E30 Aerodynamics

[Sh3rpak!ng]

Alumilite and plywood seem to be the preferred materials for the E36 guys.

I picked up a 1/4" piece of ABS this past weekend that I will test out. It's several magnitudes more rigid than the 1/8" and should provide nice impact resistance. None of the local sign shops with dibond or alumalite are open on the weekends or weekdays past 5pm which makes it near impossible for me to pickup.

I also used a version of "Alumalite" called Alupoly from a local plastics shop for my front splitter. I ended up using a 3mm (approximately 1/8") thick version, but they also offer a slightly thicker version as well. I sent in a CAD template that I made and they CNC cut it in a day.

The mounting is not the most ideal setup for fully functional aero as I just bolted to my IS lip every 6-8 inches, but it does feel very sturdy up to speed on the highway. I would also need to block the front gap on the lip for additional functional down force. This version overhangs about 3", but I also have a 5" version that I will eventually try when I decide to make the switch to a rear wing.

That's a nice piece. I just fixed my computer and am looking for a "light" CAD program to do simple drawings for parts like this. Any suggestions?

[ian e30 318is]

Alumilite and plywood seem to be the preferred materials for the E36 guys.

I also used a version of "Alumalite" called Alupoly from a local plastics shop for my front splitter. I ended up using a 3mm (approximately 1/8") thick version, but they also offer a slightly thicker version as well. I sent in a CAD template that I made and they CNC cut it in a day.

The mounting is not the most ideal setup for fully functional aero as I just bolted to my IS lip every 6-8 inches, but it does feel very sturdy up to speed on the highway. I would also need to block the front gap on the lip for additional functional down force. This version overhangs about 3", but I also have a 5" version that I will eventually try when I decide to make the switch to a rear wing.

[Digitalwave]

Alumilite and plywood seem to be the preferred materials for the E36 guys.

[Sh3rpak!ng]

Looking for advice on splitter materials and construction. I made v1 out of mostly 1/8" ABS, angle aluminum and 304SS - the aluminum and SS used for brackets and support. I liked the ABS because it's flexible and is already black, but now I see it's just a bit too flexible to be a sturdy aero component. Currently looking for alternatives. I've seen alumalite suggested and used. I also found a local source for dibond (similar to alumalite but with a solid poly core). And I'm also considering sheet aluminum. What materials have others used successfully? My untested thoughts are a toss up between all three. Biggest question for either alumalite or dibond is 1/8" vs 1/4" thick. If I went aluminum seems 1/8 is plenty strong. Only concern against aluminum is that if I smash it on something it will bend and be a pain to flatten vs dibond/alumalite which seem to a be a bit more durable in that regard. As far as construction design goes I initially mounted the splitter to the bottom of the valence by way of an ABS skirt which clipped into the IS brackets in the valence, and screwed into the splitter through angle aluminum. While it looks good, it's not durable nor very structural and is prone to popping out of position with minor scraping/rubbing against the road/driveway (which is kinda what I intended - but too much). I'm trying to engineer some planned failure mode into this whole thing so that if I smash the splitter on something like a cone or off-track adventure I don't also smash the valence along with it. So in other words I want to mount both splitter and front lip separate from each other. Splitter mounted to the frame rails with brackets + support struts and some (easily broken) plastic clips to the lip. Then the lip mounted to the valence with sturdy brackets. I hope that this will allow the splitter to be sturdy enough to provide actual aero benefit without damaging more than just the splitter in an "incident". Thoughts?

[haaken675]

According to Johnny 9 lives racing, the higher the better since you will be getting out of the air stream and into open air. Seeing that Time Trials and the like have rules against the wings being wider than the car, or higher than the roof, I would tend to think he is correct (not to mention his resume lol).

He says a lot in this thread (and is a professional aero expert for many pro teams)...

https://forum.champcar.org/topic/188...ero-questions/

Thanks for posting that link. Read through a few pages while sitting at the trade show booth twiddling my thumbs...

Also checked out Nine Lives Racing's website and it looks like they are working on an e30 kit: https://9livesracing.com/products/e30-big-wang-kit

[ForcedFirebird]

According to Johnny 9 lives racing, the higher the better since you will be getting out of the air stream and into open air. Seeing that Time Trials and the like have rules against the wings being wider than the car, or higher than the roof, I would tend to think he is correct (not to mention his resume lol).

He says a lot in this thread (and is a professional aero expert for many pro teams)...

https://forum.champcar.org/topic/188...ero-questions/

[benloveless1]

So I am finally getting to the point in my build where I can actually think about aero. I plan on doing a front splitter, rear diffuser as I no longer have a spare tire well, and a gt wing. Does anyone know if it makes a big enough difference in wing height? I was looking at an APR GT-250 or an APR GTC-300, but it looks like total height is somewhere around 13 inches. Roofline is somewhere around 17-18 inches. This height is achieved with their standard 11 inch pedestals. Apparently that being said, they offer a 14 inch pedestal that I could custom order that would likely bring the total height to around 16.5 inches.

Would that work better, especially if I went with the 2d shape of the GT-250 wing?

Still interested in knowing the answer to this^^^

[LowR3V'in]

on wikipedia a wingless mk4 supra is .33
and with the big ass factory turbo wing .34
so the e30 sport rubber strip probably is just to make it look sporty.

[TobyB]

it *decreases* drag - it doesn't increase it.

Fun fact: facelift E30s were actually wind tunnel tested. :rofl:

Yeah, by detaching the turbulent air from the rear of the car somewhat better.
That may, in fact, stabilize the car, if the turbulent air is generating lift or
buffeting on the rear end.
Or it may not, depending.

It would be fun to see the wind tunnel test results-

I've seen pix of 2002s in wind tunnels, but that doesn't mean BMW did any DEVELOPMENT in them, just stuck the cars in and said,
"hmmm, very interesting. Bratwurst or Knockwurst for lunch today, Hans?"

t

[djjerme]

I know Alpina did a lot of Aero testing on the early E30's with both their front and rear spoilers. The Alpina front spoiler definitely does make a difference at highway speeds, but I have't tried my B6 on the track yet - will do it the next open track day I think just for S & G.

[nando]

I'm sure it's very minor on E30's but isn't a rear lip also designed to keep a car stable at high speed, not in the way of down force. But increasing the drag on the car in a predictable way. I'm not very knowledgeable on car areo but we use devices very similar on rockets to increase "base drag".

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it *decreases* drag - it doesn't increase it.

Fun fact: facelift E30s were actually wind tunnel tested. :rofl:

[ak-]

Hope you guys didn't think I was talking about downforce when I said an absent spoiler can create rear-end lift. Spoilers aren't for downforce, correct.

[Motheye99]

I'm sure it's very minor on E30's but isn't a rear lip also designed to keep a car stable at high speed, not in the way of down force. But increasing the drag on the car in a predictable way. I'm not very knowledgeable on car areo but we use devices very similar on rockets to increase "base drag".

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[ForcedFirebird]

The spoiler doesn't produce downforce, it reduces drag on the rear end. It wouldn't make the car feel light if you took it off, but perhaps it would lower your top speed by a couple mph. That said, it is probably a very small difference.

Sorry, I was getting at it feeling "light" without an OEM trunk lip.

I saw somewhere that BMW claimed a 5% reduction in drag. It's probably worth a few MPH easily, but yeah, it doesn't have anything to do with downforce.

Would be fun to do back to back experiments. We do Daytona pretty much every year. Unfortunately keeping the cars fueled and full of drivers are more important. I can say a 4.10 vs 3.73 doesn't matter much, the cars are aero limited in stock form. I've driven identically built cars, with and without the OEM the lip and didn't notice, but am also a mid pack driver. :/

[nando]

I saw somewhere that BMW claimed a 5% reduction in drag. It's probably worth a few MPH easily, but yeah, it doesn't have anything to do with downforce.