Diff ratios etc - basic questions..

[dxtawagon]

what are the ups and downs of changing my low ratio diff (F252 = 4.55 - 1) to a 4.1 or 3.9 or something??

im wanting lower revs when open road driving as my car is just for cruising and at the moment it revs really high even in 5th.

i dont have a rev guage so i did a few measurements and numbers and worked out that at the moment it runs about 3600rpm at 100km.

that is based on a 4.55 diff and i think 0.85 in 5th (w55 gearbox) and the diameter of my wheels approx 585mm.

then if i substitute a 3.9 diff it works out about 3100rpm.

which seems better. but is that to much of a change from standard???

also will a IRS F series diff fit into a solid rear axle?? or what needs to be done to change it over???

cheers
daniel

[dxtawagon]

bump

[Stealer Of Souls]

I would think that going for a 3.9 isn't a major issue for the car. Providing that you're just driving it and not racing it. If the engine is standard it should handle the ratio change fine.

Good:
Improved mileage when cruising at speed.
Reduced noise at speed.

Bad
Speedo will not be correct.

Indifferent:
Will make the car accelerate slower.

For a street car the change would be fine in my opinion.

[dxtawagon]

sweet cheers

thats kinda what i figuered

anyone know whether IRS diff head can go into solid rear housing??

cheers