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Thread: MPI throttle body options

  1. #1
    Fuel Injected! JeepsAndGuns's Avatar
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    MPI throttle body options

    Now that I have my bling MPI intake, I am ready to top it off with a throttle body. There was just no way I was gonna pay almost $500 for the (very nice) edelbrock unit that may have had tps and iac that might not work with the gm system.
    So I was looking at my options.
    1. remove the injector pod and use my current 454 tb.
    I dont really want to do that. I would kinda like to be able to sell it to get back a little money.

    2. Use a dodge tb found on every 5.2 and 5.9 magnum engines in trucks, durangos, and jeep grand cherokees. Its made by holley, has a compatable tps and iac, and 1.92 in throttle blades. (only a tiny hair smaller than my 454 tbi's 2in blades)
    I picked up one at the pull a part and test fit it. The throttle lever is gonna hit the fuel rail, it would have to have a thick spacer to make it clear. And this intake is already a TALL one. I am afraid I will start running into hood clearance issues real fast if I dont be carefull!

    3. Use a large single blade tb, such as the ones on the LSx engines.
    Looking at them on ebay, seems the cable operated ones have a tps and a bolt on iac. Any chance these could be compatable with the 7427 pcm? Also anyone know what the bore of a stock one is? I find conflicting info from google. Some says 75mm, some say 78mm. What are their cfm ratings? Whatever I get, I want it to atleast equil the cfm of the twin 2in blade tb I have now. Anyone have any specs?

    If I wanted a large single blade tb that equils what my current twin blade one flows, is it as simple as adding the two together (two 2in holes, equil one 4in hole? witch translates to 101.6mm?) Or is there more to it than that?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    EFI GearHead ! EagleMark's Avatar
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    The Big Block throttle body you have would be the easiest with adapter. You could look for a old four barrel holley that had old injectors that are worthless. Pretty sure there's a four barrel throttle body on a grand cherokee. And if you go the big single barrel LS type I have one brand new!

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    Super Moderator Six_Shooter's Avatar
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    The LS TB would be compatible. The TPS for sure, and I believe the IAC was a carry over from the older design, so it should be compatible as well.

    No, 2 - 2" holes do not = 1 - 4" hole.

    You have to look at area. I can't seem to work out the equation right now, but a 4" hole would have almost twice the area of 2-2" holes.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Jeep used a 4bbl TB??? I never knew.

    I used a monoblade TB with a homemade adapter on my 4bbl smallblock Vortec intake.


    The TB is from a 350 Vortec engine. The 4bbl intake to TB adapter is made from a piece of 1/2" aluminum plate I picked up from a local scrap metal guy. The TB is bolted to a 1" TB spacer purchased from Ebay. The manifold inlet has 4 smaller holes instead of one large opening so the spacer provides room for the throttle plate to open and also allows the throttle linkage to pivot without hitting the adapter plate. A big block L29 TB wouldn't work because the cable angle is all wrong for my application. Can't say much regarding the LSx TB but the 5.7 TB was a very nice fit.

    The area of a circle is pi r squared. r is radius, 1/2 of diameter, so two 50mm TB blades provide 3927mm squared while a single blade 75mm TB provides 4419 square mm of area. This is also true of exhaust... one 3" pipe will provide better flow than two 2.25" pipes. Anyway, there are a few other considerations for TB. When opening throttle plates, the first 20 degrees of throttle angle provides something like a 35% change in airflow. With large monoblade TB's this means a little throttle can make big power changes. The Vortec truck TB uses a progressive linkage under the throttle cable to slow the throttle opening from idle to maybe mid throttle. This is nice if you don't want to light the tires up at every light, and it's great if you're a serious wheeler and need good throttle control at low speed. Also, the IAC tapers are different so you might have to play with a few IAC parameters to get idle speed correction to be a smooth process.

    Edit: Accell has a pretty neat (but pricey) 90 deg adapter for TB to 4bbl carb pattern. For the monoblade TB, GM has three different 90 degree intake air elbows which fit the top of the TB. First is from an S10 blazer from 96+. This one is angled to the driver's side of the engine. Second is from a fullsize pickup 96+, it's angled toward the passenger side of the engine. Third is from a 97+ G van with 5.7 which is aimed straight forward.
    Here's an aftermarket elbow but you get the idea:
    DSC09349.jpg
    Last edited by 1project2many; 11-14-2011 at 05:46 AM.

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    Fuel Injected! JeepsAndGuns's Avatar
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    Humm. Good info there. A few questions.
    So if the single blade tb has a significantly diffrent air flow, would that cause any negative diffrences in what tps % equils what airflow/map reading with what the 7427 might be expecting? Meaning, if I am reading it right, the single blade tb flows more air at a lower tps% than the twin blade tb. Would this make the 7427 go haywire because its expecting less air at that lower tps %? I have never worked on a vortec or LS engine, and they are still too new to be showing up at the local pull a part. Do you have any pictures of this pregressive linkage?
    So you saying a 75mm single blade tb gives more surface area/cfm than a twin 2in blade tb? Is 75mm the stock dia of the ls tb?

    The other problem I was running into with the twin 2in blade tb, was that its slightly wider than my intake opening. If you look at the picture in my injector thread, you can see the opening and bolt pattern is not the standard square bore. I was gonna have to do some grinding to the sides of the opening to clear the blades. Not much, but about 1/4in or so per side. With it being a open pleninum, I dont think I would have any clearance issues with a single blade tb. I am starting to think it might be the easyest option right now.

    What grand cherokee uses a 4bbl tb?? I have never see one, unless its on the new ones?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    I don't think there was a 4bbl on any of the ZJ's. Same as all the other 5.2 and 5.9's in the dodges. Another option may be the ford 5.0 throttle bodies. They are easy to come by cheap but I am not sure on the IAC and TPS compatibility. I'm going to have to go back and look at my ford tuning info. Its been a few years.

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    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by JeepsAndGuns View Post
    What grand cherokee uses a 4bbl tb?? I have never see one, unless its on the new ones?
    It may have been the Dodge 2 barrel I was thinking of made by Holley... still think... IIRC there's a four barrel somewhere, may be wishful thinking and confused info.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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    Super Moderator Six_Shooter's Avatar
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    I have not seen a stock application with a 4 BBL TBI, only aftermarket units.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Fuel Injected! JeepsAndGuns's Avatar
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    Quote Originally Posted by 1project2many View Post
    For the monoblade TB, GM has three different 90 degree intake air elbows which fit the top of the TB. First is from an S10 blazer from 96+. This one is angled to the driver's side of the engine. Second is from a fullsize pickup 96+, it's angled toward the passenger side of the engine. Third is from a 97+ G van with 5.7 which is aimed straight forward.
    There was a few of those vortec S10 blazers at the local pull a part. No trucks or tahoes/burbs/etc with the V8's though. So I will probably have to source one on ebay or somewhere like that. Unless eaglemark wants to sell the one he has for cheap
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    Fuel Injected! JeepsAndGuns's Avatar
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    Ok, my head is hurting from all the conflicting info out on the net.
    I have been searching for the past hour on these tb's and finding a lot of diffrent stuff. I am finding stock bore dia everywhere from 71mm up to 78mm. I am finding info that says the 4.3, 5.0, and 5.7 all use the same tb, and others say no. I am finding diffrent looking tb's from the same year and vehicle range.
    Is the diffrence one is for vortec engine, the other for ls? Are they diffrent engines? I know verry little about the chevy engines. (I know more about the injection systems than the actual engines themselfs....lol)
    Does anyone have a link to, or have any known correct info? 1project, you have one, could you mabey shed some light on this? Just wondering what vehicles/engine have what tb, and what the stock bore dia of those tb's are.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  11. #11
    EFI GearHead ! EagleMark's Avatar
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    All I ever found was same conflicting information. One difference is Drive By Wire and one cable.

    I have no use for mine if you want it? Sure it would be not only fair but lower than any new price you can find. IIRC it's 68mm. Looks just like one 1project2many posted but does not have big vacuum line on front/side, but inside has passage way for it.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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    The TB in my picture is the Vortec 7.4 / 454 / L29 part which I didn't end up using. If you look at the side view, you can see the progressive or cam shaped throttle linkage. Notice how the general shape of the linkage isn't a circle? This makes the throttle open slower at first then faster later.

    The VE and spark tables are based on manifold pressure (MAP), not TPS. So changing the TB size won't matter there. Accelerator Enrichment (same as accelerator pump on a carb) and Power Enrichment (similar to the Power Valve) are both based on TPS and will be affected. But you're using a different manifold and injectors on a non-gm engine so those are going to have to be adjusted anyway.

    There is a bunch of conflicting info on these TB's. Gotta love the internet. I used 75mm because that's what I remember the Vortec 5.7 units being from when I built that setup 3-4 years ago. This ad on Ebay says they're 71mm stock and 75 after porting. There's one on the bench at work (we're replacing the 350 in one of the vans) and I'll try to take a measurement tomorrow. The 5.0 / 305 / L30 and 5.7 / 350 / L31 units are the same. The 4.3 is somewhat different. There's an air deflector welded to the bottom of the plate on the V8 TB's which I don't remember seeing on the 4.3 units. AFAIK the throttle blade is the same diameter for all three but there may a differences in the vacuum fittings. The 454 TB is a very different beast and is designed to be mounted vertically, not horizontally. We have a couple of 6 liter LS series engines in buses at work and at least one of them uses a cable, but it's rarely in the shop and with all the vehicles I have down right now there's no way I can take it off the road or spend the time to check the TB size.



    The 4bbl Jeep thing... maybe you saw an aftermarket 4bbl TBI conversion with the injectors mounted almost horizontally? There were a couple of kits, I have a TB from one here.
    Attached Images Attached Images

  13. #13
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by 1project2many View Post
    The 4bbl Jeep thing... maybe you saw an aftermarket 4bbl TBI conversion with the injectors mounted almost horizontally? There were a couple of kits, I have a TB from one here.
    Nope, I know what your talking about. It's just a memory I had from reading a EFI conversion somewhere so I may be just mistaken...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Note to self: Take half recommended dosage tomorrow...
    Here at the shop we have all sorts of airborne solvents. Safety rules say these are hazardous, but I know full well they're a benefit. They're the real the reason I'm happy to be at work!

    Update on TB sizing. Throttle blade is 80mm. Throttle is... ummm... throttled to 71mm below blade. Intake opening (for anyone looking) is 72mm. So the guys looking to buy a 75mm TB and bolt on power increases will not see any gain.

  15. #15
    Fuel Injected! JeepsAndGuns's Avatar
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    Quote Originally Posted by 1project2many View Post
    Update on TB sizing. Throttle blade is 80mm. Throttle is... ummm... throttled to 71mm below blade. Intake opening (for anyone looking) is 72mm. So the guys looking to buy a 75mm TB and bolt on power increases will not see any gain.
    So basicly the throttle body/blade is 80mm in dia, then directly under the blade the tb bore tapers/funnels in to 71mm? The stock chevy intake opening is 72mm? That means even if you machine out the taper (to where its straight through) you will be wasteing your time. But on my engine, its wide open under the tb, so boreing it out would help.
    The tb on my wranglers 4.0 straight six was like that from the factory. The tb blade and bore was 60mm, and directly below the blade it tapered in to 55mm. I took it off and removed the blade and shaft, and had a shop remove the taper and reinstalled it. The intake opening is 62mm on the intake. So I saw just a hair improvement. I have seen aftermarket tb's up to 65mm, and those require the intake to be opened up.

    So the tb you just measured, do you happen to know the exact year/model/aplacation it was from? I may call around to some of the other junkyards in tow before I resort to ebay.

    Yopu mention the 4.3 tb. While at the pull a part, I have ran across a few of the 96+ vortec 4.3's. I looked at a few just out of curiosity (thi was before all this research on these tb's) and the ones I looked at, I remember seeing that air deflector on the bottom of the blade. I thought it was kinda odd. If all of them are in fact the same, would the air deflector on the 4.3 units simply be to restrict air so it doesnt flow as much, for the smaller 4.3?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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