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Old 09-28-2011, 12:08 PM
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4 cyl. motor/V8 trans

I have a 1980 2.5 GM iron duke (carbureted 151) completly stock runs great but the problem is I put a SBC 400 turbo out of a 1 ton truck on it because that is all I had and thought it would work since the bellhousing was the same, but when I have it in park or neutral it runs great revs up fine, but when I put it in reverse or drive it doesnt go far or very fast (I can walk faster than this thing moves) before the engine bogs down and dies. Rearend gears are stock 2.73. 205/75/14 tires

My question: Is it possible to put a lower gear in the rear axle to fix the problem or is the trans just too big for the motor to work?

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Old 09-28-2011, 12:35 PM
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At the very least you have some compound errors; whether or not the trans is installed properly or functioning correctly is another set of issues

TH400s if memory serves have a 2.48 1st gear
You have 2.73:1s in the axle
A TH400 probably consumes 30hp in parasitic losses or more
Your engine on a good day probably makes 85hp or less

Your total gear reduction is 6.77 (1st x axle ratio). This simply isnt enough. You need at least a 3.55:1 axle normally to make 2.50 1st gear enjoyable; however with the small engine size, I would go straight to 4.11s or higher.

Or trade the 400 in for a th200-4r or 700r4 and go to a 3.55. The OD will make life more enjoyable with that lil 4banger
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Old 09-28-2011, 01:00 PM
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Like I said earlier the bellhousings for the iron duke and sbc are the same all I had to was drill 3 new holes in the flexplate for the torque converter , without the driveshaft in the trans yoke spins fine.

So if I put a 4.11 or even 4.56 it will pull fine and get up to speed?
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Old 09-28-2011, 01:04 PM
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it'll help; but probably spin that motor so high it beats itself to death a lot sooner
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Old 09-28-2011, 01:27 PM
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Quote:
Originally Posted by burtondemo
I have a 1980 2.5 GM iron duke (carbureted 151) completly stock runs great but the problem is I put a SBC 400 turbo out of a 1 ton truck on it because that is all I had and thought it would work since the bellhousing was the same, but when I have it in park or neutral it runs great revs up fine, but when I put it in reverse or drive it doesnt go far or very fast (I can walk faster than this thing moves) before the engine bogs down and dies. Rearend gears are stock 2.73. 205/75/14 tires

My question: Is it possible to put a lower gear in the rear axle to fix the problem or is the trans just too big for the motor to work?
the torque coming out of your little iron duke isnt near what it would be coming from a v-8, and id be willing to bet that you dont have enough stall for that little motor. id suggest a higher stall converter, say around 2200-2500.
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Old 09-28-2011, 04:48 PM
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Quote:
Originally Posted by burtondemo
I have a 1980 2.5 GM iron duke (carbureted 151) completly stock runs great but the problem is I put a SBC 400 turbo out of a 1 ton truck on it because that is all I had and thought it would work since the bellhousing was the same, but when I have it in park or neutral it runs great revs up fine, but when I put it in reverse or drive it doesnt go far or very fast (I can walk faster than this thing moves) before the engine bogs down and dies. Rearend gears are stock 2.73. 205/75/14 tires

My question: Is it possible to put a lower gear in the rear axle to fix the problem or is the trans just too big for the motor to work?
Hi I'm working with 4 chevy in my T bucket here's a link to a lot of info that you might find handy these are fun motors in light hot rods.http://www.jalopyjournal.com/forum/s...d.php?t=144835 My motor is a 120 HP Chevy based Mercruiser 4 from a boat 153 Ci. I think.The car/mini truck 4s and the Mercruiser 4s of the same years are based on the same engines but the boat has more HP stock.My engine is also carbed I'm looking for intake/exhaust manifolds for my engine right now
Leon
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Old 09-28-2011, 08:55 PM
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Quote:
Originally Posted by tnsmith10
the torque coming out of your little iron duke isnt near what it would be coming from a v-8, and id be willing to bet that you dont have enough stall for that little motor. id suggest a higher stall converter, say around 2200-2500.

X2. Used to be the poor mans high stall converter was one out of a 4 cyl vega, behind a 350.
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Old 09-29-2011, 11:17 AM
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Would I have the same problem if I put a manual trans on it? And would a torque converter out of a Vega with a 350 trans fit in the turbo 400 ?
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Old 09-29-2011, 06:11 PM
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Quote:
Originally Posted by burtondemo
I have a 1980 2.5 GM iron duke (carbureted 151) completly stock runs great but the problem is I put a SBC 400 turbo out of a 1 ton truck on it because that is all I had and thought it would work since the bellhousing was the same, but when I have it in park or neutral it runs great revs up fine, but when I put it in reverse or drive it doesnt go far or very fast (I can walk faster than this thing moves) before the engine bogs down and dies. Rearend gears are stock 2.73. 205/75/14 tires

My question: Is it possible to put a lower gear in the rear axle to fix the problem or is the trans just too big for the motor to work?
The TH400 is a power hog designed to be mounted behind a big inch V8 with excess ponies that won't be missed from the crowd. An Iron Duke isn't so blessed.

Bogie
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