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Frontal area air flow

Posted: Sat Dec 24, 2016 8:51 am
by LaVelle
I have a '65 GTO/Lemans that I bracket race.

Looking to streamline the air flow around the front for top end MPH.
I drive the car to the races so I need street able, or easily changed modifications for the raceway.

They don't make a front spoiler/splitter/air dam, so I am fabricating one.
Any suggestions?
Straight across?
Taper back from the center out?
How close to the ground?
Should the bottom or chin be farther forward to scoop air?


I took the front grills out and made acrylic panels with drilled holes for radiator airflow as replacements. (15lbs each)
Would it be beneficial the completely seal the grill area during racing? (I have electric fans and water pump set up to cool between rounds.)
I can easily make solid panels that would change out with 6 screws a side.

Along the same line of thinking, would it help to make inserts for the holes in the bumper also?

Re: Frontal area air flow

Posted: Sun Dec 25, 2016 12:41 am
by Greenlight

Re: Frontal area air flow

Posted: Mon Dec 26, 2016 7:13 am
by LaVelle
Thank you, those will be very helpful with the front spoiler design.

I'm still having trouble finding anything on blocking the front grills and bumper holes.
I would think blocking them would have a similar effect, to one taping the holes up on a whiffle ball.

Re: Frontal area air flow

Posted: Mon Dec 26, 2016 10:26 pm
by Greenlight
The one car that I worked on for a standing start mile type competition, blocking the grille opening (2012 Mustang) was worth almost 4 MPH in the mile. I'm not sure how much it would be worth on a 1/4 car, but it's certainly an aerodynamic advantage.

Re: Frontal area air flow

Posted: Tue Dec 27, 2016 5:20 am
by LaVelle
If it made a 4 mph difference in the mile on a slippery 2012 mustang.
It should do something for my brick in the 1/4.

I'll have to take some 2" masking tape with me next time and see what the difference is.

But I still have a bunch of other tuning issues to address also.
I only made the last race of the season, so it only has 50 miles and 5 passes including driving to the track and back.

I used to race the car 15+ years ago with a 383 sbc at 11.90's, but the 468 bbc is causing traction problems.
I did get it down from a 12.65 to a 11.43 playing with tire and air bag pressure in the 5 passes.
Hopefully I have the traction issue rectified with the new ARB and shocks.

Re: Frontal area air flow

Posted: Wed Dec 28, 2016 9:01 am
by jacksoni
There is a lot of drag generated by air going through the grill/radiator. Since you want to cool between rounds leaving the radiator open may be necessary so totally block the grill. There will be enough flow with your fans and pump to cool I suspect. You want an air dam that is as low as you can get it without hitting. Keeping air out from under the car where flow is not smooth helps drag and lift issues. Spend some time looking at photos of LSR cars and you can get some idea of the amount of lift at speed as well as designs. Usually they are not projected by rule, that is straight down from the bumper. At Bonneville, "production" class cars can't run air dams unless factory available so you need to look at Gas coupe classes and sometimes Altered though other front end mods are allowed there as well. This results page from SCTA for the 2016 speed week has a lot of photos to give you some idea:

Rake of the car may be a double edge sword as yes this lowers the nose to keep air out but may in some cars serve to just increase frontal area but at the same time not help flow off the back of the car. Without wind tunnel you would just need to test it at the track. Low is good but the back way up may not be. Hard to generalize but my personal experience is that with a good sloping back window (not your GTO) rake doesn't help. It might with your car.

Re: Frontal area air flow

Posted: Wed Dec 28, 2016 10:50 am
by LaVelle
Cooling between rounds I should be Ok.
There is plenty of room between the grill and rad. to pull air through from underneath.

The speed bump down the street will probably be the limiting factor for the air dam height, but I'll try and get it as low as possible.
A light bulb came on when you mentioned the LSR guys.
Forgot I have an old high school buddy that is part of a group that run a 79/80 Monza at Bonneville to talk too.

The Ride height is a couple of inches lower than stock.
I set the rear height for best IC location and then lowered the front down to a slight rake. ( 1" or such total )

I'm just squirrel caging aero ideas for improvements in the off season.
To shave the corners off the old brick so to speak without getting out of hand and trying to reinvent the wheel.

Re: Frontal area air flow

Posted: Wed Dec 28, 2016 5:04 pm
by F-BIRD'88
GM Muscle car front shin spoilers

Re: Frontal area air flow

Posted: Wed Dec 28, 2016 5:57 pm
by LaVelle
Thank you.
They show a perfect image to fabricate one up.

Would it perform better if I made one that went all the way across the front?

Re: Frontal area air flow

Posted: Wed Dec 28, 2016 8:14 pm
by jacksoni
This was more what I had in mind. Make it removable, few Dzus or bolts, avoid the speed bumps. If you are going to go to the trouble, make it effective! :D

Re: Frontal area air flow

Posted: Thu Dec 29, 2016 1:08 am
by LaVelle
That's a little more extreme than I was thinking.
The air dam/spoiler will be a smaller more permanent unit.

A couple of grill inserts with a few screws is all I'm willing to hassle with changing at the races.
I've been part of the full on trailer queen game in the past, and don't want all that BS and hassle.
It just takes all the fun out of it.

Race day is a breeze when you can get up in the morning jump in the car, drive out, go through tech, race, and drive home without lifting a wrench.
I'd rather run a little slower and enjoy the day.
Besides here on the Olympic peninsula in Washington, we can get rain outs now and again even in the middle of a race.
So it's all steel (except the hood scoop), and still has the heater, wipers and such.

Re: Frontal area air flow

Posted: Thu Dec 29, 2016 9:08 am
by jacksoni
Understand 100%. Make it as big as you can, cover the grill will make big difference. This article also talks about things that might help: ... icks-tips/

Also these:

Have fun!!

Re: Frontal area air flow

Posted: Thu Dec 29, 2016 2:52 pm
by Nefario
How radical can you get before your competition or the organizers object?

Any cavity facing into flow like the grill openings has a higher aero drag than a flat panel. But the whole car front is kind of a brick.... There's also the school of thought that for a full body car, most of a drag run is about acceleration from zero to say, 80MPH, speeds too low for aero to make a lot of difference.

I wonder if you could run solid clip-on panels that completely block the grill flush with the body front just for each drag run? If you have a fan shroud, the car would get plenty of air for idling & staging from under the front. A spoiler could be tapered from the center and drop from the beltline of the bumper to help get air around those square front corners, like the Bonneville Monza.

Re: Frontal area air flow

Posted: Fri Dec 30, 2016 4:14 am
by LaVelle

Thank you for all the links.
You have been a wealth of information.
After pondering things I'm thinking of putting a short belly pan between the bumper and front cross member also.

Originally was hoping for 11.50's after tuning.
Went 11.43 @ 117.7 by the end of the first day.
So new goal is 10.90's.
With tuning and a few small aero mods I think it should be achievable.

Re: Frontal area air flow

Posted: Fri Dec 30, 2016 4:46 am
by LaVelle

We have small track (started as a tear down in the 60's) that if it will pass tech you can run it.
We have had everything from Geo Metro's to my old bosses alcohol funny.
Even had a road course go-cart run 13.20's one day.

So I can pretty much do what I want.
It's all brackets based on ET.

I have already made replacement panels to change out at the raceway for the street panels. (took out stock 15lbs each grills)
They fit flat with the front sheet metal, rather than inset like the factory set-up. (6 screws a side)
Working on the air dam.
Trying to have it run full with and attach to the bottom of the front fenders.

Ya' she's a big old brick, heavy to but that's fine.
Just shaving the corners a little so to speak, 2 or 3 mph on the big end and I'll be happy.