Rear Spoiler

[Jim Smolka]

How effective (amount of down force) is the rear fiber glass spoiler that can be mounted onto the lip of the trunk lid.

Interested in increasing grip when on the track. (must pass more 911s)

[Rleog]

....hope others running the fiberglass rear spoiler reply, and don't mean to wander from your question, but .... for the grandaddy of all rear spoilers, a la Chaparral days, check out the 914 in the new issue of Excellence. I doubt any 911s would want to come near that thing.

Bob G

[Jeroen]

Do a search within this BBS
There was a similar thread recently

Cheers,

Jeroen

[Brad Roberts]

Hey Jim,

The rear spoilers are just that "spoilers" they dont generate downforce.

What they do is disrupt the flow of air as its comes off the decklid.

The 914 tends to lift in the rear without a spolier (about 90mph) Spoiler's (3inch variety) will cause the air to circulate further behind the car and not circulate back up and underneath the car.

NASA buddy that works in the wind tunnels....


B

[John Rogers]

Brad is right, the small spoiler doesn't do too much, might kill a little lift if that. To get down force you need one of those IMSA type wings. In 1969, I had a 1969 Z28 Comaro that had the same small trunk spoiler and a small "chin" spoiler and wondered if it worked? Well Road & Track did a test of spoiler effectivness using all the TransAm cars that were racing in 1969 and guess what, the small trunk spoiler did nothing for downforce at all! Neither did the ones on the Mustangs, Javalins or Dodges help with downforce either. The Mustang and Camaro chin spoiler did give some at the front. But they look cool though. Good luck.

[Jim Smolka]

Brad,

Thanks for the info...

Next question, wil a 914 with the 3" spoiler gain any benefit (speed, stability etc) from the redirected air???

Thanks

[Brad Roberts]

I just noticed you have a 3.2 car. I'm going to say yes in your case. If you had a 1.7, I would say no. Every car we run has a 3inch spoiler on the rear (except our SCCA ITA cars, they dont allow anything attached to the car that wasnt factory)

As John Rogers pointed out.. the biggest benefit is the chin spoiler. We also run this on our cars.

B

[DonNewton]

I can attest that those little "spoilers" do their job. At Mid-Ohio, entering turn 4 (end of back straight), my car, without the trailing edge spoiler would want to dance around under braking. The next year, after installing the "spoiler" (emperical data to follow), I noticed a dramatic reduction in the amount of "looseness (technical term, don't try this at home)" under braking. I'm normally too busy to tell if there is any change while at max throttle, but it sure is nice to have that security when you need it, and visions of Michael Andretti are flashing through your brain pan.

[John Rogers]

Don, I was wondering how much the rear of your car comes up under really hard braking? If the front goes down an inch or two and the rear goes up an inch or two then that little spoiler could grab the air pretty well. For Jim, take a bunch of 6 inch long pieces of string and tape them all over the rear trunk lid and engine cover areas and then drive fast to see what they do, you'll be surprised. Kind of like a temporary wind tunnel. Good luck.

[campbellcj]

Be careful to check the rule books if you're considering a 'lip' (trailing-edge) spoiler or a full leading-edge (airfoil) wing on a track car.

Some classes/orgs disallow either or both, or nail you on modification points. Other classes allow them but they aren't supposed to extend out or up beyond a certain point (like the bumper, or the roof).

Many/most of the really hardcore 914 race cars around here run large, tall leading-edge wings...but you're looking at easily a $500-1000 investment there, plus some fab work.

There was a similar thread on the Rennlist 911 group the other day about the early (73-74) 911 ducktail spoiler, a lip type. I don't remember the exact figure but it was shown to reduce lift by a non-trival amount, like 80-90lbs or so. However, the cars on which it was fitted also had a modest front spoiler/dam (the 72S/73RS type). You probably wouldn't want one without the other.

I can personally attest to the fact that early 911's with no front or rear spoiler have serious lift issues over 100mph. Scary.

[derek_sf]

hopefully it does something, otherwise these things totally ruin the lines of the car in my opinion.

[Bleyseng]

Heck, I think it finishes the rear deck off nicely!
Geoff

[campbellcj]

Now THAT's a wing:

[DonNewton]

Posted this before. . .

In response to whether the rake changes by 1", front-to-rear, maybe. Pretty stiffly suspended (makes it REAL fun to drive in the wet), can lift inside front wheel at whim. Have seen 140mph into turn 4 at MO, and as I said before, that trailing edge disruption really makes a difference!

[6 Shooter]

Hey Derek_sf,
I got a set of stove burners with my car, too. Came with the car when new. When I bought the car, it had early 6s, plus the original Mahle stove burners. I just don't see them very much anymore. What tires are you running on them (5 1/2s) ?

[derek_sf]

oh that's not my car, it's a 914-6 which is up for sale around these parts now. seems like a nice car, but that spoiler is just not for me.