Rear lid lift

[Wess-RA]

I have had the rear lid lift and flap around a couple of times now. I have a total of 7 Southco fasteners holding the lid in place. I pay attention to make sure they are attached correctly but still screwed up twice. The lifting action is clearly caused by a high pressure buildup from under the car. I have seen a car which had several approx. 2" dia. sized holes drilled along the back panel of the car, to relieve the pressure. The same force causing this lid lift must contribute to some unknown amount of rear end car lift. Have any of you made mods to counteract this effect?

[panozracing]

Originally Posted by Wess-RA

I have had the rear lid lift and flap around a couple of times now. I have a total of 7 Southco fasteners holding the lid in place. I pay attention to make sure they are attached correctly but still screwed up twice. The lifting action is clearly caused by a high pressure buildup from under the car. I have seen a car which had several approx. 2" dia. sized holes drilled along the back panel of the car, to relieve the pressure. The same force causing this lid lift must contribute to some unknown amount of rear end car lift. Have any of you made mods to counteract this effect?

I had this problem only when we had the ride height set too high and there was too much space between the top of the tire and the body. We also have this problem when we run a smaller tire after trimming the bodywork to accept the 705 size tires we run (too much space above the tires).

Lower your car and do a set down. The front should be about 3" and the rear is 3.5" I think.

[Wess-RA]

I'm running the stock 17" BBS's, still with street tires. (I'll be changing to track tires in the new year) Would those heights still apply with the 17"ers? Where on the frame are you taking your measurements?

[panozracing]

Originally Posted by Wess-RA

I'm running the stock 17" BBS's, still with street tires. (I'll be changing to track tires in the new year) Would those heights still apply with the 17"ers? Where on the frame are you taking your measurements?

I am pretty sure those measurements apply to the 17's as well. The measurements are taken directly under the center of the wheels at the closest frame location. You also need scales to corner balance. I dont do it myself I take it to a race shop. Alot of this is covered in the GTS Users manual but experience and track data helps the most.

[eric1h]

We are also sealing the bottom of the underside of the car(flat bottom) with the exception of a few vents for the transmission tunnel the car should be pretty well sealed off undeneath. Just the addition of an undertray that extends just past the oil pan made a WORLD of difference.

But panozracer is right, these cars were designed to sit low to not allow a lot of air underneath. if not there is so much empty space underneath they turn into a giant parachute!

[NZGTRA17]

Originally Posted by Wess-RA

I have had the rear lid lift and flap around a couple of times now. Have any of you made mods to counteract this effect?

Yes, I had the same thing happen the first time that I tracked my car (car is on 17" wheels and was at correct factory ride height).

To fix the problem I have relieved the pressure in the fuel cell area by putting a series of holes across the lower edge of the back of the car (27 x 45mm holes). I have also replaced the 2 screw type fasteners on the leading edge of the boot lid with 5 dzus fasteners. I think that 3 would probably suffice however I wanted a fastener out on each corner as the lid tends to have a gap on the corner that I wanted to close up.

I have tracked the car since these mods were done at speeds of up to approx 145mph and had absolutely no issues.

[panozracing]

Originally Posted by NZGTRA17

Yes, I had the same thing happen the first time that I tracked my car (car is on 17" wheels and was at correct factory ride height).

To fix the problem I have relieved the pressure in the fuel cell area by putting a series of holes across the lower edge of the back of the car (27 x 45mm holes). I have also replaced the 2 screw type fasteners on the leading edge of the boot lid with 5 dzus fasteners. I think that 3 would probably suffice however I wanted a fastener out on each corner as the lid tends to have a gap on the corner that I wanted to close up.

I have tracked the car since these mods were done at speeds of up to approx 145mph and had absolutely no issues.

I have had my car at Daytona @ 186 MPH with no body modifications (before wing and splitter mods) and no issues (except the lexan windshield caving in). I think everyones car is too high. I have the car lower then factory. Dont forget the nose and crush box can be adjusted which will affect the front clearance. Something else has to be causing this. Dont forget I have 2 GTS and neither has had these issues. We run Sebring more times than I can count and we exceed 155MPH there without issues. IMHO its body trimming and ride height. relieving the pressure with holes could be fixing the problem but does not address the cause.

[NZGTRA17]

Originally Posted by panozracing

IMHO its body trimming and ride height. relieving the pressure with holes could be fixing the problem but does not address the cause.

Would be nice to be able to lower the car some more Brian but unfortunately this does not seem practicle for my endurance application. Even at the factory ride height with a full tank and 100kg driver the car will scrape the side panels in places on high speed sweepers.

I will try the suggested lower ride heights for sprint racing but would not do so for endurance. Any off track excursion with the lower ride height would result in losing the splitter and possibly the nose cone on my local circuit = out of contention for serious race places. At the moment I can get away without damage (so far that is) at the 3" front & 3.5" rear height setting.

I agree though that for applications/circuits where you can get away with this I would do so. One thing to watch out for though for those that do try lower rear ride height settings. That is to ensure that you do not end up with any binding in your watts linkage heim joints as this could have a nasty affect on handling................. Just a matter of checking that they are free to move over the new range of movement prior to tracking.

I found this out the hard way when I tracked my car for the first time and the handling was a little off as it felt like it had some 'rear end steer'. Turned out to be improperly adjusted rear joints that were binding. Easily fixed though.

[Cobra4B]

My car has 3 southco fasteners accross the front edge (closest to the rear lexan) and 2 rubber t-straps like you'd find on a Jeep hood. I've had zero issues with it. Another interesting thing is that allthough my car is plastic, it came w/ a fiberglass trunklid.

[Wess-RA]

The Dzus change out seems to be good for assurance in my "all Plastic car". I would definitely like to address to rear lift issue. I'll be taking the car in for corner weighting/aligning to a guy who is very knowledgeable about the Panoz suspension; including lift issues. Lots for me to change around-spring swap, new tires, ride height, corner weighting, alignment. I had nothing better to do anyway!
Eric-what are you sealing the bottom with- behind the under-tray?

[eric1h]

Originally Posted by Wess-RA

The Dzus change out seems to be good for assurance in my "all Plastic car". I would definitely like to address to rear lift issue. I'll be taking the car in for corner weighting/aligning to a guy who is very knowledgeable about the Panoz suspension; including lift issues. Lots for me to change around-spring swap, new tires, ride height, corner weighting, alignment. I had nothing better to do anyway!
Eric-what are you sealing the bottom with- behind the under-tray?

Alumalite panels, light, strong and relatively cheap

[boothkc]

Agree with Brian on the ride height. Lost a rear pannel on the GTRA-school car, but never on the GTS which gets to 150mph. So should not be an issue and no need to cut holes in the back.

Had issues with the hood/bonnet lifting like a parachute at the end of the straights and this was fixed with the carb induction kit for the GTS. It give more support and may "suck the hood" a bit. Not an option for FI GTRAs.

Kevin