Gearbox ratio gurus wanted :)

Hi guys,

I want to check my logic with a gearbox I'm hoping to change out the 5th gear to give a better cruising speed at 70mph.

I have an 02j FBK gearbox from a golf 2.3ltr V5 which will be fitted to my R32 engine. I'm planning to run 195 / 50 / 15's on my car and looking at the gear ratios would be over 3300rpm at 70mph in 5th gear.

The stock ratios for this box:

Final drive ratio: 3.938
1st: 3.300
2nd: 1.944
3rd: 1.360
4th: 1.034
5th: 0.816

The R32 engine produces peak torque at 2500rpm.

Now I have played around with various gear ratio calculators and wondered how true to life these would be?

I can change out the 5th gear to a 0.700  which would reduce the 70mph cruising speed to around 2800rpm but looking at a graph this would be some hike up from 4th gear and don't what the car to struggle.

Does anyone have any advice on whether this looks OK?

Cheers

Rich

 

I cant remember the ratios off the top of my head, to do a comparison plus the engine will be completely different,  but i did the diesel 5th conversion on mine.

my main comment that on your usual B road / slow A road 5th almost becomes unusable and you find yourself switching between 4th and 5th quite a lot. this is generally when your stuck behind the guy/gal doing 40-45

but heading down the motorway, although only a fairly small drop in RPM it does make it a lot more comfortable to drive.