AverageVetteNut

I was competing in the National Tour this past weekend in Peru, Indiana and I noticed that the only cars in SS this weekend were C5 Z06's.
No C6 Z51s, no C6 Z06.

Any reason? I have always read that the C6 Z51 is very close in performance to the C5 Z06, so why's no one running them? Or was this just a coincidence?

Any thoughts by you veteran racers?? BTW This was my 1st Tour event ever, so I have nothing esle to judge against.

Great thing to see all those Z06's all lined up ready to run.

Solofast

The C5 Z is generally considered to be a better autocross car than the C6 Z51...

It is lighter, (by almost 200 pounds) has (I believe) stiffer springs, and up until lately had better tires available in the 17/18 sizes as comared to the 18/19 setup on the Z51. The C6 Z51 has 8.5 inch wheels up front and 10.0 inchers in the back, but the C5Z has 9.5 inch wheels up front and 10.5 in the back.. The wheels are a big deal since you will really be pinching the front tires if you put 275's up there. In SCCA you can only change offsets by 1/4 of an inch, so you are stuck with skinny wheels in the front and that is a killer.

When you get to the top levels of the sport, it is a pretty big disadvantage..

The C6Z is obviously better from a power standpoint. With the tall first gear the C6Z will be in first a lot and will come off of corners like it was shot from a cannon.. But in a lot of cases it may end up between gears, too fast for first, and you might find yourself shifting a lot...

Also, the C5Z has about as much power as you can put down, in most cases, so maybe the extra power won't matter as much, but it will be somewhat course dependent. If the C6Z has a chute where he can wring out the 427 in the top of first, he can gain a good bit on the C5.

Still lots of folks think that a C5Z is still pretty competitive in SS. But, bringing a C5Z to run against the Porsche GT3 and the Elise is like bringing the proverbial kinfe to a gunfight...

gkmccready

And don't forget the C5 platform has been developed since '97 so people know what works and what doesn't; along with parts being available. While the C6 is similar it's not identical and the parts aren't interchangable.

Stock antiroll bars:
C6 Z51: 28.6 mm-front / 25.6 mm-rear
C5 Z06: 30.0 mm-front / 23.6 mm-rear / 4.5mm/3.5mm thickness

C6 T1: 38.4 mm-front / 27.5 mm-rear / 6mm/?? thick
C5 T1: 38.4 mm-front / 27.5 mm-rear / 6.35/6.35 thickness

Not applicable to SS, but interesting to note that the T1 package for the C6 balances out the bars to the same diameter (and thickness?) as the C5.

Stock springs:
C6 Z51: 526# Front, 645# Rear
C5 Z06: 526# Front, 714# Rear

C6 T1: 582# Front, 850# Rear
C5 T1: 582# Front, 793# Rear

Again, not applicable to SS, but look at the rear spring rate increase for the C6 with the T1 springs!

Given that's what GM is selling for T1 racing, makes you think the stock balance is quite different between the two models... and the C6 is way under-sprung in stock form.

I've never autocrossed a C5; I'm just looking at the numbers and thinking out loud...

Solofast

In SCCA solo II stock classes the front sway bar is free.

What that means is that while the front spring rates are the same, you can balance out the heavier rear spring rate on the Z06 with a bigger front bar, as many successful autocrossers have done with the car. Net result is that you can get more stiffness or, you can use the stock bar and have the car rotate better. With the smaller front wheels and lower rear stiffness the Z51 is simply not going to have as much front end grip as a C5Z, and there isn't as much you can do to tune around it.

The comment about being developed is absolutely true. Every car gets faster the more it is developed.

Problem with the C6 Z51 is that most of the hot shoes don't think it has the potential, (weight, wheels and spring rate), so nobody really fast is seriously developling it. That is probably true, all else being equal why hamstring yourself with those penalties from thje start when a C5Z is less expensive to start with.

TedDBere

Most of the top drivers in SS feel the three cars, C5Z, GT3 and Elise w/LSD, are fairly equal. The reason the C5Z hasn't been winning is the top drivers haven't been in them because they wanted to "try" something else. If you put Strelnicks, Braun, Salerno, Popp, Thomason or Stewart into a C5Z in Topeka, many think the C5Z would win.

The GT3 seems to be the car to have at the ProSolo's on asphalt. The weight at the rear really helps it launch and gives it about a 0.2-0.3 second advantage at the end of the straight. Double that advantage, since you have two sides added together, and a half second lead out of the chute is tough to make up for. The tour starts negate this advantage.

GJ Dixon drove my C5Z to third place in the DC Pro behind Stewart in the GT3 and Salerno in the Elise. Pretty good considering he never even sat in the car until his first run on Saturday! And he felt with a little more "car knowledge" he could has beaten Pat too.

The C6Z has too much power to be useful and first gear is too unsettling to the car to be used effectively, IMHO. Today's courses are all speed maintainence courses so the power available, even for the C5Z, is rarely useable.

The Z51 has the better tranny, MN12, for autox. Every shift costs you about 0.3 seconds on course, based on data aquisition testing, so shifting is something you really want to stay away from, get it into second and stay there. However the Z51 wheels and weight dissadvantage, CG higher, and the engine being moved forward a bit make it a tough car to win with at the highest levels.

AverageVetteNut

Thanks for all the input guys. Some of the points I kinda had an idea about ( Wieght, wheels and development time ), but wasn't aware of the subtleties.

Just amazed me how many Z's were there this past weekend. I was loving it.

Maybe someday.....

rhneff

Should be interesting next year, when the LS3-based Z51 cars become available for SS as well as the 997 GT3. I haven't seen specs for the new 08 Corvette wheels - anyone know what sizes they are?

RX7 KLR

The 997 GT3 is on the stock exclusion list, goes right to ASP.

AverageVetteNut

I've seen nothing at this point to say that the wheels are of different size than the 07's. Now, I don't know about those fancy new 5 spoke polished ones.

Jason

Is the C6Z06 going to be booted out of SS too?

RX7 KLR

The 997 GT3 was not booted out, it was never there. Only the 996 GT3 is in SS. The C6Z06 was just put into SS 1-1-07 and based on the performance of them I see no reason it would move.

SteveC6R

Give it time and we will be wondering why there aren't any C7Z's in about 6 years or so. The C6Z is still relatively new, someone will start running it shortly and figure out how to make it competitive. As for the Base and Z51 C6, never will be competitive at the National level. Damn GM and these small front wheels!

rhneff

True, for 2007, just as the C6 Z06 was on the stock exclusion list last year. Given the SEB's long-standing "new replaces old" classing, is there any reason to not expect the 997 in SS next year?

RX7 KLR

Yes... There is a balance in SS right now and a faster 997 GT3 would upset that. Additionally if a change was going to be made for 2008 it would have needed to be listed in the July 2007 FasTrack. So if the SEB wanted to move the 997 GT3 into SS it would now be a 2009 item.

talon95

I've seen several spec pages like this:

http://www.corvettemuseum.com/specs/2008/index.shtml (near the bottom)

and they all show the same wheels for '08.

Dave G.

Cashmo

I think you're overstating it just a bit. Alek came in 3rd at Nats last year, less than a half second out of 1st. He's also got data acquisition this year and hopes to be even better. I'm not sure he'll show it this weekend though as he's running 1st heat and there are some fairly tight spots on this years courses.

I think the biggest factor is price. With C5Z's less than $25k why take a chance on the new more expensive model?

Jeff

Solofast

If the course is a more narrow, constant speed course, the Elise has a huge advantage in that it is narrow and more nimble... Little cars that don't slow down can cover a lot of ground amazingly fast, even if they don't have a lot of power.

If the course has slow corners and demands a lot of grunt, the Porsche, with it's ability to put down power off of slow corners has a decided advantage compared to a Corvette, that can't put down as much power. While the Corvette would be better than an Elise on that kind of course, I think the Porsche would still be the better choice.

The best kind of course for a Corvette isn't an autocross course, it's a road course. In that case you are in a higher gear and can put down all of your power, and the narrowness of the car isn't a factor. Problem is here we are talking autocross, and there will always be a few good drivers in the best car for the class at nationals.

I haven't sold my C5Z yet, but an Elise is looking might attractive. At over $100,000 for a GT3 that isn't even an option....

We will just have to wait and see what we get for a course in Kanasas.

You just hate to go to nationals and find out that you brought the wrong weapon...

LehmanZ06

Say-----three times with me.

It's the driver, it's the driver, it's the driver.

A top driver in any of those cars...C5Z06, Elise, GT3.....will be at or near the top.

A crappy driver will be at the bottom in those same cars.

And guess what ? A mid-packer will be a mid-packer.

(But ASP in my "4x4"....well my car is the shizzle (hopefully with a better launch at the pro.....that's why I am raising the front end even more !)

Solofast

Well, yes and no....

Once you get to the top levels of the sport, there isn't as much driver difference as you might imagine...

REALLY good drivers get all the car has in it.

We had a test session where we had a half a dozen of the top drivers in the country driving the same car (Matthew Braun, Roger Johnson were among them) and guess what... All of their best times were within two tenths of a second.

That was repeated at a driver event that was privately held at Chrysler one year where we teaching young enginees for most of the day and then got to trade cars and compare times for a couple of hours at the end of the day in a half a dozen vipers... Same result. Two to three tenths of a second over most of the hotshoes. What was more amazing was that we had a stock viper, a development mule (tired) and a "special" tuned car (better shocks and different alignment and tires). We could see the results repeated for each car... All the times for each car among the hotshoes were within three tenths...

Yes ******* are going to be *******, but the better the driver, the more important the car becomes. Really good drivers don't leave a lot out on the course...

LehmanZ06

Ok----I'll give you that there is not too much difference, between top drivers.......NO

Sometimes there is.....this is autox where there are a limited number of runs to run your top time.

If you are a top...top driver....for HPT the Elise is probably superior in SS.....second GT3, third C5Z06......but if you aren't Thomason, Braun, Stewart....etc......IT DON'T matter.

I suck in a vette, GT3, or Elise......Don't You ?

If you suck it doesn't matter, if you don't suck it doesn't matter.

It just doesn't matter........................