ls1tuboplan

what better for a daily driver 02 trans am M6 with sts turbo(5psi) in a 12 bolt rear? Im not understanding the principle of lower 3.08, 3.27, 3.42's, 3.55's are better for turbo's because of load, whats load and what is worng with having a steeper gear 3.73, 4.10's,4.30...can anyone explain the concept with gears and turbo cars....and help me choose a gear for my app. Heres the deal 02 trans am M6, sts turbo kit,basic bolton's, expecting around 450rwhp with 5psi and boltons, it will see track(10 times a year) if that, what gear would be best, Im think 3.73's would give it better acceleration, more gear for a n/a car is better, I dont see why it doesnt apply to FI cars?

67Firebird455

iTrader: (27)

From experience, a lower gear like 4.10 (which I have) is excellent for a "lower power" non-boost 6 speed car with a short tire, but trying to get it to load the turbo long enough (full flow exhaust when the engine is put under load to spin the turbine) was a different story. I couldn't hit full boost until I reached the taller gears. It would immediately go to full boost in 4th gear, but would lag getting there in 3rd, even worse in 2nd, 1st wouldn't even think about it, I would have to shift before then. I hear that with an M6 car with stock-sized tires, people are looking at around 3.50's, even the stock 3.42's in our cars would work better than the 4.10's I have, and I believe it now from experience.

ls1tuboplan

thanks for the heads up, not that thats out of the way, so the deal is to stay in boost for the longest time, so then its between 3.27's or 3.42's or hell even 3.08's, but then having a low gear for, wouldnt it be a dog off the line, cause your at stock power with stock gears, until 3500rpm, then you get the power, so int the launch going to suck with that low of gear, or will i have to launch off the limiter just to cut a 1.9 lol, that sucks

Frost

iTrader: (45)

You need a two-step to spool the turbo off the line with an M6

fletchls1

iTrader: (10)

I had my 4.10's in still from my N/A setup and had the same problem in first but I could hardly get on it in 2nd also. Put 3.42's in yesterday but havent drove it hard enough yet to comment on each. It doesnt pull nearly as hard with the 3.42's but thats obvious. I will post back tomarrow and about what I have found out about spool times and such.

67Firebird455

iTrader: (27)

Well, it really depends on the tire, gear, stall combo you choose with the turbo (ar, size, location). I went with 4.10's with the idea of having a fast head/cam car, but went from cam/headers, 12.34 @ 112 to the turbo at 7#. I had it spike to 10# a few times in 4th and 5th, and I'm sure that's why it came apart. If you're running a 255/50/16 or comparable, I would suggest 3.42's to get the heavy beast going. It will be an all around good setup, are most of your races from a roll or stop? You can't build boost to get the turbo to work efficiently because you're not in the gear long enough to get it to spool up fully. Believe me, I could hear it in my car, sounded like NA, then before the top of 1st, i could hear what sounded like a jet engine come in, then 2nd it would get louder, then 3rd, louder, and would come on sooner, and 4th it was on full blast as soon as it went into 4th and the hammer was to the floor. It's a noticeable feel too. If you have like a 3800 stall, a rear mount 67 or 70, with the appropriate A/R, along with 3.42's on a set of MT et street radials 255/50/16 you will scream off the line with a 2 step. With the 2 step, with the clutch in, with the switch enabled, the engine "rev limits" under full throttle which allows the turbo to reach full spool, or close to it to give it a head start without having to really "load" the engine. You can fire out of the hole with the 3.42's and continue to load the turbo all the way down the track, it would work like a dream. I would be jealous, I don't even have a motor that runs right now! *sobs*

93formto98T/A

iTrader: (28)

I went with a 3.08 gear in my moser 9" with the twin turbo setup. Had a 342 before that and I love the new gears. Spools sooner and much taller gears/more time between shifts/higher mph. Highly recommended!

ls1tuboplan

well basicly im going to run the stock height tire with a DR on a corvette rim, I have a M6 thats stock...im going to do both from stop and from roll,majority of races from stop, i almost NEVER drive on the highway. im going with the rear mounted sts,no stall as its a manual. anyone else have input on what gear to run as it is sounds like im going with 3.42's. would something like 3.08's be better? or 3.27's as a good middle compromise?

frcefed98

iTrader: (16)

Right now with 3.73s with a 3800 stall and a turbo...NO GOOD. I'm swapping back to the 3.23's once I get a pinion nut from the dealership. The car is a dog with the 3.73s.

J

67Firebird455

iTrader: (27)

I'm sorry, I should've read again you were M6, I knew that, just didn't post it... strange how medication does that to you huh? =) I know I'm switching to a 3.23 or 3.42 gear, or close to it with a 9" eventually, AFTER getting the motor built and the car on the road again... Long *** process, and too much money. Guys with 2 steps and a tall gear are doing just fine. I just don't wanna slip the clutch and bog it bad.

67Firebird455

iTrader: (27)

I'm hoping with the new stroker motor it'll spool the *** mount sooner, which I'm sure it will, and the additional torque with the 4" stroke will be able to get the car rolling with the taller gears and tires. The sts is an excellent kit, I should have gotten one, but ended up much cheaper in the long run for better parts, just my own fabrication, that could have been a little better, but it got the job done. Do you already have the turbo kit, and is it installed? I'm anxious to hear which way you go with your application.

ls1tuboplan

no i dont have the sts kit, im hoping to get it within the next year...but yea i think ill go with the 3.23 in the 12 bolt. how will the car act until it reaches boost..will the car be slow on take off until 3500 rpm when the turbo spools, or will i have to launch at high rpms and dump the clutch to get a good 60 ft time or whats the deal with this?

67Firebird455

iTrader: (27)

I would recommend a 2-step, you can set it to whatever you want to, wherever you're comfortable launching, IE 5,000 rpm or whatever, you'll have full boost by then for sure, and you can dump the clutch and be full boost and near full power/torque to get the car up in the "power band" quick, without losing boost. If you go with a tall gear and tall tire on a 6 speed, without spooling the turbo first, it'll run like NA until the turbo starts spooling and then will take off, similar to a 2-stroke that has a hit. I would leave at 4000-5000rpm on a 2-step and call it done, personally.

obZidian

iTrader: (2)

what would you guys recommend... im running a 4l80e 2.48 first gear, 3000(something, unknown yet) 2.5str, with a 12 bolt running about 15psi or more through a t88?

67Firebird455

iTrader: (27)

You can get away with an even taller gear if you want with that 408 and that much boost on a transbrake (assuming thats what you're going to set up). Plan on some wheelie bars though, I can promise you that if you've got good suspension and some sticky tires, you'll flip that baby right on over. =) Really nice setup man...

Got Me SOM

iTrader: (2)

with the torque that turbos make i wouldn't run more than a 3.23. let that **** pull you thru the rpms nicely.

Works243t

Does this apply to a centrifugal SC also, or just turbo. Sorry I am still learning. But I blew my 10 bolt up (M6> 3:42's), and put in a eaton posi unit with 3:23's. I wanted to change it but if what you guys are saying applies, then I wont. I am not trying to hijack anyones thread, it just falls in line with the topic being discussed.

LastBlack02SS

iTrader: (21)

Its more for turbos. Turbos need load in order to spool up and make boost. Having a higher gear (lower number) will create more resistance or load and help the turbo spool.

Frost

iTrader: (45)

Guys considering numerically low gears and a th350, th400, or glide should remember this when choosing a setup:

If you pick a gear such as a 3.08, 2.73, etc, use the MPH/RPM calc for the tranny's 1:1 (3rd) gear and find out what your cruise RPM will be. This is where it gets sticky and can kill your streetability... If your cruise RPM in 3rd is a lowly 2500ish at 70 MPH, and you have a stall that flashes MORE, it will never reach effective coupling on the highway (remember, these are not lockup trannys) and will always be in the 'flash' area and slip. Even with heavy tranny coolers it will be hard to shed that kind of heat. I burned up a few back in the day trying to highway them with moderate stalls. The only real possible solution to being forced into running a nearly stock [tight] converter is Hughes' lockup stall for the 400, but I don't know how well it will handle a turbo app. And obvioulsy the only time for it's lockup will be light-load highway use.

Just some thoughts since I'm looking at the same thing...

fletchls1

iTrader: (10)

Here is what I found out. With 4.10's I seen 10# at 4,000rpm. With 3.42's I see 10# at about 3,500rpm.