Umrswimr

Car is completely stock aside from:

Electric WP
C5 brakes
PFC01 pads
Kumho V710's on GS wheels.

I bought the car as a cheap street/track car so I didn't abuse my C5. Plus it has a roof which I decided was a good idea.

This event was an Apex driving school on the 1.3 mi section, CCW direction. This section of track (for thise who haven't been, here's a video) has a lot of elevation changes and more than one completely blind corner.

The students in my class (the graduate class) have all done at least one Apex school, most have several track days under their belt, but nobody was a Schumacher threat. Cars included a 996 GT3 (on Hoosiers), a pair of 996's, two C6Z's, my C4, a Miata, an Elise, a modifiied LT1 Z28, and an M5. Aside from my car and the GT3, all were on DOT tires. The Z28 was the only real "novice" with only 2 track events. I've personally never run this section of track, but I have about 6 tracks days completed so far in addition to a few hundred autocrosses.

In my C5, I was usually one of the faster cars on the track. I'm not a great driver, but I'm not bad and the car was pretty fast on r-compounds. Rarely did I have to point by cars- I ended up doing most of the passing. What a change it was to move to my C4. I became one of the slowest cars, after the Z28 and the Miata. Even on R-comps, the C6Z's could outcorner and certainly outrun me, Following a Z went something like this:

Braking- I could outbrake him quite handily. I could outbrake anyting out there, actually. The R-comps and the PFC's meant I could brake later and much harder.

Turn-in to Apex. My car oversteers (more on that later) so trailbraking is a dicey adventure at best. The Z actually had more lateral grip than my C4 on R-comps, unfortunately. I could pull 1.2G's in my C5 with these tires. I suspect it's only about 1G in this C4.

Exit. Yeah. He'd roll onto the throttle and it was no contest. He'd rocket forward and I'd fall way, way back.

Despite running a better line than him (and race tires), I figure I was at least 5 seconds a lap slower. The GT3 was right there with them. I found I couldn't even keep up with the 996's unless I really, really abused the car.

Now, I still had a ton of fun. The car has some snap oversteer, so that was fun to play with. And any day at the track is a good day, so I'm not complaining. But I'm seriously reconsidering spending any more money on this car. I'm not convince that, barring an obscene amount of modifications, my C4 will never be as fast or as easy to drive as my C5.

I figure it'll need the following modifications if I continue to track it:

1) All the chassis parts for sale by R-D racing. Camber, S-T, and underbody X brace. The C4 chassis is just too flexible. I had the bolt holding the removeable top to the windshied frame work itself loose over the course of the day. This chassis has some serious flex. $1500 + harnesses.
2) Brake ducts and a bigger radiator with EOC. Despite the mid-fifties temps, I had oil temps above 290 degrees. $700?
3) Some sort of suspension work. Right now it's undersprung for sure. The suspension also tends to "hop" over bumps under heavy braking (especially if you ABS it), which I suspect is probably the crappy stock shocks. At the minimum, it needs a pretty substantial alignment done to fix the snap oversteer. Right now it's set to stock:

Front:
0.2* neg camber
6.4* caster
0.02* toe

Rear:
-0.01*,0.01* toe
-0.1,-0.3* camber

I was considering this system from VBandP. $1800

All that and I suspect the car would still not be as fast as a Z51 C5. It would be down 50 hp at least. Which begs the question: why bother? Why not just buy a C5? The cost would be about the same in the end...
Or- Does it actually matter that it's not as fast? I'm not planning on doing anything more than DE's anyway. I could buy the above parts a little bit at a time and still have a car that's cheaper to track (and possibly wad up) than a C5.

So now I'm in a bit of a situation. What on earth to do with this car?

96GS#007

Yes, it takes money to make a C4 run with a C5. By the time you mod a C4 to make it happen, you may as well pick up a used & slightly abused C5 for a cheap track car.

Some basic (and inexpensive) things will help tremendously however...

You need an alignment pronto.

Front...

Camber: As much negative camber as possible. Given that the car is stock, you'll probably end up somewhere between -1.0* and -1.3* It really varies by car and since it's 12 years old, that doesn't help
Caster: 6*
Toe: 0 toe or just a little toe out...1/16"

Rear...
Camber: ~0.2* less than the front...ie -1.0* rear if the front is -1.2. I'm assuming you're running 275/40/17s at all 4 corners? If you have 255s up front and 285s in the rear then you'll want to make it ~0.3* less than the front
Toe: 1/16" toe-in / side

Brakes...

You mention PFCs..01s? If not, switch to Carbotech. I like XP10s up front and 8s in the rear. Some like the 12/10 combo.

A DRM brake bias spring does wonders and will help with the trail braking jitters


Next up...

Shocks....

Adjustable Konis or QA1

Chassis / Other Suspension Parts...

I like the RD camber brace. It's pretty easy to visualize how the brace works...measure from upper a-arm to upper a-arm with the car on the ground. Now jack the car up with the suspension drooping and re-measure. You'll see ~.25" to .50" difference. Kinda tells you how much the chassis flexes I wouldn't worry about the other stuff.

Global West del-a-lum bushings for the front upper and lower a-arms
Energy suspension poly bushings for the sway bars and the rear camber rods (some call them the dog bones).

'89-'91 Z51 or Z07 front & rear springs combined with 30mm front / 26mm rear sway bars, and 275/40/17 tires at all 4 corners (17x9.5 rims).

Just my $0.02. Still cheaper and easier to buy a C5.

Kanmer

Ya know Jim, I have a C5. A really pretty blue one. I love that car. I think its too pretty to get beat up on the track but....

Thats why I was thinking that C4 w/ LT4. I know I want a dedicated track car. I might just take your advice and hold off until I can afford a "cheap" C5. I have seen a bunch of FRC's on here for 15.5K THats not bad. Problem is, after I bought it, then the track mods begin anyway
Hope all is well in the great white northwest. Coming to VIR?

Bob

96GS#007

The beauty of the C5 is the chassis and suspension. The very things that take time and $$ to address with a C4 are already done on the C5. Right out of the box, with nothing more than an aggressive alignment, a set of sticky tires, and a little lower ride height, the C5 is better (IMO) than 85% of the cars you'll come across at an HPDE.

Can you make them better? Sure, but that's true of any car. Just look at the guys out there stripping C6 Z06s because "they're not light enough", or "the brakes suck", or "they need more power".

Rule #1...There's always someone faster
Rule #2...Speed is a matter of money

A C5 will put you ahead of the curve on both counts.

We were partly cloudy and warm for most of today

No snow for awhile, except a few of the mountain passes.

As much as I'd like to, VIR isn't going to work out for me. I am going to be at Putnam Park with NASA 18/19 May however

Sidney004

I agree with the comments above. More aggresive alignment, perhaps the VB&P offset bushings(which I use) to get over -2 deg. The RD product line you mentioned(which I use as well) poly bushings and 32mm front and 26mm rear sway bars; that along with V710's(275's front and 295/40 rears.) If you go that route you should be able to post numbers like these:
which should put you pretty close to those other cars, except under acceleration.

asp04

I posted about the same thread a few weeks ago. "IS THE C4 OBSOLETE?" Got plenty of feedback. Generally speaking, this is what I learned. There are more than a few obscene fast C4's out there. You had better be pretty mechanical to be one of them. As far as money goes, some had invested as much as a new Z06 costs. Most replys thought the C5 was light years ahead of C4 as a 'competitive' track car. 'Competitive' @ HPDE events is an odd word at best. You probably would never be the slowest car out there with any C4, or the fastest with any C5. As a longtime autocrosser, and a new addict to HPDE, I know all street cars are a compromise to take to the track. A full race Miata could give a C6 Z06 a run for its money.
All that being said, I decided to sell my C4 and move into the next millenium with a C5 Z06. I'm going to throw some sway bars, wheels and tires, and some nice seats in it, and call it a day. Hopefully, that will move me up the 'fast' ladder a few rungs. If I had just a bit more money I'd take the elevator up to a F1 car.

BrianCunningham

The words cheap and Corvette should never be used in the same sentence.

Run a C4 because you like C4's.

What??
Gary was lapping Spec Miata with his Stock C6Z06 at Lime Rock, and he was on street tires!

c4cruiser

How does the brake bias spring affect ABS-equipped cars? I was considering one for my 87, but I was curious if it could hurt the ability of ABS to do its job on the street (I still use my 87 for occasional weekend driving). And I still run the stock size rotors with Hawk pads.

96GS#007

The ABS works fine on my '96 with the spring.

The DRM spring has been around for probably 15 years or more and I've never heard of an ABS issue. All ABS cares about on the C4 is whether or not the wheel is still spinning.

Solo2GS

No problem with ABS what so ever.

Brian, I also liked your comment on run a C4 because you like a C4, not because of the money! So true! Wish I could get a nice used C5 Z06 on of these days though!

Solo2GS

On another note with the C4, who else runs 315's (17 X 11's) on all 4's at the track?

BrianCunningham

They're all good

BTW
335's all the way around on 12in wide CCW rims

ZBRA

I have that kit, except I substituted their adjustable rear spring and a 30mm front sway bar instead of the 32mm. I stated installing it yesterday, so I can not yet comment on the results. The quality is top notch.

Like you, I bought a cheap C4 so I wouldn't tear up my C5. I bought my '04 new, and still have less than 12K miles on it.

If you are going to use the C4 as a track only car, weld in a good cage and that should take care of the flex.

I went a bit all out with mine though. It now has a 383 Golen LT1 with Lloyd Elliot LE2 head/cam/intake. I should see 400 rwhp. That'll help me keep up with the C5s.

johninar

I think that if Swimr didn't have a C5 as a daily driver, and has tracked it, it would not be as big a deal to track a C4.

BrianCunningham

uploaded an old video of mine.

Not bad for corded tires!

burners

How did you like the short track? I think it's challenging. The 1.7 is more familiar to me so I like it better. Also, I was dealing with some stability problems the last time I was on the new section so that is probably tainting my view of it.

I guess the overall question is what are your goals and your means to achieve them? Do you want a dedicated track car or do you want to keep it street worthy? I think that question alone would dictate how the car is modified/built. To my mind I think it makes sense to put a cage in it to stiffen the chassis, align it for max performance and gut the interior and the rest of the car to get it as light as possible. An alignment should make a pretty good difference in the way it handles. I think that without spending a lot of money you can be nearly as quick as a stock C5 but your C4 will be a dedicated track car. Is that such a bad thing? Like you said, the less money into it the less you worry about crashing it which makes for more fun. Lower weight will decrease the need for more HP so that saves money as well. Besides, you may pick up a few dollars by selling the things you take off the car. That is like a free upgrade or two.

Umrswimr

The short track is hard. Really, really hard. I got the impression that even Keith Verges wasn't 100% sure how to handle the "toilet bowl". My main issue was oversteer, especially on the last corner exit before the main straight at the top of the hill and the very sharp left-hander at the bottom of the hill before you start climbing back up. I had to be very careful with throttle modulation through these places. Otherwise, the course is a lot more fun than the 1.7 because it's a lot harder to master. After a day on the 1.7, I was actually kinda bored. Not so on the 1.3.

My goal for this car is NOT a full track car. right now I have no plans on doing anything more than DE's. This car is my DD as well as my track toy. However, I guess I wasn't ready for the shock of being one fo the slowest cars out there. Right now I'm just trying to determine if it's worth the hassle and cost of modifying this C4 into a car that isn't embarrassingly slow.

burners

If you don't want a full time track car then my thought is that a C5 is a better value overall. Obviously you can have plenty of fun with the C4 and you can probably do a few cheap things to make the car quite a bit faster. So the thought is then if you spend the extra $5K on track time you will probably come out ahead in the long run.

The "toilet bowl" is definitely interesting. I think the most mishandled area of that turn is the exit. I find myself (and I've seen others) continue to the right too much before turning into the slight rising lefthander. It seems to me that exiting the "bowl" earlier will give you a straight shot across the lefthander and get you to the outside (righthand side) of the track about mid way down the straight which sets you up pretty good for the sharp left onto the main straight. How where you taking that corner and the exit? What were Keith's thoughts (was he the instructor)?

Umrswimr

Keith didn't ride with me, but my general plan was:

1) Crest the hill, keep the wheel straight, pass the first right apex cone about halfway down and hit the brakes.
2) Turn-in late and double apex the rest of the corner.

The Z06's I was with tended to A) just glue themselves to the inside corner the whole way around and rely on their power to make up for it or B) really, really late apex it- basically hit the apex cone in a straight line as if it were an exit cone.

For example: this video here (CCW 1.3mi) shows a really, really late single apex corner. I really have no idea which was is faster. The fact that Keith didn't have a definate answer indicates that the jury is still out.

As for the exit-I followed the video almost exactly.

burners

I guess it's been a while since I've been on the 1.3 (or as the 3.1) because they didn't have the cones setup when I was on it. The cones definitely help with the exit. I was treating the "bowl" more like how you described the Z06's line. Sort of steady state, just waiting to pour on the power.