TEXFRC

What's the best C5, 99-00 FRC or a 01+ Z-51 Targa?

The way I see it, FRC a little lighter (40lbs ?) and stiffer.

01+ Z-51, + 5hp but + 25 lb ft of torque.

Your thoughts please.

Thanks

Tex

tjZ06

Do you know if you'd be able to put the "LS6 style" intake manifold that was stock on '01+ LS1s (F and Y bodies AFAIK) onto an FRC and stay AS via the update/backdate rule?

If so I'd say an FRC w/ the LS6 mani would be the hot ticket. Otherwise it's probably a coin-toss. Since you can run the Targa cars w/ the top off they'd probably run just as light (and that weight reduction is way up high), though you're sacrificing some stiffness there.

Either way I think it's cool the non-Z C5 finally has an appropriate place to play and I think it could very well be "the car" for AS.

-TJ

Solofast

No you can't do that.... There is no "updating/backdating" in stock like there is in SP. All of what you have as a package had to be available in the year that the car was built.

The greater weight of the coupe is in the backlite, so that weight is aft, over the rear wheels, and will actually help you coming off of corners. I thought the weight difference was more than that, more than 100 lbs, but if it's only 40 pounds a coupe is probably just as fast as an FRC.

bse53

According to the spec sheet, the 2000 FRC curb weight is 3173 lbs vs 3246 lbs for the 2001 and later coupes. The FRC apparently lost weight in the ZO6 versions, down to 3118 lbs.

It is my understanding that unlike the C4's, the C5 is stiffer with or without the roof panel.

You do gain the 25 ft-lbs of torque.

I think a big factor is the fact the Z51 suspension got a bigger rear stabilizer bar in 2004-- from .85" to 1.13". That can't be changed in stock classes and could be an advantage.

As previously been stated, the coupes move the additional weight over the rear wheels, but in autocross weight is king.

Solofast

Probably still a toss up. The bigger rear bar can be added to with the Z06 front bar (that you can legally change in SCCA stock classes) so overall roll stiffness is up and that helps a lot. More midrange torque (and 25 ft lbs is a lot) and the ability to put it down better coming off of corners (with the weight back there) are all good things. Weight is important in autocross, but where the weight is, is more important.... You end up being grip limted in autocross, more often in the front end, and weight there kills you. Some weight in the back might not make any difference at all.

What it depends more on is the tires that you can get to work on the rims available. Neither of these cars had the wider rims of the Z, so it will primarily depend on wheather or not the back tires are sensitive to the additional load and what meats you can fit onto the rear rims.

With Solstice's running 285's on 8.5 inch rims I'm not too concerned with the fronts, you can run the 275's up there and I don't think you could stretch it for the 295's anyway and there hasn't been that much difference in the 295 versus the 275's on the Z's so using 275's will probably work fine. The backs are going to be limited to 295's, and that's probably not too bad. I don't think you could get the 315's on a 9.5 inch rim, nor would you want to. This combo might need more front bar, but that's ok, you can deal with that.

tjZ06

IIRC the additional weight-loss in a C5 Z06 as compared to a non-Z FRC is that the Z06 got the thinner windshield. I'm pretty sure the non-Z FRCs do not have the light front glass.

As for the rear bar, I wasn't aware of that. Most C5Z racers would rather have less rear bar... but that's with all the Z06 suspension. I'm not sure the extra bar on a '04 Z51 would be an advantage or not since I don't know if the balance is similar to a Z or not.

Does anybody know if the extra power in '01+ actually shows up on a chassis dyno? I was still in Fbodies when the LS1s were 'new' so I remember the '01-02 LS1 Fbodies did indeed show a marked dyno advantage over '98-00s. I'd assume the same is true on the LS1 Ybodies. Of course, the key really is the low-end power. You're rarely at peak power on an AutoX course and if the '01+s only have a top-end advantage the weight of the FRC would probably win.

In the end I'm sure its all driver between a Targa and FRC, either one should be a great AStock car.

-TJ

tjZ06

IIRC the additional weight-loss in a C5 Z06 as compared to a non-Z FRC is that the Z06 got the thinner windshield. I'm pretty sure the non-Z FRCs do not have the light front glass.

As for the rear bar, I wasn't aware of that. Most C5Z racers would rather have less rear bar... but that's with all the Z06 suspension. I'm not sure the extra bar on a '04 Z51 would be an advantage or not since I don't know if the balance is similar to a Z or not.

Does anybody know if the extra power in '01+ actually shows up on a chassis dyno? I was still in Fbodies when the LS1s were 'new' so I remember the '01-02 LS1 Fbodies did indeed show a marked dyno advantage over '98-00s. I'd assume the same is true on the LS1 Ybodies. Of course, the key really is the low-end power. You're rarely at peak power on an AutoX course and if the '01+s only have a top-end advantage the weight of the FRC would probably win.

In the end I'm sure its all driver between a Targa and FRC, either one should be a great AStock car.

-TJ

Solofast

In SCCA autocross the front bar is free, the rear bar has to remain stock. You WANT a car that has too much rear bar from the factory. That way you can balance it out with a bigger front bar. Net effect is that you will be able to have more roll stiffness. Hence, a coupe is going to get more total roll stiffness when compared compared to an FRC.

Some of the fastest cars in the SCCA stock classes over the years were cars that had pretty nasty oversteer from the factory, then the front bars were upsized and the cars got fast. With the rules the way they are, oversteering cars get a benefit, understeering cars don't.

TEXFRC

Guys thanks for the input. Looks like it's 50/50.

I kind of like the extra 25 lb ft torque of the 01 +, but the FRC still looks good.

Any and all additional input is welcome.

Tex

Z06trackman

The '04 Z51 does not have a larger rear bar.

Some websites erroneously report a 1.13"/23.6mm rear for '04 Z51(these are different sizes and therefore one of them must be wrong). However, 23.6mm is what the '00 through '03 has, and this = .93", which is also what is listed for the '00 - '03. The .93"/23.6mm rear bar is also what is on all C5Zs.

The only suspension changes to the '04 are revalved shocks for the Z06 and stiffer front upper control arm bushings and different rear sway bar bushings (I can't find if they got stiffer or softer).

TedDBere

Copied from the C5 General Weights and Measurements Sticky Thread:

23mm, front; 19.1mm, rear --- FE1/Base --- Source
25.4mm, front; 21.7mm, rear --- FE3/Z51 97-99 --- Source
28.6mm, front; 23.6mm, rear --- FE3/Z51 00-04 --- Source
30.0mm, front; 23.6mm, rear --- FE4/Z06 --- Source
31.75mm, front; 25.4mm, rear --- Hotchkis --- Source
38.4mm, front; 27.5mm, rear --- GM T1 --- Source

bartekb93

The wheel is 8" wide on that car (18"), both NA and GXP. Most common size on NA cars is 285 (same wheel width and tire on CS RX-8s) and 295 for the GXP (to help gearing in 2nd I believe).

RX7 KLR

I would take the coupe with more TQ, over the marginally lighter FRC.

RX7 KLR

It has more, and both the HP and TQ come in lower with the later car.

acrace

I'm still looking for a clean, one-owner, '01 - '04 Z51 six speed vert.

TedDBere

I don't know, that small rear bar in the coupe really helps put the power down!

So far I see Isley, Radomin and Tony Savini in AS this year.

RX7 KLR

I am likely a one off. Focusing on the Runoffs this year.

Gordy M

Some more food for thought. When you talk about weight differences between the FRC and the Z06, I find it to be about 10-12 lbs. A friend has the Z and I have a FRC, when we corner weigh our cars, mine is routinely 10-12 lbs heavier--with 3/8 tank of gas in both cars, both have Z06 exhaust, harness bars, and everything else stock.

Another consideration is the body stiffness, as I recall, the vert was 22 hz, the coupe was 24 hz and the FRC was either 26 or 27 hz.

Some advise in setting up your car; the 275/17 and the 295/18 Hoosier A6 gives you a square set up, be sure to change your front rake to compensate.

acrace

Gordy M has as quick a FRC as I've seen around SE Michigan. He and I run within a few tenths consistently at local events when we run in NCCC Group I trim. I value his advice.

bse53

"When you talk about weight differences between the FRC and the Z06, I find it to be about 10-12 lbs."

That would put the weight difference closer to 120-130 pounds between the FRC and the Coupe. Running without the top would bring the difference down to 80-90 pounds.

Once again, these numbers are coming from a spec sheet, not from experience.

Unlike the C4, am I correct that the body stiffness is not dependent on the top being in place?

Thanks for setting me straight on the rear bar. The rear bar is larger on the 01-04 Z51 than the 99-00 FRC though. As has been stated, you can add a larger front bar in stock classes.