LT4Firehawk

Well, I headed out to our local track (Hallett) week before last for my first track day with the Firehawk. Here's the config on the car:
LT4 Firehawk
Level II suspension: (300-450lb/in front, 115-185lb/in rear), 32mm front bar, higher durometer bushings in LCAs, panhard
SLP Torsen with modded AAM cover
Koni DA front shocks, stock SLP Bilsteins rear
Nitto 555R II 275/40R17s at all corners
Carbotech XPs on front LS1 brakes, stock rears with street pads

First session (20 minutes): Went well and I was picking up driving an f-body again fairly quickly (hadn't had one on track in 4 years). Fastest time of the session was a 1:35 (check below for comparisons of my other cars on that track). The only problem was that there was bad rear axle hop braking at the end of the front straight depending on how aggressive I was getting on the brakes. Also, the car leans way more than what I was used to with either of the Vettes I had.

Second session (7 minutes?): Things were going pretty well, and I had just completed what I could tell was a really good lap. I was about halfway through my next lap, when I turned in a little to early with too much speed on a corner and the rear end started to come around. Counter steered, and ended up going off the inside of the corner (turned in early remember) sliding sideways. Unfortunately there happens to be a grate covering a drainage hole right there, and my passenger front caught it going sideways. Broke the wheel, bent the knuckle, upper and lower control arm (and pushed the camber full positive). At this point the shop I use should have it all back together by the end of the week to the tune of $1300 (insurance paid $1900, but I still have to get a new wheel). Anyway, the good point of the second session is that the previous lap to my off was the best yet at 1:33.2! That is faster than my modded 92 Vette, and only 4 seconds a lap down from what my 01 Z06 did. Plus, I still think with more track time, I can probably squeeze another second or two out of her as she sits right now. Add a 35mm front sway bar and maybe some gears to that and it could be really interesting.

Here's a list of comparison times:
01 Z06: 1:29 350RWHP, 315 555Rs on rear (equivalent of 3.73 gears due to Z06 tranny)

97 LT4 Firehawk: 1:33.2 311RWHP, 275 555R IIs, Koni DA fronts, LS1 front brakes w/ Carbotech XPs

92 LT1 Vette: 1:34 280RWHP, 275 555R IIs front/315 555Rs rear, VetteBrakes front spring, adj front shocks, PFC Z pads

95 Formula: 1:35 280RWHP, 265 Kumho Victoracers, rod end LCAs & adj panhard, 4.10s, PFC Z pads

The fastest stock (including stock tires) C5s at a Corvette event at same track: 1:34-1:35

In conclusion, I'm really impressed with the car. The off was my fault, and the damage is one of those things that 99 times out of 100 would never happen. Like I said above, the car still rolls too much for my taste so I'll definitely be getting Sam's new 35mm front bar. Also, it really seems like the 3.42s just aren't enough gear for the LT4 (6500 redline w/ peak HP at 5800). I was basically driving the whole track in 3rd gear with 1 shift down to 2nd, and only two shifts up to 4th. I think 3.73s or 4.10s would really help put the car into it's powerband much more of the time. Finally, the rear axle hop under braking is really annoying. It's only happening on the front straight (fastest point of track), and it is definitely a lot worse when I "stab" the brakes instead than when I tried to progressively get on them. However, it's still there even when I was trying to be progressive about applying them. I'm sure I'll learn to minimize this, but it's definitely an big irritation.

Any other thoughts, opinions or info would be appreciated.

Ken S

Nice writeup..

Just curious.. your normal car insurance covered you on a timed event/racetrack? or did u say it was like an driving class? or hey simply just covered you without asking questions?

LT4Firehawk

I didn't really say it was a track event, although they are supposed to cover non-competitive events (driver's education), I just said I'd hit something and then limped it into the shop. I was fortunate in that I could pull the camber back out some at the track and had some spare wheels with me to limp it home. When I filed the claim they asked what street it was on, and I said I didn't remember (which is true since I don't remember what street the track is on), but even though she said she needed the street name they never followed up and sent the check without the info. They even filed it under comprehensive instead of collision, which I thought was kind of wierd, but I'm not going to argue with them.

I'm sure if they'd known it was at the track they'd have given me a lot harder time about it, but I have checked the policy and it only excludes competitive events.

lateapex

To help reduce, maybe eliminate, your rear axle hop, you might try lower rate rear springs (to allow your shocks to better control them). Better yet, you could get adjustable shocks to match your fronts and increase the rebound setting until the oscillation is controlled, or you start making the car loose, whichever comes first.

A linear rate spring will also help in this regard. The lower rear spring rate may be a synergistic combination with the larger front anti-roll bar.

You also might elininate some of the compliant bushings in your rear suspension.

LT4Firehawk

Yeah, I was already thinking of doing the rear shocks. I left the rears on just to see how they'd do, but I really don't think SLP got the valving right on their Bilsteins for the Level II suspension. I'll probably put some Koni SAs on the rear, and I'll definitely be going through and doing all the sway bar bushings and endlinks soon.

lateapex

The anti-roll bar can actually be a part of the problem once the axle bounce has achieved a certain amplitude. As concerning the braking problem, I would not want the bar contributing MORE to your total spring rate if you aren’t going to have adequate shock damping to control it, so I would want compliant bar bushings. And, you can go only so far with the rear shock damping before the rear end gets skitterish. (as far as the car rolling too much, the stiffer anti-roll bar bushings would obviously help).

I was thinking more of the trailing arm, torque arm, and transmission mount bushings.

LT4Firehawk

The LT4 cars come with the 1LE tranny mount and stiffer bushings in the LCAs, panhard and lower front control arms. I really don't want to loose streetability, so I'm not sure I'd want to try rod-end LCAs and panhard. I had those on my 95, and while they did help, they also added a lot of noise. It looks like a lot of that's been corrected since then with better quality rod ends, but I'm still a little leary. I have been thinking about doing a torque arm, but while there's good feedback on them helping the brake hop, there's also people that have said it didn't make any difference.

I'd be willing to try a softer rear spring, the problem is going to be finding one that has the same drop as the SLPs. It's only about .5" lower than stock, and I really don't feel like messing with the fronts as I like the setup there. I guess I could get some stock Z28/Formula rear springs and do the old "garden hose around the top coil/remove the spacer" trick, but I'm not sure how close that'd come to matching. Of course that would at least get me a straight rate rear spring that matches the minimum rate of the SLP springs. Plus since it's so easy to do the rears I guess I might as well give it a try.

Hmm, just convinced myself to do it, didn't i?

5.0THIS

sorry to hear about the off-track excursion

Just think though, if you threw 40rwhp more, and some gears at that thing, it would probably overtake the ZO6... not bad for an f-body

cndctrdj

congratulations on the great times and nice write up