Interesting study of aerodynamic aids on a 914

[CID Vicious]

Forgive me if someone's already posted this, but I was looking around for rear spoilers and came across this article. Apparently he's hooked up with a college aerodynamics department somehow and they spent a couple of years studying aerodynamics using his 914 as a mule, and doing a lot of wind tunnel and fluid dynamic testing.

They came up with a very good rear spoiler design that produced 50lbs of downforce at the rear at 50mph, better than some very convoluted/over the top setups also tested. There's a PDF at the bottom with their results and the specs for the spoiler design.

Chris' 914 Porsche Aerodynamic Aids

I figured that others might be interested. Turns out that there's not a lot of ways to improve the stock areodynamics, at least not in any way that produces a silhouette you'd want to be be seen sitting in. Made me think twice about getting any goofy front spoilers, though I still want to get something cooking in the rear. I'm not a fan of Yellow, and I'm pretty sure that a color matched paint would be more expensive than I'd like.

I'm thinking of going in this direction, though with Rivieras (what's coming on the car), either exposed chrome bumpers and trim or completely blacked out (this is kind of neither-nor) and done with a better paint and a real spray gun. No flares either. The other thing is no clear signals (ew). Probably a lip spoiler instead of the bigger wing, but that doesn't look all that bad either. Sad thing is both probably add to drag while producing no real downforce...



I'll have to see though, might be cheaper to get a small pint of mixed paint and swap out the door. I do love that look on this car though.

[Dave at Pelican Parts]

What are you doing that you need the downforce? Most aero aids that look at all streetable don't have any noticeable effect until you're going somewhat faster than freeway speeds. Most autoXes won't get that fast, and relying on aero grip on the street is suicidal...

That leaves the Big Track. You need to check the rule set of whomever you run with to see what sorts of aero aids are allowed in your class. It's very annoying to find that one simple mod (like a wing, or a set of headers) puts you into a fire-breathing class where you're nothing but a rolling chicane. It's even worse when that class requires more safety equipment than you have on the car, and you find that out at the track...

--DD

[SirAndy]

Originally Posted by Dave at Pelican Parts

Most aero aids that look at all streetable don't have any noticeable effect until you're going somewhat faster than freeway speeds. Most autoXes won't get that fast, and relying on aero grip on the street is suicidal..

I agree.

I can feel the rear end getting light at 110+, probably mostly due to all the air being dumped under the car right now.

A front air-dam should help with that ...
Andy

[URY914]

[Flieger]

Originally Posted by SirAndy

I agree.

I can feel the rear end getting light at 110+, probably mostly due to all the air being dumped under the car right now.

A front air-dam should help with that ...
Andy

You realize the front air dam will only make that worse because the balance will shift forward and lever the rear end up. You need a rear wing in clean air.

Or an F1 style diffuser.

[Tobra]

Dude, he was kidding, note crazy big wing a foot taller than the car

[Flieger]

URY914 actually races his 914 like that. I was referring to the other poster's suggestion that he needed a front air dam to keep the rear end in line.

[SirAndy]

Originally Posted by Flieger

You realize the front air dam will only make that worse because the balance will shift forward and lever the rear end up. You need a rear wing in clean air.
Or an F1 style diffuser.

You realize that a front air-dam, if constructed correctly, will not add any downforce to the front of the car.

We just went through this on our 911 spec racer. The front air-dam substantially reduced the rear lift at high speed.

Shape is everything when it comes to aero aids ...
Andy

[Flieger]

So, if the air is notgoing under the car and lifting the rear, and it is not generating front downforce over the front, it is just being plowed out to the side? Sounds like a tradeoff of less lift for more drag. I think you could use that air with a splitter to gain some downforce or at least duct it to the brakes or oil cooler. Whatever; you got me.

[jhora]

what's interesting is that the study shows the stock configuration to be pretty darn good just as it was delivered

[Jagshund]

I've always operated under the assumption that you usually cannot focus on one end without upsetting the other; the exception being situations where someone else has already upset the balance.

[Tobra]

Originally Posted by jhora

what's interesting is that the study shows the stock configuration to be pretty darn good just as it was delivered

I remember reading some aero numbers for the stock 914, not too bad for a brick.

You have to have air going where you want it(cooling, etc) and not going where you don't. You can mess things up pretty bad when you start messing with stuff that a whole crew of smart German dudes spent plenty of time in the thinking caps dreaming up

[Flieger]

Norbert Singer said that the reason why the customer 956 teams reported increased downforce on the front end with those airfoils was that the wing was spoiling airflow to the rear wing and lessening the lever effect. That is why, after wind tunnel testing, the factory never ran them, citing no benefit overall for total downforce/drag. They could just back off the rear wing. Customers steadfastly held onto their belief, though, and won some races.

[SirAndy]

Anything that redirects air-flow will add drag. The question you have to ask yourself for each item you add is simple.

Will the benefits outweigh the detriments?


In my experience neither the 911 race car nor my 914 need any more down-force in the front. Both cars have plenty of grip in the front at high speeds.

A huge wing works but may not be the best approach for a street car. And just to be clear, a wing will add drag as well.

As for the air-dam, the one on the 911 is constructed to route the air that otherwise would go under the car to flow off to the sides.
That is in addition to the normal air-inlets for brake cooling and oil cooling of course. Those things are not mutually exclusive.

Andy

[Marankie]

The combination of rear wing and deep front spoiler work well a Willow springs where speeds in turn 8 are about 125 mph and turn 9 about 100 mph. Wing and spoiler for sale. Send pm and I will email pictures.
Martin

[Flieger]

I think the front spoiler looks good but the taller rear wing seemed a little "look at me" when not at the track. I like how your car looks with the front spoiler and clean tail.

[retro356]

My interpretation of a 914R. It handles very neutral, front and rear aero seems to work well, and be balenced. However I am still getting allot of dirt through the holes, into the trunk. Which tells me I am still getting suck back. I am going to do a Gurney Flap, to see if that gives me cleaner air release.

[yeahmag]

I'd love to know more about this car.

[retro356]

What would you like to know?
So as not bore the rest, you are welcome to e mail me at retro356@gorge.net

Retrotech: Classic and vintage Porsche cars, accessories and Porsche parts