aerodynamics of seven

[sdcat]

I still don't have my car back from the shop (wow, three months now), but have been thinking a lot about aerodynamic improvements. I haven't found much, except the rear diffusers that Freestyle makes. Anyone have any ideas or experience with the following?

1. I don't know too much about aerodynamics, but doesn't a forward rolling cylinder produce less lift than a staionary cylinder? If this is so, it would seem that there would be less lift on the front wheels with no fender. Of course, the drag might be more, but it might be worth it? I couldn't find any information on fenders vs no fenders for aerodynamics.


2. What about a little lip on the rear of the car to reduce drag, something like a gurney flap instead of a wing?

http://www.allamericanracers.com/gurney_flap.html

3. It shouldn't be too hard to fashion a front spoiler to hang below the nose.

4. Would Freestyle's rear diffuser really reduce lift much?

I haven't seen any references to windtunnel tests with body work on sevens. Maybe it wouldn't be worth the effort? I already have a wind deflector in place of the windshield, so maybe that's the only worthwhile mod?


Thanks!

Justin

[Michael Murphy]

Justin,

All good questions and comments. My advice is "don't go there". The seven has the aerodynamic attributes of a public works construction site. Best left alone. You could spend an entire 401(k) account to build a car that goes fast and looks ridiculous.

I am experimenting with small adjustments to reduce front lift, which is my main concern. I lowered the fenders as close to the tire as possible. I added small spoilers to the fenders (rather nice, if I do say so) and a chin spoiler under the nose cone, fashioned out of grand old American oak and a couple of clamps. I cannot guarantee that it will reduce lap times but it gives me the satisfaction of trying.

As for the underside and back of the car, forget about it. If you must have an aerodynamic car buy a sports racer.

Cheers

[sdcat]

Mike,

Yes, probably good advice about not trying too hard to make the seven into a completely different car. Do you have pictures of the spoilers?

[soareyes]

This is about as aerodynamic as I could imagine a Seven to be. But when does it lose its "seveness" as become something else?

[Elv15]

how about the "black brick"

http://rides.webshots.com/album/354242006MIvJEj

[moosetestbestanden]

Stan: don't ever post a picture like that again:D

Stokes asked this question big time after the Fontana event this year. He and I both spent some time researching the issue, he stateside, me w/ UK contacts. What we found is...

The diffuser is a waste of money. Full stop. Period. Don't even bother.
The CSR front wings will reduce lift by about 3% (+/- ISTR)
The little aero winglets on the nose of the CSR help reduce lift another 3% (again, +/- ISTR).
There's nothing else you can tack on that helps out much, if at all.
Getting rid of the windscreen is about the best thing you can do.
"Doors" may provide a little better airflow over the car.
Putting some kind of roof on would help a lot
The 7 is an aerodynamic brick.

At issue is handling in high speed corners and terminal velocity. The best way to cure the former is to work on balancing the car via suspension while running slicks, and the latter by adding more power (w/ a high horsepower Duratec of course:D). Remember that there is the fact of diminishing returns to consider in all of this.

Conclusion: Due to the aerodynamic, um, challenges of our cars we bite the weenie at Fontana but get it all back because of weight and handling just about everywhere else.

[JohnCh]

The best way to cure the former is to work on balancing the car via suspension while running slicks, and the latter by adding more power (w/ a high horsepower Duratec of course:D).

Chris, I believe you meant to write "w/ a high horsepower 2.0L Duratec" right? ;)

I've read claims that louvered front cycle wings as shown below also reduce lift. Did you folks look into those as well?



Thanks,
John

[sdcat]

Thanks for all the thoughts and the photos. I still might try to fashion a front chin spoiler if I can do it without ruining the looks of the car. Although, without side skirts I'm not sure it would help that much.

I still only have one track day on the car, since I took it to the shop two days after I bought it. Can't wait to get it back.

Justin

[Michael Murphy]

Justin, I will try to take photos of the spoilers at some point. THe front suspension is in pieces right now. Note that if you fit a front chin spoiler you won't be able to jack the car from the front without removing the spoiler. I made mine so that it can easily be removed but it is still a pain.

[sdcat]

Mike,

Thanks. Good point. I was thinking of a spring loaded plastic spoiler like the Z06 - it folded back when hitting low lying objects. But it would be a hassle not to be able to jack from the front.

[Elv15]

wishbone foils?

What about something like this:

http://www.fluke-motorsport.co.uk/pr...oducts_id=1039

[Sean-og]

I talked to some You-Row peein' 7 guys (Brits, actually) about underbody airflow, and the two who had diffusers on their cars both said a large part of their reasoning for fitting it was to offer some protection of the differential and/or fuel tank. Can't say that I thought of them as being particularly susceptible to damage myself, but that is how those two saw it, anyway.

While you will never make it "aerodynamic" by any definition, but even small improvements can only help - provided they are actually improvements. From the Wikipedia page on the Lotus Seven:
"While the car's frontal area is small, the Lotus Seven has the highest drag coefficient of any known production car--ranging from 0.65 to 0.75, depending on bodywork. The introduction of the Series IV Seven improved the car's Cd.
Additionally, the clamshell front fenders, or "wings," develop lift. This lift creates a high-speed understeer tendency."

edit: Super Seven Cars, Inc. in Canada offers an "Aero Kit" consisting of front spoiler, winglets, and rear diffuser. No price is listed, just "POA". Check it out at: http://super7cars.com/price/06gsx1300R.htm (the next-to-last option on the list). May be a one-stop shop for what you seek, if the price isn't too high. I should add that I have absolutely no experience with their stuff - never even seen one of their cars or products.
In my experience, Freestyle could be considered to be somewhat slow to respond and/or deliver.

[moosetestbestanden]

John: I don't know about louvered wings, the information I read was from an Englishman whose car was wind tunnel tested. Stokes has a more exhaustive document that may say something about em. And yes - the 2 L is vastly superior to those truck motors:D

[Roll a 7]

About 5 years ago Jez Coates and the boys took a 7 to the MIRA (Motor Industry Research Association) wind tunnel and did 32 runs with the wind tunnel pros providing advice on how to improve car. A writer from Autocar tagged along.

At 100 mph the car developed 74.1 lbs of lift at the front and 4.1 @ the rear, which suggests a good reason for understeer @ higher speeds. The Cd was a horrid .59. Mods included a diffuser, cardboard taped around the cage to make it a bit more aerodynamic, nose winglets and an aerodynamic cone fitted in front of the silencer. Removing the cardboard from the cage yielded 77.1 @ the front and 5.1 @ the rear.

After numerous mods, large and small, the 32nd run produced downforce of 31.4 @ the front and 31.5 @ the rear, an almost neutral balance. The car lost a great deal of its 7ness in the process. Uglier, but much improved from an aerodynamic point of view.

[magnusfeuer]

Brad. Are there images of the end result?

/Magnus F.