Want 3.91, ZL1 diff or just gears?

[csorrentini]

Hello all,

I just had the GPI Max Performance Package installed in the car andhave 525RWHP/479TQ NA. This is my daily driver still and enjoy every moment of it.......other than traffic....that sucks. My question is, keeping it simple and not crazy expensive for a daily, should I just do a simple gear swap to the 3.91 or upgrade to the ZL1 rear?

[Benman]

Are you M6 or auto transmission? If you’re not planning on going to the drag strip and launching really hard with sticky tires then you can just install the 3.91 gears and use a LPW diff cover. That cover will need aftermarket bushing, the kits start at about $45 and will have 3 bushing, 1 for the cover and two for the front differential mounting points. These are made from polymer and will be harder than factory rubber bushings. They help reduce wheel hop. Replacing the subframe, control arm, and trailing arm bushings with aftermarket units also helps make the rear end more reliable. The tradeoff is an increase in NVH, although most say it’s minimal and worth it. Jannetty offers a rebuild that claims to handle 650 rwhp on M6 cars and 900 rwhp for autos. Stock axles are a concern as well, wheel hop kills these quickly. G force offers a couple of upgrades, but they aren’t cheap.

[csorrentini]

Hey there thanks for the write-up. I have an M6. I currently purchased the BMR trailing arm, toe rods, sway bars, Rear cradle bushings and 1" lowering kit. So by the sound of it just the 3.91 and those bushings should be fine.

[acammer]

Originally Posted by csorrentini

Hey there thanks for the write-up. I have an M6. I currently purchased the BMR trailing arm, toe rods, sway bars, Rear cradle bushings and 1" lowering kit. So by the sound of it just the 3.91 and those bushings should be fine.

Anything less than 4.10s is not doing that combination justice. You've got a rowdy camshaft with heads and intake that want to REV.

LPW cover is a good idea as well to give that case some extra strength, and subframe and diff bushings to cut out wheel hop is very important to keeping things alive. There really isn't a downside to the 4.10s - a VERY minimal difference in fuel economy from the 3.91s. If you're building a stout all motor combo you've already thrown fuel economy out the window - so might as well maximize your performance. GPI sells the Motive kit which many are having good success with.

Do yourself a favor, and just buy a trutrac if you're having the rear end built. The stock LSD clutch are not real strong, and eventually will leave you doing one wheel burnouts. It gets expensive fast, but if you're gonna make that kinda power, you'll find you'll be investing just as much in the driveline if you want to use it.