Hi, everybody. I'm really excited to go for an all out track car project.

I'm really puzzled at this dilemma: could a 98 Z28 be modded to match or surpass the handling of a C4 with Z51 like susp (Crossmember and camber brace mods)?

I may be able to trade my 98 LS1 Z28 for an auto '95 C4 (and like 3K of cash, and I would swap a ZF6 and mod susp). C4s are not so cheap to get in my country (as opposed to fbodies), let alone C5s. I was just about to swap a T56 (with relocation crossmember, Z06 clutch, etc) on the Z. Before I just do either of it, I want to make sure to know if I can achieve handling capabilities of a Z51 C4 or close through modding (shocks, tires, rims, sfc, kmember, a-arms, torque arm, lcas, panhard, strano swaybars, rollbar, a little diet, etc). Guys please be honest.

I've seen biased opinions on the C4 side by people who do not really focus on track improvement (and take stock form as a reference) so I thought this would be the right place to ask.

I want to make sure to invest time and effort on the car with better handling potential (modded) on the following couple of years. (Ultimate purpose: Road Racing and a little of AutoX).

Augusto,

The only information I can add is that my friends in American V8 Supercar Series racing told me that the C4 was turning into "the" car to have in that series (against Camaro's, Mustangs, and such). I haven't pulled the race results, but I know he was considering selling his heavily modded Mustang and buying a C4 to build at one point.

I don't think the Camaro will ever catch the Corvette (if both are taken to the max and make similar HP).

With the mods you listed the C4 vette will always be in the front.
Here is a vid from a very well prepared C4 ZR1 with Movit brakes. This car is a monster and a serious to highend latemodels.
C4 ZR1 at Hockenheimring

Check historic autocross results here:

http://www.scca.com/contentpage.aspx?content=73

C4 Corvettes (~3350lbs) and 4th Gen F-Bodies (~3450lbs) are pretty close in curb weight, but the Corvette has better weight distribution, a lower center of gravity, and better suspension. The 4th Gen F-bodies do have more horsepower (10-30 more) than the typical C4.

I would choose the Corvette if I only cared about being faster in autocross and road racing.

Thanks, guys. Really appreciated.

I'm going to have to disagree, but only because of personal experience. In my series (Grand Bayou) this season, we had 3 C4s and 2 F-bods (my LS and an LT). All our cars are very modified, but worth less than $50k (no "unobtainium" mods). Discounting DNFs, the F-bods beat the C4s almost every race.I don't think that their suspension is better. I have higher cornering speeds and Gs, even though I have less tire. On straights, I was outgunned - all made 400+hp and one had around 700. Now, it can always be argued that we were better drivers than them. I guess it's possible. But, I'd rather have my F-bod than a C4.

Auto-x classing and results (in AS vs FS, BSP vs ESP, and BP vs CP) says that C4's handle better. Matt's experience is unique, as auto-x results have shown very repeatedly when equally well setup and equally well driven, the C4 does handle better. This isn't really surprising, however, as it SHOULD be faster, with better weight distribution, lower CG, and better suspension geometry.

I own both a C4 and an LS1 4th gen, and I'd take the C4 every time. Which one is better for YOU depends on your own personal preferences, as there is definitely something to be said for beating guys in a pony car.

Be aware that the auto C4 has a Dana 36 rear diff, vs the Dana 44 that the clutch cars came with. The auto gear ratio will probably be less desirable, too, so budget for a clutch car batwing assy to drop in.

Mine may very well be some skewed results. I know that the other F-bod driver (John Brannan) is one helluva driver. There's a great video of me and him fighting for 1st over on Youtube, shot from my car. For about 12 laps, he made that car dance and sing, and I did everything I could to go around. We were all alone, so we had some fun.

I don't remember C4s being well-regarded in the suspension department. Mind you, I was just getting into modding cars when the C5s came out. But, i remember all these articles saying how bad the C4 was - how it creaked, groaned, didn't absorb bumps, and wasn't as good as 4-door BMWs - and how good the C5 was in comparisson.

Oh, and I don't think autox results/PAX is a good indicator. According to those, I should be worse than a Miata. Autox is NOT a good place for an F-bod. At least, it never was for me. Sure, I'd do OK, but it always felt like my car was being held back and not fulfilling its potential.

I knew there was soemthing else I wanted to say!

If you are planning on doing road racing, and C4 parts are hard to find, then I'd DEFINITELY go with F-bod. When it's 2 weeks until a race, and you need a new rear axle/torque arm/transmission/etc., you'll be glad you went with something you can get your hands on. Running a car that has scarce parts where you live is probably not very fun.

Creaks and groans aren't suspension problems, they are chassis stiffness problems. The C5 chassis is worlds ahead of the C4 in terms of chassis stiffness, but if we are arguing built road race cars, it's nothing a cage won't fix. There is zero doubt the C5 is better, but that wasn't the question.

I think auto-x numbers are an excellent comparison from a pure handling perspective. Yes, f-bodies are slow in auto-x. Even CP is slow compared to some Miata classes, like SSM (formerly SM2) and D Prepared. I'm not saying we should all go get Miatas or they are more fun to drive, but years and years of national results make it very clear: pony cars suck at auto-x. Now, in your local region these trends may or may not play out due to drivers, prep, courses, sites, etc, things are much more equal on the national level and the trends aren't pretty.

I'm aware the first mod to an A4 C4 will be ZF6, c-beam, m and slave cyls., etc dana 44 rear end. Same would be on my Z28 (t56 crossmember t-arm relocation, z06 clutch, etc). I like very much my LS1, but when I took a test drive on a harsh two-seater FX3 ZF6 C4... I fell in love.

C4s are not exactly few, but there are few LT1s on sale (no more than 15) with the price tag twice of a 98 LS1 z28. (9 or 10 K vs 5K). Dana rear ends are more common than a Moser type, T-56 can be had for 800 and LS1 for around the same on junks. Most performance for both of these is through US website vendors.

Personally, is to choose carefully (as I can't afford upgrading both cars) which would be the car with better handling capabilities where I can tinker, tune, learn and grow as a better driver.

The C4 chassis is fixed with way less cage than a Fbod needs, and can be made lighter with less work. The biggest expense in upgrading the suspension is replacing the rear links, no need for a fancy TA or front arms.

Augusto - If you don't have the ZF yet, there are other solutions that will work and have better repair part availability - but you'd need some fab work done.

Just curious what are c4's weighing in at in full road racing trim? How much tire can they fit? I've seen a few TPI c4's go very cheap w/in 250 miles, a little tougher to find an 89 or 90 though. I've been really tempted to go that route with a 408 sbc sitting in my garage that just needs freshened up.

I want a '91. It's the last year of the SBC, the first year of the LT1/ZR1 style body, it has the 6 speed, not the earlier 4+3 gearbox and after 1988 they fixed the rear suspension geometry on the Corvettes, so it benefits from that upgrade as well.

Not that I've been looking for a Corvette or anything...

They fit 315's on all 4 corners with 17x11 50mm ZR1 wheels, or 335's on all 4 with custom wheels with just the right offset. This is with no fender mods, other than some very minor rubbing at full lock on the inner front liner.

My C4 weighs 2876 on 17x11's with 4/5 tank of gas. No cage, no interior, doors are untouched though (door bars, power windows, locks, etc).

That one in the Video is a full caged car weighing in at 2990 or so the guy claims.

I have a T56 on the garage. I've been following a couple of C4 LS1 swap threads and info (I'm really fond of LS1s) and seems very very messy. (dashboard wiring, cbeam, alignment with the tranny). Still, main goal is handling not engine power.



Mmmm. good to know. I just limited myself to 94-96 C4s because of improved suspension geometry I didn't want to miss.

I will still borrow my brother's thirdgen for a couple happytail fun heats. Long live the thirdgen and the king of the hill. :-D

AFAIK nothing significant happened to the C4 suspension after 1988. The later, rounded corner rear bumper cover will bolt on to the earlier cars, for a nice update. 315's on 17x 11 fit perfect, 335's on 12's stick out a little.

I have a couple of ZR1 rear bumper covers in storage, and a whole bunch of other C4 parts.

I put a TKO in this one: Evan Ginsberg's C4R Dry weight, as I recall, was about 2850#, before dry sump and front dam/splitter.

This one was a little heavier, with full street exhaust and glass: Scott McClung's C4RACER

I'm getting an 88 in on consignment, soon. Full cage, 406SB, Lexan, coolers, Kirkeys, etc.

Does anyone have any other head-to-head results?Here's why I ask. Given equal prep, an LS will make more power than any engine the C4 came with (except a few of the expensive ones). They will weigh just about the same (2800lbs). They have equal rubber. They have same weight distribution (53/47 or better) and cross weights (49 or better). So, let's assume that the C4 IRS is actually better. Is a slightly better suspension a bigger advantage than 20 or more hp?I'm talking about RR, since the original guy said RR with occasional autox.

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**.

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 -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

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.

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:

Poetry...Meet Photography.