Tonycpa

Guys,

I have a 2004 coupe with magnetic selective ride control.

I have a budget of approx. $4,000 to spend on upgrading my suspension (including installation since I don't work on my own cars).

Please advise me what I should get based on the following requirements...

1) Must have the ability to slam (lower) my Vette as low as possible and not rub my Toyo Proxes R888 tires 275/35ZR/18 (18 X 9.5 wheels), and 305/35ZR/18 (18 X 10.5 wheels).

2) 90% of spirited driving will not be in a competition at a track.

3) Extremely important for suspension to be able to handle 600 RWHP (with potential to upgrade to 750 RWHP).

4) 90% of spirited driving will be on straight roads but I need for the car to be able to handle lane changes at high speeds, and also be stable for top speed runs.

5) Approx. once a month the car will be raced 1/4 mile from a dig. So, having the ability to adjust the suspension to optimize quarter mile times is extremely important to me. Don't want to see wheels come off the ground and want to keep the car as straight as possible (obviously).

6) Interested in doing autocross (and possibly non-competitive road racing) about once a month. I am not interested in drifting at this stage...just entry level.

The Pfadt Aggressor II package caught my eye. Please provide your thoughts on whether this package will meet my goals stated above, or if you know of a different suspension system that you feel is better suited for my particular needs.
http://www.pfadtracing.com/catalog/i...hp/cPath/23_33

Thanks.

Tonycpa

Also, need something compatible with my traction control and active handling systems.

GrantB

Be advised that this goal is at odds with some of the others. Lowering a RWD car reduces longitudinal weight transfer, reducing the grip of the rear tires under acceleration. It does of course reduce other forms of weight transfer which is beneficial to handling, but if your car has little traction or a lot of power (or both), it may not even improve lap times. When modeling my C5 in Bosch LapSim, I've seen the car actually run slower laps with a lower ride height.

Of course the biggest problem encountered with an excessively lowered car is hitting the bump-stops. This is Very Bad, especially if it happens in the rear (= snap oversteer). If you really want to slam the car, make sure you get a coilover package with enough shock travel. Fortunately, C5/6 suspension doesn't have nearly as bad of geometry and camber curve issues as other cars do when lowered significantly (i.e., MacStruts suck).

Bushings can help a lot, especially in a compromised car that doesn't run full-race alignment settings (i.e., the car can handle well with less camber). However, install will be expensive and they may have other complications (noise). As I mentioned in this thread, I'd highly recommend pfadt's bushings over VB&P's if you decide to go that route.

I'd also recommend Pfadt bars. Even if you aren't experienced enough to know how to adjust them at first, you probably will be eventually. Plus you can start out using them to dial in some more understeer for safety. If you're going to do an install and alignment, you almost might want to go ahead and corner-weigh the car. I'm not sure what people charge for this (I have my own scales), but it would be cheaper to do it all at once (since you have to re-align after corner balancing).

If you're really going to track the car with 600 to 750 whp, suspension is only one of many things to worry about. Keeping the brakes, coolant and oil cool will probably take some work. You'll need good brake ducts (be advised these often don't fit with pfadt bars very well), race pads and a beefy oil cooler at the least.

Solofast

GrantB is right, what you are doing at the drags is at odds with good performance on the track.

Don't even think about slamming the car since you will have a pig at the drags, and if it is too low it won't work at the track either since the geometry goes into the toilet. Same thing with alignment. If you set the car with a serious road racing alignment, (higher amounts of negative camber at both ends and toe out in the front) you are going to have high speed stability issues and the car won't get off the line well at all.

Probably the best compromise would be to put the C5 Z06 parts under the car. The springs, sway bars and shocks are all a matched package that works great with the car lowered a reasonable amount (like an inch or so), and if you keep the rake correct, the car will work reasonably well at both the strip and at high speed. It isn't excessively stiff, and if 90% of your driving is on the street, you really don't need to waste the money on a set of coilovers. For what you are doing it isn't necessary or desireable.

What you need is a moderate lowering of the C5Z parts, coupled with the right tires for what you are doing. When you go to the drags you are going to absolutely need drag radials to cope with the power and try to make up for the lowering effect, and on the track (autocross or track day) you need serious track tires.

Set in a proper high performance alignment (like 1.5 deg negative camber front, and 1.25 degrees rear with about an eighth of an inch of toe in in the back) and corner weight and lower the car about an inch from stock keeping the rake correct. Front toe would be the only thing to change when you go autocrossing or road racing, and you can do that in about two minutes when you change from your street tires to your road racing tires. Mark your tie rods at zero toe and crank in 1/2 turn of toe in for the street and high speed work, and toe it out 1/2 turn from zero (one full turn per side from your street/high speed setting) for autocross and track days.

Get a set of C5 Z06 wheels for your track tires (light to start with and best bang for the buck and can be had for less than $600 for the set) and add an extra pair of wheels for the drag radials and you are good to go. You can do it all for something a good bit less than your budget, figuring about $1,000 dollars for wheels, $1500 for tires, and not a lot for the C5Z parts and installation, which can be done at the same time you do the corner weighting and alignment at a decent shop.

Spend the money on extra wheels and tires that will give you the hook you need at each track and don't get think about the sexy parts, the tires are what do the work here....

Tonycpa

Thanks guys.

I make 600 to the wheels now. So, I should focus on what I have now because I may never increase to 750RWHP.

I run Toyo Proxes R888s on the street and I would hope to be using this same tire if I ever decide to try an autocross or road racing day. I have never tried yet but it is something I may do this Summer. I have 275/35ZR/18 and 305/35ZR/18 on C5 Z06 wheels.

If I ever decide to see what I can do in the 1/4 mile, I would be running Mickey Thompson ET Streets Drag Radials.

Since I know I want the car slammed (for looks), you are recommending that I get the C5Z06 leaf springs, shocks, and sway bars? Right now my car is slammed on stock bolts...keep it that way when converting to the C5Z06 suspension?

Happy Easter.

0Robert@SPEEDSOUTH

GrantB's first sentence sums it up pretty well. Anytime you deviate away from the OEM's original design you begin a new direction with the car. A car setup for autocross is going to be entirely different than one that is used for drag racing.

The entire post would be pretty simple to do with one car until this one portion. “…the ability to adjust the suspension to optimize quarter mile times is extremely important to me.” You’re at a crossroads at this point, you need to decide what is more important to you, time slips at the dragstrip, or the car’s performance on backroads and autocrosses. I would have to think that because so many of your wants revolve around uses other than quick ETs at the drag strip, that you should focus on the cars suspension with an eye towards better handling. Everything that you mentioned so far. except the line I copied above, could be handled by Pfadt’s standard coilover. The adjustment that he has with his standard unit will allow you to adjust that setup when you go to the dragstrip, but in no way, will it perform as well as the kit he has listed as the drag package. So because the standard coilover can be adjusted to do “ok” at a dragstrip, and the dragstrip setup could not be adjusted well to work on an autocross course, I would suggest, based on your wants for the car, to buy the standard coilover kit and adjust it as nec. around your different uses for the car. Pfadt’s coilvers have 16 adjustments so at least for a little while I would keep a notepad in the car when you’re using it at the drag strip and autocross, and take some adjustment notes on what worked best for that particular use.

Also, if the offsets of your wheels are the same or very close to those of the stock C5Z wheels you shouldn’t have any clearance issues even when lowered.

I hope this helps.

Tonycpa

Yes. Thanks.

Datawiz

Holy crap! You do NOT need all that power to autocross.

Sounds like it's going to be a wicked car though!