These holes are not your friends: filling in the C5 Corvette’s useless “grilles” while adding a tow hook | Project C5 Corvette Z06

J.G.
Update by J.G. Pasterjak to the Chevrolet Corvette Z06 project car
Apr 27, 2022

So, those two big holes to nowhere in the front bumper of a C5 Corvette? Time to deal with them.

Now, for some C5 owners, these holes don’t actually lead nowhere. Some aftermarket induction systems draw intake air from within the bumper, but in our case our Breathless Racing intake drew air from the same airstream that fed the radiator and oil cooler. As a result, that large area behind the bumper didn’t actually serve any purpose.

[Project Z06: Breathe Freely with Breathless]

Well, except that of an air brake.

When we did some basic testing with a magnehelic gauge–look for a deeper dive in the June 2022 issue of GRM–we found high-pressure air collecting inside the bumper that had no real place to escape except downward, thus creating lift. Blocking off these openings with some cardboard showed that the high-pressure bubble was eliminated.

Rather than leave the cardboard in place–sure, it looks fine, but we’d have to replace it after every rain shower–we went with a bolt-on solution from Trackspec Motorsports in the form of some pre-bent, powdercoated covers that cleanly fill these gaps and cover the fog lights as well. These covers considerably clean up both the appearance and the aerodynamics of the front of the C5, as well as blocking off that pressure trap inside the bumper.

Trackspec is at the forefront of the NASA Spec Corvette series, building all the parts necessary to turn a C5 into a competitive ride. We previously used some Trackspec vents on our Mustang project, so we were familiar with the fit, finish and quality of its bits.

Installing the panels is easy–they come with rivets, but we used screws so they’d be more easily removable should we need to take them off at any point. Simply line up the panels over the gaps and lights, and affix them with your chosen fastener.

Our only complication came on the passenger side, where we had our tow hook extending through the front bumper. Our tow hook had been hastily assembled from an old cable bike lock the night before an event. It wasn’t pretty, but it worked fine, and also allowed us to lock up the Corvette when we rode it to school.

Being flexible, however, and affixed back near the headlight mechanism, the cable did deflect quite a bit depending on the angle the car was being winched from.

As a result, cutting a hole in the Trackspec covers large enough to account for all this potential deflection would result in a fairly large opening. That, combined with the fact that the tow hook itself was a little, shall we say, rough, gave us a good excuse to build a new, more appropriate tow hook.

The C5 has a large bumper beam easily accessible right behind those openings, so that made for the easiest mounting location. We would need to bring the mount in a downward direction from the bottom of that beam–a straight line forward from the beam would pass through the bumper cover itself–so we needed to fab up something with some offset.

Bending steel of the proper thickness to support the force of pulling the car wasn’t really within our abilities, but we found a nice piece of box-section rectangular tubing in our scrap pile, and it would provide the necessary offset to clear the cover.

We would use the “top” surface to mount the hook to the bumper, then use the bottom surface to create the hook itself, using the side of the tubing to provide the offset necessary to clear the bumper cover.

We marked up our workpiece–mostly by holding it in place and referencing clearances right from the car–then got to work with the cutoff wheel removing everything that didn’t look like a tow hook.

After we had the piece roughly cut to shape, we smoothed out things with a hand grinder and bench sander. We left the sides a bit extended to increase strength, and made the hole by connecting two hole-sawed openings with a cutoff wheel. We then finished it off with some hand filing.

From there, it was a quick test fit followed by drilling some mounting holes in the bumper. We’d attach our hook to our bumper using a couple of grade 10.9 10mm bolts, each having a shear strength enough to resist nearly 12,000 pounds of force. That should be plenty to drag our C5 into a trailer, or out of a gravel trap. (Hopefully we’d never need to test the latter.)

Once we were happy with the fit, we prepped our hook in the media blast cabinet to remove any rust or scale while giving it a nice, even texture. We then powder coated the hook using our Eastwood powder coating system, which produces a hard, durable finish.

Powder coating at home is easier and more affordable than you might think. Check out our video on it here:


The biggest hassle is finding a place to store your dedicated powder coating oven, and remembering to not use it to heat chicken wings once you start using it to cure powder. We picked up a used oven for $60 on Craigslist and threw it on some casters so we could roll it out of the way when it wasn’t in use.

Our hook came out of the oven nicely finished, so it was bolted in place and the bumper cover reinstalled. We then did our best to transfer the outline of the hook to the face of the Trackspec cover, and cut a generous slot for the hook to pass through. We gave it some extra space to account for flex so it wouldn’t be in danger of wrinkling the Trackspec cover.

Finally, we used some neoprene to cover the gap around the hook, figuring that it will allow any deflection. We secured the neoprene cover with some spray adhesive, and it nicely finishes out the front end. All that’s left is to winch it into the trailer and head to the track.

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Comments
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Appleseed
Appleseed MegaDork
4/26/22 12:45 p.m.

Not very attractive to the eyes, is it?

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
4/26/22 12:57 p.m.

Yeah I was expecting an insert that would leave a more factory look...also black is an odd choice of color for a tow hook, don't many rulesets (that require cars to have tow hooks fitted) require tow hooks to be red or yellow?

Toebra
Toebra Dork
4/26/22 1:26 p.m.

Yeah, you need to paint those red or yellow

John Welsh
John Welsh Mod Squad
4/26/22 1:38 p.m.

That tow hook looks like its gonna be a real shin splitter!  A clean cut gash to the lower leg!  

Could this been better done with metal up to the cover and then finished with some soft webbing/seatbelt type material as the actual "hook" that sticks through to the outside?  A tow strap?

MotorsportsGordon
MotorsportsGordon Dork
4/26/22 1:51 p.m.

Here's a couple different set ups on c5rs



 

JG Pasterjak
JG Pasterjak Production/Art Director
4/26/22 2:26 p.m.
GameboyRMH said:

Yeah I was expecting an insert that would leave a more factory look...also black is an odd choice of color for a tow hook, don't many rulesets (that require cars to have tow hooks fitted) require tow hooks to be red or yellow?

Yeah, many road race organizations require brightly colored hooks, along with "TOW" and an arow poiinting at it. Most of the TT stuff I run just requires "a mounted tow hook" with no other specifications. If we ever go road racing with the car I promise to powdercoat it red :)

As for location, it's the easiest access to the strongest point with the most longitudinally aligned leverage of anyplace on the front of the car that didn't require major bumper surgery. I woul dhave loved to have stayed with something flexible, but after living with something flexible for a couple years it started to become more trouble than the ability to tuck it into the bumper was worth. Having a fixed hard point is far more convenient for the way our trailer winches are set up.

And it's well inside the limits of the splitter, so if you bonk your knee on it, you should have learned your lesson when you hit your ankle on the splitter.

John Welsh
John Welsh Mod Squad
4/26/22 3:07 p.m.

In reply to JG Pasterjak :

Ah, yes.  I now see that it wont stick out farther than the Dewalt work shelf.  And, in that picture I now see the old black "floppy" tow hook.  

Toebra
Toebra Dork
4/26/22 3:19 p.m.

How about a decal to hide that ugly insert, faux carbon fiber or something.

JG Pasterjak
JG Pasterjak Production/Art Director
4/26/22 3:44 p.m.
John Welsh said:

In reply to JG Pasterjak :

Ah, yes.  I now see that it wont stick out farther than the Dewalt work shelf.  And, in that picture I now see the old black "floppy" tow hook.  

Actually that was a prototype of a much nicer floppy hook that was also abandoned when I realized a rigid hook was going to be the only thing that truly did what I needed it to do. The original floppy hook was just sad.

grover
grover GRM+ Memberand Dork
4/26/22 6:53 p.m.

How badly do you think that hook affects aero? More or less than the covers? 

deaconblue
deaconblue New Reader
4/27/22 8:41 a.m.

So you closed off the nostrils due to the fact that the added air flow only adds to under hood pressure and lift (and presumably does not add to any cooling effect) - but you are using a vented hood to relieve the high under hood pressure.  Also you opened up the area behind the front license plate - what is located behind there that requires the added air flow?  Sorry, just seems confusing, but maybe this is all for high speed oval racing.

Noddaz
Noddaz GRM+ Memberand UberDork
4/27/22 9:53 a.m.
Appleseed said:

Not very attractive to the eyes, is it?

Function over form.   At least there is plenty of room on the right side for the word tow and an arrow.

But I agree.

JG Pasterjak
JG Pasterjak Production/Art Director
4/27/22 10:18 a.m.
grover said:

How badly do you think that hook affects aero? More or less than the covers? 

It has like 3/16 inch of frontal area, so not much.

JG Pasterjak
JG Pasterjak Production/Art Director
4/27/22 10:20 a.m.
deaconblue said:

So you closed off the nostrils due to the fact that the added air flow only adds to under hood pressure and lift (and presumably does not add to any cooling effect) - but you are using a vented hood to relieve the high under hood pressure.  Also you opened up the area behind the front license plate - what is located behind there that requires the added air flow?  Sorry, just seems confusing, but maybe this is all for high speed oval racing.

Those nostrils don't connect to the area under the hood. They open to the inside of the bumper, then vent downward past the front subframe toward the ground. 

The license plate cover is vented directly through the radiator shroud dumping more air onto the rad and oil cooler. It's separate from those nostrils as well.

deaconblue
deaconblue New Reader
4/27/22 12:12 p.m.

I thought this was a really nice job of make those nostrils functional for directing air to the radiator.

https://www.corvetteforum.com/forums/c5-general/3629950-made-the-foglight-vent-inlet-hole-duct-functional.html#post1589316524

Toebra
Toebra Dork
4/28/22 9:36 p.m.

yes deacon, that is much better

deaconblue
deaconblue New Reader
4/29/22 1:38 p.m.
Toebra said:

yes deacon, that is much better

That's what I thought too.  I am not that talented at fabrication, but I bet a simple 3"x 8" inside dimension  (I have fog lamps in mine, without them you would need something wider) brake duct inlet, trimmed to fit and mounted behind the nostrils on each side along with a pair of 3" inlet flanges in the plastic radiator shroud, connected by 3 " black neoprene brake hose would do the trick as well.  Might want to also have a screen insert in the nostril to keep out large debris.  

I have to pull the bumper cover off my C5 to install the Improved Racing oil cooler kit, so I may order up these part now so as to have handy and try it out.

Brake Duct Offset Single Hole ALL42141 Allstar Performance

3" Duct Connector Flange Inlet Fitting,Plastic Straight Pipe Flange for  Heating Cooling Ventilation System ABS Duct Connector (3 inch/75 mm) - -  Amazon.com

Neoprene Flex - 2 ply HD” Heavy-Duty Hose – Ducting.com

ian sane
ian sane Dork
4/29/22 2:06 p.m.
deaconblue said:

I thought this was a really nice job of make those nostrils functional for directing air to the radiator.

https://www.corvetteforum.com/forums/c5-general/3629950-made-the-foglight-vent-inlet-hole-duct-functional.html#post1589316524

Holy hell that car looks beautiful.

z06king
z06king New Reader
6/26/22 9:55 p.m.

In reply to JG Pasterjak :

did you vent the front wheel arches to let air go from the front tires out the lateral hood vents?

JG Pasterjak
JG Pasterjak Production/Art Director
6/27/22 9:46 a.m.
z06king said:

In reply to JG Pasterjak :

did you vent the front wheel arches to let air go from the front tires out the lateral hood vents?

No but that job has been on my "to-do" white board for months. It's like I'm emotionally blocked from continuing because I can't decide between a bunch of round holes or one big rectangular one.

dculberson
dculberson MegaDork
6/27/22 10:45 a.m.

Don't confuse pretty with functional. Remember that this is first and foremost a race car and JG's been mopping it up with this car so any criticisms should be followed up with lap times.

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