Looking for some advice on which gear to put in my car. The car is a 69 BB, SS x-66 coded car with about 500 hp. Right now I have the stock posi 3.31 gear and driving around town I am lucky if I get to third gear. It needs a gear. I am afraid that if I do go with a 4.10 gear that I won't be able to drive it on the highway. I would like to be able to drive on the highway in a decent RPM range and not go deaf. That is why I am leaning to a 3.90 gear. I figure if I go with the 4.10 at 70 mph I will be at 3400 rpms. not sure with a 3.90 though. Any thoughts or input would be appreciated.

thanks
kissel

 

3.9 will reduce rpm by about 5percent over the 4.1.
What size tire you got?
How often does it go to the track and what speeds to you currently run versus what you wish?
The extra gear will only knock off about .05second at the most. I would go with a 3.9 and play with various tire heights until you find something that hooks and still gives you the rpm you need. You might have to settle on slightly slower speeds on the highway.

 

There is not much difference between those two gear sets (IMHO). What transmission do you have an auto or a 4-speed ? Without more info, I would say 3.08 or 3.42's. With a big blocks torque you shouldn't need alot of gear. Your 3.31 should be fine. How fast are you going in town, and what RPM ?

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69 Camaro Z28 "clone" 327 AT
DAYTONA YELLOW WITH BLACK Z28 STRIPES
327 - "461" camel back heads. TRW,Edelbrock,Ultradyne,Hooker
TPI 700r4 automatic transmission

[This message has been edited by TJS69 (edited August 03, 2002).]

 

Well the Tire is around 28 inch and I have a M21 tranny. I mostly am going to use the car for local driving and on the highway around once or twice a week. Right now in first gear at 30 MPH the prms are 2700 and 40 in second gear it is also around 2700 rpm. I definately need a lower gear. driving on the highway yesterday i was only in third and going about 60 about 3300 rpms or so. It is hard to tell because the speedomotoer cable is not hooked up yet.

hope this info helps ...........

kissel.

 

What is wrong with those RPM figures ? I would leave it alone. IMHO

Also you can use these calculators, to help you decide.
http://www.randysringandpinion.com/calculators.shtml

[This message has been edited by TJS69 (edited August 04, 2002).]

 

I have installed/run the following gears on street cars, in the follwing order: 4.88 (yowza!), 4.10, 3.73, 3.42.

Notice a trend? Deep gears on a non overdrive vehicle are a pain. I've learned to build for more torque, and run a reasonable gear, like 3.42's.

I will say this, the M21 has a 2.2 1st gear, and with a 28" tire, your launch ratio is really low. 4.10's would be great, but BUZZZZZZ on the highway. You might want to consider installing a Richmond (nee Doug Nash) 5 speed.

These have deeper 1-4 gears, but 1-1 first. So it's like having a 4+ gear in the diff for the first four gears, but you go back to 3.3 when you pop it in fifth.

The math: M21, 2.2 * 4.88= 10.736
5 speed, 3.25 * 3.31= 10.7575


[This message has been edited by angel71rs (edited August 04, 2002).]

 

the only thing that is not factored into the previous math is the rpm drop between shifts. If you have a single plane intake and large cam, the motor is not going to take too kindly to going from 6200 to 3900 on the 1-2 shift. Spacing of other gears is almost as bad.

ODs (manuals and 700-4s) nice but they also don't take loads of torque in the overdrive gears. Most od gears are very small.

 

here is another calculation page that I believe is quite complete...

http://www.1bad69.com/calc.htm

it will show several gears and allow you to fill in any number but one and caclulate that (regarding gear, rpm, mph, tranny ratio)

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69 Camaro among other toys.