I race on a 3/8th mile track, have a stock 350 with a .390 cam, 275/60-15 wheels and I don't know what rear gear ratio I have in my Gm 10 bolt rear end. The car runs up to about 5400 rpm and currently hit that 5400 limit 3/4 down the straight. I think the tranny is a 350 as well. Does anyone have a starting point for a rear gear ratio that I could use. Thanks

So a 373 would be good start, only wanting to pull 5400 rpms?

when you race , do you race with the tranny in first or second gear? If you race with it in first you probably have a 2:73 gear in your 10 bolt. If you put it in second gear and race, that will most likely put your 10 bolt with a 4.56 gear or so. what you need to know is the FINAL ratio, you find this by taking tranny gear X rear gear.

2.73 x 2.52 (th350 first gear) = 6.87 Final gear.
     OR
4.56 x 1.52 (TH350 second gear) =6.93 final gear

Those final gear rations will probably put you about 5400 rpm down the straights with a stock 350. Once you know what you have , you can dial in what you need

What are you trying to achieve? do you want to change your gears for More  or less rpm? Or do you just want to know what gears you have. If you race in first gear and slap in some 373 gears, you will be tachin' darn near 5400 rpm  on the caution laps  

with my 2 speed powerglide i run low about 6500 rpm.

The most rpm my car can turn is 5400

Whys that? Is that what your cam recommends? You would be better off re gearing and running in 3rd gear it's one to one I believe and less rotating mass and in the factory stock class you need to keep your momentum up as much as possible

You gotta know where you are at now,  to know where you are going.

When you get the 10 bolt out pull the dif cover and figure out what gear you have now. once you have that you can figure out what gears to go with when you get the 9 inch

http://www.thedirtforum.com/gearcalc.htm

that site my help you figure that out

Redalert144 wrote on 04/27/11 at 12:06pm:

I did'nt read you engine rules, but based on the info you stated that motor should be turning 6200 to 6400 rpm. As suggested pull the cover and ID the ratio. If you find that the final ratio is in the ball park of the others running in your class, then you have a problem with the motor.
A bad tuneup ( wrong timing), fuel, or ignition could make the motor layover. Bad valve springs can cause a RPM limit and be hard to feel.
Good luck.

Going to adust timing and go through the valvetrain tomorrow to see if we can get some more rpms out of her tomorrow. Thanks for your help guys

We pulled the valve covers and it turns out that we had 3 or 4 tight rockers, and one of the caps on the valve spring had broken. So hopefully getting that stuff fixed we can get some more rpms