i have a 2006 with a z51 pkg automatic, i would like to know if i could have installed a set of 3.73 gears without losing alot of top end. if not what would you recommend.

 

First, the answer, I think, is yes, you can switch this ratio out -- I think you can find gears to fit.
Second, if will give you a lot of acceleration increase at lower speeds.
Third, this will increase your RPMs in any gear at any particular speed by a good deal. I think you have a 3.15:1 ratio right now (haven't paid too much attention to the lastest Z51 package content details, I'm afraid . . . ), in which case you are looking at an 18% increase in RPM at cruise -- at a speed where you used to be at 2000 RPM, you'll be at 2370 RPM. That doesn't seem like much but it will become a big deal on a long trip.

As to top speed, the top speed in each gear will be about 16% lower. I don't know the exqact gear ratios, but with the 6 speed auto, if the higher gears are overdrive ratios (as in the 6 speed manual) then you will not really lose anything in top speed -- just have to move up a gear.

 

Well I was told today that all 6 speed autos had a 2.56 gear ratio,but the Z51'S tranny was much lower geared in the first 4 gears.The car has 2 over drives so I think a set of3.73 would do nicely.I had a moser 9"in my Z28 and was geared with 4.30's I did not have to shift untill 7k and I could bury my speedo in 5th gear and had more rpm's to play with.

 

Wow. A change from 2.56 to 3.73 represents nearly a 50% increase in gear ratio. Personally, I would never do anything near that much: I'd expect a change of that magnitude to alter things I could not anticipate and to screw up driveability and programming in ways I never anticipated it would affect.

If the ratio really is 2.56, I'd suggest a 2.73 or 3.15 at most.

 

Thanks the 3.15's might do it.

 

go with the 373,s you wont regret it and to be the top dog ya got 90% out put a 3400 rpm stall,pull TQ. max shift psi and get much better rear tires.you wont ever have to mod your motor. my opine

 

That's what I was thinking because my wife has a 06 gto with the 6.0 and has less gears and has a 3 series gear ratio.I was thinking of vortex ram air,headers,x-pipe,B&B exhaust and a set of 3.73's with tunning.Does this sound like a bad idea.

 

I think a change from 2.56 to 3.73 is way too much.A 3.73 is a great gear to retrofit to an M6, basically a 10% increase in ratio from the 3.42. Its also an extreme gear change on f-bodys and vettes that have the older 4-speed auto -- too much gear to leave them really streetable but if its only a drag car, suitable if you don't have a lot of power (if you do,you run out of gear before the end of the 1/4 with a 3.73). But the 6 speed auto with the 2.56 is a different set up and I would expect it will prove disappointing on several fronts unless you want only a pure drag car -- not even sure it would be good for that.

I'd be interested, though, it seeing someone do it, as long we weren't experiementing on my car or with my money.

 

he wont run out of gear ,hell he still can twist 150 and above

 

Taking what I said in context, I still think the 3.73 would "run out of gear": I was talking strictly about really powerful, modded cars (say 700 or more RWHP). With the older 4-speed automatic, going to a 3.73 means you would 1):have very low shift speed out of 1st off the line and 2) be shifting into 4th, an overdrive gear that even with 3.73 is pretty low and pulls poorly, well before the end of the quarter. Better to use something like a 3.15 or a custom 3.23 (easy ratio in an aftermarket solid axle for the f-body, not so easy in a vette): then let a high RPM stall converter do the work off the line and finish the quarter in a 3rd gear that taps out at about 155 mph as easilycomplete in the 9s.
I know all about running out of gear from recent experience. I am facing inow n my Camaro (M6) with lots of juice: with the 3.73 I now have to shift out of 4th into 5th before the end of the quarter: I either waste time on a shift into what is really a lousy gear for acceleration, or stay at the rev limit in 4th with the final 100 feet. I'm going to 3.42 in it. And I'm going to 3.15 in the vette (also M6, now with 3.42), mostly there so 1st gear is useable again (I normally start out, even at the track, in second just to avoid too much shudder or wheelspin), and I am at the rev limiter in 4th at the end of the 1/4.