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

[Jack Olsen]

'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.



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.

[Randy Webb]

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

Have fun & good luck!

[Mark sP]

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

[petevb]

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.

[Jack Olsen]

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



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

[Randy Webb]

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 Olsen]

[masraum]

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.

[Jack Olsen]

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.

[widebody911]

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.

[Stuttgart951]

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

[David]

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.)

[Jack Olsen]

Here's another angle on the side pieces.

[Tyson Schmidt]

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.

[Porschekid962]

BB II with a batmobile paint scheme now

[Jack Olsen]

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.

[juan ruiz]

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

Turbo Baby Turbo.........

[klaucke]

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

[Craig 930 RS]

Jack -

Here are some ground effect ideas

[campbellcj]

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.