air flow through decklid

[aftermath]

Silly question, but which way does the air flow through the decklid? Does the lid cause a aerodynamic effect that pushes air down onto the engine, or does it pull air up and out? Or is their a air pressure pocket under the car that cause it to blow out ?

[stlrj]

If you really want to know you could always tape some Kleenex to your decklid and see which way it blows.

[Hugh R]

Your joking right? Start the car, put a piece of kleenex on the deck lid louvers and see what it does.

[stlrj]

Got a better idea?

[ischmitz]

I don't think this question is silly at all. Without a wing and a front spoiler the airflow into the engine bay is not very high. The non-spoilered 911 body acts like a wing producing lift at speed. I noticed this at high speeds. By adding a duck tail the engine ran cooler and the car became much more stable in high-speed turns such as #8 at the big track at Willow Springs. By adding a wing or duck tail you will produce downforce and lots of positive pressure forcing outside air into the engine bay to assist the fan.

Ingo

[JohnJL]

Does anyone have any firm data on whether the area above an SC with "whaletail" is high- or low-pressure area? Would a "cold air intake" constructed such that a cone filter or OEM filter was in a container with the open end against the tail grill be fighting against a low-pressure area in any appreciable way?

[JohnJL]

Does anyone have any firm data on whether the area above an SC with "whaletail" is high- or low-pressure area? Would a "cold air intake" constructed such that a cone filter or OEM filter was in a container with the open end against the tail grill be fighting against a low-pressure area in any appreciable way?

Like this but with a bottom and two more sides, so the open end is up against the grill...

[randywebb]

Kleenex?? What is wrong with you people??


You are supposed to use organic wool tufts -- and you have to use a Super-8 movie camera shot from the top of a freeway overpass....

[JohnJL]

why can't you post a pic when editing your message?

[Wil Ferch]

Cliff's note version...it's all been said here with a search...

The basic body will create lift at the rear...air will "want" to go up on the grill...although the raucous fan will ultimately suck air in....

A tail ( duck..any Carrera tail) will help the pressure front and help move air in the proper direction *into* the engine bay.

Tbiz did a nice instrumented test that says adding an air intake near the grill did lower temps...against common wisdom that said the huge amount of fan cooling air flow overwhelms any need for a "cold-air" package. ...however....

....Jack Olsen says we're back to the "common knowledge" of this cold air intake not being of any benefit...because Tbiz's tests were run at a single rpm/car speed....Jack's test showed as the rpm/car speed went up/down.....that a "Cold air" package made no difference...

See... simple ! .......

Wil

[76carrera3.2]

Sounds like an interesting thesis. I've noticed when I put the cabrio top down my engine runs warmer.

[AZ1977911]

76CARRERA3.2, Good observation! My engine runs warmer when the targa top is removed. Seems like about 10C.

[bkreigsr]

to the best of my knowledge, the duck produces no downforce. it does eliminate the 60+ lbs of lift generated by the stock body at speed.
bill k

[masraum]

Originally posted by bkreigsr
to the best of my knowledge, the duck produces no downforce. it does eliminate the 60+ lbs of lift generated by the stock body at speed.
bill k

no downforce, or is it negative lift?

hahahahah

Sorry

I think the duck eliminates more than 60#'s of lift.

[bkreigsr]

haha
check Karl Ludvigsen, Excellence was Expected.
good info, plus pics of which way the air really flows thru the duck and the whale

[edward993]

Just an FYI/reminder,

Paul Frere's book says (paraphrased, don't have it in front of me) that the duck and Carrera/Whale tails don't "create" downforce, but they reduce lift substantially when used in concert with a chin spoiler. At speed (can't remember what that "speed" was but it was up there), the duck reduced lift to under 50lbs pounds, IIRC; and the tea tray reduces lift a bit more, and the Whale further still ...w/o any tail lift was in the 300+lbs neighborhood (again, IIRC).

The motorized wings of 964/993 variety were purportedly about as effective as the duck, but not quite as effective as the fixed tails, but those cars benefitted from undercarriage smoothening to address airflow there. And so the 993, for example, has a nearly net-zero lift at full speed with the stock motorized unit.

Edward

[masraum]

If I remember correctly the lift at 150mph is around 450-500 lbs, and with a tail and front lip it goes to about 50. That's for both axles.

[drl911]

I saved this from a thread sometime last year.....

[ischmitz]

Finally a justification for all those hilarious wings out there

[Yellowbird RS]

Porsche 993 Carrera data :

Front lift (at 157mph) Rear lift (at 157mph)
Wing down 64 kg 136 kg
Wing up 5 kg 14 kg