Raoul-Duke

iTrader: (6)

Hi guys,

I'm going to be putting a 9' in my LS1 Z28 in Spring and will be boosting the car the following year (D1SC).

I heard 4.10's are too much gear with my planned setup. What is best? 3.90's or 3.73's to put in my new rear end??


I want to get the most that I can out of my forced induction setup but also somewhat driver friendly.

1999Black_Z28

iTrader: (1)

how fast (mph) do you plan to run in the 1/4 mile?

Raoul-Duke

iTrader: (6)

As fast as I can lol I don't want something that I am going to run of of gear with. Is 3.90 too much?

1999Black_Z28

iTrader: (1)

A 3.90 is not that different than a 4.10

I'm switching from 4.10 to 3.50 which is good for 140ish mph depending on how high you rev it and tire diameter

My recommendation is to search similar setups to determine an approximate mph in the quarter and select gears based on that.

Raoul-Duke

iTrader: (6)

Damn, Yeah Ive been searching on here but cannot find anything really. So I guess my best bet would to go with 3.73.

brians91formula

iTrader: (12)

http://www.f-body.org/gears/

The Alchemist

iTrader: (19)

I have a D1 with ~15psi of boost with 3.73s in my M6. There's sometimes that I think I'd rather have 3.42s instead since I blow off the tires in 2nd gear as soon as I hit boost. It's better now with the new R888s, but still, I think a 3.42 gear might be better.

dschmittie1

iTrader: (64)

I ran a 3.70 when I was still Procharged with an M6 and a 28" tall tire.

Raoul-Duke

iTrader: (6)

Thanks for the feedback guys. Im planning on running 17 inch 315 M/T et's out back. I'm hoping that will hook if I go with 3.70's or 3.73's.

But overall 3.42's would be better huh?

The Alchemist

iTrader: (19)

Well, Dschmittie1 had 3.70s with a 28" tall tire, so maybe like a 3.50 gear with a 26" tall tire would be best.

Raoul-Duke

iTrader: (6)

Sounds good. Thanks again.

btw would the fact that I will be putting a blower cam in the car before I throw the blower on make any difference? Prob not but jw.

Ryans99ls1

iTrader: (16)

I want 140mph out my 4th gear. I dont want to run around on a 28" tall tire all the time so im putting in 3.25s

A 3.70 rear gear with a 28" tire works out to nearly the same as a 26" tire and 3.25s.

I have 3.70s (w/ 26" tire) in my car now and i hate them with a turbo. im out of gear just after 120 and the car is really starting pull at that point, it sucks. I wouldnt even be able to make a full 1/4mi pass without hitting 5th.

fotoboy

iTrader: (1)

I was a little nervous about staying w the 3.42 but at 6500 rpm in 4th gear I'm looking at 147 mph w 26 in tall tires. I spin easy with 335 dr hoosiers in 2nd now.

nick.celis

iTrader: (11)

This is a good thread, as my build ill be keepin the built T56 i have, and im ordering a new rear end, and this thread just helped me pick what gears i want to run with my new rear end

Raoul-Duke

iTrader: (6)

What gear would you change to if you could right now?

So I guess I will be going with 3.42's as well. My only concern is that the 3.42s are going to take away from the performance of my blower cam that I will have before the blower installed. The car will be cammed only for at least 1 year before the blower comes. But I guess that is just how it is lol 3.42's remain.

Im glad you think so man, I was searching for a similar thread before I posted but could not find anything really.

Tally TransAm

iTrader: (17)

same as I run

Ryans99ls1

iTrader: (16)

I would go with 3.25 cus im running and 26" tire (seems like you are too)
If i was going to run a 28" all the time, id go 3.50. Both of those combo's give me 140mph in 4th.

I should probably mention im only spinning my car 6k, so if you spin higher, youll get more out each gear combo.

A 28" tire and 3.70s will take you to a lil over 130 in 4th. A 3.50 rear gear with 26" tire will do the same thing.

Now what does change somewhat for each combo of tire/gear is your 1-3 shifts points. Some combos let you get a lil more mph in each gear which may or may not be what you want. if my memory is correct, then with a 28" tire and 3.50s i can stay in first gear to nearly 60mph. with a 26" tire and 3.25s i barely get over 50mph in first. (if my memory is wrong, then the opposite applies)

it may be beneficial to dyno your car, look at your powerband and go from there. its also easier to get traction with a 28" tire. just some food for thought

Sales@Tick

iTrader: (3)

I'd go with a 3.50 in a 9" maybe even a 3.60" since you're a M6 car and your gear ratio spread is much different and wider than a M6 car.

Turb0Z28

iTrader: (4)

I am running 3.24 with 26's cutting 1.5 60s but i break traction 100 feet off the line. May have to go with 28's. have not been to the 1/4 with it yet just the 1/8th

Ryans99ls1

iTrader: (16)

breaking traction 100' out can usually be cured with suspension adjustments. Martin (above) just wrote in someone else's thread about this and how to go about fixing it.

28" tires do simplify things though