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Diff Ratio And Rwkw

RB SANDY

By RB SANDY,
in Engines & Forced Induction

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salad Veteran

salad

Posted
Posted

theoretically if you have a higher final gear it means that your drive shafts, wheels and what not are spinning a little bit slower. this should mean that you will have a TINY bit more power as there is less power lost through the spinning of these components. this difference is incredibly small though.

dyno runs done in different gears dont have much difference in power outputs and these have a much larger difference in gear ratios

dont think its worth worrying about.

mad082 Grand Master

mad082

Posted
Posted (edited)

changing the ratios so that you rev higher for the same speed will make the car feel more powerful and make acceleration faster, at the expense of top speed. if you go the other way you will make the car accelerate slower.

Edited by mad082
Cubes Grand Master

Cubes

Posted
Posted

Power won't change... Torque to the rear wheels will.

On the note of faster acceleration.

The R32/R33/R34 ratio's are well sorted for the engine size and gearbox ratio's.

I run an RB30 using the std 4.363:1 diff ratio. The car feels buzzy through the first two gears. First simply sucks.

I'm going to be dropping in a 3.9:1 diff ratio in the next week or so. After driving a mates VL making similiar power but with 3.45:1 diff ratio I could immediately feel the benifit of having longer diff gears behind the rb30. The 3.45 did feel a tad long as it appeared to be off the boil leaving corners, I've done a few calcs, the 3.9:1 ratio is pretty much spot on for what I want and the speed I drive at.

I don't like holding out gears to gain adequate road speed, the rb30 limping around keeping up with traffic can do with a gear change at ~2000rpm, the rb20det requires around 3000-3500rpm.

Allthough the car 'may' be slower I don't care, it will feel faster and hold me in the seat longer, it will return slightly better economy on the open road and simply be nicer and cruisier to drive.

I'll have to take a vid of how it drives with the stock ratio before I pull it out, you will see what I mean by buzzy.

I have noted that I've seen one bloke post here that had an rb25det in his R32, he dropped his ratio from the 4.363 to 4.11 and claimed it felt much better to drive, with such a small change even he said the 4.363:1 felt a little short for the 2.5ltr.

rev210 Grand Master

rev210

Posted
Posted
So if the car accelerates faster won’t it have more power at the rw.

A car can accelerate faster without more engine power through other means, like dropping the cars weight , reducing weight on rotational parts, changing the final drive ratio etc..

You could measure accelleration changes to ratios and rotational weight by plotting a time taken against the rpm on a power run. This can be overlayed on the power curve too. I am not sure if dyno software has this function built in, it would be very sensible to have it included. Anyone know if dyno dynamics software does this?

Cubes Grand Master

Cubes

Posted
Posted
having a taller first gear would probably be a little better as the turbo could spool up a bit more.

Which is exactly what I am hoping happens. All though it still spools up perfectly fine in first at least I will be able to get just a little more speed and hopefully a little better traction, at the moment its lunge it off the line and short shift to second instantly where I can get some power down.

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