3.9's or 4.11 gears - Thoughts & opinions

[Louie_D]

Got the car at VCM this week for an LS3 conversion & changing the diff gears while we are at it. Not sure if i go 3.9's again or 4.11's. Car is an M6 with a largish cam, whats peoples thoughts on the 4.11's?

[duke5700]

I've driven both and both are pretty good. Have had more experience with 3.9's as it is what I ran in my car for quite a while before the turbo setup. There was half a litre to a litre per 100km's between 3.9's and 4.11's.

Is it a T56 alah VX era or one of the later HSV/VE ones with the differing ratios?

How hard are you going to rev the engine? If you are sticking with the factory limiter, I would go 3.9s, if you are going to buzz it hard, 4.11's.

[Louie_D]

Its an m12 box out of a hsv so not the standard ratios. Its a decent size cam in the car so I would think we are going to stretch it out abit

[IJ.]

May or may not be a factor but 4.11:1 tend to be a noisy ratio.

[duke5700]

Yeah 1st, 2nd and 3rd are shorter, 4th is 1:1 or 1:1.15 and 5th and 6th are shorter vs a T56.

I would go with the 3.9's.. it will be like 4.11's in a normal T56 equipped VX. Not like you're going to be lacking power to pull it. :lol:


Its an m12 box out of a hsv so not the standard ratios. Its a decent size cam in the car so I would think we are going to stretch it out abit

[QldKev]

I'd probably go 3.9 due to the shorter ration g/box, but realistically there is only 5% in the diff ratios.

[white lie]

Wouldn't be much in it, either will work but I'd go 3.91's for the possible noise factor like IJ mentioned

[Blown Monaro]

If your going to drag race it you should have a think about what tyre size youa are going to run, your expected mph and rev limiter setting, if its a streeter go the 4.11's.

[heavyduty1340]

Got both in 2 cars - I'd only go 4.11 if you are into giving it stick

The 4.11 make it just that bit more responsive!!

[macca_779]

with an m12 box fitting 3.7's is like running 4.3's in an mm6. Ie crazy. Running shorter than 3.73 with the ratios in the m12 and later boxes is just to much imo. Will certainly mask any lack of torque in a massive cammed car. But you would want to rev well past 7000rpm to get the most out of 1st to 3rd. When i went from my original mm6 to an m12 i lost 20km/h out of 2nd gear with 3.73's revving to 6800rpm.

Think wisely, as if all you want to do is make a car that will break traction on command out of corners, perhaps you should consider a cam with some guts not just all top end

[Djbarnstar]

I've had both and would say go for the 4.1's. Heck 6th is HUGE so go for the smoke bro!

[Louie_D]

Thanks for the advice guys, ive decided to go the 3.9 to try and avoid the whine from the after market gears although I have been told that I will probably still get a whine with the harrop diff cover/nolethane bushes

[ittwgn]

stock lsd ?? or take advantage while your there and throw in a trutrac !!!

[Louie_D]

Already got the trutrac fitted