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Old 02-21-2006, 09:45 PM
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Need rear gear suggestion for my setup

I'd like to know whether or not I should stick with the 3.27 gears I have now, or change out to 3.73. I'm using the uncommon Borg Warner 9 bolt on my 85 Trans Am and I only have these two options because that is all I can find for it.

I'm after maximum 0-60 performance, seeing as how this is not a drag car and I just want to have some fun with it. I have all aftermarket suspension upgrades done to the car and I get great traction with the wide tires on the back, so I don't need to worry too much about wheelspin. I'm sticking with a stock stall converter for now, but if it helps to increase the stall a bit to go with numerically lower gears, I might consider it.

My biggest problem in deciding which gears to use is the 700R4 they are running behind. It's such a wide ratio tranny that it seems it's either a much too low first gear, or a sluggish second gear after the shift depending on which rear gears I use. I've tried to build my motor to produce a broad torque curve instead of a peaky motor to deal with the huge RPM spread between gears. The motor is a well built roller cammed 355 that should easily crank out 400 HP and 400 torque with the parts on it, but still stay strong at 2000 RPM for a good launch. Also to be considered is that the car weighs 3414 lbs (on a scale)

I know it's easy to use the wrong gear for the application, and being no expert on proper gearing that is why I came here for some advice. If something other than 3.27/3.73 would be best, I would appreciate anyone telling me a place that sells a different ring and pinion for the 9 bolt.

Oh yeah, I don't have the $$$ for a rear end or tranny swap so please don't suggest this

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Old 02-22-2006, 02:53 AM
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With the TH-700R4 you will be more impressed with the 3.73's.

I have the exact same setup in my 1981 Malibu with the little 267, any more engine will be just that more impressive. Mine chirps the tires when it upshifts from 1st to 2nd with a bit more than half throttle, and it gets an average of 19 MPG with the 25 year old 2 barrel carburetor.
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Old 02-22-2006, 07:32 PM
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With the 3.73 gears, I'm looking at a 11.4:1 ratio in first gear. I've heard that 10:1 is about the most you should run. Putting traction issues aside, is there any other reason to question running a first gear this low? I want to make sure that I'm not actually hurting acceleration by changing to the 3.73 gears.
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Old 02-25-2006, 02:38 AM
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Quote:
Originally Posted by Mad Maggot
With the 3.73 gears, I'm looking at a 11.4:1 ratio in first gear. I've heard that 10:1 is about the most you should run. Putting traction issues aside, is there any other reason to question running a first gear this low? I want to make sure that I'm not actually hurting acceleration by changing to the 3.73 gears.
There is information I have never heard of before.
This combination is a very common setup in many hotrods and street machines with the 700 transmission.

You can also tinker with the tire size to slightly offset gearing in both the transmission and axle.

I forgot to mention in my other post that I am also running a 26.1 inch (235/60/15) tire, when I upgrade to a different engine I will also move up the tire size to fit within my planned calculations for highway cruise RPM's. I really have no plans on racing the car, even light-to-light.
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