93 GMC 1/2 ton w/4bd2tc/5spd.....Have questions!
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Thread: 93 GMC 1/2 ton w/4bd2tc/5spd.....Have questions!

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    Default 93 GMC 1/2 ton w/4bd2tc/5spd.....Have questions!

    Howdy! These questions go out to all you Isuzu guru's as I am a novice with playing with these engines. I recently bought a 93 GMC light half ton truck (6000 gvw) 2wd with a bad 6v engine. It is a bean can model with only real options being the auto trans and air. Has 96K miles really straight body interior & paint and a 10 bolt (8.5") rear with 3.42 gears. I want to build a work truck thats gets GREAT fuel milage as I sometimes drive 200+ miles with work. Dont really plan on towing anything with it, I only haul about 4-500lbs of equip. I already have a 94 4bd2tc with the stock 5 speed trans that I want to put into this truck. By looking at the chart below, it seems the engine peaks torque 1900-2200 rpm in stock form.(taken from engine specs in sticky section) For best fuel economy, in what range would I need to keep my rpm to achieve best fuel economy and cruise? Is the 19-2200 the range to shoot for?? I know the stock 5 speed has no overdrive but I can play with rear end gears and tires to make up a final drive pretty equal to overdrive. It also appears that the engine keeps making horsepower up to 2800 but economy must fall on its face in the upper rpm range. Thanks for any and all your help and comments in advance! Chic
    Last edited by chic; 11-06-2012 at 11:57 PM. Reason: spelling

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    1900-2000 would be my cruise RPM target.

    Do you have the wastegated turbo, or the freefloat?

    Sounds like a decent combination if you don't tow a whole lot (it being a 1/2 ton).

    Yes, the power curve continues to 2800, and beyond.

    Stock defuel is 3200, mine is turned up, with the HY35W it continues to build power well over 3000 RPM.

    You are absolutely right, the fuel economy goes down the toilet up there (I would expect the longevity does to, but I do my best not to run it there for any length of time).
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    I have a non-wastegated turbo, the thing that came stock with the engine. I know by reading the threads that I can do all kinds of mods but I am looking at getting this thing running for right now and playing with it later. Using a gear ratio calculator, I can get 75mph with a 2.73 rear, 31" tires at about 2200 rpm.......70mph just under 2100 rpm. 33" tires drops both close to 150rpm. The truck has a 3"lift on it (why I do not know) but with the lift it looks like I can set the 4bd in it without any major mods to motor.....ie, starter flip, remote oil filter, oil pan mods ect fby mounting engine higher in the frame. 2.73 gears are the best I can come up with in a truck rear but 2.56 and even 2.41 were avail in a full size car like a caprice or a caddy.......What would you think about installing one of those rear ends?? I could run smaller tires and still keep my rpm down. Thanks, chic

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    I think you'll be fine with 5th direct and 2.73 gears, but I would try the 3.42 you have. We have 3.54's in our Scout and we rarely use the o.d 5th until 60-65 mph. Let us know how you plan to shift.

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    Quote Originally Posted by chic View Post
    I have a non-wastegated turbo, the thing that came stock with the engine. I know by reading the threads that I can do all kinds of mods but I am looking at getting this thing running for right now and playing with it later. Using a gear ratio calculator, I can get 75mph with a 2.73 rear, 31" tires at about 2200 rpm.......70mph just under 2100 rpm. 33" tires drops both close to 150rpm. The truck has a 3"lift on it (why I do not know) but with the lift it looks like I can set the 4bd in it without any major mods to motor.....ie, starter flip, remote oil filter, oil pan mods ect fby mounting engine higher in the frame. 2.73 gears are the best I can come up with in a truck rear but 2.56 and even 2.41 were avail in a full size car like a caprice or a caddy.......What would you think about installing one of those rear ends?? I could run smaller tires and still keep my rpm down. Thanks, chic
    With the manual trans you will be able to keep the Rs up so the freefloat turbo isn't as big an impediment, but you will want a better turbo shortly (maybe not till after you try a better one, but you will want one).

    If I were in that big of a hurry to get one going, I would use the rear ratio that's in there already.

    I've heard of a 11.5" 14 bolt with a 3.08 ratio, not sure if that was bum information, but it's worth a look. (late '70s early '80s camper special 2WD C20/30 from what I've heard)
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    What I am trying to achieve is a truck that can keep up with the crazy drivers here in SoCal......70-75mph or so cruise and still stay in the 1900-2200rpm range. The way they drive here, if you dont keep up they will run you off the road! (not really but you will get honking and flipped off alot) They should call this the "Road Rage State". Thanks, Chic

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    Quote Originally Posted by nexxussian View Post
    With the manual trans you will be able to keep the Rs up so the freefloat turbo isn't as big an impediment, but you will want a better turbo shortly (maybe not till after you try a better one, but you will want one).

    If I were in that big of a hurry to get one going, I would use the rear ratio that's in there already.

    I've heard of a 11.5" 14 bolt with a 3.08 ratio, not sure if that was bum information, but it's worth a look. (late '70s early '80s camper special 2WD C20/30 from what I've heard)
    14 bolts are 9.5 semifloater or 10.5 full floater, semi floater can go up to 3.42 gears and full floaters do not go below 3.73 as per randys ring and pinion. in the 80s chevy also used a D70 for some of their duallys and they can be geared to 3.08 or so not quite sure but a buddy of mine had one in a stock 88 cummins dodge with a 727 and 3.08 or so gears.

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    do you still have the isuzu with the manual transmission, i am looking for rer end for manual isuzu

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    Yes, I still have it! My # is 951-906-5200 Chic

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