Aerodynamics question(s) - Page 2 - Vintage Mustang Forums
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post #16 of 261 (permalink) Old 03-20-2015, 01:07 PM
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It sounds like the cause of the crash you described had less to do with aerodynamics and more to do with some less than stellar driving and poorly timed weight transfer.

I would keep the rake that you have (slightly higher in the rear). A chin spoiler could help, as could raising the rear of your hood slightly.

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post #17 of 261 (permalink) Old 03-20-2015, 01:59 PM
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It sounds like the cause of the crash you described had less to do with aerodynamics and more to do with some less than stellar driving and poorly timed weight transfer.

I would keep the rake that you have (slightly higher in the rear). A chin spoiler could help, as could raising the rear of your hood slightly.
I just watched a few Youtubes of crashes at PR , and I would say you are 100%correct,cresting the hill causes the suspension to rebound at the point you need more grip on the front.

OP if your car wants to loose the front there some (very) good shocks are in your future to control the rebound.
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post #18 of 261 (permalink) Old 03-20-2015, 02:02 PM Thread Starter
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Front springs are the 620 Grab a Trak. The car has the full TCP subframe/x-brace package with a Fays2 Watts link and is generally very stiff. Typically, the car has a rake until I approach ~90 mph, then it sits level. At 100mph+, it still appears level (from photos), but I just get that "feeling" of it lifting in front. Mind you, I'm limited to about 5 seconds at this speed due to the transmission/rear end ratio, but still.

I've read about the string test, and that's why I was wishing for access to a test track.

What I'm reading about is that a 1-2* rake is desirable, and that the addition of a chin spoiler, while adding drag, more than compensates that amount of drag by adding downforce. I don't see how I can really make a difference in drag elsewhere without adding a rear splitter of some sort. And that's getting into $$$. I'm more concerned with the front end lifting.


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post #19 of 261 (permalink) Old 03-20-2015, 02:06 PM Thread Starter
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Originally Posted by cyclone03 View Post
I just watched a few Youtubes of crashes at PR , and I would say you are 100%correct,cresting the hill causes the suspension to rebound at the point you need more grip on the front.

OP if your car wants to loose the front there some (very) good shocks are in your future to control the rebound.
Yeah that track wants to kill you. "DON'T LIFT AT TURN 1" is drilled into everyone's heads. Not just Mustangs...but Vettes too. It's tricky.

Funny, but that's not where I find it getting light. It's about mid way down the front straight.


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post #20 of 261 (permalink) Old 03-20-2015, 02:07 PM Thread Starter
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And stupid question: How would I lift the rear of the hood? Add a shim in between the hinges and the hood?


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post #21 of 261 (permalink) Old 03-20-2015, 02:08 PM
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Hey Sparky,
That transition at Pacific pulls a lot of folks into the wall, listen to your instructor and do what he says...you'll be fine. Edit: my bad, T-9 will cause problems also!

Cheap aero...If it were me I'd be looking at a chin spoiler and a spare "track hood". I'd hit up your local wrecking yard and look at vents from some of the 80's and 90's imports and cut them into your spare hood.

I've found the biggest improvements in aero are keeping the air out from under the car (which causes lift) and relieving the engine bay of incoming air. The spoiler does cause drag but the benefits of eliminating the pressure under the car out way the drag from the spoiler.....think about all the "hang ups" that cause drag under the car, control arms, exhaust, rear axle....

While not an early mustang, I picked up 3mph at Bonneville by cleaning up my aero, free horsepower!


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post #22 of 261 (permalink) Old 03-20-2015, 02:19 PM Thread Starter
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Thanks Dbasher, exactly what I'm leaning towards.

BTW, that friend that I mentioned earlier is my coach at that track. He now races an E30 race car.

The spare hood is an EXCELLENT idea. I doubt any wrecking yards around here have any first gens, but I do know a guy that restores them, so he's bound to have one eventually :-). I'm thinking along the lines of the New Edge Mustang heat extractor hoods - the vents are behind the "scoop" if you will, near the cowl.


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post #23 of 261 (permalink) Old 03-20-2015, 02:26 PM
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As we have thrown out the idea of a track hood, how about rear trunk lid too? Lift/snap over steer is going to ask for more rear traction and not more front end bite. It must be balanced! I must concur that this turn is more weight transfer than aero.....but your straight away lift that you are complaining is certainly the aero brick your driving.

Clearing air out of engine bay without shoving it under you is going to help. You need air flow to cool but you need to clear this too. If you open can funnel this appropriately you can achieve benefits in both. On these old Mustangs with NO aero attention done to underside, I don't think the increase in frontal area vs possible lowering of cd is going to be a net loss. The Trans Am guys, though 40 years ago, were pretty sharp. The vintage racers of today are VERY sharp. Just copy them within reason. They are pretty fast for what they are given as a palate.

I don't think an air dam is even a question. I also think experimenting with a cheap trunk lid with an adjustable rear spoiler for height or a deck lid with wing and adjustable wickerbill/Gurney to dial in balance is worth thought when discussing aero balance. Many a Porsche 911 has met its end to aero inbalance as they are like trying to get a "wing" to not fly.

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post #24 of 261 (permalink) Old 03-20-2015, 02:27 PM
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Sparky, just put a "want" in classifieds. If you weren't across country I could give you one from previous restorations.

69 351 TKO Sport Roof, Ride Tech coilover
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post #25 of 261 (permalink) Old 03-20-2015, 02:29 PM
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Small world, I've reconnected with an old high school friend that does the same, he's now moved into the new class. C. Hurley, hell of a wheel man!

Keep your eyes peeled on Craigslist for a hood, I've seen a few that would be perfect for this kind of set up go for cheap.

See you at the track!
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post #26 of 261 (permalink) Old 03-20-2015, 02:39 PM
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I lifted the rear of the hood by loosining the hood hinges and pulling them as far upward as possible then added spacers between were hood and the hinge bot togeather. Taller spacer at the rear. Had to do some hood latch adjustments too I THINK.

mY 69 Shelbey GT 350 got realy sweet after lowering the front about an inch. Think that front bumper acted a bit like a spoiler and the rear vent holes in the rear of the hood helped also. At speeds around 90 and above the car would settle downwards about an inch or so and stay that way even at 200 MPH.
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post #27 of 261 (permalink) Old 03-20-2015, 02:43 PM
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When mine started to try and fly on the drag strip I lowered the rear 2 inches and the front 3 through a combination of springs and tires. Tucking the tires up in the fenders helps quite a bit. The rake angle puts down force on the hood also. Once the car rises up to level, the hood on these cars acts like a sail.

Put a thin plate(aluminum) between the grill and the radiator support also to keep air from running up in there.
You can see what they do on the trans am cars;

Do something along the lines of this;


I haven't had to fab up one of these yet.


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post #28 of 261 (permalink) Old 03-20-2015, 03:14 PM
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Okay, now that's just sexy. I don't even think I care if it works or not. I just want it.


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post #29 of 261 (permalink) Old 03-20-2015, 04:59 PM
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I agree that the Trans Am guys had a lot figured out, and the current serious Vintage guys have modernized that path, copying what they are doing will certainly put you on the right path.

If you have a sufficient cooling system during track use, you could start experimenting with limiting the air incoming through the radiator, in conjunction with the chin spoiler (to clean up air below the car) to help minimize the air coming in under the hood and reduce the "sail" effect. The backup hood, along with the rear spoiler/spare truck lid sounds like a good option. In the future once I get lots of other things sorted out, I will be sourcing a functional hood scoop and a spare trunk lid that will have a spoiler/foil on it for autox and track use.

Another thing to check out are all of the high dollar classic pony cars that are playing in the Ultimate Street car series .... tons of aero and venting getting added in to vintage bodies to try and keep up with the aero, cd, and tech assist advantages that the modern cars have (C5/C6 vettes, 5th gen Camaro, Mustangs, and GTr's)

Thanks for all of the replies on here, good info

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post #30 of 261 (permalink) Old 03-20-2015, 05:28 PM Thread Starter
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I agree that the Trans Am guys had a lot figured out, and the current serious Vintage guys have modernized that path, copying what they are doing will certainly put you on the right path.

If you have a sufficient cooling system during track use, you could start experimenting with limiting the air incoming through the radiator, in conjunction with the chin spoiler (to clean up air below the car) to help minimize the air coming in under the hood and reduce the "sail" effect. The backup hood, along with the rear spoiler/spare truck lid sounds like a good option. In the future once I get lots of other things sorted out, I will be sourcing a functional hood scoop and a spare trunk lid that will have a spoiler/foil on it for autox and track use.

Another thing to check out are all of the high dollar classic pony cars that are playing in the Ultimate Street car series .... tons of aero and venting getting added in to vintage bodies to try and keep up with the aero, cd, and tech assist advantages that the modern cars have (C5/C6 vettes, 5th gen Camaro, Mustangs, and GTr's)

Thanks for all of the replies on here, good info
Agreed - MUCH thanks for all the info!!

And that '70 is PERFECT. Seriously. I need a tissue.

I don't have any cooling issues, even in hot/humid traffic. I USED to, but since I added the flex fan, shroud, Water Wetter, and lower valance cut-out ala R model valance, no probs whatsoever. BUT I had an inkling that the hood was acting like a sail...you'd think my first clue would've been that one time before hood pins and it DID sail up O_o. This was at 38mph. It did a number on my original hood, hinges, and inner aprons.

Funny you would mention OUSCI, as I was all set to do the weekend in Portland in July...until they released the schedule for 2015. Nothing in Portland, just Thunderhill at the end of February. Siskyous in February? No thank you. Killed my whole year, as that's EXACTLY the kind of stuff I love to do with my car. And what it's being set up for . I saw all the final competitors at SEMA, and while a lot of them *were* very high dollar builds, a lot were not. But it was interesting to see their setups at the very least.


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