Wanting to research changing the ratio of fifth gear on my Ver 2 sti RA V Lim and wondering how one goes about interpreting ratios, ie. what speed will I get for what revs with differing ratios. I'm having to hold about 4000 rpm at mo to get 70mph and is hurting the fuel!!

 

Ah the joys of a type RA
Its normally published what the mph/kmh is per 1k rpm, though you could check out some sites like www.sidc.co.uk and see if they have any info on it.
Just to put your ratio's into perspective, my MY03 Spec C does about 90 at 4k and the top end is just under 170mph.

Tony

 

Thanks Tony. Think I might just face the fact that this car is not built for motorway driving - can always borrow my wife's TDi Polo and enjoy the RA for what it is!

 

You have a couple of choices. I leave it for you to verify your current gearing but you probably have a 4.44 final drive ratio, (F and R diffs) and fifth gear will be .825.
If you confirm this to be the case and give me your tyre size I can work out accurately your mph per 1000 rpm in each gear.

You have several choices.
Change 5th gear for a .738.
Change from 4.44 diffs to 4.11 (not much of an improvement)
Change to 3.9 diffs.
or a combination of .738 and diff change.

 

Tyre size is 16".

Have managed to track down the ratio, is as follows:

1st - 3.454
2nd - 2.333
3rd - 1.750
4th - 1.354
5th - 0.972

This is the ratio for the ver 1 WRX Type RA and apparently is the same for Ver 2 STi Type RA.

How easy/costly would it be to change the 5th gear to give me a longer spread?

Thanks, Dave

 

I have been looking at this issue on my 95 WRX, it has
5th 0.825 and a final drive of 4.111 which gives 21.1 mph/1000rpm = 84@4000
yours I believe has (My mate has one, gearbox VB4CA, check your VIN to see if yours is the same)
5th 0.972 and a final drive of 3.9 which gives 19.8 mph/1000rpm = 79@4000

So there isn't that much difference if you were to go this route.

Have a look at these 2 pages for some more info

information page

speed/rpm calculator

HTH

Mick

 

Thanks Mick,

Really useful calculator and yes, the trans type matches mine. Looks like easiest way to get more out of it would be to put on some huge wheels!! Guess i'll leave it as standard for now...

 

Glad you have a calculator/spreadsheet now. It saves me doing it for you.
If you want to increase your gearing with the tyres make sure you get accurate circumfrance information before you commit any cash.
For instance 205/50/16 is taller than 215/40/17 and to give my WRX longer legs I actually fitted 205/55/16.
In the end I actually increased the top speed going from 7000 to 8000 rpm limit but that is another story.

 

Pleased to save you time! Any idea what cost i'd be looking at if I decided to change 5th for a 0.738, as according to the calc would give me a theoretical top end of about 170?

 

Ask a gearbox specialist such as Townend Garage/TEG sport. 01524 733837.
Warton, Cumbria. Box out and in, say £150, split box and rebuild, maybe the same again. Secondhand gear??? Not a lot. Just a guess.