Z28 VS C4 handling (modded for road racing), Handling potential of an f-body vs C4 Options

[Augusto]

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).

[trackbird]

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).

[roy]

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 (IMG:http://www.frrax.com/rrforum/style_emoticons/default/nutkick.gif) to highend latemodels.
C4 ZR1 at Hockenheimring

[prockbp]

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.

[Augusto]

Thanks, guys. Really appreciated.

[00 Trans Ram]

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.

[Mojave]

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.

This post has been edited by Mojave: Jun 21 2009, 10:25 PM

[Blainefab]

and I would swap a ZF6 and mod susp

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.

[00 Trans Ram]

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.

[00 Trans Ram]

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.

[Mojave]

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.

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.

[Augusto]

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.

[Blainefab]

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.

[roostmeyer]

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.

[trackbird]

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...

[Mojave]

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.

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).

[roy]

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

[Augusto]

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.

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.

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...

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

This post has been edited by Augusto: Jun 23 2009, 05:06 AM

[Blainefab]

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.

[00 Trans Ram]

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.