Crazy to think about a R&P change?, the search for the ultimate gear ratios Options

[PlaysWithCars]

This is really more of an academic exercise, but hey, what else am I going to do this morning?

Looking at options for the elusive 'ultimate' gearbox for my car. The car is used primarily for autocrossing, but I want to be able to take it out for cruises on nice days so don't want some crazy low gears on the top end. I'm running a 2.4E motor is I have more torque than the cars originally came with.

First question: are the low gear ratios in a 914 an advantage or disadvantage in an autocross? Lower ratios contribute to quicker acceleration, but they also mandate a continuous rowing of the gears between 2nd and 3rd. I'm thinking that staying in one gear is ultimately an advantage. If you accept that being able to stay in one gear is an advantage versus shifting, then there are two choices: taller R&P to get longer legs into 2nd gear, or try and get a short enough 3rd that you can use it. If you can get a low enough 3rd though, it becomes a big compromise to street driveability.

This line of thinking is what's led me to look at alternate R&P ratios. The standard R&P for a 901 is 7:31 but there was an optional 7:27 available. With the optional R&P ratio it becomes conceivable to stay in 2nd on an autocross course and leaves nice 3rd/4th/5th options to get good gear splits and cruise ~3,000rpm at 70mph.

So, what do you guys think? Anyone using the taller R&P ratios in cars with higher torque motor swaps?

[Dave_Darling]

First question: are the low gear ratios in a 914 an advantage or disadvantage in an autocross?

Yes, it is.

Seriously, there is no one answer. I was able to do very well at a lot of autox events with short tires giving me short gearing, but there were a few events where I was between 2nd and 3rd all the time, where other 914s with taller tires just motored along in 2nd.

The alternate R&P is super spendy, if you can find one. Not to mention having to re-do all of the measurements for engagement depth and backlash and everything, which is kind of a pain.

Changing the R&P changes the overall gearing--something you can accomplish by changing overall tire diameter. Either just changing sidewall height, or changing wheel diameter. Guess which one is about a million times easier to do? (IMG:style_emoticons/default/wink.gif) Depending on which way you go, you can wind up with a lot bigger selection of tires, or a much smaller selection, so that does require consideration.

--DD