dandrea86

iTrader: (13)

I know this question has been beat like a dead horse but i searched and couldnt come up with an answer for my setup..


I plan on having a 408 built for my trans am in future. Car is a 6speed, I am running a 26" inch tire. 408 will have around 500-525 rwhp n/a..i do plan on spraying it with a 250-300 shot at track.I am really torn on what gears to get in 9". Car is a weekend warrior that will see some 1/4 mile. I plan ordering rear soon. im torn between getting 3.42 3.73 3.90 or 4.10.. I most likely will not be spraying on street. I could also run a 28" slick at track when spraying.
Please help me out guys. I want to start getting the driveline in order for power.

MeentSS02

iTrader: (11)

There is more to this than just the rear gear ratios...you need to know the max engine RPMs you are willing to spin on your 408. It makes a huge difference if you are turning 6,500 vs. 7,000 vs. 8,000+ RPMs (at which point you'd most likely be solid roller). You are going to want to cross the traps at the track in no more than 4th gear, so you need the engine RPMs and tire diameter, and make the rear gear ratio the variable. Do a quick Google search for "ss 670 gear ratio calculator", and plug in the numbers to start playing.

I'll tell you right now that with bolt-ons only and street tires, 4.11s on the street are a handful in 1st and 2nd. A 408 with a 250-300 shot would probably benefit from a numerically lower gear ratio if only to get traction. I'm gonna guess you'll end up with 3.73s or 3.42s, but I'm sure others will chime in with their opinions.

danhr

iTrader: (18)

4.10's

with 4.10's and a 28" tall tire, you will be at 142 mph at the top of 4th...

I'd guesstimate you'd be somewhere in the mid-high 13x range

dandrea86

iTrader: (13)

to be honest with you guys i was kinda swaying towards either a 3.90 or 4.11in rear. I think it would have plenty of na power on street. Then when i sprayed it at track i could slap on my skinnies and 28" slicks.. I do not have the motor built yet so im unsure on how high im going to spin it. Im thinking its gonna be around 7000rpms...keep the opinions commin

getusum

iTrader: (42)

Bingo.......I have exactly this set up. 408,m6,4.11's, and 28'' slicks...I trap on motor 122-125mph.....I've never sprayed the car....Going to 4.56's.
Since your going to spray, you can use 3.90's..I really wouldn't go any lower. Depending how much spray( Iknow what you said) you could go as high as 4.30's.....

You will bog out of the hole if you hook with 4.11's and the 28'' slick....On motor.....
My car dead hooks, then bogs and picks right back up. This is why I'm going with 4.56's....Get a stiff side wall slick since yo have the m6....
Also, If your rear can take it, you'll need to side step it no lower than 5500 rpms if you on a motor pass....I drop mine of the limiter(7200) and I have the bog issue...

Hope this gives ya a little insight. Now the real experts can chime in..Ask Coach he'll give ya some great tips..