3:7 or 3:9 diff gears ?

[Gusto1dtp]

Hi I got a 2009 ve Calais 6L it was the AMF version until

I
Also a ramjet 3 OTR, x-force extractors , hi flow cats, with 2 1/2 stainless exhaust system
It’s an auto an I still need A 3000 stall converter
I plan to put a garret turbo where the air box was.
I still need to do my diff as it’s a 2:9 and non lsd my mechanic said 3:9 LSD but reading everything people have been saying I’m wondering is he right or do I go 3:7?

 

[markalan1two]

i had 3.9s and used to rev a little high

 

[Gusto1dtp]

Thx so your saying 3:7

 

[07GTS]

depends what power u are wanting to make and how much can get to the road, if ur going turbo and more boost u run then the higher gears will make it too easy to spin so u may want lower to help

 

[gtrboyy]

Do stall convertor first to suit turbo set up.....buy lsd diff that was out of manual if shorter or truetrac your diff.

Won't need short diff gears with a turbo...

 

[Gusto1dtp]

I need to get a tune done but been told I'll have about 310+ rwkw once it's done but I'll let u all know what it comes up at when it gets done. I think it was around 260 without otr an had stock headers an exhaust system then an he said he couldn't tune it properly cos it needed more air flow but from the research I did do just an otr an tune Gives u an extra 25 rwkw plus what ever u would gain from extractors an cats with exhaust. An then whatever they couldn't get out of it before cos it couldn't breath.

as for the diff I'm trying to get a 3:9 truetrac diff Off a mate but his being reluctant so not sure how I'll go an yes I'll be doing the turbo last need to keep the misses happy in between mods lol. (although I don't like my chances of ever pulling that off at least I can say I tried. ) thx everyone who's replied but I still don't know exactly which diff to go if I can't get this true track?

 

[Immortality]

Get the engine mods done and tuned first. Then once you know where the torque/power curves are you can work out your optimal diff ratio.

 

[Vin999]

whats the difference between 3.7 and 3.9 @ a small rpm difference, why bother with 3.7 ratio

 

[Immortality]

Probably about 100rpm @ 100km/h.

 

[vr304]

If your definitely going turbo then try and get some 3.45s from a manual model and a true trac centre