mark28

why to people do this, what so good about 3.9 diffs

am i missing something here or just being stuppid


cheers if you can help. mark

stockcar

it depends why they are changing the diffs??
the lower numerical number will mean a raing of the o/all gearing................

if they have higher power cars then its normally a good idea to lengthen the gearing to maximise their power

could be any number of reasons without a qulification of their intent??

alyn

mark28

ok i get the power thing,

i guess with less teeth they are a wee bit more stronger as well. not alot but just a very little bit

StickyMicky

not true

less teeth, more load placed on each tooth

mark28

but less teeth regs les room. so the teeth are thicker (just like me), this making them stronger.

Brit_in_Japan

Perhaps it's related to matching the right gearbox with the right diff? Japanese spec cars have lower final drive ratios in the gearbox and therefore need a different drive ratio for the rear diff. If a gearbox has been swapped for a JDM version then you would need to change the rear diff to match it.

GariYaRally

That goes without saying, g/box ratio must match the diff ratio.
With a 'closer' gbox, power lost through the drive train to wheels is less too.

doug2507

iTrader: (6)

Most people that change the diff from the std 4.4 found on the RA's and R's do so for competition or for better cruising speeds on the road. A 4.4 diff coupled with a close ratio box make the car rapid off the mark but means you run out of gears at higher speed. On the road it can be 'uncomfortable' cruising as the rev's for the given gear will be higher.

I have a type r v.ltd with the short box and 4.4 diffs and it doesnt really like motorway driving as at 70-80mph the revs are close to 4000rpm. It also puts more strain on the engine running at a higher rpm and will induce more wear and tear on the engine in the long run.

In competition i found a perfect example at Crail this weekend. There was a lovely RA v.ltd with oodles of power but was in 5th gear way before the finish line. With a more spread out gearing, longer diff combination (4.1 or 3.9), he would probably have had a higher terminal speed and fewer gear changes getting the most from the power available.

I may stand corrected but that is my opinion of it/way i understand it. The strength of the CWP does not really come into it. Its all down to gearing.