How to calculate your final drive (if you do not know...)


ek9osaka

ek9osaka

EK9 in Japan
Joined
May 27, 2010
Messages
78
Hi all!
Can you please help me with my shitty maths?

I am trying to figure out if I have a swapped final drive or not.....

I have an EK9 with an ITR S80 gearbox. This would give me a 4.785 final as standard.
I do not know if the final drive has been swapped out or not, because the dealer who sold me the car did not know....

Anyway, on 205/45/16 tyres, I do 3400rpm at a reading of 100km/h, but I think with the tyre difference from stock I am probably actually doing 98.5 km/h at 3400rpm.

From these figures can somebody figure out if I either have a FD or 5th gear swap?

According to the MFACTORY calculator, I should be doing 101km/h.

Or.....maybe my speedo is just 2.5km/h off / calibration is out of whack.....
:blabla:
 
just because its a s80 doesnt mean its a 4.78 FD as the 96 and 98 spec ITR have different FD but the same s80 gearbox...
 
elchunk said:
just because its a s80 doesnt mean its a 4.78 FD as the 96 and 98 spec ITR have different FD but the same s80 gearbox...
Click to expand...

x2

But going by the MFactory site it probably is a 4.7FD , give or take some km/h rpm because both dials can be off a bit
 
One thing gear calculators do not account for is the amount the tyre enlarges with speed. Not sure how much effect this would have at 100kmh but this does have a minor effect on the speeds you see vs what you expect, coupled with the speedo error probably accounts for the difference you are seeing.
 
ElChunk - Yes good point, but surely it could not be a 4.4, if it is revving at 3400rpm at 100km/h.....
 
ek9osaka said:
ElChunk - Yes good point, but surely it could not be a 4.4, if it is revving at 3400rpm at 100km/h.....
Click to expand...

Due tothe different 5th ratios, the total ratio is virtually the same in either box, the difference in engine speed at 62mph (100kph) is less than 30rpm.
 
Ok, thanks guys. For the time being, I am going to assume it is stock S80 and that my meters are slightly off perfect....
 
Which S80 though? If you give us a speed/rev in 4th and we can tell which one it is as the 4th gears are different.
 
The 98spec S80 (4.785 FD) comes out at 4457rpm at 62mph, 96spec S80 at 4375rpm. Sounds possible you do infact have the later box with the 4.785 final.
 
From your post you are doing
3400rpm at 100km/h in fith gear
and
4500rpm at 100 kmh in fourth gear

This tell me you have standard 98-01 JDM ITR S80 box with 4.785 FD

or an s80 with 1.034 ratio for 4th, 0.787 ratio for 5th and 4.785 FD.

hope this helps
 
hey guys im knid of new to all this and all the types of things. you may think im thick but im going to as but..........what if finsl drive???
 
Final drive is the final reduction gear in the gearbox before the power is sent to the wheels. It scales all the other ratios by the same amount.
 
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