Noahs944

Yes, but also the air that goes through the hood vent is not adding to pressure the car down because it's on top. An absolutely brilliant concept.

Dash01

See the air pressure graph above, and take in cooling air at point 4 and exit it at point 11. That's the path the cooling air would take if and as it can. At speed the car becomes a linear pump.

This also relieves high pressure at the stagnation point (~4) and vents it at the area of high lift (~11), so you simultaneously get better inter-cooler performance and reduced drag and lift. Great way to dump unwanted engine bay heat, too.

924srr27l

It's nothing new and has been used in Competition for decades...

Here's one example from 1969





R

924srr27l

Wow, this sounds scary!

I've not been past 120.., but another member on here has a 931 that does a genuine 165mph ! that must be doing a Wheelie! with the severe front lift?


How about this...?





R

morghen

How do you know that? whats significant? how many milimiters..inches...feet?


Required in order to do what?


So was the 924 and the 944, but the target was lower, both the 924 and 944 were not designed to spend much time above 110mph nor to corner above that speed...the 968 on the other hand was designed for higher speed driving.

V2Rocket

While I don't doubt there are significant lift forces on a stock 944 at speed, I don't buy the statement that it's sketchy at speed...I've heard that before, entirely from the V8-swappers who are trying to defend for the added nose-weight...

I have taken my 944 to 120-130mph plenty of times in the last 11 years...and I've said it a lot...it drives/feels the same as half that speed, just a lot more wind noise...

odurandina

Then you'll like my car at 170mph. it feels more like a brick,

as in 'dammit this thing is planted' than 150mph.

i'm gonna have to do a very well built belly pan/splitter, though, if i plan on getting near the forbidden zone.

91K-Man

Wind Tunnel testing will give the answers. Stock 944t has about 70 lbs lift @120 mph. www.mantissport.ca

V2Rocket

so the force on the tires is ~70 lbs less than the weight of the car when parked?

Dash01

Do the undertray and front splitter, and you may not need draggy downforce wings, especially if you do a proper diffuser at the rear, too.

Study Bernoulli's law, noting that pressure varies inversely with air speed: The faster the air, the lower the pressure. Have another look at the pressure point graphs above. With a front splitter, undertray, and diffuser less air goes under the car (reducing pressure underneath); the air that does go underneath is flowing WAY faster and more efficiently (less pressure and uplift); and the rear diffuser of <~15 degree upslope causes the exiting air to flow upwards with subsequent downforce vector while simultaneously filling in the turbulent zone behind the car: Less drag and more downforce.

As for speed in an aerodynamically unmodified car, ask Brian from Vancouver (has Family Guy dog avatar). About 12 years ago he, I, and about 30 other Porsche guys did a yuuge high speed ratrace through the southern BC interior. (Pics were posted on this website, so may be archived here.) As I recall, he tested his 944 Turbo to top speed, which was 160ish, evidently with no ill effects. He can tell you about stability at high speed in aerodynamically stock configuration.

Noahs944

Dash01, I enjoy reading your comments very much.

Would you kindly provide a picture as an example? I'm having difficulty visualizing this type of diffuser.

DasSilberWedge

+1. I've had my S2 at the same speed on multiple occasions and it felt fine..

morghen

Fill up your washer fluid and don't clean it of dead insects and you should be back to normal

Voith

Interesting fact, w201 also is 0.33 and compared to 951 looks like a brick.

Dash01

Google images for coroplast diffuser, coroplast undertray, coroplast belly pan, etc. and click on the pics for further information. Ecomodder.com aerodynamics forum has scads of posts on this, as well as efficiency measurements of before and after fuel economy, and methods of attachment. Zip ties work well. Also look at what Ecomodders has done with pizza pan wheel covers, to smooth air flow. I'm not suggesting pizza pan wheel covers on a Porsche, but such aero research very strongly suggests using Porsche sewer lid or Design 90 wheels. I use D90 wheels because they are virtually as light as Fuchs, probably stronger, WAY more streamlined, but at a fraction the cost. Not bad looking, either.

Google images for, say, "Ferarri diffuser" and note the upswept angle of the rear diffuser, the flow fences, etc. This could easily be made of Coroplast. The air flowing from under the car is faired gently upward under the rear bumper, filling in the turbulent wake, and giving some negative lift, i.e., downforce into the bargain.

Election day is next Tuesday, so 4x8 Coroplast political signs will be taken down soon. Get a couple, preferably ~1/2" or so thickness. This may be the ONLY contribution most politicians will ever make to improving your life... Besides, you'd be doing a public service by removing roadside eyesores.

If you don't like the politician, remove the writing with a rag wet with acetone or paint thinner. Nobody will notice your new belly pan hidden under your car, so you won't get snarky comments from Porsche purists.

Also, ask your local library to borrow a copy of Hucho's book on auto aerodynamics. Inter-library loan from, say, a college engineering library, will cost you nothing to borrow for a few weeks, study, make copies of relevant sections, etc.

In the 1930s the Germans were decades ahead of everybody else. No car yet has come remotely close to the 1938 Schoerwagen pill bug in aerodynamic efficiency.

PS: Using short tufts of yarn, dental floss, string, etc. and bits of tape, attach to your car around wheel wells, mirrors, rear hatch, header panel, nose, etc. and have someone take pictures at at highway speed. An attached GoPro camera would be perfect for this, too. You want the indicated airflow to be straight from front to rear, without waving or backflow. You'll find much improved flow with wheels most flush to the side of the car, teardrop mirrors, and good fairing around the lower front tires.