VR SS 3.9 diff ratio.

[vc commodore]

I'd be interested to know how you go changing the ratio. I have the 185i vr ss hsv spec , as the 3.08 diff , the car takes off from the line like a slug. By having the 185i spec I would have thought that it be a little more punch off the line but it's not all that great , I had a standard vp SS many years ago now 5.0 even with no extractors and as far as I knew it was stock as a rock but that thing was insane with power. It would knock off any 215i vr/vs commo's with ease. As far as I know that one was a 165kw. It used to keep up with the gen 3s. For some reason it blew away all other SS with ease , maybe it was just a freak engine but little did I really know till I had to sell it for financial reasons. After my financial situation improved so five yrs ago I got the vr SS and was really a dissapointment and I'm actually thinking of a diff ratio change , as you I don't drive her much and a lot of advice ppl have given me as a simple power fix is the ratio changed

Don't think he'll reply....Hasn't been on since 2017

 

[vc commodore]

Would the 411 be the best bet then as opposed to 3.9 ? The 3.08 with mine , feels like I could run faster on its take off from the line , it's a 185i vr ss hsv spec and am not all that impressed with the way it is?

This person was banned in 2013, so don't think they'll answer you some how

 

[peteinoz]

Would the 411 be the best bet then as opposed to 3.9 ? The 3.08 with mine , feels like I could run faster on its take off from the line , it's a 185i vr ss hsv spec and am not all that impressed with the way it is?

I've got 3.9's in mine.

What I learned is to use really tall side walled tyres.
I'm running mitchelin 235/55R/17 on the rear and man they are grippy. Even in the wet they've got grip with 305 rwhp.

Love it on the street etc..
Those exact tyres at the 1/8 mile street drags at Lakeside, I beat an 850 rwhp Malloo Ute

Though over the 1/4 mile I think I'll hit the limiter before the end, so might go 3.55 next.

 

[losh1971]

I've got 3.9's in mine.

Though over the 1/4 mile I think I'll hit the limiter before the end, so might go 3.55 next.

3.45?

 

[EYY]

There’s not enough difference in performance between 3.7-4.11’s to really compare. If you were purchasing a second hand diff - settle for 3.7’s, 3.9’s or 4.11’s.

Otherwise I’d probably go 3.9’s if purchasing new. Just a personal preference thing. They don’t rev that hard, or use extra fuel as some people try to tell you.

They do rev a little higher at cruising speeds, but are under less load due to greater mechanical advantage. You won’t save on fuel, but you generally wont be using more either.

 

[losh1971]

Can you buy OEM gears for these again now? If not it will be best to give them to a place who has the lapping tank. If not they could end up pretty noisy.

 

[Immortality]

Just to put some numbers on it. With 4l60e trans (.7 OD ratio) and standard wheels (235/45/17) and assuming your converter lock is working correctly you should see the following engine revs @100km/h

Diff

3.08 - 1770rpm
3.45 - 1990rpm
3.73 - 2150rpm
3.91 - 2250rpm
4.11 - 2370rpm

Those numbers are mathematically accurate but you need to account for slightly different tire rolling circumferences, speedo and tacho gauge errors etc and those with older cars converter lockup slip which is common on the 4l60e on higher mileage vehicles.

 

[gtrboyy]

Yeah diff gears for m75 now available again.

Personally I like 3.7 gears as consider it allrounder gear for street car...not too short nor too tall gearing for 4l60e cars.

If more drag orientated with very limited highway use 3.9 or 4.11's no issue...although if more for skids apparently 3.9 gears are stronger less teeth on pinion was the excuse so less likely to strip teeth off it.

Manuals I go straight for 3.9/4.11's.

Shiftkit,memcal tune & shorter diff gears with decent extractors/exhaust really liven ol' 304 efi setups.