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

[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. 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.