SONKIST

I'm building a 500 - 550 rwhp Z51 coupe. Manual transmission. Strictly for street use.

I'm putting in a DTE stage 3 rearend so I have the opportunity to change the gearing. I don't want the 4.10's because I don't want to be shifting all the time. I'm not going to the track or the dragstrip.

I had decided on the 3.90's but then my tuner said that was really too much gear and suggested the 3.73. Then someone else said, "why bother" as the 3.73 are so close to the stock 3.42's. Now I'm all confused.

Anyone out there got experience they can share with these two ratios?

Goodwood

I had a 472 RWHP LPE 383 in a 91 C4 that we put 3.73's in and I didn't like it at all for the street. 1st gear became completely unusable for me. I switched back to the 3.42's right away. I actually took to starting off in 2nd! Keeping the 3.42's in my soon to be delivered LPE 427 too.

Jim_H

The 3.73s are nearly halfway between 3.42s and 4.10s, so they're not that close if you're gonna R&R the diff to install the other DTE stage 3 goodies anyway. If you aren't going to the track you probably won't be shifting that much more, except to use 6th because it now has a reason for being there.

Just my opinion, but if it were my car and only for street use as you say, I'd get 3.90s or 4.10s and go for less HP.

SSJCreeper

3.42's are plenty for what you are describing. I have a similiar setup right now.

I'm due to re-dyno this month and should be in the 500-550rwhp range. With 305/30ZR19's out back, the Z-51 manual, and the 3.42's... the car is capable of massive wheelspin anywhere in 1st or 2nd gear. Mash it to the floor and you can wiggle the rearend in 3rd, up to roughly 100mph. I thought about 3.73's myself, but honestly... the car is putting out plenty of power for me right now. Gearing out the rearend just means you spin in 4th.

ZO6Gal

Have you asked Phil at DTE? He's the man. I followed his advice totally and am glad I did. 4.10's all the way for me but I don't have 500 rwhp either. Give Phil a holler and he will do you right.

welcome2try

Those Magnusons and roots type blowers make instant torque at low rpms,, 4.10's are not necessary with these applications (IMHO). However, procharger blowers will need some grunt in the low rpm band. 4.10's might be the remedy since prochargers don't wake up till like 3,500 rpm..

Lexicon

Gears Gears Gears....The good news is there are few bad choices.

I have an 07 C6, and a stock 67 GTO that came with non posi 2.92s. The only time the GTO was raced it got 3rd out of oaver 600 cars. My other experience is racing motorcycles where you change out sprockets so that you top out at the fastest spot on the racetrack.

These cars have so much pwr that they can spin no matter what. Gears are fun but only help if you can launch the car. A set of DRs will do more for you in the 1/4.

If you go too low, such as 4.10s, you end up with a car that is not so good as a daily driver. The faster shifts may make it slower on a road track.

On the road I like 1st gear to be usefull so that the RPMs are high but leave some range coming off of the slowest corner on a road course. Otherwise, you get into needing to be in 2nd or having to shift when the car is fighting for traction as it leaves the corner.

In summary...I would probably go with 3.7s since 6th is a bit too much of an overdrive and the car has a lot of rev range esp after tuning.

hamad115

I would go for 3.90 , my frind has corvette C6 Z51 with heads & cam and it has around 450rwhp and with the 3.90 you will be very Aggressive on the rod

xtacy187

With 500+ RWHP, I'd lean more towards the 3.73's than the 3.90.. If I had the choice between either a 3.42 or a 3.90, I'd stay with the 3.42.. If my choice was between 3.42's and 3.73's, my decision would depend on whether I could maintain adequate traction with the 3.73's or not.. If you think you can, install the 3.73's and you'll feel as if your car has lost weight! Trust me though, with 3.90's and 500+RWHP your car will be all over the place!

stopltracr

I've got a 501whp Procharged C6 Z51 and I just installed 3.90 gears. In my opinion the 3.90's are perfect. I've had no problems tooling around town, 1st is still usable, and it's a beast from a roll. I also added 325/25/20 PS2's on the rear to help with traction. With this setup I spin the tires through 1st, about halfway through 2nd, and it hooks hard in 3rd. My best run with the Procharger, stock wheels/tires, and 3.42 gears was 12.10 @ 126.5. This was with spinning the tires all the way through 3rd. My best with my current setup is 11.80 @ 129.3.

AutoCutter

All things considered, I might be inclined to try a 3.15 which would make the Z51's 1 & 2 shift a bit more usable for street fighting. That said, the 3.73 would be a little easier on the rear end and doesn't kill the highway mileage in a big way. Personally, since there is no racing in your future, I would leave the ratio alone.

chuckclanton

Leave the car alone. With that much power you don't need more
gears! In fact, on the street they could be down right dangerous. if
anything, I would goto a 3.08 gear like the Vipers!

drewcorvette

I just did the 4.10's on a my procharged z51 540 rwhp and its a day and night difference. The car gets into boost so much quicker, you will love it talk to chuck COW and he'll explain it to you. Lots of fun around town.

Doug411

I agree with others' suggestion of lower ratio. I recently switched my Z51 to Z06, and I love the 1st and 2nd gear. Z06 is not comparable to your aiming rear-wheel power, but even so, power is plenty and it's very pleasant to use on streets. One down side (or up side?) is that 6th gear gets little usage when you're keeping the legal speed limits (65mph and below, in MD).

Try with stock gear first after you add HP, and then you can decide.

robz

I would definitely get gears. I have an m6 with around475 rwhp and 4.10 gears and its perfectly streetable. I believe the m6 needs gears. Either 3.73 or 3.90 would work well for you. The 3.73 are not very close to the 3.42's. They will make a nice difference. 2 of my friends have 402's with about 550 rwhp and 4.10's. You can't go wrong with either choice but IMO you will love the gears.

0Chuck CoW

I can tell you this.....Lots of critics of the 4.10 gears don't consider them cause they "don't look good on paper"....but, the reality of it is that nobody that has had them installed would ever consider changing them back.....I can honestly say that there is NO DOWN SIDE to installing them....

The most common thing I hear when returning from a road test with a new 4.10 customer is.....

WOW! They shoulda come like this from the factory!!!

You will say the same thing!
Chuck CoW

SONKIST

Phil is the MAN! I spoke to him for about an hour and he takes into account everything you are going to do to the car and how you intend to use it.

On my Z51 manual, and anticipating about 535 rwhp, he told me to go with 3.73. I'm not going to drag race, I live in the country and use the car about 50/50 city hwy. If I didn't have the Z51 pkg he would have recommended 3.90's for me. 4.10's were out of the question for MY application.

I was on the fence about what to do gear wise, but after talking to Phil, I'm positive that 3.73's are the right choice.

Wicked Weasel

thats a fair amount of rwhp and if you are not doing 1/4 mile racing or road racing then staying with the 3.42s might be a good idea. 4.10s IMHO are out. I had them and when I ran the 1/4 with Drag Radials on I loved them, but when I started to road race the 4.10s were just way too much. Engine would heat up from high rpms, clutch would heat up from shifting, and the tranny was geting full time use.

3.73s is waht I run now and overall they are a good gear for everything. You will get quick starts without having to run an agressive rear tire and if you want to hold the gear longer then do that.

TEXASRANGER

Wish I could get 3.90 for my 07!!!

0Chuck CoW

Hey there.....

We have done MANY sets of gears in 06 and 07 C6's in the past few months.....

There are some subtle changes in the rear ends of the later cars, but...we figured out pretty quickly how to make em work....

We're VERY pleased with some of the changes GETRAG made in the new diffs....

By the way, DON'T BE AFRAID OF GOING WITH 4.10'S NOBODY that we've ever installed them for would ever consider changing them..Even in S/C cars, they give back the lost "bottom end" power.

There are only afew cases where 4.10's are not appropriate....but rare.

Chuck Cow