i have a 95 trans am six speed with 150 shot nitrous 52 mm throttle body all msd whisper lid hooker long tube headers with straight 3 inch exhaust to the back i just bought 4.56 gears and i currently have 3.42 what will be the difference good or bad and also what time do u guys think i will run in the quarter mile.

 

wow your gonna be crossing the line in 5th. I looked into it myself. Do a search on my name about 4.56s... I would also look into a cam with 240's duration with those gears

 

yea, those will keep your rpms way up on that
and yea, you will have to cross in 5th which sucks unless you can shift to 5th quick
one major thing you're gonna notice...is how much gas you're gonna burn
expect to lose a couple of mpg

 

I;m running 4.56's in my Impala SS with a T-56 and love em. If you can rev your car to at least 6k you wont have to shift into 5th in the 1/4. I am right at 6k as I'm crossign the traps. But as these guys say, a cam will make it a lot better. As for hwy cruising, I run right at 2500 @ 80mph, so it isn't that bad. Though for an F-body I would have gone 4.10's teh 4.56's wont hurt you as much as you think. Good luck getting that thing to hook though.

 

Grimpala, he's running a 150 shot of nitrous, not sure what you're running or your trap speeds but he's going to be in 5th gear at the top of the quarter mile. If you use a gear calculator, 4.56 gears at 6,200 rpm is 104 mph. A stock Z28 without nitrous should be good for 100 mph trap speed.

 

A LT1 modded to his level should be hitting 105 traps or more. A 150 shot on a bolt-on LT1 is good for 115-120 traps, if not more. I'm leaning towards suggesting 3.73s since he's running a hefty shot of nitrous. My car would hit 120mph in 4th at 6000rpm with the 3.73s (when it had the T56 in it), so they might be better suited for him.

[edit]- just to be clear... i say the above IF he stays with the stock cam since you don't really want to run it more than 6k rpm. If he goes with a larger cam, then i agree that 4.10s would be better. He'll need some sticky tires for those though, all the LT1s i've seen with 4.10s couldn't get traction for **** on street tires.

My $.02

 

Yea even with 3.42s and my 100shot i spin in 3rd... I would imagine with the 4.56s traction would be a major problem. Im going to upgrade to 4.10s soon, but thats only because with my cam and 110lsa i get some surge, the 4.10s will keep me out of the surging RPM...

 

4.56 gears and a decent enough amount of power and you'll be turning street tires into cheater slicks in no time. I'm probably going to go with some 3.73's in mine as I have plans for a forged 396 stroker and possibly a small shot of juice, 100 HP or so.

 

The general rule of thumb for gears is to choose a gear so you'll cross the finishline at about 2-300rpm higher than your HP peak in the 1:1 ratio. Now, we don't know all of your future or immediate plans for the car, but running a pass and seeing what you trap at can give us an idea of what gear may be optimal. If you trap 115 with 3.42s, then you can guess that you'll gain 2-3 mph from a gear like 4.10s. From there use the gear calculators to see what rpm you're looking at and see if the steeper gear is what you can efficiently use in your cam's powerband. Most of the dynos i've seen of bolt-on LT1s (i have about 12 saved on my computer) shows that headers, CAI, etc (the other bolt-ons, excluding higher ratio RRs) will raise the hp peak from about 51-5300 up to about 54-5600... obviously since the engine isn't as choked as when stock. So with bolt-ons I'd shift at about 6k with the stock cam. Remember, you get the most torque multiplication in the 1:1 and lower tranny gears so select a rear gear that will allow you to cross the line in 4th (1:1) like mentioned above (~300 above peak). Generally this will give the most average hp/tq to the wheels during the pass in a close ratio trans like the T56.

[edit] Another thing worth mentioning is the stock tach, it's not completely accurate. I noticed when mine was stock with the A4/2.73s the tach always showed 6k rpm shifts, even though the PCM was programmed for 5700rpm shifts like all LT1s are. With the M6/3.73s, 4th is supposed to go to ~118mph at 5700 (as indicated by the gear calculators)... but when i shifted at 5700 as indicated by the tach i was only going ~110. When i ran the tach up to 6k and shifted, guess what, i was running a touch under 120 (~118). When switching back to the A4 and this time with 3.23s calibrated for 5700rpm shifts, the tach indicates 6k. Pretty confusing. There's been a lot of discussion on this board about how stock LT1 tachs are off about 2-300rpm at redline. It's accurate at idle though, just gets farther off as the rpm increases. Just some random thoughts to keep in mind.

 

alucero please just go 4.56 gears. dont be a wimp i have 4.56's you notice everyone with 4.56's is telling you 2 do it. and people who dont have them are saying not to please put the 4.56's in your car my car all stock with a fake intake a cut out and a 75 shot my only run and my first run i hit a 12.6 and a 175 shot i hit an 11.6

 

Got a slip 93m6lt1z??? Just curious.

 

4.56 gears with the deep 1st gear ratio of a 93 M6 seems unusual. Which tranny do you have the M28 (3.36 1st gear) or M29 (2.97)? What diameter tires are you running?

With an M28, you'd be running 15.32:1 overall in 1st gear. With his 2.66 1st gear, he'd have to run the equivalent of a "5.76" rear axle ratio to have the same overall ratio. Something sounds odd. Are you running 30+" slicks? And of course, all the gears in your 93 tranny are different than the later years, inclucing both O/D's so it wouldn't seem reasonable to directly compare results.

 

Gear selection has nothing to do with being a wimp.

 

The tach may be off, but I think the speedo is off more than the tach is.

 

I don't know... i tried that theory out too. Got a couple of friends to ride beside me going down the road and the speedo was spot on (one jeep, one expedition). I know one of the town cops close by and he shot me going 46mph when my speedo was saying 45. So it's close.