones to get. Tuning for good street operation will take some time so if you get frustrated quickly with an engine that doesn't run right you might want to practice on some stock or mildly modified vehicles before tackling this one.

[Byron]

I wonder about progressive dual TBI's - could it be done with 2 separate ECM's - separate TPS and maps for each?

[1project2many]

I've seen some very interesting stuff over the years and I think a determined person could make the dual ecm solution work. But I'd prefer to stick with a single ecm to reduce the number of variables. Yes, pun intended.

[Byron]

Both ecm's would share the distributor, coolant temp sensor, ???

[Six_Shooter]

No modifications are necessary to run 4 injectors from a TBI PCM. I have a friend with two cars running stock (unmodified) '7060s, running home made 4 bbl throttle bodies made from pairs of GM throttle bodies. He simply wired the injectors in series pairs and has had ZERO trouble for years this way.

I agrre a single ECM solution is best.

Also progressive is not easily do-able with a stock GM ECM, since it has no provisions for progressive secondary injectors. If that's a must or highly desired a Megasquirt is what I'd recommend. The problem with trying to run progressive throttles without also running progressive injectors is that you will get a large amount of fuel puddling above the secondary throttle plates and then when they do open will cause a rich condition. This will not always happen at the same load or RPM, so it would be difficult to tune around, also if you stab the throttle let off and then right back into the throttle, you'd likely not get that excess fuel on the second stab, so that would cause a lean condition. Best to just keep the throttle linkage 1:1 for all throttle plates if you go with an ECM that's not capable of progressive injector control.

As a side note, I like the crossfire system. I have on eon my grandfather's '71 truck, running off a '7427 PCM, that is also controlling a 4L60E. :)

[1project2many]

Yes, shared sensors.

GM ran staged injectors on the ZR1 with an RPM triggered external driver module. It'd be interesting to scope the injector pattern if the VE is set to "0" for a range of cells as that approach to staging the injectors would work with multiple ecm's. And of course, if the code is acessible then it's possible to use custom code to zero injector output below a specific TPS.

[Six_Shooter]

The LT5 didn't use staged injectors, it used a set that could be switched on and off. And to switch them on and off the engine had to be off, and the switch turned with the ignition key, then restarted. All 16 injectors were AFAIK always on when the high power mode was engaged, just using a different VE table than the 8 injector mode.

[Fast355]

The LT5 didn't use staged injectors, it used a set that could be switched on and off. And to switch them on and off the engine had to be off, and the switch turned with the ignition key, then restarted. All 16 injectors were AFAIK always on when the high power mode was engaged, just using a different VE table than the 8 injector mode.

Actually I am fairly certain 1 project is correct. The switch disabled the secondary throttle plate (s) on the ZR1 but the secondary set of injectors and throttle only opened at higher rpms.

[1project2many]

The LT5 didn't use staged injectors, it used a set that could be switched on and off. And to switch them on and off the engine had to be off, and the switch turned with the ignition key, then restarted. All 16 injectors were AFAIK always on when the high power mode was engaged, just using a different VE table than the 8 injector mode.

This seems like a mix n match of system info. LT5 TB had tiny primary blade and larger secondary blades. Also had primary / secondary runner combination. When secondaries were active, second set of 8 injectors came online. Activation was RPM and TPS based (I said RPM only). LT5 also came with "valet" key which would disable secondary operation. That system would prevent secondaries from opening and would prevent secondary injectors from operating. There are some descriptions, pictures, and maps for OEM TPS v RPM curve to activate secondaries on this page:
http://www.corvetteactioncenter.com/forums/c4-corvette-zr-1-a/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html

[Byron]

Damn Mercruiser engines. LT5 built by Mercury marine. total POS to work on. DIS under intake manifold made changing wires a bitch.
I work on Vettes all day and cringe when a ZR-1 drives up.

[1project2many]

Yep. I went from GM dealer land in '91 to Corvette specialty dealer in '98 and lived through ZR1 then LT1 days. I fix school buses now so maybe my Vette experiences did more damage than I realized.

[lionelhutz]

I posted that the Crossfire is useless because it's wrong for this application and the stock computer is too simple and badly supported to bother with. You can use the manifold and throttle bodies for a swap with success and even make a stock system work if you want, but the throttle bodies and ECM are completely wrong for this application.

Trying to run progressive on the throttle blades and/or 2 ECM's is over-complicating things for no good reason. Carburetors used progressive linkage secondaries to help correct various issues caused by their mechanical operation. EFI systems use the software to take care of those issues so a mechanical fix isn't required.

On a separate note, you can try to create a more progressive response in the throttle linkage between the throttle pedal and the TBI units. For example, make it so the first part of the pedal travel moves the blades slowly and then have the blades go faster as the pedal moves more. The amount of progressive really depends on how sensitive you want the pedal to be in the "cruise" range.

[Keithnh]

Wow got some good info here, not sure I mentioned I would not be running an electronic transmission just a simple turbo 400, and the intake I have looks like it has 2 isolated sections with a rectangular hollow connector ( I call it the "warehouse") connecting the 2. The sections fuel the front 4 and the back 4 respectively ... it is not interlaced. Although no expert I believe progressive is not the ticket and would cause uneven fuel distribution and a very rough running engine. Would prefer to run a single computer if possible with only the basic necessities to keep the engine running as well as I can make it. WAS thinking I might need 2 computers and sets of sensors as the sections appear to be very distinct, but would like to have a s few components and variables as possible. Will have individual header tubes to locate oxy sensors in and since this is an experiment, don't mind adding connection spots to manifold for other sensors if I have to. I was worried about throttle likkage but do have machinist buddies luckily :)

[dave w]

I wonder about the option of using a Dynamic EFI EBL Flash system, which can operate 4 TBI Low Impedance injectors with the 4 injector upgrade?

http://www.dynamicefi.com/EBL_Choice.php

http://www.dynamicefi.com/EBL_Flash.php

dave w

[Keithnh]

I used to be an electronics tech and think of this as a bit of a challenge. I wish I had a diagram with computer inputs and outputs to start with. Just helps me collect my thoughts as I am used to them. Would like to know what exactly the computer is saying to the tbi. Understand there are adjustable fuel pressure mechanisms that enable tuning but I don't believe they are computer controlled. So if the computer is just saying "squirt" and "stop squirting" to the injectors according to the sensors and the throttle position they will be delivering more fuel in between the "squirt and stop squirting" instructions at a higher fuel pressure. The computer makes it possible easily most likely to respond to its inputs thousands of times per second, probably far faster than an injector has the capability to react. Was wondering however how injectors alone could respond as accurately to changes as the multiple systems of a carb idle,primary,secondary,accelerator pump,power,choke without all the mechanisms ... will be interesting to see this project through and find out. It appears the computer is possibly modifying the spark advance in some applications, not sure if it needs to in my application, don't know whether there is a sufficient advantage over vacuum and centrifugal advance and complexity would probably be far greater for computer program most likely.

[uncabob]

Keith: Welcome to the forum. Best info you will find on Fuel Injection. The Crossfire system was originally used on the L83 engine in 82,83 and 84. The Corvette crossfire was on the 1982 and 1984 Corvettes. (There was no 1983 Corvette). I feel the crossfire was much maligned because of tuning difficulties. You should know injectors on the crossfire were not identical and were plumbed in series. The fuel was supplied to the first injector which used an accumulator and the excess fuel went on to the second injector which had the regulator. This was the reason for the mismatched injectors. The L83 Corvette engine in 82 was rated at 205 horsepower. The manifold is rather unusual and I understand some machining is required to fit up to a later block. The computer is very slow and I don't think you would find any up to date source. You could however use a later computer and plumb the TBs in parallel by using blocking plates instead of the accumulator and injector mounted regulator. You would need to regulate fuel pressure with an external regulator. My setup is as suggested above using a 1227747 ECM and treating the the separate TBs as a dual truck throttle body. I have higher volume injectors than the original and a RV cam. The horse power I can get is less than 300. You may get more fuel by using BBC injectors but there would be some machining. I also believe the cast iron heads may be a limiting factor. You are in the right forum for the info you're looking for. Good luck. Bob

[ScottP]

Great to see another Pontiac on its way to getting EFI! Mine is a 455 with a port intake manifold
from Professional Products being run from a 12200411 PCM. I swapped in a 4L80E at the same
time as the EFI conversion.

The dual-quad Offy setup will look great with the TBIs on top, and was something I seriously
considered before I got a great deal on the Professional Products kit. As others have alluded,
running dual TBI can be done with a GM ECM, but there are a few considerations. You can
run the injectors in series, which means both injectors on that driver see the same peak and
hold currents. You can also run them in parallel (this is what I've done in the past), which
requires the injector drivers inside the ECM to be upgraded and the current sense resistors
to be swapped out. I believe this is what Dynamic EFI does when you select the 4-injector
upgrade.

One thing you might want to track down soon if you're going to go the GM ECM route is a
distributor. The distributor used on '81 Pontiac 301 & 265 applications is a drop-in on your
400, and has all the correct interfaces/signals to feed a variety of C3 and P4 ECMs that were
used from the early 80's all the way up til '95. They're getting a bit scarce in the junkyards,
but make the swap to a GMECM on a Pontiac a bolt-in affair. The one you want is casting
number 1103453.

-Scott

[dave w]

I used to be an electronics tech and think of this as a bit of a challenge. I wish I had a diagram with computer inputs and outputs to start with. Just helps me collect my thoughts as I am used to them. Would like to know what exactly the computer is saying to the tbi. Understand there are adjustable fuel pressure mechanisms that enable tuning but I don't believe they are computer controlled. So if the computer is just saying "squirt" and "stop squirting" to the injectors according to the sensors and the throttle position they will be delivering more fuel in between the "squirt and stop squirting" instructions at a higher fuel pressure. The computer makes it possible easily most likely to respond to its inputs thousands of times per second, probably far faster than an injector has the capability to react. Was wondering however how injectors alone could respond as accurately to changes as the multiple systems of a carb idle,primary,secondary,accelerator pump,power,choke without all the mechanisms ... will be interesting to see this project through and find out. It appears the computer is possibly modifying the spark advance in some applications, not sure if it needs to in my application, don't know whether there is a sufficient advantage over vacuum and centrifugal advance and complexity would probably be far greater for computer program most likely.

I think these links are what you are looking for? The links are for the 1227727. I can't find a link for the 1227747.
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html
http://www.exatorq.com/ludis_obd1/1227749schematic.html

dave w

[Keithnh]

Wow , more great info ... will have to hunt a Pontiac 301 distributor ... now I have an excuse to go grab the whole engine that has been sitting on a shelf at a local junkyard with the factory turbo on it if its still there think they want 250$. That crank is supposed to have rolled fillets though the turbo setup was not exceptional. Will have to print out those 9 schematics and study them ... didn't find a legend for the abbreviations ... may be able to figure out with some brain burning :) Have to speed read my tbi book that's coming ... get my feet a little wetter :)

[Six_Shooter]

The park input on the '7747 does not negate the benefit, or need, of a VSS on the '7747. EVERY '7747 swap, or equipped vehicle I have worked on has ALWAYS benefitted from a VSS being used, and most other people have seen the same results.

Also the '7427 does indeed have a park input, it's just not a simple on and off single input. There's a set of 3 pins, that depending on which ones are grounded at any one time tells the PCM which gear is manually selected.

[lionelhutz]

In case you have missed it, there is a forum dedicated to bin files, definition files and wiring diagrams on this site. Just search for the ECM you want to use. Some appear multiple times due to having multiple applications and bin definitions.

http://www.gearhead-efi.com/Fuel-Injection/forumdisplay.php?20-GM-ECM-Bins-TunerPro-Definition-Files-Wiring-Diagrams-Tuner-Info!

[dave w]

Also the '7427 does indeed have a park input, it's just not a simple on and off single input. There's a set of 3 pins, that depending on which ones are grounded at any one time tells the PCM which gear is manually selected.When the '7427 is "seeing" park input, would this default the '7427 to Near Idle Fuel / Spark tables? Would setting maximum TPS% for Near Idle to ZERO default the '7427 to use Off Idle Fuel / Spark tables when it "Sees" park input?

dave w

[Six_Shooter]

Not likely that simply, and that's not how the park input of the '7747 works anyway. The '7747 uses other variables to switch between the Idle tables and off idle tables, one of those parameters being vehicle speed.

I don't know why you continually want people to not use a VSS with the '7747 or say that it's not needed. you're the ONLY person I've ever seen that suggests that this is even a good idea. Even on a boat there can be a VSS signal, either from engine output speed (which would be tied very directly to RPM, obviously) or ouotput shaft speed to the prop, which depending on the boat could differ from the crank speed.

The fact of the matter is, claiming that the '7427 doesn't have a park input is just factually incorrect, it's just not as simple as grounding a single input.

[dave w]

Not likely that simply, and that's not how the park input of the '7747 works anyway. The '7747 uses other variables to switch between the Idle tables and off idle tables, one of those parameters being vehicle speed.

I don't know why you continually want people to not use a VSS with the '7747 or say that it's not needed. you're the ONLY person I've ever seen that suggests that this is even a good idea. Even on a boat there can be a VSS signal, either from engine output speed (which would be tied very directly to RPM, obviously) or ouotput shaft speed to the prop, which depending on the boat could differ from the crank speed.

The fact of the matter is, claiming that the '7427 doesn't have a park input is just factually incorrect, it's just not as simple as grounding a single input.

It might appear that I advocate not using a VSS. Quite often members are looking for the absolute lowest cost / simplest / bare bones system. It's unfortunate that JTR has "back ordered" (for over a year now) their affordable 2K VSS ($85). http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html

I welcome your Technical Write Up on connecting a Park input to a '7427.:thumbsup:

dave w

[Keithnh]

ScottP was wondering how many injectors on your 455 Poncho and how does it run compared to a carb'd car? I know my 90 Z71 tbi seems like it stumbles if I do a quick to the mat stab ... something I used to test quadrajets I rebuilt with. Beyond the stumble it runs very nicely and buries the speedo quickly if I let it as long as the sensors are working and exhaust is tight. Is the fuel economy much different than a carb'd 455? The 6000lb p/u gets a solid 15 mpg with a computer tranny I believe. My 444 is a custom short stroke (4.040) 455 basically with a punched 400 block and modified 428 crank. Was planning on it being located in a 71 Formula 400 and being a summer cruiser and occasional strip attendee. Not sure I can afford the electronic transmission at this point, maybe down the road apiece. Was thinking I might gain an average of 5mpg or more with it. Would love to make the car a worker bee since my miles to work has decreased from 110 round trip each day to about 20 ... was thinking 20mpg avg (probably impossible or at least miraculous with my current thought process) and some serious weatherproofing. I got 15mpg with my 400 some years ago in a 64 gto with 3.23 rears and 780 Holley 3310. I also have a sbc project almost done that might make use of a single tb with 2 injectors on a GMPP RPM 2-plane manifold with 314 ci to feed. It also is short stroke (3.074) and meant for an expanded operating range to 7500 with fastburn heads. The donor engine is an 89 350 I have the entire electrical/sensor setup for untouched on my parts p/u.

[ScottP]

My 455 uses a port fuel injection manifold specifically for Pontiac engines, so there's a total of (8) injectors (one per intake port/runner).
The difference in driveability over my old Quadrajet is simply night and day. My carb was setup well and ran nicely, but the EFI setup has
simply transformed the car. Keep in mind, I went EFI and electronic trans at the same time, so some of the driveability improvement
also came from the 4L80E (was previously a TH400). I can't report on fuel economy improvements yet, mostly cause I've only had the
swap running for the last year, and in that time I didn't have a working speedo. As part of the 4L80E install, I lost the provision for my
stock cable driven speedo, so I didn't have a means to keep track of mileage for the season. I've since fixed that this winter with a
mechanical cable drive box from Dakota Digital, but won't be able to get mileage results til the spring.

BTW - can I infer from your screen name that you're somewhere in NH?

-Scott

[Keithnh]

Hey Scott, Yes I live in Pittsfield near Concord NH. So your 455 is a TPI setup not TBI right? Actually I think Pontiac had fuel injection in the late 50's ... not sure what kind of setup , surely didn't have a computer :) maybe experimental or race only Super Chief ??? Still getting my feet wet with this idea ... maybe over my head ... going to read the book I got coming soon as it gets here. Probably should start with the chevy single tbi first but the Pontiac block is done and crank is in work. Chevy is going in an 84 Cutlass with a 4-speed stick conversion. My 89 parts p/u is a tbi with stick ... was thinking everything including wiring might be usable on the Cutlass. The donor tbi 350 still runs but tranny missing 2 gears and it smokes alittle. I have most of the motor parts and fastburn heads are finished. I haven't chosen Pontiac heads yet, have about 15 sets ... was looking for about 90cc chambers and like 6x-8 ports, need to be angle milled quite a bit they are 101cc, just got a set of late 46 supposed to be 89cc most likely be one of the 2. The Pontiac d-ports can be ported to flow very well ... I will be setting them up myself initially. Will probably leave 350 running as a model to help if I choose to pursue dq-2tbi 1st, I may try and if I fail I have plenty of carbs to throw on the Pontiac ... wouldn't hurt to get the custom motor running and broken in with a carb so I can see how much the fuel injection improves it later either. Have a trips manifold and a 64 GTO that would be cool fuel injected ... that might work progressive as the linkage came that way ... center carb most of the time then the secondaries are the outer 2 ... 2injector tbi for center and 2 singles for either end might work nice. Will start collecting parts, would like these 2 motors to run this year. Keith

[1project2many]

Actually I think Pontiac had fuel injection in the late 50's ... not sure what kind of setup , surely didn't have a computer :)
It was Rochester mechanical FI similar to the smallblock Chevy. You can read more about the mechanicals here. (http://oldcarmanualproject.com/manuals/Chevy/53-75Corvette/Rochester%20Fuel%20Injection.pdf) It was a rare item in its day and parts of a complete system command crazy money now. The SBC -> Cutlass swap should go well. If the Cutlass had a 260 the SBC will be a little heavier but the manual trans will shed pounds to offset. Starting and breaking in the Poncho engine on carbs is a great idea. Good to keep some variables out of the mix. Truly progressive TBI with operation on only one TB at idle would be neat but use of TBI ecm will require external circuitry to disable outboard injectors at idle. Better might be using low flow injectors and small diameter outboard TB's then setting throttle plates to allow some airflow.

[Keithnh]

Not sure how quickly this will go ... was thinking the computer in the truck might drown the smaller displacement (350 low compression to 314 high compression) but it is supposed to be self adjusting, possibly "learns" continuously as well? That swap Im almost positive is doable the question is will the tbi feed the smaller mouse to the higher rpm I want (7000+). I think with the dual quad Pontiac I would want to fool the computer to think there is only one carb and flow test/match the tbi's so they flow the same and dead nuts match the throttle position via linkage, maybe somehow have mechanical adjustments on each. Then use just one set of sensors so it would really be very similar to the chevy setup.

[1project2many]

The ecm is limited in how much learning it can do. With the stock program it will not help the 314 make best power.

You don't need to fool the computer. It doesn't know anything to begin with! ;) You give it numbers for how much fuel the injectors can deliver and how large the engine is. Throttle angle is measured on one TB. The second TB angle must be matched to the first by measuring ported vacuum with a very sensitive gauge. The IAC valves from both TB's are wired together so both operate when the ecm commands.

7000+ RPM is higher than most stock ecm's have tables for. Most stop at or near 6375. The computer can function at higher rpm and there are some simple fuel and spark curves for tuning but you have less control than at lower rpm. How much HP are you expecting the small engine to produce?

[Six_Shooter]

Most TBI cals have limts of between 4400 and 4800 RPM, IIRC. SOME of the MPFI cals seem to go up to 6375.

[Keithnh]

Had to start my'90 z71 today, first time in a month or 2. Battery cranked very slow but started right up and seems to run perfectly instantly. Let it charge battery awhile and zoomed the throttle several times before shutting it off. Crisp sweet acceleration ... bought this truck used with 98K on it 165K now ... still runs silken, uses no oil, no vibration at all. Is it early TBI? I would really like the custom Chev and Pontiac motors Im building to feel similar and still meet my performance goals. The small chev was/is my first custom effort ... I had read an article comparing similarly (stock hp) built sbc motors in which the smaller motor 302 whipped the larger 327 and 350 in both torque and hp above 6000 rpm it did lag in both areas below by the approximate difference in percentage less displacement. Beat the higher displacements at high rpm with lower flowing heads tho! My thought being heads not choking due to less flow requirement at high rpm. So my little idea forms to build a new age old school 302 with fastburns that are circle track 350 heads but meant for a medium operating range on a 350 with hydraulic roller LT4 hot cam. They destroy the 302 DZ heads in flow from .100 to .600 and several local people who race that I have spoken with have had high praise for them on 350's. "They like to run lean tho" was said. This I believe is a Vortec trait that helps improve fuel economy .. why not? I do up a little chart and see that displacement of a 350 at 6500RPM is roughly equal to that of my 314 @ 7250RPM. I chose a CC solid roller cam 268 Mag with a lift just below where the heads stop increasing and made choices aimed at higher rpm(light pistons-Scat 6.0 wi/ARP2000) although sticking with a factory baby LT1 crank. Have the GMPP RPM dual plane was looking at GMPP single plane, it might adapt better to tbi. Have a real pretty Demon 650 that might start things off. How many horses? Stock DZ heads in their shootout peaked @ 356 HP @6500 352@7000, 331 TQ @4500 264@7000 With these far superior heads Im looking for 400 and 400 peaks. I do want something that will rev, I just like the sweet music.

So does the computer squirt a shot of varying length for each piston? or does it say "well they are all going to need this much till next time" and squirt enough to feed several from the plenum at once? If I was looking for more rpm within limits what about telling the computer its a 628ci instead of 314 and dividing the tach input by 2. Maybe the reason for table limits is the injectors wont function reliably at higher levels?

[1project2many]

I've got two 3" stroke engines running. First was built back in the '90s using a classic recipe: 327 block, 283 crank, 350 hp 327 camshaft. I found a guy in AZ selling cast 9:1 pistons, bolted on a set of 1.84/1.50 58cc heads and a crossfire, and I've been running it ever since. It's no high rpm screamer. The truck cruises at about 2600 rpm but it's seen a best of about 18 mpg cruising in MT. It's gone way faster than a mostly stock '57 Chevy truck should ever go and that's all it needs to do.

The second engine is a little closer to what you built. '96 4 bolt block, baby LT1 crank and rods, cast flat top pistons, Vortec heads. Nothing fancy inside, just pay attention to make sure the machine work is where I wanted it. I spent a *lot* of time with good dyno software modeling cams and intakes though. Short stroke engines with long rods almost always seem to do better with milder cams and smaller ports. Learned that building engines for the vintage Sportsman roundy-rounder. I ended up with a very mild cam for my Suburban. It doesn't do badly although there are times towing the trailer that the small displacement is obvious. I keep thinking I'll throw on a turbo but the truck will probably rust out before I get a chance to start that project.

For injector control the ECM figures how much air is entering cylinder and delivers fuel to match. Snapping throttle open requires extra fast shot, snapping throttle closed requires quick drop in fuel. There's really no thought about the future. The reason for the table limits is because the stock pickup TBI engines are dead by 4500 rpm. I don't think anyone at GM thought the TBI computer would be used for a 400 hp engine at 7k.

It's probably not a great idea to start trying to fool the computer right away. Doing that right usually takes some practice. Some 93 and then most 94 & 95 TBI trucks use an improved computer. That's what's running my Crossfire engine right now. The main spark table goes to 6000 the main fuel table reaches 6300 rpm. I think that will work.

[lionelhutz]

When feeding injectors with a fixed fuel pressure, once you reach the point they are are constantly then that's all the fuel you can get out of them. It doesn't matter what you tell the PCM the engine is.

You can't divide the tach input or the computer can't control the timing right because it would only send back the corrected "spark" signals for 4 cylinders.

[Keithnh]

Think I need to read my book before I pester you guys with silly questions :) I was thinking why not simplify and use computer only for fuel control and not spark control. Not sure why it needs to control both but Im sure the additional information and ability to modify timing could be used to enhance efficiency just thinking it over in my head.

So more rpm is more a matter of a higher capacity injector? and subsequent computer reprogramming? Or maybe just stick em in there and raise fuel pressure? If using bbc throttle body doesn't it have a higher capacity injector? Would a higher capacity injector negatively affect efficiency when its extra capacity is not being used? It appears to be a common performance swap to put bbc throttle body on sbc. At least advertising implies it.

Glad to find a 3.0 stroke compadre! Really wanted to make some engine changes and see if I could make something I wanted to actually happen. My main interest is Pontiacs, I have several ... thought an sbc would be simplest and cheapest to get my feet wet in customization with and I really like the way the Z71 runs. My small mouse will go in a relatively light car, 84 Cutlass with a 4spd. Figuring 3.42 rear 3200lb car. Not sure what element of the DZ302 made it wind, believed the Cross Ram dual 4 barrel might have helped but the shootout results that I quoted earlier had the 302,350 and 327 with similar factory 024(LT1 equivalent) intakes and single 4's(Holley 750). Possibly the shorter stroke, slower piston speed and smaller flow requirement fill the cylinders more efficiently at high rpm. Figured I would try to beef the low rpm side of smaller displacement by adding compression, solid roller cam and improved heads and build short block for rpm. I was going to have to have piston tops milled .035 till I found 350 pistons designed to be used with a factory stroker created by maximizing stroke when reducing rod journal to 2.000 vs 2.100. Diamond still had them as a shelf piston. Still does I think. 100 + gm weight reduction and stronger. Lighter pins too. Have a shaft rocker conversion setup too that looks really nice. Time will tell of its durability. Fasties have light sodium filled valves ... my used set still had them in for 700$ complete and my picky machinist gave thumbs up on all not even needing a valve job. Heavier 7/16 ARP add 10gms I think to the Scat rods ... haven't done a weight comparison with factory. Want to do a belt drive and that may happen with this motor. Had beehive springs installed to replace the fastie springs for the mild solid roller. They will either be just right or rpm limiting in which I will go with a stronger spring and use them on the flat tappet Pontiac possibly. Crank will be stroked 3.074 just enough to hit zero deck( 6.0+3.074/2 +1.488=9.025), bullet-nosed nitrided cryo'd and balanced to lighter weight. Already being done on Pontiac crank now (10.220). Doing it first and am hoping for a good result between 3 shops as it is the biggest challenge to get right. Trying to set up a bit of a "system" as I have several motors to do. Possibly fuel inject all of them. We'll see :)

[1project2many]

Higher RPM is one issue.
Fuel and air to support expected power level is second issue.
They may be related but not always.

BBC TB has larger bores to allow more air. Original BBC injectors flowed much more fuel than SBC at same pressure. Later BBC injectors flowed slightly more fuel but were run at higher pressure to make up the difference. Often people install larger BBC TB but choose a different injector than the BBC parts and modify fuel pressure so delivered fuel is correct. Sometimes a higher flowing injector causes problems at idle or low load when trying to deliver small amounts of fuel. Unless the injector delivers a very large amount of fuel there usually aren't any problems as long as the ecm is tuned properly.

RPM is related to the ecm and how its programmed. It can run the engine to a higher speed but it's just not set up with tables for high rpm control. That doesn't mean it won't work, just that you have less tunability. It's kind of like a distributor and carb... at high rpm you're at max advance and the throttle plates are wide open so the only thing the carb does is dump fuel to match airflow.

I've driven real DZ cars. The car is deceiving if you're used to torque because it never feels really fast, but it pulls and pulls. I think the slow piston speed and smaller pulse size created in the intake allow these engines to work with smaller plenums more common in the '60s. I know they worked well with many of the old roundy-round favorites. There are plenty of stories around of track built 302's (301 to the old racers) keeping up with the BBC powered modifieds on short tracks where traction was a problem. Lighter car with better balance, higher gears, rpm up, corner exit speed up, and you're playin' with the big boys. These days it's a whole different world but the 302 worked really well with what we didn't know back then.

[Keithnh]

I know I use forums sometimes to collect my thoughts (guesses sometimes :) ) as well as gather and share information. Spent some time on Pontiaczone pondering what makes rpm increase exactly and came to the conclusion it is mainly delivering and igniting enough fuel in the cylinders to generate enough heat to make more force than is necessary to keep the crankshaft turning at its current speed against its current load. I believe there is a certain ratio of that force that controls acceleration (the higher the faster) and determines where the engine stops "making power"( nearing 1 to 1). The ignition source plays a vital role timing the delivery of the force but doesn't affect the level of it much if the entire charge is consumed.

Most have given a thumbs down for my 302 project. One machinist said it wouldn't make enough power to overcome the weight of the rotating assembly. Strange how for many years the L76? 63 Corvette 327 was reigning monarch of sbc engines (I believe in HP per inch) at least per Wikipedia and my project is just 13 CI less. With far superior heads. Saw a neighbor kids 64 chevelle with dual quads lift the front wheels with a dual quad 283 in my younger days. Also saw a 55 Chev State Trooper restoration near the Petro in Beaumont Texas with a factory 200mph speedo years later in my over the road trucking days. So my plans continue for the 314, have accumulated most of the parts ... heads are done ... the induction system was a matched GMPP RPM dual plane to the GMPP fastburns with a Demon 650. Demons are supposed to flow up to 100cfm+ their rating.

[Keithnh]

Lost last portion of post ... didn't lose whole thing because of auto-save, a nice feature I haven't seen on other forums. Is there a hidden key or something you can hit to do that manually, I sometimes spent awhile on posts and then my computer boobs and I lose it one ... maddening. I had mentioned the 650cfm Demon carb rated flow was 1123200cim that corresponds to what my engine 314 displaces @ 7154RPM exactly. Also that the bbc tb rating is in that neighborhood above 600cfm somewhere and so basically if it does the same as a carb beyond the table limit then it may possibly still do what I want. The fuel supply has to keep increasing or the rpm will not increase unless load diminishes so there must be a way of it doing that, more air flow added to a set fuel supply would just weaken charge.

[1project2many]

You're definitely on the right track. Engine acceleration is the result of producing more power than it takes to maintain crank speed. And it goes to zero when the resistance, or load, equals the power. Ultimately a large part of your power goes into defeating wind resistance, or drag, as the car's speed increases. Doubling your speed quadruples the drag! If your car needs about 11 hp to overcome drag at a steady 60 mph then it would require 75 hp at 120, about 150 at 150, and 350 at 200 mph. In addition you've got to overcome tire rolling resistance and friction in the powertrain as well so it will take a fair amount more power than the numbers above suggest to maintain speed, let alone produce an increase in speed.

The machinist who gave you grief probably thinks like several I know. It's something like "Why bother building small displacement engines when you can go big for the same money???" They don't get it. I got plenty of criticism when I said I was putting mine in a Suburban but I've got enough years with it to know that it wasn't a bad choice. It cruises in OD on fairly level ground but needs to downshift to accelerate on hills. That's ok though. It can pull the hills on 9 outside Keene fast enough to get me a visit with the judge.

The "more fuel" answer is usually solved with port injection. You can increase fuel pressure some and you can go to multiple TBI's. 85% duty cycle is the max that most people use. There is a different style injector used on medium duty truck TBI units and there may be one that flows more than 90# hr. A guy could swap the injector "pods" and run the smaller injectors. This would also help clear out the air path.

[Keithnh]

Really Im just having trouble accepting a 302 Chev would turn 8000rpm in 1968 and wont turn 7500rpm in 2016. Early 302s had the smaller main crankshaft but later ones didnt and held up better at high rpm. Was going to set my rev limiter at 7250 and pound away on it with some safety factor believing I wont be near the end of the motor building power when the limiter kicks. The cam per Comp Cams software has a very wide power band and the motor shows unbelievable HP and torque numbers with the cam and heads combo I have with exact flow numbers punched into program. Per Chevrolet Power Handbook the LT1 factory crank is good to 7000RPM handling 350CI at factory bob-weight. I have significantly stronger rods and rod bolts, less piston speed and a lower bob. I figure 7500RPM for the 314. Will iron out my calculations before I test that limit, if I do. I figure 7250 will be concretely safe and would like to be able to provide the proper fuel mixture to build hp to that point reliably. One way or another. Don't have a good grasp of mechanical part of fuel delivery between various injection systems. A quadrajet has mechanical secondarys on the throttle body with vacuum operated air valve controlling flow, adjustable secondary air valve opening spring secondary ... accelerator pump "wells" on some, vacuum break and secondary tapered metering rods that vary fuel delivery with throttle position like the mains. Somehow the computer must be recreating their "responses" by varying injector shot if it stops because top of table is reached what varys the fuel amount? Vacuum does not control an injector it is squirted, right? Seems like upgraded "tables" might be offered in a chip with higher capacity injectors for enthusiasts to use the entire rpm capacity of their tbi motors. So it is very difficult to program the tables for higher rpm. Guess I thought with a computer I might possibly get better performance AND fuel economy with a light weight car.

[1project2many]

Really Im just having trouble accepting a 302 Chev would turn 8000rpm in 1968 and wont turn 7500rpm in 2016.

What you have to remember is this: The original 302 was built as a high performance engine from the get go, and was available with parts designed for racing. It was not equipped with a 2bbl carb, restrictive intake and heads, low compression pistons, and low flow exhaust. What you are asking about in 2016 is using parts that were designed to work with a low performance, air restricted engine in a near race application. It's not going to be easy but I believe you could get there if you pick the right components. For your goals I would opt for port injection over throttle body. But if I had to use TBI then I would run twins. I would not use the ecm from a 90 pickup. I would use the computer from a 94-95 pickup. I would not run the injectors in series. I would modify the injector driver circuits to retain peak and hold control. I would not choose to use the large bodied fuel injectors found on light duty trucks. I would obtain replacement injector "pods" to switch to the smaller bottom feed injectors as used in medium duty trucks and Holley TB's. I would not use a stock small cap HEI. I would prefer coil-on-plug controlled by an "E-dist" type electronic distributor. Barring that I would prefer a large cap HEI. I would opt for a high flow fuel pump delivering fuel from a properly baffled tank to both TB's connected in parallel and I would remove the individual regulators in each TB to install a single inline regulator for both TB's.

You seem pretty sharp. I think you would do well to spend time learning about GM EFI before tackling this. The factory service manuals do a good job of describing system operation so you'll have a fundamental understanding. There are also some very good books around and likely some good pages on the 'net. You can do a *lot* with a GM computer and EFI but there's a pretty steep learning curve to get you in the door. You might also want to look at Dynamic EFI's offerings. They modify stock GM computers so they are easier to use in high performance applications. They also include tuning software that is helpful for a "carb and points" guy to work with EFI. That might help shorten the time to get your engine running on EFI. Ultimately you can get good economy, response, and power from a computer but you're tackling an advanced level project which means there's a lot more going on than just putting the system in the car and driving.

[Keithnh]

Probably best idea is to get both engines up and running on carbs that I know more about first. Both engines are customs that may need to be dabbled with before trying out converting induction systems. I am not after the fastest drag thing either, although I love hearing a V8 sing and getting shoved back in the seat. My redneck caddy I bought for 500$ from my biker neighbor surprised me one day, 94 Eldo with a Northstar, leaks oil a little but doesn't use a quart between changes - he thought the tranny was bad .. just needed a fuse, doing 72mph in the hammer lane going to work and an Audi kept pulling up on my bumper like a child when someone next to me on Rt 101 EB, I tapped it hard which is something I had never done ... made a lot of noise that surprised me, I glanced over at tach noticing it move into the 5 grand+ range ... then back at speedo 125+ nearing 130mph. Only took a few seconds. Audi was way behind me and stayed there till I got off :) Whatever fuel injection setup on that Northstar works pretty good! Eventually I hope to become a "convert" :) Might have just added a new member to my stable .. 77 Pontiac Astre .. going to check out today possibly.