Remove Inner Fenders for Autocross Car?

[sandiego74]

I’ll be corner-weighing the Camaro soon, and plan to go full-on autocross car on a budget. It still has to be street-legal in order to drive to events, though. I’ve been wanting to remove the inner fenders for a while now, mostly to lose frontend weight and to clear bigger front tires. So, I know most everyone agrees they are integral for structural rigidity up front, but I do have the pro-G-braces that tie in the firewall, fenders, and subframe. Then there is the idea that the inner fenders keep a lot of air from getting trapped under the hood, and removing them creates a lot of lift at speed and puts a lot of stress on the hood (concerning since I have a fiberglass hood with pins in the front). Can I mitigate this with thin aluminum sheets under the front of the car? I also don’t care how dirty the engine bay gets; it’s never been a show car, and it won’t be driven in the rain.

So, is it okay to pull them, or would it be wiser to leave them in, and, if so, why?

 

[Lowend]

I don't have any data on this, but keeping the front-end rigid for the relatively low weight of the inner fenders seems worth it. The inner fenders will keep you from coating the engine compartment with whatever you run over, and probably keep some air out.
Money better spent on a strip of rubber between the front spoiler and the ground to keep air out from under the car.

 

[BonzoHansen]

I've seen trimmed fenders crack with no inners. And you'll probably need to if you want to run wider than 275s and a stock frame.

Worry more about tightening up the nut behind the wheel. They'd more time there.

 

[sandiego74]

I've seen trimmed fenders crack with no inners. And you'll probably need to if you want to run wider than 275s and a stock frame.

Worry more about tightening up the nut behind the wheel. They'd more time there.

Not to sound cocky, but I was one of the fastest in CAM before COVID and the loss of our local autocross stadium lot. I beat most of the veteran field who had a lot more money put into their cars, and have been approached by them asking what my secret is and where I learned to drive. I always tell them, “Grand Theft Auto.” I’m nowhere near professional, but I do pretty well. I would rather make the car lighter, and grip/balance better rather than throwing a ton of power at it right now, hence this predicament.

You’re right, though, as I am thinking about cutting the fenders in order to fit 305’s. Cracking isn’t something I had considered.

I also am planning to add ‘78-‘79 Z28 fender vents to my fenders. Would these make a difference with getting that air out from under the hood? Wouldn’t they work far better with the inner fenders removed, since they block the air path to them, anyway?

 

[Lowend]

You're thinking about this right with weight being a priority. In my experience running big wheels/tires on front, the sport where clearance issues come up is at the rear lower portion of the wheel well. Just above the ground.

If you are worried about weight, have you relocated your battery yet? Moving the 40lbs battery from in front of the front wheels to the right rear of the trunk (counter balance driver) is a massive difference in weight distribution on the car.

I have my doubts if fender vents really make a difference at auto-X speeds. I know quite a few auto-x guys who use Trackspec Hood louvers on their cars for cooling and to reduce underwood air-pressue. https://trackspecmotorsports.com/universal

Are you allowed to remove the front bumper? That thing weighs a ton

 

[sandiego74]

You're thinking about this right with weight being a priority. In my experience running big wheels/tires on front, the sport where clearance issues come up is at the rear lower portion of the wheel well. Just above the ground.

If you are worried about weight, have you relocated your battery yet? Moving the 40lbs battery from in front of the front wheels to the right rear of the trunk (counter balance driver) is a massive difference in weight distribution on the car.

I have my doubts if fender vents really make a difference at auto-X speeds. I know quite a few auto-x guys who use Trackspec Hood louvers on their cars for cooling and to reduce underwood air-pressue. https://trackspecmotorsports.com/universal

Are you allowed to remove the front bumper? That thing weighs a ton

Exactly! I had to hammer that spot in quite a bit with the sledge to get the 275’s to clear, so could I just cut out that area of the inner fender? I was literally just thinking of doing this instead since the consensus seems to be to keep them in.

I’ve already moved the battery to the rear and took out the crash beams from the front bumpers. I’m planning on gutting the interior (rear seats, doors, etc.) and anything under the hood even further, but I’ll wait until after weigh it with corner scales.

I mostly want the vents to get heat out from under hood, but I also think they’ll look cool and match the ‘14 SS vent I have on my hood. I am contemplating trackspecs stuff, since I’ve heard it’s good. Their fender vents are cheaper and nicer than original Z28 vents are, but the originals would go better with the hood vent. I am also considering removing it and putting a larger trackspec hood vent on, but we’ll see. I like the look of the ‘14 vent, and it’s pretty unique.

 

[berg2695]

I love that picture of the car in the rain.

 

[Lowend]

It that over by the Maritime Museum?

 

[sandiego74]

It that over by the Maritime Museum?

Actually, on Coronado, just north of the Amphib base where the Seals train.

 

[BonzoHansen]

OK, some rambling thoughts...

Maybe trim inners as needed vs removing them. I think 315s will make a bigger difference than 30 lbs of inner fenders. You'll need wheels for 315s, and not crappy cast wheels. spend wheel money to save weight. Not cheap. But I'll take saving 8 unsprung pounds a wheel over that inner fender sprung weight. being ready to buy on black Friday can help.

All the fast cars I see are all running splitters and bigger rear spoilers or wings. I'm not doing that to my 77. But my 67 I will.

They are also running better steering boxes. 10:1, 8:1. I'm planning a 10:1 in my 67.

What trans are you running? The ST10 4 speed is lighter than the T56 I'm running now. So I plan on keeping it in my 67 once I get that racing. I want to keep that car at 3000, which I think is the cam t limit.

What engine are you running? What rad and fan? Is there weight to save there? Or more power?

Mmmm... more power. My 450hp sbc is out gunned more often than one might think. Damn new CAM cars have more factory power. I can't keep up with a 6th gen ZR1 as an example.

You'll need a higher clearance sway bar to run 315s. PTFB and UMI have alternatives there. My hotchkis bar was detrimental to wide tires. That's my only change this year, along with a frame brace. I can't talk myself into adjustable shocks quite yet, but I kinda need them. The 67 will have Viking Crusaders all around.

Are you keeping up with cam s and cam c cars? Where are you in the PAX? The cam T regulars i run with locally swap 1/2/3 most days, but we're 5+ seconds off PAX. And occasionally a guy with an insane Mustang shows up and smokes us. He's nice though lol.

Can you find other events than the local scca. See other cars, check your measuring stick. The events I go to at UMI are quite helpful and yet humbling at the same time. I'm thrilled to now be mid pack when I'm there. I know who my targets are now, and I reeled a few in last year.

I'm still not consistent enough. But I know it's there, I'm good for a hero run or 2 every day lol