diff ratios

[oldFEsteel]

G-Day all,
My FE runs an HR disc front end,an HR LSD and an aussie 4 speed behind a 186 red...at 100klm's she screams
her head off cruzzzin down the highway...my question is would dropping the diff ratio help reduce the old 186
from reving it's head off?.....
cheers Denis...

[FCRB26]

HR LSD what ratio im guessing 3.55 or 3.36 so run a 3.08 or a 2.78 problem solved.


Pete

[zulu]

Denis

It could also have something to do with you tyre /wheel size diameter, if you were to try a larger rolling diameter, either wheels, tyres or both, could reduce the revs

Gary

[oldFEsteel]

G-day there...I forgot to mention I'm running 13x7 steel rims...and diff is a 3.08..
sounds like I should try a 2.78...thanks will start looking.. :-)

[jack_fc]

Denis,
 
what size tyres? If you have a tacho, what rpm at 100 kph?
Seeing as tyres to suit 13 x 7 rims are not easy to get, maybe you could consider 14" rims instead of a 2.78, thereby giving you a much wider choice of rims, rim widths and tyre sections....

cheers, jack

[EffCee]

Denis,

I am sensing that something is not quite right here, I am assuming that the tyres that you have on your car woulod be something like a 205/60/13. If that is the case then when you take into account the final driver ratio through the gearbox is 1:1 and a final drive of 3.08:1 then at 100km/h the engine would be developing 2738 rpm.

even if you are using 50 series tyres, such as a 225/50/13 then this would translate to 2841 rpm, 205/50/13 takes it a bit further to 2948 rpm.

All of the above scenarios indicate less than 3,000rpm, which is hardly what I would call revving it's head off.

Have you checked to see if the clutch is slipping, or have you checked if the revs are about what I have indicated with a tacho? Are you sure that the diff ratio is 3.08:1?

Keith

[FCRB26]

3.08 and a 4spd should be ok??

like others have said sounds like a clutch or something.

i would stick with 3.08 LSd they are worth a bomb and are like rocking horse poo.

[colt]

Denis, as Keith said. Do you have a tacho? Is your car naturally loud? You may think it's revving hard when it's actually not. With a 3.36 diff you would be doing about 3000 revs at 60 mph, with your 3.08 diff, you should be doing less.

Colin.

[OldGMHolden]

Hi All,
Unless you change the speedo drive gears, you will always see the same INDICATED speed at the same RPM, no matter what diff or tyre sizes you run.
First thing you can do is check the speedo with a GPS, then you will have a good starting point.
If you then change diffs or wheels/tyres, check again.
You will quickly see the results.
Cheers,
Gaz

[newman]

Why not grab a Navman or similar and check that the speedo is reading correctly first before reaching for the spanners and trolley jack

Mick

[FB_MAD]

Why not grab a Navman or similar and check that the speedo is reading correctly first before reaching for the spanners and trolley jack

Mick

  Very good advice there  . I am running a 3.08 with 185/60/13's and I can definately say that in top gear ( 1:1 ) your speedo will be reading incorrect relative to actual speed unless you have installed the correct speedo driven gear for the 3.08 and 13 inch combo.

 A  GPS is a good way of checking for speedo error.

My engine is a 149 and I can't really say that it is over revving with a 3.08. and 13's.

I've just gone to 14 inch  Tasman rims and 215/60 tyres and it's approx the equivalent  (at 60 mph engine revs )of going down to a 2.78 if I was still using the 13's.