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Thread: 4 barrel throttle body with gm computer?

  1. #16
    Super Moderator Six_Shooter's Avatar
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    Re: 4 barrel throttle body with gm computer?

    In some applications dual IACs will work better to have more balanced flow to all cylinders. Take the Crossfire system that I have on my Grandfather's truck, with the way the TBs are laid out, using both IACs, just like when the system was new, works best.

    In a system where the TBI is a single or dual unit more centrally located, you can usually get away with just one.

    I mentioned it more to do with how people say you "can only run one IAC," which is simply not true.

    Only one TPS would be needed in anycase.
    The man who says something is impossible, is usually interrupted by the man doing it.

  2. #17
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    Quote Originally Posted by 4554x4
    Eaglemark, You have asked some good questions. I will research fuel pressure cam specs etc. I will need some equipment to record data. Where can I find this equipment Emulator etc?

    Ant thought to running two tbis on a dual quad intake? I do have the intake manifold and it would look cool!
    It's been done and I have always liked the look. But duel quad intakes are high rpm type thing. But with EFI tuning they idle and run from idle up fine. Most high performance intakes like that have no hot air crossover to warm intake in winter so they are sluggish when cold. But I have found the hot air intake from headers to intake using the delvac valve from just about any GM car fixes that. No vacuum lines needed. Just put the flapper into a hot air from headers to intake and it will let hot air in when cold and turn off to let only cold air in when warm. Also prevents TBI icing when temps are like 35 degrees and high humidity... rushing air and evaporating gas casuse temps to drop and TBI ices up... It's a North Idaho canada type thing!

    I have an AutoProm. It's the only emulater I have ever had and I can't find a reason to change. I do everything with TunerPro and can't find a reason to change. Guess when you get something that works you stick with it.

    The AutoProm is also set up to burn the chip when your done. It also has circuts to wire in your Wide Band. So it's hard to beat considering it all works with TunerPro.

    As far as emulating, burning, recording, chipping equiptment I would say look around Moates website. Cover what we do and more. Fair prices, great support. They always have whatever I need. Well once I bought a JimStim from another vendor because Moates doesn't carry them...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #18
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    Quote Originally Posted by 4554x4
    I definately have much to learn. Would it be possible to have too much CFM available, like over carb'ing or would the programing take care of that?
    To much CFM is hard to do with EFI since the fuel is controlled by ECM. What your talking about by overcarburating is you don't have enough air flow over venturies to suck out gas. with EFI gas is determined and injected. Cylinder still only takes in volume of air it can hold. So no you can't have to much CFM and cause that problem. With MPFI it's even elimanated because no air fuel mix in intake.

    But you only need so much CFM and a duel quad intake with two SB TBI and your still about 1000 cfm. You can loose some bottom end response. I noticed this in off road EFI systems I do I like smaller CFM (throttle plates) because of the low end response. Your always looking to idle and blip throttle. Total precise throttle control. But for a street/strip I don't think you would notice it, or have any issues you could not tune out.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  4. #19
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    Re: 4 barrel throttle body with gm computer?

    another issue with TBs that can flow massive amounts of air is that even the smallest amount of throttle can produce a significant difference in airflow, which can't really be worked around unless progressive linkage was used, but i have yet to see that on a EFI motor.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  5. #20
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    I'm pretty sure Holley four barrel TBI was progressive and simultaneous cause I had to change one from progressive to simotanious cause the rears were filling up at idle, then I just gave up on the old holley injectors. Toyota also has a progressive two barrel TBI but only one barrel has injector. But I understand what your saying... there's a point where you loose top end or you loose bottom end. But still not as bad as what he was talking about with over carburating. That is a gas problem, not an air problem... sortof... just not enough air forced over venturi to suck out gas cause the hole is to big for volume of air cylinder is sucking in. It's like a planes wing not causing lift because it's shaped wrong.

    OK, when I was about your age I remember you could not only change jets in a carb (that's like VE) but you could change venturis as well. So that was like AE? Pump shot has also got to be increased with larger CFM.

    I still don't think he can over CFM a BB Chevy unless he really tried to... it'd be the same thing as if he had two 1000 carbs on it. No it's not going to run well from idle to 3000 RPM. But then again if you have two 1000 CFM carbs chances are your cam is designed to idle at 2000 and power band starts at 3000 RPM.

    Don't know his cam specs yet but just some quick figuring looks like 2 5.0 or 5.7L TBI units would fuel and air his big block quite nicely.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  6. #21
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    Re: 4 barrel throttle body with gm computer?

    maybe progressive linkage isn't the term i want to use? been a long time since i've been around a carb/TBI.

    i was thinking more along the lines of when near fully closed throttle plate, pushing down the throttle half an inch would open the butterflies from 0 to 10*, but near WOT that same half inch would produce a far greater difference than 10*.

    ???????????????????
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  7. #22
    Electronic Ignition!
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    Re: 4 barrel throttle body with gm computer?

    Here is my cam specs. the cam is a Mondello, part #JM-18-20
    0.488 lift intake, 0.496 lift exhaust, 260°/266° adv. lift intake/exhaust, 216°lift at .050 intake, 226° lift at .050 exhaust, 112° lobe seperation, 1000-5000 rpm range.

    I am trying to find the specs on my fuel pump. No luck so far. It is for a tpi camero as I recall.

  8. #23
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    Those cam specs are considered max EFI capable. If you look at aftermarket EFI companies you will find near identical numbers, then bigger fees for tuning. In a big cubic inch motor easier. With a TPI pump and TBI injection you will have enough fuel!

    Well enough if you run 3/8th line both ways! There will be a lot of extra fuel at idle/low end and hardly any top end. Don't think you'll get by with 5/16th return as return presure will not be 0 PSI. When I did it return pressure was 3 PSI which rasies inlet by 3 PSI. Went to 3.8th return and all was well.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  9. #24
    Fuel Injected! gregs78cam's Avatar
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    Re: 4 barrel throttle body with gm computer?

    WOW, I should have checked this thread last night. Yes 2 IACs are possible and yes Crossfire had them, however the common problem with those is over time they may become out of synch with each other. So you just do an IAC reset and all's well. The other way around it is to run 1 or 2 IACs and use a 3/8 hardline to connect the plenum side of one to the plenum side of the other. This would of course be if you had two TBIs with no common plenum.

    My cam is slightly larger than yours and it still runs great with TBI. Better in open loop than closed, but it may just need a little more work on the tune. I would be surprised if your 455? even needed any real tuning other than injector flow and idle speed set to your preferences. How much vacuum does your current setup pull on a gauge? 15" or better and it should be fine.

    As far as having too much airflow potential - not a problem. With a carb, as stated earlier the vacuum signal, and flow past the venturi is what determines how much fuel is metered in. With EFI MAP, TPS, O2, CTS, etc is used by the ECM force feed the fuel to the engine. It really dosen't care how many CFM it will flow.

    Fuel lines? I am running 3/8" supply and return, and have no problem feeding my 425hp 383. I would also suggest getting a pump assembly from '93+ Grand Am/Cavalier and using the entire bucket assembly to prevent fuel starvation from uphill/downhill, and off camber situations. Yes they are rated for less flow at higher pressure but it flows plenty for me at 13psi. You could probably fit your TPI pump right into it. I have a stock van style pump and pickup tube in my '74 Chevy Truck and it will stall under hard braking with less than half a tank in it. It will be getting a J-body bucket assembly when I can get another one from Pull and Save.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  10. #25
    Super Moderator Six_Shooter's Avatar
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    Re: 4 barrel throttle body with gm computer?

    I remembered tonight that Rick (The guy with the 4bbl TBI) had said that a couple pictures of one of his 4 bbl TBIs were published to the web, so I did a quick serach.

    I should be able to get some better pictures, but this is one of the first 4 bbl TBIs he built.





    http://www.ssgm.com/news/aftermarket-fr ... 000199226/" onclick="window.open(this.href);return false;
    The man who says something is impossible, is usually interrupted by the man doing it.

  11. #26
    Fuel Injected! gregs78cam's Avatar
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    Re: 4 barrel throttle body with gm computer?

    See, I was initially thinking about something like that, but I didn't want to mess with getting the geometry right with the linkages. Looks like real nice work though.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  12. #27
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    Now that is some sweet work!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  13. #28
    Super Moderator dave w's Avatar
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    Re: 4 barrel throttle body with gm computer?

    Sometimes I think differently than others. I think my approach to a 4 barrel TBI would be similar to the Holley design. I would use an off-the-shelf 4 barrel throttle body and modify the GM injector pods? I really don't have the time to figure out the details. I think maybe some sand casting would be required to make a 4 barrel GM injector pod?

    dave w

  14. #29
    EFI GearHead ! EagleMark's Avatar
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    Re: 4 barrel throttle body with gm computer?

    or you could buy the newer holley?

    I've got an older holley four barrel here with the fishing sinkers COUGH injecotrs. I have not had time to see what it would take to put GM injectors in it...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  15. #30
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    Re: 4 barrel throttle body with gm computer?

    Quote Originally Posted by Six_Shooter
    I remembered tonight that Rick (The guy with the 4bbl TBI) had said that a couple pictures of one of his 4 bbl TBIs were published to the web, so I did a quick serach.

    I should be able to get some better pictures, but this is one of the first 4 bbl TBIs he built.





    http://www.ssgm.com/news/aftermarket-fr ... 000199226/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
    That is some sweet work, on an torker manifold for an Olds! I like it!

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