Hey guys, I am getting ready to build a powerglide for my 383 LT1 turbo project, and I need some professional input on what low gearing you think I should go with. Its going in a 93Z28 with around 1000hp (or more) to the wheels via a fully built 383 LT1 and a T100 (100mm) T4 turbo.

My choices are:
1.76
1.82
1.89
1.96
2.03
2.11

Keep in mind the higher the low gear ratio the more rpm drop you have from low to high gear shifts, and with a turbo you want to keep it in its useable powerband.

Also around what rearend gearing would you suggest and with what size rear tires?

thanks!

 

To make a reasonably accurate guess, a horsepower or torque curve for the engine would be useful. From that you could choose both a converter and rear gear if tire size was known.

There are a few drag simulators which would help. I have an old one which seems to work well.

I just guessed at a power curve and 3450 all up weight. I got 9 flat at 140. This was with a perfect hook.

For starters, if you shift at 7000 with a 5000 rpm stall converter there won't be much difference in engine rpm after the shift. Surprisingly I only got about 100 different. 7000 > 5400 with 1.76 and 7000>5300 with 2.11. That's due to converter slippage. After the shift with the 2.11 there is more converter multiplication. The biggest difference was starting line traction. It took more hook with the 2.11 gear.


Your results may vary...a lot! With a real torque/hp curve I can come a lot closer.

From this preliminary look, I don't see a real big difference. If a strong 1.76 or 1.82 is a lot cheaper than the higher gears, I'd go there just due to traction.

My $.02

 

I just bought a 1.76 powerglide for my race car, however it weighs 2600lbs with me in it. I was told by my tranny builder that the 1.76 isn't for everybody, i am running a 31 inch tire, 5.13 gears and the car is very light like i said so we can just barely get away with it, if u don't have a setup like this its gonna be a major slug out of the hole. Most everybody has to run a 1.82 but they are weaker than the 1.76, in order to beef them up stronger (aftermarket internal gearing) it costs an extra $850 dollars, so to have one built it will cost about $850ish to build, plus the extra $850 for the stonger internals.. I dont know about the others you have listed so i can't comment on them at all, good luck man!

 

great stuff!
keep them coming...
thanks guys!

 

I use stock 1.76 gears. The 1.82 ratio is nicer but the whole part of the carrier for 1.82 is weak.

If money is no object get a set of 1.80 (no typo) straight cut gears. they're only $1250

I use 29" tires and 4.56 gears. I shift at 7000 rpm somewhere around half track and cross the finish at 7000. I'm swapping in a set of 4.30 gears just to bring my shift point down a couple of hundred rpm. My engine combination is starting to go over the hp curve at 7000.

My converter is an 8" and stalls at 5700 rpm on the transbrake. It has a 2.6 multiplier. I launch at 4500 rpm.

It doesn't take much to build up a PG. Hardened input shaft with turbo splines so you can use a TH350/TH400 torque converter. Steel or aluminum clutch hub (the factory cast one will break). Dual seal servo piston. Manual valve body or transbrake although it takes very little to convert a factory valve body to a full manual.

There's more needed but it's more for safety. An SFI tranny and flexplate shield. A Ultrabell and or Ultra case is better but it's expensive. Deep sump pan. You can even get a larger output shaft that uses a TH400 slip yoke.

Basic cheap race buildup is around $1500 including a transbrake but not a converter. Full blown race powerglide start around $5000. Prices of converters depends on what you want. For a good race converter you can expect to pay $800+

Even better is to buy a Lencodrive.