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Old 06-09-2005, 11:18 AM
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Need a good Rear-end ratio for project

Hey,
I have a 1981 4-door Malibu with a factory 3-speed on the floor, no joke. 78,000 miles and the body is straighter than the salt flats.It's a mid-life-crisis family hot-rod. I'll be 40 in August. I have a 396 that is making about 425 hp, not sure where the torque curve is, I assume it is low. Ill find out the cam specs from the previous builder.
I'll be using a Super T-10 4 speed with a 2.64 1rst gear ratio.My tires will be no taller than 28 inches.I want this car to pull like a banshee but I dont want to be screaming on the highway. I considered a 5 speed, but after previously owning one, I got tired of shifting...yes I know...pansy. I also considered a taller 1rst gear, but the jump from 1rst to 2nd gear is over a full point in some cases, like the 3-speed that is in the car now. So the 2.64 will suffice. The car is full body stock with a/c, which will hopefully remain. I know slapping low gears in there will make it fly, but I like alot of pull, not just a quick rev. I always had sucess with tall high way gears.Now I'm trying to cut it in the middle and try to get the best of both worlds.My opinion is somewhere around 3.23 to 3.53.I need a formula to calculate the rpms also.Any advice will be appreciated.Thank you.

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Old 06-09-2005, 11:23 AM
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I have 3.55s in my 51 Ford truck....350/350 turbo and I love it....best of both worlds.
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Old 06-09-2005, 11:49 AM
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http://www.smokemup.com/auto_math/index.php
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Old 06-09-2005, 01:43 PM
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Calculator

Gelphish: go for the 3:55's or so. You'll be ok. big blocks make touque; thats what gets the job done.

If yo have Excel i have an attachment i could send if you have an e-mail address you don't mind trusting me with
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Old 06-09-2005, 11:47 PM
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Might look into a bigger rear end if you can find one. If you still have the stock 7.5" unit in the car, that 396 will spew rear innards all over the neighborhood if you're not careful. An 8.5" rear from a later Buick GN would fit with only a small driveshaft shortening, but they're rare, therefore very expensive. Southside Machine offered special control arms to adapt an early A-body rear end to the G-body, but I don't think they're in business any more. You might find a used set if you look real hard.
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Old 06-10-2005, 05:35 AM
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Thanks Fellas

I figured some where around 3.50 rear gears,but I dont know with the short tires if I will be turning to many R's. The 7.5 rearend is just a pacifier. Im putting an Auburn or Eaton posi unit in it for the time being.Eventually Ill grab a 12 bolt or I'll cross-breed and go for a 9". thanks for the input.I really appreciated it.
Gelphish
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Old 06-12-2005, 01:11 AM
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Nice to meet another Malibu Sedan owner

I put a set of 3.73's in mine last year to make effecient use of the TH-700R4 that slowly moved me along with the original 2.29's from the factory. it helped the semi anemic 24 year old 267 small block.

I went that high only because of the overdrive ratio of .70:1 and my 26.1 inch tires.

With the 396, and the 28 inch tires you stated, along with the ST-10 fourth gear ratio of 1:1 will net you the following:

3.08 gears, 2050 rpm's @ 55mph
3.42 gears, 2250 rpm's @ 55mph
3.55 gears, 2350 rpm's @ 55mph
3.73 gears, 2500 rpm's @ 55mph
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