[Mk2] [NA] Final drive options for the S54 + helpful spread sheet for people

[jakeymears]

I've been thinking about changing my final drive ratio to get more acceleration as the car as it is is geared to 160mph+ which it will never get to nor would ever it ever spend much time over 70-80mph during normal use, ok the odd track day it will go faster (driver willing ) but I doubt there's many tracks you could get 120-130mph+ in an N/A, and that's about the same point that the aero becomes a massive limiting factor for the N/A's that the engine just doesn't have the grunt to deal with.

so I think going for a higher ratio diff would make the car more fun and actually have a few benefits, pulling away would be less strenuous on the clutch and the fuel savings around town might actually go part way to offsetting the increased fuel usage at duel carriage way/ motorway speeds.

My diff ratio is 4.176:1 and after doing a bit of research the only possible option above mine would be a 4.529 from a C59/60 or 66 transmission (Celica gts, lotus elise or corolla 99+) but I cant find anyone who has swapped in this ratio into this transmission?

Some Info found in these two threads,

Interchangeability between "S" and "C" series transmissions
http://www.mr2.com/forums/archive/index.php/t-7966.html

more up to date transmission ratios including newer gearboxes not mentioned above
http://www.midshiprunabout.org/mk3/gear-ratios/


To compare the lot I made a quick spread sheet to calculate things like acceleration in gear, road speed in gear, Aero forces, 0-60, 0-100, top speed. It is pretty accurate but it obviously has assumptions and limitations but it allowed me to compare the UK, Import and 4.529 ratio

UK - 3.944 (0-60=7.2, 0-100=19.2, top speed roughly 130, RPM @ 70 3200)

Import - 4.176 (0-60=6.8, 0-100=18, top speed roughly 130, RPM @ 70 3400)

Target - 4.529 (0-60=6.5, 0-100=17.2, top speed roughly 130, RPM @ 70 3600)















Would be great if some one could point me in the right direction or confirm if this diff ratio would fit (looks like the 77 tooth ring gear is whats needed) as previous cars I've swapped the final drive on have been amazing to drive, also if anyone wants a copy of this spread sheet let me know.

Thanks

[Black Light 93]

I have been thinking of doing a similar thing although I'm not sure I would want 4.5 diff as I tend to have to use the motorway more often than I'd like to. I would say a diff closer to 4.3 would be more practical (although still annoying at motorway speeds).
Unfortunately I can't help you on the compatibility of the other gearbox internals (I'm sure some of the traders on here have looked at this at some point).
I would love a copy of that spreadsheet though if you don't mind.

[jakeymears]

I'll let you know how it goes, i had a 4.4 in my S13 and that combined with the gearbox ratios was a bit much that said it felt like having another 50-60bhp, I think I could settle for the 200rpm hike as its mainly B roads and town driving. PM me you email address and i'll ping it over

[PW@Woodsport]

I'm afraid it is not possible to swap internals between the S and C series gearboxes, they are completely different.

In stock form the S series is already pretty short geared, i think if you make 1st any shorter it will become redundant.

In short you need to make the engine more powerful to optimize your current gearing, with the V6 engine for example there is so much torque in 1st gear you need to change quicker than you would with the 2.0ltr NA.

[jakeymears]

Hi paul, thanks for replying. shame the final drive doesn't fit but it saves me a bit of money at least

Yes i totally agree the most effective option would be to bump up the torque but i was looking for a something else to do while changing my clutch and i'm not really sure at this moment what direction to go with the car as I only really bought it for track days, that said there could be an engine swap on the horizon, the V6 is tempting and the noise is intoxicating but I also love boost

[twizzlemytash]

bump, has anybody found an answer to this ??? Im looking for a higher final drive for my gearbox and am very surprised to find there seams to be no options out there ???