Poor Man's Ground Effects -- I need some input

[jyl]

Jack, I have a brilliant solution for you.

Find a way to "reverse" the engine cooling fan so that it sucks air out from under the rear of the car and exhausts it through the engine lid grille. Combined with your side skirts, you will now have pukka ground effects just like the F1 "fan car", plus reduce the drag from the sloping rear of the car.

Until your engine overheats, anyway.

Will it overheat? I would think so, what with air being pulled past the exhaust system before it hits the cylinders. If not, then maybe this could actually be a serious suggestion . . . maybe if you wrapped or shielded or ducted air around the headers or something.

I'm assuming you don't have enough time on your hands to figure out a way to reverse the cylinders so that the intakes are on the bottom and the exhausts on the top, together with the reversed fan. Would make for nice long intake runners, plus think of all the weird underbody "ram air" you could use.

I'd better stop drinking.

[masraum]

According to Frere the engine tray of the 964 not only helped with aero because it smoothed the bottom of the car, but also because instead of the air from the engine fan blowing out the bottom of the car it was now exhausted out the back of the car which reduced the pressure under the rear and also helped with some other aero thing that I can't remember right now.

To further develop Banjomike's idea...



If the two rails running under the center of the car flared out that may further some of that effect.

[Craig 930 RS]

"According to Frere the engine tray of the 964 not only helped with aero because it smoothed the bottom of the car, but also because instead of the air from the engine fan blowing out the bottom of the car it was now exhausted out the back of the car which reduced the pressure under the rear and also helped with some other aero thing that I can't remember right now."



That also would help tremendously with managing air for a diffuser in the rear - air coming down from the engine messes up the concept of air exiting horizontally through a diffuser -

[Randy Webb]

I was think about all these long aero threads the other day....

What we really need is a real smart student to adopt something like this as a grad. thesis/dissertation or as (more likely) an undergrad. project. A kid at Cal Tech would be perfect.

Trying one thing after another on a full size can help (JO's lap time decrease = case in point). But we really need is something more comprehensive (and I don't see PAG investing $$ in a 30 year old design).

Conceptual thoughts are fine but can never get you to where a physical model in a flow tank would or some real equations and numeric finitie element modelling. Somebody has to know somebody who ... knows a smart student at an engineering school. Your tax dollars at work....

[Bill Verburg]

You will never see a Cup car or RS w/ the engine tray in place

[Craig 930 RS]

Exactly. Helps with the 'aero' -- kills the engine.

[BigD9146gt]

Originally posted by Craig911
Exactly. Helps with the 'aero' -- kills the engine.

Not neccesarly. You can install ducting that will help suck air out of the engine comparment and create more air to go over hotter areas.

I haven't read all 7 pages, so please forgive me if this has come up before, but i remember a "story" about the POC banning all ground effects becuase of a local guy, Franz. Apperntly the guy gets contested as soon as his car rolls off the trailer because he finds any way possible to exploite loop holes in the rules (just like Porsche and everyother race manufacture/group has done). Back to the story at hand, he studied up on ground effects, and made a complete fiberglass underbelly for his 70's era 911 racer. I think it had a pumped up 2.7L, and during the first race with the ground effects, he was passing 3.6L 911's with obviously way more power. Now he was kicking ass, and the big boys with all the money were butt hurt, so it was banned.

Anything is possible, placing NACA ducts and luvers in the approperiate places will keep your motor cool, but for the speeds your going to be working at on the street, its kind of over kill, although its more noticable, the 3.8 RS wing should do the same trick, and not cost you a motor if you make an oopsy with the cooling.

[Bailey]

Jack - I love the work you are doing to your car. I am planning some winter projects to get more speed, brake and safety in my 930. My mechanic has already put together an incredibly well sorted, fast car but I am a sponge for all ideas. Can you describe the fabrication of, material used, and method for mounting your aids.

[Rob Channell]

Cool thread.

I was going to suggest reversing the engine fan, but John L beat me to it. Maybe some cold air ducts brought in under the engine and directed up between the cylinders along with a horizontal fan on top of the motor. Could going back to a stock decklid increase the speed of air across the decklid and create a venturi effect to suck air out of the engine compartment? It would have to be combined with a monster tall wing so you didn't create more lift at the rear. Might require some seriously insulated exhaust headers.

The rally drivers use some slick plastic/teflon type material under their cars for scrub strips. You could try some of that and get your skirts even lower. You could also add front spoiler and skirt extensions of a thin, stiff rubber or equivalent material with less friction that extends almost all the way to the ground. Something that was stiff, flexible, and maybe low coefficient of friction would be ideal. Maybe something like they used on the "sucker cars" in A-mod Solo competition a few years back.

I probably haven't added anything to the thread, but thanks for the brainstorming opportunity. Keep us posted.

[masraum]

I think one of the benefits of the cooling fan blowing down is that the engine stays clean, having the thing suck from the bottom would get it really dirty, and that dirt would not only cover the whole engine, top and bottom, but also the entire engine compartment and the trunk and back bumper. Just imagine if you got an oil leak at the mess a fine spray going straight out of the trunk grill at speed. Besides the whole back of the car being covered in oil, you'd really piss off everyone that was ever behind you because you'd cover their car with oil too. Good idea, but probably not very practical.

[BigD9146gt]

You definatly don't want to suck air up, but sucking it down wouldn't be difficult at all. Just use NACA ducts, they are the ones that Lambirginni (con't speel) used on all the old countash's. They start out narrow/ shallow and hour glass out and get deep. Depending on which way the air flowing over them creates a vacuum; facing forward (like an arrow) pulling air in, or facing backwards pulling air out. This done on the underside of the ground effects would be very efficient, expecially if you were able to make the underbelly low in the front and higher in the rear, creating vacuum in the rear of the car. That vacuum going over the NACA ducts should really suck... in a good way.

[Chuck Moreland]

Jack

I see you had the skirts back in action at the alfa event. Any further observations or conclusions?

[Craig 930 RS]

These are huge -

[Jack Olsen]

I don't have hard data from the Alfa event, since my data logger appears to be broken. (I had the fastest time of day, though.) I tore off the front piece again, which is getting expensive.

Here's version 3.0 of the chin piece. I still won't have any good data, since the data logger will still be out of commission. But this version moves the ABS splitter up high, with an aluminum skirt down below.

The advantages of the new design include a shape that will encourage folding back under impact (as opposed to tearing off, with the splitter being so low), and also low replacement cost. Three pieces of 6"x24" .025 aluminum. $15 at the hardware store, and significantly less at a sheet metal shop.

[Bill Verburg]

Looks good Jack, now carry it out to the whele well then up deflecting flow from the well area.
sort of like this

[Jack Olsen]

That's actually the idea, down the line. The thing I cobbled together for tommorrow could be turned into essentially a one piece unit, all aluminum, with it going a little wider in front of each front tire.

The next iteration of my sideskirts will also extend out a couple of inches farther than the current ones do.

This picture shows how the side pieces are still a little short:

[Bill Verburg]

I think that you are on track

[Jack Olsen]

At least 3 of my wheels are on it, at least.

[Bill Verburg]

most of the time any way

[Randy Webb]

Once you get it all fixed up, you should remove it and see how far down your lap speeds fall....

There's a mag. article in this somewhere.