Hey, calling all you Civic geniuses. I race a 91 Civic on a paved oval and just had to do a tranny swap. I had a DX and that committed suicide, so I have an Si trans in my car now. There is a difference in the final drive and I was wondering how much that would affect my cars performance.

I have a stock D15B2 engine and am running 175 65 R14 tires.

I know the final drive is 4.25 in the Si, and the DX was 3.888

I have found several websites that have calculators to figure out the cars speed in each gear at the rev limiter. Unfortunately I don't know how to figure out something like the acceleration will be affected by the different final drive ratio.

Any ideas or tips?

 

I believe with a higher numerical gear you'll have faster acceleration, but a slower a top speed.

 

Higher gear ratio means higher engine rpm for a given road speed in the same gear. The effect on acceleration depends on where that rpm is on the engine's horsepower curve.

 

Thanks for the replies fellas. I will find out today I guess when I take the car to the track. I run the car in 2nd and 3rd gear, and was hoping that I wouldn't lose any speed or quickness in acceleration. Anyone have any idea about tire sizes and what effects different ones would have on the car? 13 and 14 are the wheel sizes I can run.

 

the taller the tire/wheel combo, the WORSE the acceleration but the BETTER the top speed.

However, keep in mind a shorter sidewall will also improve handling.

now please realize I don't know a whole lot about racing paved ovals, but I would recommend running as short a tire (at least short sidewalls as possible) to keep rotational mass as low as possible (which improves acceleration), and also to gain the benefit of good handling in the corners.

I think a good size to look at is something like a 195/60/14.