Poor Man's Aero Package, Version 2 - Page 4

Jack Olsen · 03-30-2005, 08:58 AM

Just to be clear, my expectations on the diffuser are nil.

I fabricated the more-aggressive splitter and side skirts, and I expect that by limiting air passage under the car, I'll see a benefit. There are loads of race cars out there doing the same, so this isn't that big a leap. My home-made skirts are probably less effective than commercially-available pieces, but mine are cheap and easy to remove for the drive home.

The flat plastic panel under my car was also an easy decision. My testing was by no means scientific, but it was less than $30, and produced an immediate reduction in my lap times. Remember that my car has an underbelly AC condenser, which (apparently) had a detrimental effect on the 911's under-car aerodynamics.

The diffuser was an afterthought. I already had the tools out.

My thinking is that if I'm able to come up with a fairly reliable way of measuring the effect of these pieces (as well as different wing settings and different tails) -- whether it be a couple of bicycle wheels or a set of strain gauges, wool tufts, or a combination of all three -- then I'll test everything I've got, including the diffuser.

But it's the one piece of the whole group that was done just for kicks.

randywebb · 03-30-2005, 09:27 AM

It doesn't have to be as flat as a pancake (or as Kansas, which is now known to be flatter than a pnacake).... but the flow has to be pretty "flat" w/o many large eddies.

Now -- Jack how far are you willing to have stuff stick out behind the car? That will help with the issues above. You could even rename it "Langenblack."

Or if you don't like that one, "Black Booty II."

Jack Olsen · 03-30-2005, 10:02 AM

Some final pictures, before I take it back off:

Smooth, from head to tail:

The next step is to find a way to monitor cylinder head temps, so that I can be sure the experiment doesn't do more harm than good.

randywebb · 03-30-2005, 10:21 AM

Think about bashing the leading edge of those holes upwards -- for more air flow. Maybe NACA ducts would be good to use on the undertray also (or you can use the more advanced NASA ducts).

nostatic · nostatic's Garage

I think the Keebler elves could use that to slice cookie dough or something...

chrisp · 03-30-2005, 10:39 AM

Jack, when do you sleep? or do you not work?

bigrubberjeep · 03-30-2005, 10:50 AM

Jack - Seirously, how did you make it?

Jack Olsen · 03-30-2005, 11:45 AM

Quote:

Originally posted by randywebb
Think about bashing the leading edge of those holes upwards -- for more air flow. Maybe NACA ducts would be good to use on the undertray also (or you can use the more advanced NASA ducts).

I actually angled up the trailing edge, which didn't make any sense to me (which might mean it has a chance of actually working). I copied the factory one I have as a model... sort of.

I assume the factory did it this way in order to prevent a high-pressure pocket from forming?

Do you think it might work? (Or am I more like a monkey who's found some old circuit boards and a suitcase, and thinks he can turn it all into a laptop computer?)

Tyson Schmidt · 03-30-2005, 11:51 AM

Jack, the slots on the sides of my 964 undertray are very important. They are there to let the air escape from the cylinder heads. The big middle openings are only for the cylinders.

You can see that I had drilled more holes in the undertray to aid in cooling before I simply took it off altogether.

widebody911 · widebody911's Garage

That's neat looking - now you need a CF version...

Jack Olsen · 03-30-2005, 12:12 PM

Quote:

Originally posted by Tyson Schmidt
Jack, the slots on the sides of my 964 undertray are very important. They are there to let the air escape from the cylinder heads. The big middle openings are only for the cylinders. You can see that I had drilled more holes in the undertray to aid in cooling before I simply took it off altogether.

Most of that area is already open. It's the part I labeled 'A' below. Should I drill out the corresponding area (labeled 'B') that remains?

David · David's Garage

It's a cool idea, but I don't think the curve is gradual enough so I suspect the air is separating before it gets a chance to accelerate.

1987 Ferrari diffuser:

JeremyD · JeremyD's Garage

Cool idea. I would recommend cutting up a kite (nylon, lightweight ripstop) and taping that to your car. Then I would get someone to follow me with a video camera in their car and record my car and the streamers on it. That will give you a good idea on laminar flow before you get to the track. There is an optimal curve for air (just like water) you might do a search on line, believe it a NACA prfile and you may be able to download profiles/templates before going further.

randywebb · 03-30-2005, 01:00 PM

It makes sense now that i see the other side...

re monkey issues... Well, that is pretty much the way fluid dynamics works. Nothing is better than an educated guess b/c the fundamental equations have never been solved. All the models you see are simply numeric approximations...

Just be careful with the head temps. - I know you will be... And if not, your car will be even faster when the new 3.8L RS engine goes in...

air-cool-me · 03-30-2005, 02:38 PM

put CHT's on the two heads that are not uncoverd... run it...(or all... to be safe)

i bet those will get the the most toasty...
you can always pit and remove the thing before the CHT's go way up...
or... bring a drill and add some hole's
then you can collect usefull data on just the sideskirts and the front...

but i think i am suffering from "not my car syndrome" or NMCS

or maybe "MWSFT"
(my wallet safe from this)
or maybe even "TSIBIDHTPTRBSIWTHTJDI"
(this sounds iffy but i dont have to pay the repair bill, so i will tell him to just do it)

Yargk · Yargk's Garage

Quote:

Originally posted by Bill Verburg
It looks neat but if these guys aren't worried why should you?

I'm assuming that you mean since these racers don't have diffusers, why should Jack? I believe that they are not allowed to have diffusers in Le Mans GT classes, the bottom of the car must be flat. This is one of the reasons we have a maserati and not an Enzo in GT racing. If diffusers were allowed, I'm sure every one of them would have one.

Yellowbird RS · 03-30-2005, 09:17 PM

Jack the diffuser looks great when do you going to test it?
about GT rules:
maserati have one
gt race car:

st. car:

enzo:

ferrari CS:

F50 LM

Jack Olsen · 03-30-2005, 10:39 PM

Quote:

Originally posted by Yellowbird RS
Jack the diffuser looks great when do you going to test it?

Thanks. Track testing will be done on April 13th. I'll try to do some video with wool tufts sooner, but not before my new CHT gauge arrives.

Yargk · Yargk's Garage

Yellowbird,

After looking more, I think I'm half wrong. I remember hearing that the Maserati was a racing version of the Enzo and that they had to remove the diffuser, this is plainly wrong as you have pictures of them with diffusers. However, after looking at ALMS rules and finding some pictures it appears that the higher GTS class allows diffusers, but the GT class, which Bill's GT3RSR pictures were from does NOT allow diffusers. Check out the GT class 360 below. It doesn't have a diffuser. However, I'm sure if they allowed it, this car would have one and maybe the RSRs too.

So in summation: it seems GTS allows it, GT does not (from what I've gathered). Now GTS is called GT1 and GT is called GT2 (I think), I'm not sure if this policy with diffusers has continued.

Jeroen · 03-31-2005, 02:49 AM

I think you need a spot where you can exit hot engine/exhaust air (and the air you're scooping up from the openings under the engine)

If you look at the pics of the other cars, you can see they all have that (above the difuser)

How about putting some louvres (openings facing to the back) in the sloping part of your difuser?