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powerglide manual shifting mods


richard gray

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Richard,

There is a wealth of knowledge about Powerglide modifications for drag strip use, as well as a number of vendors who specialize in these mods. You will find that the majority of the participants in this forum are focused more on stock restoration than modification. I'll suggest that you'll likely get more useful answers at Hotrodders.com.

I do have one question, however. What is your intended use of the PG and 250? If the primary use is street driving, or if the intended vehicle is heavy, I strongly recommend a different trans. The 1.76:1 first in the PG doesn't do a lot of torque multiplication off the line, especially with a small motor like the 250. A 200-4R or 700R4 with a much steeper first gear (2.74:1 and 3.06:1, respectively) will make a tremendous difference off the line. Now if your building a dedicated drag car where you can use a steeper final drive ratio and match the engine mods to the shift points to maximize performance, then having fewer shift points will usually result in a lower e.t. If you intend any street driving, you'll be disappointed with the PG.

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Richard,

There is a wealth of knowledge about Powerglide modifications for drag strip use, as well as a number of vendors who specialize in these mods. You will find that the majority of the participants in this forum are focused more on stock restoration than modification. I'll suggest that you'll likely get more useful answers at Hotrodders.com.

I do have one question, however. What is your intended use of the PG and 250? If the primary use is street driving, or if the intended vehicle is heavy, I strongly recommend a different trans. The 1.76:1 first in the PG doesn't do a lot of torque multiplication off the line, especially with a small motor like the 250. A 200-4R or 700R4 with a much steeper first gear (2.74:1 and 3.06:1, respectively) will make a tremendous difference off the line. Now if your building a dedicated drag car where you can use a steeper final drive ratio and match the engine mods to the shift points to maximize performance, then having fewer shift points will usually result in a lower e.t. If you intend any street driving, you'll be disappointed with the PG.

Joe: thanks for info!! I have a dream to build an amphibious vehicle. i retired from the marine fab industry, and decided to build the design i have scale modelled. i have a 350 gm engine to connect to a 250 power glide <beefed up, manual shifted>> which will connect to a divorced dana 20 transfer case that will drive a 2004 cadillac independent rear end(clip) the dana20 can be shifted to drive the front drive output only (high gear) that drives the jetdrive .the lower hull framing is ready for the drive train.i was told the stock trans only needs a manual shift kit modification(strong enough) i was told it would require a shaft bearing added at the turbo 350 converter if used? will probably use the 250 converter on a 350 flex plate and starter, 250 parts are hard to find.
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Joe: thanks for info!! I have a dream to build an amphibious vehicle. i retired from the marine fab industry, and decided to build the design i have scale modelled. i have a 350 gm engine to connect to a 250 power glide <beefed up,="" manual="" shifted="">> which will connect to a divorced dana 20 transfer case that will drive a 2004 cadillac independent rear end(clip) the dana20 can be shifted to drive the front drive output only (high gear) that drives the jetdrive .the lower hull framing is ready for the drive train.i was told the stock trans only needs a manual shift kit modification(strong enough) i was told it would require a shaft bearing added at the turbo 350 converter if used? will probably use the 250 converter on a 350 flex plate and starter, 250 parts are hard to find.

Wow, quite a project. I'll be the first to admit that I have no idea what the gearing requirements are for an amphibious vehicle.

One thing, however. Be sure you know exactly what trans you have. There's no such thing as a "250 Powerglide", unless you are referring to the 250 cu in six that was bolted in front of it. GM did make a TurboHydramatic 250 (TH250), which is a three speed trans - a less capable version of the venerable TH350. The Powerglide has always just been called a Powerglide as far as I know. There is another two speed trans, the Super Turbine 300 (ST300) that most folks confuse with the PG, even though they are two completely different transmissions with nothing in common except that they are two speed transmissions.

While you can swap the converters between the PG and the TH350, why? Are you trying to get a different stall speed? Prior to the advent of readily available aftermarket converters in any stall speed you want, it was common for drag racers to use a PG converter in a TH350 or TH400 to get a higher stall speed. Going the other way would give you a lower stall speed, which means less driveline slippage (good) but also less torque multiplication (bad). Frankly, there is such a vast array of aftermarket parts for the PG, thanks to it's popularity for drag racing, simply figure out what stall speed you need and buy the correct converter. This project doesn't sound like it's a low-buck project, so saving $50 or $100 by using a compromise converter is not a wise choice.</beefed>

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