'Ground effects' is almost certainly overstating what I might be accomplishing, here. The panel on the bottom of the car reduces drag. The front splitter and side pieces will reduce the amount of air that goes under the car.

I finished iteration 2 of the rockers, today. I'll maybe get some white yarn and tape and try to shoot some track video on Wednesday.

http://forums.pelicanparts.com/uploa...1095635484.jpg

These things are all aluminum and fiberglass and are very light. I only had to add one 1/8 inch hole to the brackets that hold the AC condenser in place. All other mounting points were already present. The splitter is held in place with 8 bolts. The side skirts are attached to a long L-shaped support, which itself has three mounting points. It seems plenty rigid.

It may deform under air pressure -- your video will tell you if it does.

Have fun & good luck!

Well my hats off to you Jack. Keep up the good work.

Sorry Jack, I think I steered you wrong with my previous estimates of how low you can get that splitter.

I guessed that with 600 lb springs you’d want to keep the front splitter 3.5” off the ground. I still think that’s true for the car I played with, but thing I don’t think it works for your 911. You can probably get it a bunch lower.

First, our car had almost twice the weight over the front wheels, so it was moving up and down a lot more over bumps. Second, our car had a good size diffuser creating real rear downforce that went away when the front got close to bottoming. Third, the lip on the diffuser was over twice the size of yours.

In any case, I think my guess was well off- like everyone is saying you can probably get the front a bunch closer to the ground without problems. If you wanted to get fancy you might try a stepped air dam a la some of the touring cars- this was partly designed to cure the issue I had. For what it’s worth.

But you haven't seen how frequently I go off the track. ;)

http://forums.pelicanparts.com/uploa...1078046387.jpg

I think I'll try it at this height, and if I don't tear it off I'll try lower later.

If you drive a single track all the time, you can figure out how low you can go by mounting some pieces of plastic or wood at various points and seeing if they have scrape mounts. Keep moving them down until they do. There's your answer. You can make a little groove for them with a set screw to lock them.

Jack, I love it, you and Thom being the DIY will try anything once guys are my hero's. One thought. If you find that the sideskirts are a problem because they rub or something you could probably find a stiff rubber to use similar to what many people use when making a front lip. I seem to remember there was something like that on the 80's Chrysler Lasers.

Yep, definitely need to have the rocker flare out in front of the rear tires. The factory had small lips in front of the rear tires on the 996 GT3's. I remember a reference to it in a magazine, so I'd say that is important.

I've thought about that. But my thinking is to maybe add another inch of rubber sheeting all the way around. I'd adhere it in small sections (maybe 6 inches), so if one piece comes off it doesn't pull a whole strip with it.

But I think I'll see what kind of contact issues I have with the 3-inch clearance before I go lower.

Jack - have you tried a wicker bill on your wing yet? I added one to mine (1/4"), and it felt like I was going faster @ TH last week, although the wind was a factor.

This is OT... but damn, Jack.. do you even have a bad shot of that car?

I can't believe no one's suggested gear driving the fan in the opposite direction and creating a sucker car :)

(Yes, I realize this won't work for several reasons, but wouldn't it be nice to use the fan for air manangement, ala McLaren F1.)

Here's another angle on the side pieces.

http://forums.pelicanparts.com/uploa...1095728794.jpg

Poor man's neon?


Jack, you're kind of killing the plan I had for your car. I was shooting for NOT increasing drag.

I thought we were looking for smoother aero to combat the flares and rear wing. I was thinking we already had plenty of downforce, and were trying to get back some of the top-end we lost.

My original plan was to simply bring the front splitter down to belly-level, and continue the pan back to the rear. What you've got there is a little over-the-top, IMO.

But hey, it'll be interesting to try! I wonder how much it affects the top speed on the front straight, and in turn 8.

BB II with a batmobile paint scheme now

There are two things I don't like about the new red stuff.

1) It doesn't look remotely stock. Granted, BB2 isn't a 'stock' looking car, but the curtains and chin spoiler do not look like they would survive on the street, which makes the car look like it wouldn't survive on the street.

2) I nearly put my damned eye out machining a piece of aluminum.

However, I'm game for trying anything. If it makes the car faster, it's worth at least having in the tool box. If not, the pieces go back to the crusher. ;)

However, I'm game for trying anything. If it makes the car faster

Turbo Baby Turbo.........;) :eek:

Looks good and I think it's great your trying some DIY aero like this!

Jack -

Here are some ground effect ideas:p


http://forums.pelicanparts.com/uploa...1096516397.jpg

http://forums.pelicanparts.com/uploa...1096516471.jpg

I think it's possible to completely flat-bottom the car but only testing will show if the aero benefits vs. heat or other trade-offs net a beneficial result.

Here are a couple pics of the 914-6 I mentioned. I believe this car was very competitive in short race events at Willow and other hot-climate tracks.

It does have substantial oil and trans coolers, but I think you do too.

http://www.nosubstitute.org/events/H...2/DSCN0026.jpg

http://www.nosubstitute.org/events/H...2/DSCN0028.jpg

Just for the record, my red skirts (version 1.0) in action:

http://forums.pelicanparts.com/uploa...1097789158.jpg

Well whaddya think?

so... how did it affect your track times/top speed?

The car was MUCH more stable (and quick) through high speed sweepers. It was a little less predictable through elevation/camber transitions that involved a lot of lateral loads. I suspect I was getting some odd moments where one side was almost totally blocked off while the other was raised a couple of inches (from body roll).

All in all, I was very happy with them. Of course, I also went off the track, twice, and tore up the front piece, which I'm trying to re-fashion in a stronger way.

Lap times were down close to a full second with the skirts. A competitor who runs very similar lap times to me had his laps remain consistent (and now slower) than mine.

I'm going to test the new verion a little more scientifically, next time, with my data logger, which is now installed.

Any chance of a blind test??

Have a friend who can install/uninstall and then you drive er...

Very cool, Jack. Not only is it cool to see you trying things, but it's even better when they do something (positive).

One thing that I've been curious about. I see some cars these days that look like they have a notch in the center of their air dam. I'm not sure if the reason is because the front center is what takes the most abuse or because a fast smooth flow under the center of the car might help with the low pressure under the car.


this first photo has a bonus
http://www.wheelkinetics.com/html/hr...0F40%20547.jpg
http://wallpaper.net.au/wallpaper/au...%20800x600.jpg
http://wallpaper.net.au/wallpaper/au...%20800x600.jpg
http://speedycars.chinacars.com/wall...0%20-%2003.jpg
http://speedycars.chinacars.com/wall...%20-%20014.jpg

Of course, if you look at the GT2, GT3, and CGT, they don't have this same "feature" so nevermind. Forget I said anything.

http://www.super-sportwagen.net/imag...sche%20GT2.jpg
http://www.abdulkadirozcan.com.tr/up...rrera%20GT.jpg
http://www.albertweb.de/Porsche/Karosserie/GT3RS-b.jpg
http://www.autogaleria.pl/tapety/img..._1999_01_s.jpg

This is the kind of thread i HATE! 6 pages, and I had to read every damn one of 'em! Jeeez..I got 911 work to do!

Jack....please...PLEASE go back and retest with and with out...very interesting stuff, but back to back testing is so important!

Jack -

As an aside, what brand/type tires do you run at the track?

Those are BFGoodrich g-force T/A KD street tires. They scream a lot, but are cheap (one set per year).

Regarding the first picture with the girls, I dont think those were the 'skirts' that Jack was referring to:)

Yes, the black art of aero tweaks are interesting and sometimes difficult to theorize, much less test.

Jack, I think its great you are exploring the 'other' facet of racecar performance!

Now, just get BB2 to really minimize her roll, and these aero bits will shine even more so..

Chris Walrod

Here are some pics. of the CTR underbody.
http://forums.pelicanparts.com/uploa...1097814676.jpg
http://forums.pelicanparts.com/uploa...1097814725.jpg

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

I'll admit it, I'm too lazy to read all 3(make that 6) pages of this, so if somebody already addressed it - sorry!

But don't forget, your exhaust system has a constant heat source (exhaust gas) and requires a heat sink (airflow) in order to keep from turning into a giant ball of liquid hot MAG-MA!! So, no, they don't lose most of their heat out the tailpipe, the heat of the exhaust gases is actually mostly dissipated in the first lil' bit of exhaust headers - that's why headers like to get hotter than the sun, and the exhaust coming out your tailpipe is only warm....SmileWavy

Awesome. I love it.

I also think the 'blind test' would be neat, if it could be pulled off.

Jack, is that something you would be willing to try? Or would it be too time consuming/logistically improbable to accomplish?

I'll do A/B tests with it on and off, but I don't see a practical way to do the test blind. I'm not going out for a session on the track without being able to walk around the car, first.

The bottom line is that it's pretty easy to get max speeds through turn 2 (a 90-95-mph sweeper) and it's also fairly straightforward to look at max speeds at the end of the front straight. In fact, with the DL-90 I can look at dozens of segment times from different sessions with all the lateral g goodies and (if we get it hooked up) engine RPMs, as well.

Assuming I have the pieces ready to go again by next weekend, I'll have two days of sessions to run it both ways. And that will produce tons of data to look at.

Jack,

I began to put these together when this thread first started, and had trouble posting them. I forgot about it until I saw the thread resurface just the other day. I'm glad that your side skirts seemed to have helped.

My idea was to run skirts down the sides of your underbelly tray. Body roll would have less of an effect since they are closer to the center so the "seal" wouldn't be as likely to break.

http://forums.pelicanparts.com/uploa...1097864890.jpg

The way your underbody tray sags a bit (from the measurements in your photo) is very much like the groud effects tunnels the pros make. I was also thinking that a material like (I looked this up in McMaster Carr) "cloth-inserted neoprene rubber sheeting" (basically a material like tire rubber impregnated with fibers) would be good because it would be okay for the stuff to actually drag on the ground (as long as it was mounted well enough) would be a good skirt material. Finally I had some diffuser thoughts. The pictures sum up my original ideas.

http://forums.pelicanparts.com/uploa...1097865098.jpg

http://forums.pelicanparts.com/uploa...1097865013.jpg

A workable maximum angle for the diffusers could be determined using some simple Reynolds number calculations, but I'm supposed to be doing billable work right now...

anyway just my $0.02

Do a walk-around for track readiness -- and then have the add-ons removed. No risk and you have a true nearly objective comparison. Si?

yes I'm thinking about cpoy the rear diffusers of the VW bettle RSI. with some mods. to fit on a 911.

Also remember that there is little effect from the diffusers - and to a lesser extent the front and sides - until 70/80 mph --

Cool project. I would love to see a rear diffuser for a 911 - I will also build one once the ideas come forth......

Jack, do you know what your typical speeds on the track are?

And... any sense of how much time is spent at what speed? Say x minutes between 80-90 mph; y minutes between 90-100mph, etc.?

Willow Springs is a very fast track, considering there is no banking. If you run a 1:30, your average speed is 100 mph. There is one section of the track where speed drops to just below 60 mph, but the rest of it is generally between 90 and 130.