[cvrob]

Background:

A customer of mine has this project car which is a 01 C5 Z06/FRC.

The issue at hand is front end lift at high speed.

Ive seen this and similar issues before and it’s almost annoying that most always default to downforce which in my opinion is something you do at the end and not the goto/root cause.

99 out of 100 times in my experiences the problem is usually solved in the suspension.

This one I believe is the 100/exception.

The body is stock, the trans is stock and the engine is mostly stock. I did install an lighter, underdriven crank pulley for him to solve a serpentine squeal problem. I could watch the stock pulley walk off the crank and bounce back when it hit the sway bar! Lol

rims and tires are stock

Brakes are stock but Suspension is not stock. Has a full coil over kit with adjustable shocks and some of the most massive sway bars I’ve ever seen.

He said it has a 38mm front sway bar from gmpp and a 31mm rear sway bar off of a C6 ZR1.

All the rubber bushings have been replaced with poly. I’ll give props for that bc you’d be surprised how much trouble a $12 worn rubber biscuit can cause.

I originally thought it was a dampening issue but after 100 adjustments I do not believe it is so, I’m not 100% certain unless I mount a video camera in the front wheel well but I’d say I’m as certain as I can be.


The Present:

after some reading I have a short list of suspects.

first this was taken care of by the customer but the car is already quite low and has a good amount of front rake.

appears to be lowered 0.5 inches in the rear and 2 inches in the front.

other suggestions include chin spoiler and extraction hoods.

I see 2 more clandestine issues that on most cars really do not matter but from what I have been reading engine bay air pressure is a real problem on the c5.

The first issue I see is the screens have been removed from the front fascia; I believe this is a secondary contributor.

The second issue I see is the air dam. It looks to be a 3 piece design but the 2 end pieces are missing.


The Questions:

replacing the air dam or its proper name which is really important for the C5 air deflector is a no brainer.

Next is not so cut and dry for me but these screens….or more importantly the openings in the fascia.

do they serve a purpose such as ventilation for the engine bay or simply aesthetics?

meaning I can either try to utilize the openings for engine air intake or perhaps reinstall the screens and put a block off plate behind the screens depending on how the guy wants to go about it.

Next the fender vents are they functional or no? The drivers side seems open but the passenger side looks obstructed.

from the looks of them I would say at best they may serve as low pressure heat extractors for the engine bay.

Based off the info I have absorbed so far and the looks of the car I am thinking the best way to go about this to the customer’s dismay is to completely remove the front fascia and really focus on the radiator area in regards to both deflecting, slowing down and redirecting as much air as I can with the use of baffles, ducting, isolators and windage screens etc..while retaining full functionality.

other than that if the fender vents are functional then perhaps increase their efficiency by relocating the battery.

if they are not functional then perhaps relocating the battery and use them for ducting outlets for targeted airflow or inlets for engine air intake.

lastly, air extractor hoods. I think I seen where the ACP hood was recommended.

any other recommendations to consider?

Sorry for the long read and thanks in advance.

thoughts?

 

[Norm 1]

Welcome. Sorry can't help but there are some folks here that will, good luck.

 

[bodysurfin child]

you might investigate into some detailed info about the side strakes, an unfortunate looking option that I have read are useful to hold the car down once aero effects kick in.

I have no detailed information , I was searching the web just trying to understand why the side strakes were on my car that were messing up the looks, and that is what I found. I didn't pursue the issue further because it will be a rare day I am over 100mph. I never much cared for the side strake looks, but I can live with the things now that I know they have an actual function.

The missing rubber air deflectors on each side of the center air intake just allow a better front airflow around the front tires when aero is a consideration. other than that effect of pushing the air flow out to the sides so it doesn't get upset by the rotating tires , I would consider them neutral as to lift

I would suspect that the changes done to the front end should be returned to stock as the first step to solving the problem, since you didn't indicate they were opened for a reason . Any openings in the front without reason are going to screw things up from the original aero thinking. And even then the opening would be a trade off, is the increased drag worth the need of an opening. while they might possibly be benign in effect, they hardly seem the best starting point to solve this problem, since the effects are unknown from this modification., and stock has a known result

I think you might be working with some bad information, I have never , before this post, heard of "engine bay air pressure " being of any concern to anyone. I really don't see any reason that would effect anything inside the engine compartment, unless the hood blows off.

High rise hoods are only for modified engines that need them and are not to my knowledge designed for any aero effects, so unless you know of a high rise hood that has actual aerodynamically engineered qualities, it would just be magical thinking as to a different hood effecting a solution.

relocating the battery as an aero solution is bewildering . As is rebuilding the front end with your own aero ideas. unless you can out engineer a professional crew of engineers with a big testing budget, I wouldn't bother.

These cars spent time in wind tunnels with an engineering team and computers, if you can out engineer the original design team, have at it, it is not just some "that looks good"intuitive final aero design, it was a careful working of aero considerations and testing into the design.

And redesigning the radiator position is another example of trying to fix something before the problem is identified. Any change in the engine air flow is going to be problematic to the designed ignition event. This is a system engineered to squeeze the the last amount of available energy out of the fuel , with supercomputer time involved. Any change from stock will decrease power, just the simple act of changing the flex section of the air intake to smooth, although intuitively it looks faster, actually changes the efficiency of the sensor readings, as the air is no longer tumbled as designed for a better sample, but is now smoothed out and faster, so sampling of the air conditions is decreased . The fact that such connectors are sold as "power tubes"or some other name that implies better performance just confuses the issue.

The C4 is aerodynamically faster in a straight line, the C5 aero was improved to also consider the air flow across the car at angles, to improve cornering, where the aero on the C4 was only considered with the car going straight ahead. Just to give some idea of the detail of the aero considerations worked into the design.

Good luck is about all I can offer towards a solution, but hope another perspective might help.

 

[c5d]

A good start is to know exactly what the owner is looking for when the car is dialed in. Bonneville isn't Watkin's Glenn.

What comes to mind without much consideration is the lowering effects and massive sway bars, emphasis on "BARS" as up front. Excluding the modified front end openings, the rest of "issues" could be more just chasing your tail.

If you could post what this build hopes to accomplish across the board, I'll try to be more specific.

C'ya back here.. gotta run out for a bit.

 

[c5d]

At inception (‘97) the Corvette had the lowest CD (.29) of any No. American car produced and any sports car in the world.

Aerodynamic Test and Development of the Corvette C5 for Showroom Stock Racing 2002-01-3333

This paper documents a 10 hour wind tunnel test on a Corvette C5 prepared for Sports Car Club of America (S.C.C.A.) World Challenge racing at the Canadian National Research Center in Ottawa, Canada. Areas of testing included front fascia and undertray, rear air discharge, rear wing configuration and angle, B-pillar configuration, and ride height. In total twenty-six separate configurations were evaluated for front and rear lift, total drag, and lift/drag (L/D) with ratios provided for each test configuration. The cumulative effects of the aerodynamic changes evaluated in this program, calculated at 192 KPH (120 MPH), increased front down force by 318 N (72 Lb.), and rear down force by 770 N (173 Lb.). Lift/drag ratio was improved from -0.597 to -1.016. These changes increased total drag by 381 N (86 Lb.). Further testing lowering ride height 2.5cm rear and 5.0cm front reduced drag by 326 N (73 tb.) and resulted in a L/D Ratio of -1.247. Although data specific to the C5, the general principles may be applied to any production-based race car. These modifications should be validated on the racetrack prior to competing to ensure the handling balance can be optimized for the driver and car combination.

So for SCCA purposes:

• Install front splitter & rear spoiler (1” to 2” maximum height).
• Lowering the front 1 or 2 degree rake (create more downward force).
• Open front wheel ducts, vent turbulent air created by front tires (reduce drag/lift).
• Install a vented extractor hood, (increases down force w/o drag penalty & improved engine cooling).
• Block off (full or partial) front/nose grill (that alone eliminated the positive lift according to the study).

And you may want to chuck that massive sway bar... JAT.

C'ya, Over and Out... ..unless you're doing Bonneville...

 

[bodysurfin child]

really enjoyed the contribution of an informed opinion, and learning facts that align with my interests are always fun. I don't know much about suspension, but your suggestion about the sway bar in relation to this problem gave me a lot of insight. plus the information certainly improved on my thought of returning the front to stock as a starting point.

Strangely enoughI am a certified CES alignment specialist, so one would think I would know a bit about suspension. Turns out I was at a trade show , had the time to attend a lecture, and maybe 40 minutes later , I was certified. The certificate was free, but I didn't need one, and I would have to pay to have the patch mailed.

 

[The Torch]

Like c5d asked. What is he looking for? Straight line or cornering or both. AND how fast is high speed. I have an '04Z. Mostly stock with a few power mods. Suspension is stock. Lowered about .5 but still looks stock height. I've had it to 160+. At 135-145 the front end seemed like it was lightening up but after that is seemed to squat back down

 

[c5d]

really enjoyed the contribution of an informed opinion, and learning facts that align with my interests are always fun. I don't know much about suspension, but your suggestion about the sway bar in relation to this problem gave me a lot of insight. plus the information certainly improved on my thought of returning the front to stock as a starting point.

Strangely enough I am a certified CES alignment specialist, so one would think I would know a bit about suspension. Turns out I was at a trade show , had the time to attend a lecture, and maybe 40 minutes later , I was certified. The certificate was free, but I didn't need one, and I would have to pay to have the patch mailed.

I don't do much tuning..

Dick G. sponsored the '70 ZR1, SCCA Auto Cross, 7 National wins. Dick slip fit my 'new '77 rear wheel bearings and straightened the suspension out. The first C4 in his shop was my factory fresh '84 Z51 (build Nov. '83). It took him two days of work to dial it in tight. For some reason it just wouldn't hold the tune the way Dick wanted it to.

Access to THEE BEST Vette suspension shop on the planet had its advantages.

Richard "Dick" (Goldie) Guldstrand,
1, Dec. 1927 - 2, Sept. 2015

C'ya sooner or later, "Mr. Corvette"..

 

[c5d]

Like c5d asked. What is he looking for? Straight line or cornering or both. AND how fast is high speed. I have an '04Z. Mostly stock with a few power mods. Suspension is stock. Lowered about .5 but still looks stock height. I've had it to 160+. At 135-145 the front end seemed like it was lightening up but after that is seemed to squat back down

Hand building (bare block to full rock) my '62, 327, .30 OB, F.I. heads with hand lapped valves (ask the oldZtimers how that goes), 10.5 TRW's forged pistons, moly rings, cross drilled crank, Duntov 30-30 hydraulic cam, Holley 1050cfm 3bbl, Muncie Rock Crusher, 4:11 posi, 4 Indy 10.50x 5.50 Goodyear Racing (changed from dry to wet after a rainy day 360, lucky the street was 4 lanes, wide, and no traffic) on America mags....

After a zero visibility fog (greyout), that had just lifted 20ft., and ZERO traffic on the 1-10 (L.A.), I couldn't resist. Buried the needle at 160mph and still had some left. The front end lift was close to floating before I backed off.

When I had the opportunity to flatten the '84 at 152, there was no appreciable change in suspension feel, zero lift. After a Formula Ford weekend race at Laguna Seca, I got back in the '84, driving home HWY 1/PCH, loading the curves, I couldn't tell any difference from the past 3 days.

C'ya in the twistees..

 

[bodysurfin child]

really enjoyed the contribution of an informed opinion, and learning facts that align with my interests are always fun. I don't know much about suspension, but your suggestion about the sway bar in relation to this problem gave me a lot of insight. plus the information certainly improved on my thought of returning the front to stock as a starting point.

Strangely enoughI am a certified CES alignment specialist, so one would think I would know a bit about suspension. Turns out I was at a trade show , had the time to attend a lecture, and maybe 40 minutes later , I was certified. The certificate was free, but I didn't need one, and I would have to pay to have the patch mailed.

I noticed I quoted the incorrect initials when recounting my trade show certificate. I guess it shows I never paid much attention to that stuff.