600whp Street Gearing
 

I have an 04 Z06 with just under 600whp. It's running stock M12 gear ratios in the transmission and 3.73 ring and pinion gears. With this power level and shorter gearing I find that 345 Nitto Invos offer pretty much no traction in 1st and 2nd and can often spin 3rd. The car is strictly a street car, and I only intend to run it in the 1/4 mile occasionally, so I'd prefer to keep with a street tire if possible.

I'm considering going to a stock 3.42 ring and pinion ratio, or maybe even 3.15. I've had 3 cars prior to this with standard MN6 gearing and 3.42 rear, and found the gearing to be nice at 400whp. Using gear/speed calculators it looks like the M12 with a 3.15 rear would be almost identical to that gearing. Does anyone have any experience with this combination of ratios? Is it likely I'll see a meaningful increase in traction by lengthening my gears out some? I can't really see a downside to the 3.15s... I hate the higher 6th gear rpm and short 1st and 2nd gear as is.

Thanks for the help. Here's the comparison of gear/speed with different combinations:

Attachment 48349929

No experience yet, but I've done the same math and came to the same conclusion you did. I'm putting together an M12 + 3.15 combo for my twin turbo street car as well.

The m12 is good for what it was setup for. Road course racing with 400ish hp. Gives you good power coming out of curves and spend most of the time in 1, 2 or 3. The ratios in 1st, 2nd and 3rd are similar to having 3.90s pinion gear. Then you go to the 1 to 1 gear and have a huge drop from 3rd to 4th. As you make more power you are better off going with m6 gearing. If you just change your ring and pinion to 3.15 you are still going to have the big drop on 3 to 4. Switching to a m6 trans will have better results.

m12 gearing sucks with lots of power. That 3rd to 4th is terrible.

Yeah, really big rpm drop going from 3rd to 4th, which is especially not great for a centri setup. If you can rev out the engine safely and torque not drop like a rock, that may be the most helpful thing to do. RPM drops (ballpark), 6500->4500, 6750->4700, 7000->4900.

edit: sorry this may not be entirely helpful for what the OP asked. I think a better long term plan might be getting the MN6 gearing, but I would almost be afraid of 3.15s being too long and not set you up for a MN6 swap if you ever wanted to do that one day.

I think something else to look into is a better tire... 345 is big but the Invo isn't known for great traction. Compound > size. At this power level it might be time to consider a R compound like the R888R, NT01, NT05R, etc. Or even something in the 200 treadwear category if there's a good selection.

2002 Z06 w/m12 and 4.10's at 611rwhp. No traction until 3rd at best, usually 4th with M/T SS 305/40/18. Hated it!

Same car w/m12 and 3.42 at 770rwhp. Traction in 1st now, same tire M/T SS 305/40/18. Love it!

I have same power with 3:42 and have trouble with traction. You have road race gearing in the tranny, and more 1/4 mile gearing in the rear. You can change out tranny for a MN6 and get some longer legs, or even better, T6060 conversion. The other option is to go back to the 3:42 that belongs in the car or as you said, 3:15 for much longer legs.

Hi Quickshift_C5, are you running those 305/35x18 R888's on OEM Z06 wheels with a MN12?
Christian

Thanks Quickshift,
What tire pressure did you ended with to get max efficiency with those because it seems to be all over the place?

Christian

I just finished getting my car done and ended up with 635whp. I was so tired of reading up on tires I just ended up with 2 more Nitto Invos, 345 30 19. I really regret it lol. I was gonna get drag radials but I couldn't decide and said screw it.

I may have been a bit harsh on the Invos, admittedly. But let's face it, they're just out of their element. Designed more for hard parking than hard driving. To answer the question above, I run 32-34psi on the street and don't have any real traction issues unless I flat out instantly floor it in 2nd at low speed. I do lower it to 24psi at the drag strip and 1/2 mile events and it definitely helps. I haven't gone lower since it's a road race tire and not a drag radial.

For someone wanting good traction on the street without compromising cornering and handling, the R888 and NT01's are a great option. They do amazingly well in over 700rwhp. Those who are more hardcore dragracers may want to look at the other suggestions mentioned here like the drag radials and Hoosiers. They'll give you the traction you want for sticking the car on the launch and slamming it hard into gears.

Do t forget the nitto nt555r drag radials, i run the 305/35/18 on my base with thinspokes and 450-500 flywheel horses, and they are pretty sticky.

I used the 555R-II (road course version) for a while with somewhat similar results to the R888. I do feel the R888 had a little better grip. All of the tires were excellent in the rain until there was about 40% of the tread left, IMO. Everyone has a different comfort level, but I found them perfectly fine until I had about 40%. At that point, I was having trouble maintaining 65mph without feeling like I was constantly correcting the steering due to floating on top of water in heavy rain. Not good. The 555R should behave in the same way, only providing better dry grip while sacrificing cornering.

I guess you need to decide what you want to trade. Better dry straight line grip while losing cornering, or better cornering while losing a little straight line grip. The 555R should do a little better at the dragstrip and 1/2 mile launches as well since you can run much lower pressures.

Here's an example of my car at 640rwhp at a 1/2 mile event from a dead stop using 305 wide R888's on an un-prepped runway. This was with cold tires (I never do burnouts) at 24psi on an 80F day. I rolled it off the line with light throttle to get it moving, then progressively squeezed it to full throttle in 1st very quickly. It hooked, then a very slight spin going into 2nd and was wide open throttle the whole way. No issues, but while I was shifting reasonably fast, I wasn't slamming gears either.

since i do mostly street driving with occasional road trips & still didn't want to buy 2 sets of tires, i rolled the dice this time around with the 140TW NT05s instead of going all-out with NT01s. we'll see how they do.
that's coming from Invos... which weren't the worst but definitely left a lot on the table.

as for gearing, i contemplated a 6060 build with MN6 1-4 and C6 ZR1overdrives (.81 & .67) mated to a 3.15
maybe if i break something in the new t56 or my stock rear end.

I had a C6Z rear, trans, and cradle but sold it. Didnt think I'd ever get around to putting it in. Really kicking myself in the ass now.