I think the C4 will come up lighter with better distribution, as the engine sits a bit futher back relative to the front wheels, and the driver sits closer to the rear wheels. Also, the C4 front geometery is better with less unsprung weight (aluminum a-arms and spindles), more avaliable caster and (I think) less scrub. The biggest advantage of the C4 IRS is no braking wheel hop, but there is also less unsprung weight, and the easily adjustable camber and toe (yes, you can camber and toe a solid axle, but it's much easier to adjust with IRS). LSx will definitely make more power, but LSx swap parts are out there, which at the very least is 75 lbs more off of the nose.

All that said, another comparision point is the NASA TT classing structure:
Chevrolet Corvette C4 ('85-'91) TTD**
Chevrolet Corvette C4 ('92-'96) (LT1) TTC*
Chevrolet Corvette C4 (LT4 option) (330 hp) TTC**

Chevrolet Camaro 3.1L TTG*
Chevrolet Camaro 3.4L TTG*
Chevrolet Camaro 3.8L TTF*
Chevrolet Camaro 5.0L carb (170 hp)('87) TTF**
Chevrolet Camaro SS ('98-'02) TTD**
Chevrolet Camaro SS ('96-'97) TTD*
Chevrolet Camaro Z28 ('98-'02) TTD*
Chevrolet Camaro Z28 (pre '98) TTE**

These are for totally stock cars (down to the shocks), but the fastest listed F-body is LS1 SS cars at TTD**. The TPI C4's are in the same class, with the LT1 a class up in TTC* and LT4's in TTC**.

For those unfamiliar with the NASA structure, TTA is the fastest, TTF the slowest. The * indicate the number of class points you start with at base, so a TTC** is faster than TTC* which is faster than TTC, all of which are faster than TTD**.

This post has been edited by Mojave: Jun 23 2009, 08:08 PM

I'll give the better suspension, front and back. But, I've gotten my car to 50.9/49.1 front/rear, with a 49.7% cross weight. If I take a crap before a race, my weight is perfect. C4 won't get it better.

Braking wheel hop is a problem. I still fight it. But, when it doesn't happen, I'm outbraking all 3 of the C4s I run with. I'm about even with the GT1 Viper and Vette that are classed above me.

I don't mean to be arguementative. More than most comparissons, this would be a great example of "it's down to the driver". And, if I were the OP, I would follow the advice of the 7-8 people who think the C4 is the best bet. But, all of my (limited) experience shows me that the F-bod can be a superior racecar.

I will say one more thing, though. One of my favorite things about winning in a Trans Am is beating BMWs, Panozes, Corvettes, Vipers and Porsches in a "Mullet Mobile". People seem to expect those cars to win. But, I still have drivers come up to me shaking their head after I've passed them in some high-speed turn or outbraking them into a turn. It's that little bit of satisfaction that doesn't come with any trophy or points - I love it!

This would set both cars really close, with the slight difference of IRS and suspension geometry. What kept me from upgrading my Ls1 Z28 was: C4 Z51 like susp (Crossmember and camber brace mods) VS FBody upgrades (k-member a-arms -upper and lower with rod ends-, t-arm, LCAs, panhard, strano hollow swaybars and konis).

At a first glance it seems fbody upgrades will cost a lot more (what about a 9moser w/ truetrac tranny), but hey: with the C4 stock clutch cost I can buy a t56 spec3 lightweight clutch, the C4 would need soon an aftermarket optispark and a turnone pump. Both would benefit from C5 brakes (what about nice brake lines with speed bleeders), the list could go on. For what I've seen aftermarket for LS1 fbodies is huge compared to C4s (hell, you can put the 6speed automatic with paddles (IMG:http://www.frrax.com/rrforum/style_emoticons/default/blink.gif) -something I would't-). and I don't know how C4 suspension parts endure racing.

Seeing as you care more about racing than being mods posers, your oppinion is really appreciated. While I'm hunting for a nice C4 I'm also considering buying back my Z28 (which is already a little modded) from my dad and using the cash for a nice 275/315 set of wheels and start right away at the track. (seat time and having fun).

Damn, this C4 pic kills me: http://para.noid.org/~c4racer/C4RACER/Oct-...s/image011.html

This post has been edited by Augusto: Jun 25 2009, 10:57 PM

You're not going to go wrong either way.

Let me throw some fun day autocross numbers out there from beaver Run. On a fairly fast sweeping course with a couple tight corners and a very tight dogleg with cars running 44-47 seconds, here's a comparison.

C4 Vette with factory electronic adjustable Bilstein shocks (L98 engine) 6 speed on R compound tires- 40.25 to 43.5 seconds.

00 LS1TA with 1LE fronts on Strano Bilsteins, 114# rears with Koni's, 35mm front swaybar, Avon 275/40/17 street tires- 42.5-45.5 seconds (3 different drivers).


Based on those times the cars were running pretty close to each other. The vette has the advantage of being smoother and flatter while the TA has the advantage of 500 extra RPM and some extra HP.

This post has been edited by wannafbody: Jul 5 2009, 01:23 PM

Here's my personal experience, I've tracked 3 different f-bodies (LT1, LS1 and LT4), a 92 LT1 C4 Vette (6 spd), and a C5 Z06. At my local 1.8 mile roadcourse the LT1 Formula (moderately modded with full slicks, widers wheels, some suspension pieces, and 285RWHP) was still about 4 seconds a lap slower than my stock C4 on street/track tires (Nitto RIIs). My LT4 Hawk is about 1 second a lap faster than the C4 was, and the Z06 was in a whole different league. Here's how it broke down:
Modded LT1 f-body (285RWHP, modded with slicks and race pads): 1:38
C4 (270RWHP, stock, with Nitto RIIs and semi race pads): 1:34
LT4 Hawk (311RWHP, stock w/ Nitto RIIs and race pads): 1:33
C5 Z06 (~335RWHP, stock (tires, pads, everything): 1:29

Looking at the numbers, you'll notice that the C4 was faster than the LT1 f-body that had more HP. The other thing that's not apparent from just looking at numbers is the "feel" of the car. The C4 is way easier to drive on track than an f-body. Yes, you can make an f-body go fast (the LT4 shows that), but it's not as easy. If I was just doing track time, I would definitely take the C4 over my LT4 Hawk, it was much easier to get a fast time out of it, whereas with the f-body you really have to work at it. The C4 is much more neutral at the limit, and is very easy to recover if you go slightly past the limit. It's also much more of a "driver's car", giving much better feedback to what's going on. The C5 Z06 takes all of the C4 characteristics and raises them to the next level. I only had it on track once, and was hitting those times after just two 15 minute sessions.

Perhaps I need to borrow a C4 and see what I can do in that. Maybe there's something to them that I don't know about.

This goes back some time. But in 1999 there was a category in ProSolo that pitted ESP cars against stock class C4 Corvettes (don't recall if they were AS or SS classed at that time). But they were both very, very competitive with each other. I beat Matthew Braun a number of times in my '91 (which is in no way as fast as my 2001). But lost the Championship to Gary Thomason.

Point being if an underprepped ESP 3rd gen (11's w/R-comps, headers, good LSD, shocks, but not much else) can run with a stock class (meaning shocks, bar, R-comps) what do you think a much more prepped, more powerful 4th gen can do?

This:

(IMG:http://i119.photobucket.com/albums/o145/mpatterson1410/F-bodyvsC4.jpg)

Poetry...Meet Photography.