Tom, the problem with comparing C5/6 to C4s is that I'm used to seeing Z06 versions of the former, whereas there really was no equivalent to a Z06 in the C4 generation. I think a Z51 or Z07 C4 (of any year) is pretty close to a base C5 or even C6. But a C5 Z06 is a good bit lighter with wider rear tires, a stiffer chassis, probably more rear weight bias, and definitely more power (especially on most autocross courses, where the C5Z's gearing puts it in the meat of its power band), and better suspension geometry. It's also wider, which may or may not help depending on the course. They seem faster than any stock C4, and honestly my well-modded C4 may not be much faster than a stock C5z on equivalent tires. The C6Z brings similar light weight and bias and even wider tires to the game. It's wider enough that it can be hobbled on some courses, and at typical autocross speeds it doesn't have much more acceleration in 2nd gear (much taller gearing). It is basically tied with a C5Z, if tire model and driver skill are held constant. Both in full stock (A Street) form are at least as fast as my modded C4.

I know what you mean about feel and feedback - that tends to fall in favor of the C4 (especially the early ones). But to some extent this can be tuned out even in Street class with a change to one swaybar (allowed) and dampers. But the C5/6 is definitely a more street-driver-friendly car, so it's cushier and better isolated, which translates to less feel. I suspect that if we'd ever gotten a later C4 with a curb weight of only 3100lbs, 9.5/11" wheels, and at least 375rwhp (i.e., what either Z06 brings to the table), it would have been competitive with a C5/6 Z06. I remember when the C5s first came out, it took several years for the autocrossing community to realize it's speed potential. But once the C5Z came out, the C4 was instantly relegated to relic status.

Zak, the C5/6 is probably a bit more rear-biased due to that transaxle. It's not a lot different, though. Dropping an aluminum LS in a C4 might give it the advantage here. The LT5 C4s were hobbled by mass. The LT5 is probably close in power to an LS6, but the engine is really heavy and it's all up front. I think for autocrossing it isn't the best answer, same as a C6 ZR1 isn't the best answer (same issue of more weight, and for autocrossing mass trumps power). For the same reason, the Miata and S2000 are examples of cars whose small size and mass makes them great for autocrossing despite not having much power. Small width and wheelbase are huge advantages in autocrossing, and light cars are seriously advantaged as well. Those cars are fun to autocross, but IMO the lack of power (especially in early Miatas) makes them less fun on tracks and on the street. But that's just my opinion. Finally, don't give up on a C4 as an autocross tool. The hardest thing to find is good stiff springs, now that VBP is out of business. You can still get coilover setups for them, though, and another vendor may soon release the equivalent of the VBP Xtreme springs (stiff and adjustable for ride height). You can get at least decent shocks, just from less companies. Anyway, a friend of mine recently won the NOLA Optima event in GTV class with a C4 with LS7 power and stock geometry, so they aren't slow!

 

So for the time being, who do have for suspension mods? Just Van Steel and DRM?

 

Banski, Prothane/energy suspension, global west, Bilstein, Koni, Ridetech, QA1, and others....


I think people -due to Chevy's marketing, and mag authors "re-tweets" of the OEM- tend to exaggerate and give too much credit here. Remember, while the trans moved to the rear, the gas tank moved forward, and the rear axle moved back.

'92 LT1: 51/49

'97 C5: 51.8/48.2

...Effectively the same. Chev mad ea BIG hoopla over teh C5 transaxle and "weight distribution"...but what they REALLY did was move the trans and gain a bunch of foot well room. Any diff in weigh distribution between a base C4 and a C5 could be mitigated w/a battery move.

Here is a cool read, for a perspective on "handling" for the era. 300ZX's "handle awesome"...right? Check out PAGE 2

There are tons. Here is another. Porsches handle awesome...right? I like PAGE 3



.

 

Very interesting. So a standard 1990 C4 with a LS1 swap is the ultimate C4 over the ZR-1?

I didn't think the Lotus LT5 was heavy as I thought it was all aluminum etc and made to be light.

I agree the Miata is undepowered. I guess had it been a V6 it could probably be the best of both worlds? Still be great at autocross while being fun on tracks and on the street.

By the way, your red Corvette in your avatar looks great. Do you have larger pictures?

 

I agree. Besides the advantage of transaxles in general seem to be exaggerated. The Miata for example has always been marketed as a 50-50 weight distribution car, is famous for fantastic handling and has no transaxle. While the Maserati 3200 GT and Coupe have a transaxle and handled like a bag of potatoes till they sorted the suspension out.

 

Right. It's not at all impossible to modify a C4's suspension, it's just that there are fewer choices among manufacturers.

I'd buy that. I believe part of it had to do with gaining torsional stiffness in the chassis (which is related to the footwell space, too). And actually, looking it up it appears that the Z06 (and probably the FRC as well) are actually more front-biased, since most of the weight they removed came from the rear of the car. I certainly didn't mean to imply that the transaxle design is required to get a rearward bias, or that it automagically accomplishes that. Too many examples of front-trans cars with 50/50 or better weight distributions exist: Vipers, Cobra kit cars, etc.

Unfortunately, the LT5 is huge. Although it may be be all-aluminum, it appears to have more mass than the LT1/LT44/L98. And more of that mass is up high (heads and valvetrain), where it causes more weight transfer. I've never seen it verified with an actual scale, but the curb weight of a ZR1 is listed as being about 200lbs heavier than a standard C4. Some of that is the bigger wheels and tires, but some appears to be the engine as well. OTOH, an aluminum-block LS is almost 100lbs lighter than the L98/LT4/LT1. And depending on your budget, you can take it well into BBC territory in terms of displacement and power (468cid and more is routine now). My budget says "Stick with a stroker LT4," though...

Okay, just one, because I don't want to hijack this thread:


That's with VBP Xtreme leaf springs front and rear (1125f/550r), urethane front control arm bushings, Banski rear suspension links, an assortment of OE sway bars, a mashup of custom-valved Bilsteins and Koni sports (would like to try the Ridetech offerings someday), and 18x11 wheels with 315/30 Rival S tires at all four corners. It's close to full weight - only the a/c is missing and it probably still weighs over 3200lbs.

There are a few others on the forum that are at least as heavily modified. Here's Chris Ramey's Optima-winning 84:


I would bet his car is 300lbs lighter than mine, with 50% more power and 335 tires at all four corners. And Chris can flat drive. Also, look for Nokones' car on this forum, among others.

 

Thanks Matthew. I wasn't aware of the draw back of the LT5. I thought the LT5 was the most desirable engine in a C4. So it's looking like instead of searching for a ZR-1, I should just find a nice standard C4 and do a LS1 swap instead? Or the chassis ad suspension of the ZR-1 is so much better than upgrading a standard C4 there would bring the price up to ZR-1 level?

Buy the way, your car is stunning! Where can I see more photos?

 

Off the top of my head, a ZR1 or 96 GS don't have any special parts in their suspensions. They came with wider rear tires, but otherwise I think their parts are the same as other C4s. If you are planning to run in a class that doesn't suspension modifications (i.e. you have run the setup the factory put on the car, except maybe for shocks and one swaybar), then the best suspension would be found on the 84 Z51, and the next year or two are runners up but with the far better L98 engine. the 84cars had the stiffest springs the factory ever put on C4s, but also the lamest engine. As the years piled on, the factory spring rates generally got softer, which is not good for road course and autocross work.

OTOH, if you're going to a class that allows changes to spring rates and wheel widths, it doesn't matter what factory suspension you run because you'll ditch it all anyway. Also, if you're only focused on autocrossing instead of track competitions, I'd focus less on the engine and more on the suspension and wheels/tires. They are far more important. You can upgrade the engine later, but get the suspension and driver skills sorted first. In general, that means stiffer/lower springs, offset lower control arm bushings up front (for more negative camber), rod-ended links in place of the rear camber arms (same reason), much better shocks, and 11" wheels with 315 tires (or more if you are willing to flare the fenders). Also, source a few different OEM swaybar sizes so you can dial in the front:rear handling balance. More can be done, but this is an excellent starting point. I'd start there and start mulling engine options over time.

Re pics of the car, I appreciate the compliments. It's really just a stock-looking C4 except for being lower and on much wider rolling stock than the factory gave it. And it has a hole in the hood (long story). I don't totally know why, but that seems to really grab people's attention. I get compliments frequently. I guess getting any C4 lower and putting fat tires on it really highlights the great lines of the C4 (GM really hit a design home run with the C4 IMO). I don't have too many pics, but one of these days I should get a photo page going where I can link people to an album. Okay, you lit a fire under me, and it was super easy to load a few into Google Photos. So here is a collection of pics of my car. The first couple are of the previous owner tracking it (he is MSR, still lurking around this forum).

 

Following up here, if you're interested in doubling the power of a stock C4 without the hassles of an LS swap, this 414cid SBC would be pretty awesome. It's ready to drop in and run, with a proven combo of parts. It won't be all that nice on the street, so it depends on what your true uses for the car are. It also depends on what your emissions requirements are. Where I live, if the car is older than 1996 it doesn't have to pass any emissions tests. It'd be fun to drop this engine into a pre-1990 C4 (so it could go into vintage class in Optima events) and have fun with it.

 

If you're after all out performance and intend to modify, starting with a nice standard C4 is the way to go (if you're set on using a C4)

The ZR1 had a slightly wider rear I think. Not very obvious. And the LT5 is cool, a unique engine in the world of Corvettes. It's not worth it modifying a ZR1 for racing though. Better keep them in good condition as if any C4 is going to be collectible, it's the ZR1.

 

It's only wider because they used 11" rear wheels with only 36mm offset, and they had the wider fenders to clear them. The suspension dimensions (links, upright/spindle, etc.) are the same dimensions as other C4s.

 

Thanks. I actually have the intention to buy a C4 as a road car. I would love to take it to autocross and other track activities. But it wouldn't be a dedicated track car. It would have to work as a road car. Basically make it as good as possible of a sports road car. Something which can keep up with today's road sports cars.

By the way, for some reason I can't access the photos. It says: " 404. That’s an error.

The requested URL was not found on this server. That’s all we know.

"

But thanks for taking the time to post them.

 

This is interesting. Are the wider rear quarters of the ZR-1 available anywhere as a kit or something? Or converting a C4 to ZR-1 looks would take too much to be worth it?

 

Okay, for that purpose I stand by my suspension recommendations. But you would want a milder engine with a streetable clutch. A stroked version of the stock engine, with good heads and a smallish cam would work well for this. That's actually pretty close to what I have (I probably have more overlap in my cam than most would want for street use, but it's not peaky at all). A stock or near-stock LS3 would be great, if expensive, for this application.

Okay, it looks like they are not viewable by the public by default. Try this link: https://photos.app.goo.gl/mUkWcjM92TnPwdXZ7.


I imagine a kit is out there, or if not then the fenders can be found...at a considerable price. If you want the wide-rear look, then it may be worth it to you. If you are only interested in performance, skip it. You can still fit 11" wheels and 315 tires inside the regular fenders - you just need 50mm offset instead of only 36mm like the ZR1 had. You'll get the same handling benefits. Or you can flare both front and rear fenders and go for 12-13" wheels with 335 tires for even moar/bettuh grip.

 

Ok, thanks. All of that is kind of changing my mind a bit. I was thinking about finding a good ZR-1. But now I'm thinking of finding the cleanest standard C4 I can buy and doing a engine swap. Although I do like the ZR-1 wider rear a lot and it seems to upgrade a standard car to that would probably be expensive.

Thanks for the pictures. Your car is one of the nicest C4s I have seen.