mountainbiker2

I have an 04 Z06 crate motor that I've been revving to 6800. At 50% of my autocrosses (24 in a year) I've needed a few more mph. What happens is, I just sit on the rev limiter for 1-3 seconds. I think raising up to 7100 should take care of it. I know one T1 racer that has his set at 7100. I'm not looking to get 100k miles out of the motor. I also drive on Hoosiers A6's to every race. So I'm not looking for the perfect solution. Just some real race experience. What do you think?

thanks,
Steve A.

AU N EGL

You could, but not sure I would with stock valve springs.

CHJ In Virginia

The motor bottom end will take it for intermittant use. The valve springs should be changed to something more substantial than stock if you want it to live. Have you thought of changing differential ratio or tire size to get the MPH you want without buzzing the motor so high ?? You are beyond the HP and Torque peaks anyway. Those changes would be a lot cheaper than a fragged motor.

Olitho

Steve, some of the local T1 guys and I are probably who you are referring to.

I don't think 7,100 RPM on a crate motor with stock springs is a problem at all.

My current engine has 10,000 track and race miles on it and I regularly buzz that powerplant up to 7,100. I don't recall how many miles my previous powerplant had, but it did fine, too.

There are a few guys with the rev limiter set to 7,200 or 7,300, but as I understand it that is where you really push the envelope. I will only testify that 7,100 has been fine for me.


Oli

sperkins

I'm looking forward to running my crate LS6 to 7100 since my stock LS1 obviously can't handle 6201.

trackboss

It makes sense to rev a motor a few hundred rpm over the peak in exchage for an upshift in many cases, but turning a legal t1 motor that high seems kind of crazy. Peak power is under 6k. I've never seen one on a dyno turn that much rpm, but I'd bet the power is down quite a bit. Seems to me an up shift would keep the car more in the powerband. Is there any reason the t1 guys choose to turn the motors so high?

Bill Dearborn

What gear are you running in?

Bill

mountainbiker2

2nd. gear.

Some of you guys are asking why not shift. It's very hard to on an autocross track that will make you better time. Were talking about shifting to 3rd. then leaving it for maybe 1-3 seconds then shifting back to 2nd.

I like Oli's answer, but just want to make sure. Valve springs are pretty cheap with labor. But sometimes it seems to cause more problems when you change from stock.

I also posted on an LS1 website that they suggest springs also.

Steve

Olitho

I am not allowed to change springs in T1 so mine is all stock crate. The engine has never even been opened up.

I rev to 7,100 for the same reason Steve does. On some straights I would rather just buzz it out a bit more rather than shift just to have to down shift a very short time later.

The third to fourth ratio is a fairly wide spread so I often would rather wind out a bit past the stock redline to land the car in the sweet power spot in fourth gear.

If you watch this video http://www.vimeo.com/11298617 at 27:30 I execute my final pass of the race for the win. By revving up higher in third, the tach actually hits 7,124, I gain the needed car length to make the pass. By not shifting when Schmidt does I jump over to the right and catch him off-guard going into the esses. Once I get my nose in there he couldn't do anything about it. I could then shift to fourth in the esses, but his option to get me back was gone. I go into the esses slower, but I owned the track position at that point.


Oli

mountainbiker2

Here's a small video of me hitting the rev limiter at 6800. Listen carefully. The music is already in my You Tube video so I can't change it.


http://www.youtube.com/watch?v=MBDONDNKWbE

Timz06

I wouldn't expect it to last too long.

davidfarmer

GM durability testing was at 6900rpm. You are probably fine for limited use, but I wouldn't recommend for constant usage.

L98Terror

I did it for short periods in a stock LS6 no problems but did change springs often

C5ZEE06

+1...aside from valve float, stock rod bolts are the next weak link.

SIK02SS

IIRC, I turned power out to about 6400..but my dyno sheets are with my log book, which is with the car, which is 7 hours from me right now

RX7 KLR

If you change the springs (from OE) you will be back in SSM. You are worrying way to much about winning a local autocross.

Just change to a taller rear tire if you need more gear.

Just some quick math (assuming you are still using an M12):
Right now you should be seeing 73mph in 2nd.
7100rpm would get you 76mph.
6800rpm with a 26.8" tire (345/18 or 19) is 77mph.

sperkins

Is that even possible?

mountainbiker2

Your kidding right.

No 18" rims for one. Cost. Fender will hit. Inner fender liner will hit. Higher gear for slow corners. Lose/lose is how I see it. Of course that's what you would what.

I race SS with Tom D. in SCCA.

Zenak

MN12 = 2nd
72mph in a STRAIGHT on level ground for the rev limiter stock LS6/Z06

I have a MN6 right now, and because of this i have the privileged of shifting all over the place in an AutoX which is why this winter Im building a MN12 setup to drop into my 99 FRC.

Bright side, once in 3rd you have a nice range, so often I will enter 3rd and just chill in 3rd excpet where i exit corners on the AutoX. In HPDE 2nd is only ever for getting out of the paddock

RX7 KLR

So all of this is to win at a PCA event. Shift to 3rd you lazy bastard.

18"s are less costly than another crate motor. As for rubbing, raise the rear ride height, or run stiffer springs.