Project Z06: Making a Hole (In the Hood)

Update by J.G. Pasterjak to the Chevrolet Corvette Z06 project car
Sep 25, 2019

We’d previously added some aero elements to our C5 Corvette to move air around the body in a more favorable way, but until recently we’d neglected to address the way air moved through the body—specifically the engine bay. This neglect was driven home when we saw a photo from a recent Time Trial at Daytona International Speedway:

Yes, that’s the leading edge of the hood pooched up a solid inch or more at speed—the result of extremely high-pressure air being trapped under the hood.

We’d previously added some additional openings for engine cooling in the space formerly occupied by the front license plate. These vents directly fed the Ron Davis radiator with cool, outside air. But once it got under the hood, that air had nowhere to go.

Enter AJ Hartman Aero—yes, the same folks who made our wing and canards. AJ Hartman produces some lovely, light, carbon fiber vents for your hood that can be installed on nearly any flat or semi-flat surface.

Hood venting is important for a couple of reasons. From the perspective of cooling, remember that it’s not just about how much fresh air you get through the radiator, it’s also about getting that now hot air back out once the heat has been exchanged. Venting an area directly behind the radiator on a low-pressure area of the hood can facilitate a great deal of outflow and keep cooling efficiency at a maximum.

There are also aerodynamic benefits to venting a hood. Take another look at that photo of the hood lifting off the car. That’s a lot of high pressure on the underside of the car. High pressure under the car is also called lift. Lift is good for airplanes, but bad for race cars. So, venting the high pressure from under the car can reduce that lift and create a more beneficial aerodynamic setup.

We installed a total of three vents on a stock fiberglass C5 hood. No, we’re not going to cut up the carbon fiber commemorative hood. While the stock hood is 11 pounds heavier than the carbon hood, we removed 6 of those extra pounds by cutting the vent holes.

Cutting out all the vents is a similar operation. Start by taping off the outline of the vent where you’d like to place it, so you have something to write on. Then you can measure out and trace your actual cuts, leaving plenty of room for the flanges on the vents. We like to cut fiberglass using a cutoff wheel, but a jigsaw with a medium blade will also work fine. Same for steel and aluminum hoods. Actually, the jigsaw may be a better choice for the metal hoods, but pick the tool you’re most comfortable with, wear eye, ear and breathing protection and go slow, since you can’t un-cut any of those materials.

Once the holes are cut, we needed to do some trimming around the throttle body to accommodate the very deep universal “waterfall” style center vent. A vent that simply exited through the hood wouldn’t need additional fitting, but the waterfall-style vent actually creates additional low pressure and provides a more direct path for the air to flow through and out of the radiator. It also looks rad.

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View comments on the GRM forums
PowerKraut New Reader
9/25/19 6:49 p.m.

Are you not concerned that the ‘waterfall’ might flood your throttle body or other electrical components in the engine bay? 

pilotbraden UltraDork
9/25/19 8:05 p.m.

In reply to PowerKraut :

Perhaps this is the source of the name?

mazdeuce - Seth
mazdeuce - Seth Mod Squad
9/25/19 8:09 p.m.

I'll wait for Stafford1500 to see this, but I suspect that a small Gurney flap at the leading edge may help? 

malibuguy GRM+ Memberand Reader
9/25/19 8:11 p.m.

sweet no hood lift PS level check mod ;)

JG Pasterjak
JG Pasterjak Production/Art Director
9/25/19 8:15 p.m.
PowerKraut said:

Are you not concerned that the ‘waterfall’ might flood your throttle body or other electrical components in the engine bay? 

It should get no wetter than when I'm washing the motor. It's not like it sits out in the rain or anything. 

JG Pasterjak
JG Pasterjak Production/Art Director
9/25/19 8:16 p.m.
mazdeuce - Seth said:

I'll wait for Stafford1500 to see this, but I suspect that a small Gurney flap at the leading edge may help? 

So it's hard to see in those photos but the front flange is actually sculpted with a little built-in spoiler. Someone's on the same page as you already :)


StuntmanMike New Reader
9/26/19 7:35 a.m.

Looks good but too bad you had to trim the center vent. Did you consider the Track Spec vents? I think your carbon vents look better but at least the TS require less trimming. How about some full body shots with the black hood! Also not to nitpick but you should have used black head rivits

MadScientistMatt PowerDork
9/26/19 8:46 a.m.

Is it wrong that now I want to put a similar hood vent on my '98 Buick Regal?

mad_machine GRM+ Memberand MegaDork
9/26/19 10:55 a.m.

If you are going to paint the vents to match the hood and car, I would consider molding a cover over the throttlebody into the vent just to make it all look better

Scooter70 New Reader
9/27/19 8:15 a.m.

I came here just to make sure that you weren't going to cut up that Commemorative Edition carbon fiber hood.  wink


I have the Trackspec vents on my C6 hood.  Getting that dirty air out from under the hood definitely helps the front end float / lift at speed.

wearymicrobe UberDork
9/27/19 10:04 a.m.

Any thoughts on venting on the fenders above thw eheels to remove that lift as well?

JG Pasterjak
JG Pasterjak Production/Art Director
9/27/19 8:49 p.m.
wearymicrobe said:

Any thoughts on venting on the fenders above thw eheels to remove that lift as well?

Yeah. It's a good idea. I put the side slats close enough to the edge where we can build some chimneys from the wheel wells out the hood eventually. We'd have to move the coolant tank and windscreen washer tank, though.


RC45 New Reader
9/28/19 3:20 a.m.

I have been running a carbon fiber vented louvred waterfall hood on my 580rwhp LS7 powered C5Z06 since 2006.

Also have vents on the top of the front wheel wells and vents at the rear of the front wheel wells as well as full front splitter and under tray running to the front axle line combined with a 70" wide carbon rear wing.

Never had any issues with water in the engine bay, it is all water proof anyway and with the heat extractor vents and the air flow vents never suffered any front end lift at any speeds ever.

I cannot imagine how your folks car has been running these speeds for this long without proper front aero treatment.

Venting the C5 engine bay is like C5 Aero 101 :)


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