black 2001Vette,Nightmare

One of these tranny gurus on the board can answer that better than I, but all I know is OD is an overdriven gear, and it's more difficult to capture spinning mass, when revolutions are farther apart, as in the case of that overdriven ratio, which in turn can produce more heat, since it takes longer to catch up to the input inertia or torque produced...and heat is what kills tranny fluid, which in turn incapacitates your transmission, and causes it to fail.
That scenario is more pronounced with the greater torque produced by some of the high horsepower set-ups there are so many of on here and elsewhere. It kinda goes without saying that once everything is spinning at the same revolutions per minute, heat is reduced, so the sooner that happens, the safer your tranny will be. The longer it takes, like at extremely high rpm or very high torque levels, the more likely you will suffer transmission damage of some degree. The preference for staying in third, is due to the fact it's a 1:1 ratio, and will respond to that spinning mass much sooner than OD can, and will usually keep you where you want to be, in the power band, as you're nearing the end of the race.
You will see a lot of guys recommending a 3:73 or 3:90 max gear ratio...because they don't want to encounter 4th/OD before the finish line, at the track.

So I guess it just depends on how much torque is being generated, how many rpms you're spinning at the time of the shift, and how well built your transmission is, as to how long it will take for the situation to deteriorate.

Sorry for the inept explanation. Only way I know how to put it.

300bhp/ton

Cheers.

This is being a real problem area for me at the moment.

I currently have a 2.73 rear on the 10 bolt, which I love because it will bang the 158mph limiter in 3rd.

But 2.73 isn't an option for a 12 bolt. If I went if 3.73 and upped the rev limit to 6200 with 400rwhp and similar torque.

I want the ability to go from a stop to 150mph at WOT, or from say a 60-70mph roll to 150-160mph as quick as I can, this would mean going into 4th at WOT, and by the sounds of it this wouldn't be good on the tranny.

So I'm a little lost on what to do.

BlackHawk T/A

iTrader: (3)

One of the reasons im sticking with my 3.23 set

300bhp/ton

3.23 is that with a 12 bolt?

chris718

look im not trying to sound like a broken record here but if you re read my posts the answers to your questions are waiting to be heard again.as for the numerically highfinal drive ratio example the rotating speed in the trans will not change on a ratio / gear change regardless of final drive ratio .the final drive will only dictate the road speed that the predetermined ratio changes will occur.the 3.42 final drive ratio will reach a higher road speed in mphour before a 6000 rpm wide open throttle ratio change will occur in comparison with a 4.10 which would reach 6000 rpms at a lower road speed in mphour ,remember shifts points at wot are controlled by driveshaft rpm.this being either with a governer driven off the output shaft to produce a hydraulic road speed signal for the valve body to use for shift scheduling or via a magnetic trigger and speed sensor to read output shaft rpm and produce an electrical signal for the powertrain control module to intercept and use for shift scheduling via electromagnetic shift solenoids and the valves they operate.

300bhp/ton

Cheers Chris I understand all that. But final drive is important to me.

Example:

0-150mph at WOT

With a 2.73 rear it will do this with ease and stay in 3rd.

With say some 4.10's it won't and will have to shift into 4th at WOT.

I understand that the rpms will be the same for each shift point, but it is the actual mph speed that I'm interested in.

BlackHawk T/A

iTrader: (3)

Stock rear, stock gear.

darrensls1

I checked out texas speed & performance and found out the best gear they offer in a moser 12 bolt (to suit your needs) is 3.42

I played a little with the gear calculator and found out that with stock tires (245/50/16) you would hit the 6000 rpm redline in third gear @ 134 mph with 3.42's. If you up the redline to 6200 then you increase the third gear redline to 138 mph.

I don't see why 138 mph couldn't be sufficient. You would never trap that high and faster then that on the street is insane IMHO. But you always have the option of running taller tires if you really must hit 140+.

Hope that helped. Here are the links if you want to play with the options for yourself.

http://www.texas-speed.com/shop/item...mid=60&catid=6


and the gear calculator is here:

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

300bhp/ton

yeah ta thanks. I've spoken to a few othersand they have also recommended 3.42

And yes high speed is insane, but there's some roads where it's safe to pull out and just keep your foot down for over 2 miles. So the 158mph limiter is easy to reach. Oh and a whole lot of fun

Plus I'd just like to have enough up top to keep with Poarches and Ferrari's and such.

1999Z28

i shift into OD at WOT all the time (at 110...112 if i keep it in 3rd it'll hold it out longer). im probably up to 200 different occassions on stock trans wiht 78xxx hard miles on her.

Z2K_MrJ

Why would you want to shift into OD at WOT? anyway i am curious . Most ppl dont know that the 4L60E will shift itself into OD either way when a certin speed /RPM is attaind REGARLDLESS is you keep it in Drive.The tranny has many safty fetures that ppl just have no clue of or lack the knowlage and think doing such things or Not will cause Harm.When they really are unsure

300bhp/ton

It's not that I 'want' to shift into OD at WOT. It's about getting to a particular speed.

If you want to go from a dig or 5mph roll to 150mph as quick as you can then all of the final drive ratio's offered in the 12 bolt rears will NOT allow you to reach 150mph in 3rd, therefore you MUST go into OD (4th). And if you are trying to accelarate at maximum speed you will evidently keep your foot at WOT.

Yes I am unsure and I certainly don't want to ruin my tranny.

For regular 'spririted' driving I leave the tranny in 3rd (D), this allows me to top 158mph in 3rd which is the electronic limiter, I think this is about 5600rpm and it will hold this speed very happiliy (have done it for well over a mile or so). If I move the shifter into the OD (4th) position while still having my foot buried it does not do anything because it isn't reaching the 5850rpm shift point. If I lift off the throttle a tiny bit it will then shift into 4th.

jimmyblue

iTrader: (11)

I'm surprised you can't get a lower 12-bolt gear set,
though I haven't looked; however I know other older
GM differentials (like the BOP 10-bolts) went as low
as 2.56:1 (buddy's Skylark, with posi no less).

It all still smells like speculation in this thread, with
little or no input from people who put their hands in
the guts (stock, that is).

The answer may well be, to make a shift table which
does not allow you to upshift at WOT but requires
you to back out; have to make the WOT and part
throttle downshifts enough lower (substantially) to
accommodate this without kicking you back into 3rd
again when you go back to WOT afterward. This is
a "poor man's torque management" which in fact is
better than the spark cut, because the spark cut
looks to me like it does not persist for the full shift
plus pull-down-RPM time but just some predicted
interval (by some of the logs I have seen).

300bhp/ton

According to Moser's website 3.08 is the highest gear offered in the 12 bolt, however I haven't seen it listed on any of the vendors websites.

I'm just so uncertain, I really love my 2.73 rear, although living in the UK there arn't many Fbody's about, so I have no idea what a 3.73 gear car drives like.

If I new the tranny would be fine and stand the abuse of being used as a 'proper' 4 speed box then I'd go for 4.11 rear on 275/40/17 tyres a wild cam with a sensible stall and up the shift points to 6200-6500rpm as it would still allow easy access to 150mph+

But I don't want to spend the money doing this and after a few weeks find that the tranny has had enough. I'd rather settle for the lower in-gear accelaration of the 3.08 set so that I could retain the larger speed range.

But I guess I'll probably end up with 3.42 gears as a compromise.