ms4z28

I am thinking of doing a 408-ish ls2 block with a front mount turbo and I'm not sure what gears to run. I've heard deep gears like 3.90 or 4.10 would not spool well is that true? If so would I be better off with a 3.42 or should I go lower?

Sluggish

iTrader: (10)

3.42.

ms4z28

Okay well could I get some explaination why? Is it the turbo spool and if it I were to swap to a4 or th400 with 3600 stall what would be a good set of gears?

Modern_Muscle

iTrader: (11)

I have 342's in my car.
Perfect, in my opinion. I still blow the tires away in lower gears, so any more gear, and it would almost be useless til the top of 2nd, to 3rd gear...

If you DD the car, I would suggest 3.42's to keep you from shifting all the time, and to keep your RPM's down on the highway.
I sit at 1750 @ 70mph on my car, and still manage 27-30mpg's, since I cruise everywhere out of boost/in vacuum. I start spooling at 2600. and am in full boost by 3500-4000.
3.73's would be do-able and anything higher than that would basically make your car a strip car IMO. It can be done, but I would stick with 3.42's

MY99TAWS6

iTrader: (3)

3.73s are snappy off boost and you will spend a lot of time off boost with a 408 and decent turbos. I have m6 in my car currently and am now running 3.54 gears. Since going to 4l80 figure the 3.54 are fine. I don't really care if spin the tires off on street tires with the 3.54. that just keeps me from being tempted to street race people.
I have to put on something sticky like et street radials to hook up so have an extra set of them lying around for when want to play or go to the track.
I just hate the feel of really low gearing like 3.23, 3.08 or anything under 3 especially. Autos can also compensate with good stall. Going to run a 3400 stall with the 3.54 so that should be nice combo.
I would for sure stick with 3.42 to maybe 3.73 in your m6. I have still seen many cars run fine times with even 4.10s and turbos so not that convinced that you really spool up that much faster with the low 3 or less series gears.
Besides as said with a big power turbo car like mine you are not in boost much around town and even on the highway and not for long..unless you like Jail!

I posted a bunch of cars from the boosted lists that used to be sticked on this forum still no idea why they are not stickied anymore maybe to save space.
There were lots of pretty high geared high meaning like 4.10 very fast turbo cars.

Also spool up is a function of many things..engine size,turbo choices.And some don't want the turbos to come in too soon and too hard. Lots of opinionso on this gear thing. I couldn't go under 3.54 anyway with my dana and so far pretty happy with my dana.

cablebandit

iTrader: (37)

3.42 to 3.73 is what i would suggest

longrange4u

iTrader: (2)

I would suggest the 3.42's.. boost comes on a little slow so its nice to not have run out of gear by the time your turbo is in its efficency range... Zombie did some interesting playing where he advocates 2.70 something gears.... keeps you in boost longer (by maintaining the load throughout the curve).

I run 3.50's in my 9"... would say 3.42's in a 12bolt... IMHO

Zombie

iTrader: (2)

High gears like I'm an advocate of are for A3 transmissions and street cars, not 6spd's. 3.20-3.50 is a nice gear for a turbo 6 spd street car.