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69 Malibu Pro Touring build

I think I'm going to do Nankang CR-S 275/35 on one set, and the Yokohama A052 295/35 on the other.
Nankangs are almost as fast, but $100/ea cheaper.

For Goodguys, I'll mix and run Nankangs in the front, and Yoks in the back because there's a 285mm Front tire limit for Street Machine class, and the 295s will put me in "Pro" class.

I still have about 25 runs left on last year's Yoks also, but they have too many heat cycles in them and are well past their prime. This stuff is stupid as hell, but I love it... wish it was cheaper though.
 
I was signed up for UMI Autocross Challenge 2021, and decided if I wanted a shot at winning an invite to KOTM, I'd need the fiberglass parts and the spoiler mounted. I didn't have time to get blocked smooth and painted, so I shot them with black epoxy primer and installed them unfinished for the rest of the summer.

Fresh 295/35/18 squared Yokohama A052s, as well as taking 40lbs off the front, 18.5lbs off the back, and adding the spoiler did the trick, as I won the invite by 0.059 second over 2 days.

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That’s one nice looking 69
 
Dad and I traded cars for the winter. Neither of us wanted to work on our own junk, but we're both getting stuff done on each other's cars.
His skills, garage, and tools are better set up for paint and body, and I'm better set up for chassis and mechanical work.

He got my Chevelle hood painted while I installed power steering and did some suspension work on his '68 Camaro.

The trunk lid should be done in a week or two.

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Curious, when you're sitting still, can you feel air coming out the hood holes?
Do you think the air flows out when you're driving or do you think it creates vacuum and air goes in?

Maybe put a piece of tape or string to see the flow?
 
Curious, when you're sitting still, can you feel air coming out the hood holes?
Do you think the air flows out when you're driving or do you think it creates vacuum and air goes in?

Maybe put a piece of tape or string to see the flow?

I'm betting the radiator fan alone benefits and pushes the air through those.
 
Sitting still you can feel heat radiating out, and some air flow comes out when the fans kick on, but not a lot.

When moving, the air pressure under the hood is higher than on top of the hood (except further back by the windsheild) so it draws a lot of air out, reducing aero lift.

The difference in front end stability at 130-140mph is staggering. It used to get really unstable from all the air pressure under the hood trying to lift the front of the car. Now it feels planted and very stable. These cars have huge grille openings, and high clearance to the bumpers so a lot of air gets under the car. This hood made a bigger difference than the front spoiler did. It used to be pretty scary over 120. Now I'd have no fear of trying to go 160+ if I had the room and the power to do it.
 
The difference in front end stability at 130-140mph is staggering. It used to get really unstable from all the air pressure under the hood trying to lift the front of the car. Now it feels planted and very stable.

Never thought of that, but it makes perfect sense.
 
Interesting.

What about putting a pan under the engine? Enclosing the bottom?
I plan to add a 6" (per the SCCA rules) splitter to the bottom of the chin spoiler, and if I do more big track roadcourse stuff, I'll be adding an under-tray from the bumper back to the front crossmember as well.

For autocross, the gains are pretty minimal.
For roadcourse, I should just run my Corvette because it's already engineered to do all this stuff really well. :ROFLMAO:
 
The holes in the hood are located in the green low-pressure zone shown on this diagram, which draws air out reducing pressure under the whole car.

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