TopSpeedNeed

This is kind of a weird question, I just got back from Roebling Rd, this past weekend, I have a 04 Z06 commemorative edition, Z16 with the Carbon fiber hood, I had a friend of mine take some pictures of me coming down the fron straight, historically, I had heard the hood rumbling at the end of the front straight, but in the pictures the front of the hood, along the front bumper, and right behind the front head lights, the front leading edge of the hood is literally lifted up about an inch behind the headlights, and about 1/2 an inch behind the front bumper, the only thing holding the hood on is the two hinges in the front and the obviously the locks in the back of the hood, the hood literally looks like its about to come off on the front of the car, I've done a bunch of Drivers eds, and am going to Daytona in Dec. with the audi club, I am wondering if the air is getting under the hood from the gaps around the headlights and front bumper, or coming from underneath, the car has never been wrecked, so the body lines are all good, I dont know if I should duck tape the gaps up front, or what, I have some pictures but I dont know how to attach the photos..had this happened or happening to anyone else, I have a picture of a friends Z06 and his hood is fine, but his is a 03 with a regular hood...

wallyman424

the hoods will move around a little, but definitely NOT 1/2 an inch in the front of the hood. Check the fitment of the front hinges, make sure everything is tight.

if you email the picture to me i can host it for you: wah(at)jhu.edu

Jeffvette

Apparently some do it more than others.

Picture was taken by me as the car went by at 158 for a mile shootout event.



Car at rest.

wallyman424

christ, that thing is floppin around. I guess the CF hoods arent heavy enough...

varkwso

I have had the hood on both my '02 ZO6 and '99 FRC lift up ~140mph and really start to vibrate to the fastest I have been (~168). Cannot see the front edge - but the back and sides really are pushed up.

I have put a vented CF hood on the FRC but it has not been track tested at high speed yet...

petefias

It appears that car is lowered in the back, but not the front. It probably catches a lot more air this way and no downforce on the hood.

GM engineered the car to be a little lower on the front so this does not happen.

TopSpeedNeed

Hahhh, thats it, thats exactly it, so what do you do to fix that, since we took a sequence of pics done the front straight, at the beginning, I estimate I was doing around 110 to 129ish and as the car got closer you could see the hood coming up higher, I estimate I'm doing 150ish at the end of the straight,..I am going to Daytona in December, and I anticipate 160 +, any ideas on what to do ????

gonzalezfj

Your C5 should have 1/4 to 1/2 inch rake (rear higher than front). These measurements are made at the front and rear of the flat portion of the chassis under the car on a flat surface.

Lowering the rear more than the front is a no-no for high speed driving.

TopSpeedNeed

Just sent you the picture, thanks for the help

UstaB-GS549

If yours is like the one in the picture, it looks like you might trapping a lot of air under the front end with nose high attitude. Maybe you should check to see that the front of the frame is a little lower than the rear to help out.

I noticed my hood fluttering at the back around 140+ last year at Road America. 2002 Z06. Could be the C.F. is not as rigid as the stock heavy hood?

63Corvette

"They all do that"

wallyman424

that just doesnt look right

ErnieN85

yes a lot of lift, check the tire to wheelhouse clearance!
Check the rake and maybe open the fender vents

davidfarmer

common problem. Lower the front adjustment bumpers on the hood if you can, to get it below the bumper/headlight line.

if not, you need to tape the leading edge and/or install hood pins.

AU N EGL

Frank is correct here.

I had my normal hood bounce up and down and all over the place at speeds above 145. Then I changed the rake of the car to 3/8" which helpd. The hood still dances somewhat, but not that much

TedDBere

Here's an old thread discussing this issue:

http://forums.corvetteforum.com/show...t=hood+lifting

Measure your rake and get back to us.

Good luck.

73-84 IMSA Widebody

SCCA race at MidOhio 2007.
That hurt, lost front hood pins.....broken hood, cracked windshield, bad weekend.

Bill Dearborn

The problem isn't just air build up under the hood. It is a compound effect of the air coming in through the grille and the air deflected over the front fascia which continues upward in an arc and comes back down at the base of the windshield creating a low pressure area over most of the hood and quite a high pressure area at base of the windshield. The high pressure area is why the old L88 C3 cars had their hood scoops facing to the rear and why current NASCAR stock cars get their carb air from the base of the windshield. This is also why the air intakes for the HVAC system are at the base of the windshield.

Increasing the rear rake can mimimally reduce the lift and bleeding air from under the hood can probably reduce it more but there may be side effects that I don't know about. Since this is a problem for all cars I would suspect that bleeding air from under the hood has detriments as I don't know of many race cars that bleed the air from under the hood.

Bill

TopSpeedNeed

What do you think about duck taping the front air ducts/grill, and maybe duck taping the leading edges of the hood...