This is just a fantastic forum! Being quite the newb, forgive me if I'm on the wrong thread. I need some advise and I know that it'll be freely if not copiously given. I like it already!

We've got a '74 that, at the moment, is in pieces. It's a street/track (little more focus on the track) baby that is getting some minor additions to help with high speed stability. One is the addition of a rear wing. There are two choices. As you can see from the pics, it's not pretty but at this point that's not the point.

What do you think about aerodynamics/functionality and also aesthetics?

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Don't have any advise on the spoilers vs wings just wanted to say...

I like the first one the most, I have been wanting to put just a lip spoiler on the back of mine. I think it all really depends on the overall look of your car.


But, be careful some of the wings can bend your decklid....

You're in the right place!

Regarding spoilers; personally

T

any aero device mounted down on the decklid or a wing that low will have no aero advantage. I had a 6" tall rear spoiler on my car and it was pointless (tho' it looked really cool ).

So, I would just pick whichever you like the looks of as it will be aesthetic only. Without any additional aero devices such as vortex generators across the rear of the decklid, any wing needs to 1) have an actual foil shape, and 2) be mounted within a couple of inches of the roof height. Slightly higher above the roof, the cleaner the air and benefit.

My wing after selling the spoiler

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I have a wing it is functional and it doesn't bend the deck lid.

Niether of the ones posted in the pictures will have any effect on downforce or stability at speed.

Because if the vertical rear window the air is insanely dirty and scrambled. Only way to get air to a wing is put it up high or use vortex generators on the roof and the wing only needs to be half as high.

and a splitter is absolutely required with the use of a wing. I have tried the wing with no splitter DON'T DO IT !!!!!!!

is there an echo....echo....echo... haha. Hey Joe, I saw the post and was sure you would be one of the replies, so imagine how happy I was to get in a reply first


yeah, what he said that I said that he and I have probably said before.

I almost forgot again... the reason for the post

The Paddock is another forum here in 914World that has some great older threads with pics and discussions on the wing builds of both of those awesome 914s seen above. For sure the wing+splitter is going to give more downforce, but unless you got lots of HP planned you may want to run w/o either to reduce aero drag...just like the OG 914 factory GT race cars. Great to see more race projects!

I agree with all above - and welcome to 914world!!!

However, its your car man, do what you want and if I was choosing for you it would be the first one.

without a wing your car will spin off into space.

Thanks all for your input. I should have mentioned that we're building a dam with splitter as well. I'll post some pics of that when available. I really had no idea that the vertical rear window would mess things up that bad. Yet on the other hand, it precludes the use of an effective wing! Less messing around before you can get out on the track.

Another responder said that horsepower should be a prerequisite for using a wing. Well, we've got a little LT1 that does the trick. This past season's track sessions proved the necessity of a dam with splitter to keep the front end from "sight-seeing" at over 120mph.

Thanks guys, again. Your input is greatly appreciated.

My car is 5 MPH faster with wing and air dam than without and a heck of a lot more stable. Also bumped MPG so it's really not a fluke. Real air foils don't need a huge angle of attack to be effective.

Yes this very same wing mounted on a civic hatch with 10 degrees of angle slowed his car down 7 MPH.

I run my wing about 2 or 3 degrees high speed 100 + and crank it up high for Autocross. It has lees effect under 60 MPH.

For byndbad914 and joe, question:

What distance are you running your front dam/splitter off the ground for maximum effect? And how long/wide does a splitter have to be to effectively prevent air from "rolling" under the air dam?

We're in the midst of constructing a dam for the street with adequate clearance and then have an extension that would be even lower that would have the splitter attached to that to give us the required ground effects.

And, don't paint ot the wrong color or you'll blow the engine!









I keed, I keed!! welcome to the club.


Keith

I think your wing has to be high.

But I would get the front planted before I add downforce to the back.

My free advise on vortex generators on a 914.....

When engineers put vortex generators on a surface they are ususally trying to get the airflow to stay attached (in an unfavorable condition).

The rear window of a 914 is less of an unfavorable condition and more of an impossible condition. I am unaware of any way to keep the airflow attached over the back deck of the 914 short of making a "fastback".

The vortex generators that got a buzz here before apparently were designed to cleanly separate the airflow from the surface much like a small spoiler will do. So while there may be some benefit, there is still not "good air" near the rear deck. I do not know if this type of vortex generator or a small spoiler would allow for lower wing, but it won't allow for a fuctional device near the deck.

I am not an aeronautical engineer so you were overcharged for this advice.
Check out this webpage Chris Cassedy's Webpage on 914 aerodynamics.

Splitters tend to work more with how far they stick out v. how low they are to the ground - they do as implied and split the air. So that said, the longer you can make the splitter stick out of the front of the car, the more downforce you get because air attempting to bend down under the bumper and travel along the air dam is forced to stay above the splitter and therefore that creates downforce. I would put an air dam and splitter as absolutely close to the ground as possible. I heard a rumor in NASCAR that the splitters on the COTs are needing to be changed out regularly because the guys were basically dragging them on the ground.

So to recommend a splitter length is a bit hard as really you want it adjustable (able to be slid out further when necessary) but I would say have it stick forward at least 2-3" in front of the dam.

My splitter height is frankly set by the dam the nose had built in and the suspension travel I needed for the local 4x4 track they like to call a road race course I was much lower on overall height in CA for Willow Springs...

As for the comment about vortex generators and how they separate flow, that is a specific type of vgen similar to what you see across the rear roof line of a Mitsu or out on the wing of a jet the next time you fly.

Go to the paddock and search out the thread race914 had started about vgens being used on large trailers with flat backs. I am still a bit skeptical (you will see my posts) but he ended up going to ButtonWillow and seeing an increase in speed and some effect from his rear spoiler finally. I plan to put them across my rear deck and lower the wing some more to increase overall stability. The idea is those supposedly bend the air down, but I have to wonder if they kick the air up first, then it bends back down not much more than where it was to begin with...

But they may also decrease drag at the rear section of the car by flowing better behind the car where it meets with the under air again.

edit - oh, and to agree with Joe's comment on wing angle, I was essentially "flat" across the top of the wing which is about a 3-4deg chord angle at Willow Springs (really high speed track) and you can see in my pics, I run much more angle (last time I tried 12deg and that is what you see in the pics) trying to use it more as a spoiler than wing, since the track is much slower. But I also slowed down a couple mph in the front stretch (I hit between 130-135mph at Pueblo but was 150+ at Willow on the front stretch). Before the wing and splitter I was ALL OVER the front stretch at Willow around 135-140mph and the car is much more stable now.

So does anyone have any good pictures of how you made your splitters and attached them to your air dams?

As for pix of attachment, mine wouldn't apply the nose of my car is a Sheridan part and the underside is all tube chassis. To make it, I bought a sheet of 1/8" aluminum, made a heavy paper template that I duct taped to the dam and so forth and cut to the shape I wanted, then simply laid the template on the alum sheet, traced it with a sharpie and cut it with a little hand-held band saw. 'Bout as easy as it gets. Attaching to whatever dam and car structure you have is just a matter of "doing it" as it takes more effort than thought... it is pretty easy to figure that stuff out.

cool. I guess I should just go buy some aluminium and do it.

It really won't make any difference in an autocross situation Jon. Only on the track do these ground effects really work wonders. On the track a splitter also needs to be balanced by a spoiler.

Humph.......tell it to this guy.

Giggle giggle snort.

Yes they do work at an Autocross if the event course layout is fast. anything over 45-50 MPH.

I have been to 4th gear before because I hit the 6250 RPM rev limiter in 3rd.

Anyway I lowered my air dam to the hieght if a 4x4 (3 3/4") when the car is at normal ride hieght (4 1/2")

It is even with the bumper pad when viewed from above the blade is 6" deep.
the under belly splitter board goes back to the line of the front axle and join nicely with the steering rack cover. made of 1/8" Luan laminated with layers of fiberglass. Strong enough for my 7yr old sone to stand on. and hit a cone without worry going over 60 MPH

I can feel the effects of heavier steering starting around 45-50 MPH.

My next one will be built to the limit of the rules and require struts to hold it up.

Ok, they will make a difference, if they're big enough. And if you are going fast enough. A little Al one that sticks out an inch or 2 won't do anything at those speeds (kind of like the things that are on alot of ricers), and you still need to balance it out.

Hey Joe

Could you please send me some pics of your air dam/ splitter so I can see what it looks like. I am crafty, but my father in law is the one who really knows how to work with composites. If I have a picture to show him what I need it will help greatly in making it.

Thanks.

IF I could come up with a 200 sq in wing at a resonable price.....that I knew worked & a splitter that didn't stick out past the front bumper.....same requirements as above, I'd go fer em'. I get airflow to the spoiler as is, but I'm not convinced that it does much good......there is a cool factor tho.

so the discussion is bringing up some good points - all aero stuff is very car and use dependent. So if you want to AX and have "high" speed oversteer ("high" being quoted as 55-70mph on larger courses is high for AX but not for an interstate hwy let alone road course) then you want a big, FAT wing (fat in foil shape) and will probably run a maximum angle (right near wing "stall") to get both a spoiler and wing effect. So first you add the wing, which tends to overshoot and create understeer. So now you start adding splitter to counteract that to the point of how you want the car to feel.

So my car had NASTY high speed oversteer (125+ mph sweeps at Willow Springs thru T8) with the V8 and 930 trans (both much heavier than stock stuff) but not necessarily low speed oversteer (I can use the go-pedal with all the power to get what I want). So the car was scary. I then went to a whole new car setup (tube chassis, etc) and also added a wing at that time. I have a short splitter because I wanted to tune the car to just a slight plow (At speed expectation of 150+ thru T8 I wanted a safe bit of plow). So if I had stayed in CA to try a longer splitter, at some point the car would have gotten neutral and I would have scaled back to be somewhat safe. That is why I recommend an adjustable splitter that you can slide back and forth to fine tune the front downforce to match the rear and get the driver feel you like (slight over, neutral or slight understeer). You tune the rear to the max downforce that doesn't drag mph down (unless the car is still unstable, then you go up to wing stall to fix that issue even if it slows the car slightly).

I used to work with Tyson Schmidt, Wevo guy, when he lived in Seattle. My old boss goes down to see him about twice a year and they go to Willow. I think your 914 is the one they tell me about. They are very impressed, and they have some very nice 911's.

Phoenix - that may be. I never met Tyson tho' I know of him from guys that ran out there (he used to work on some of the 911s out there when he was in LA before going to WEVO) but he mentioned digging my car one time on the bird board. I never got to run the full tube car there with those guys tho' (I ran on a test and tune day about a month before moving to CO).

found this link about the COT splitter to give some of you guys ideas (maybe). Notice that pretty much exactly as Joe has done (and typically the rule of thumb), the splitter extends out about even with the bumper length. As stated, I started a bit shorter (which you can argue is stupid on my part as I could have easily removed material to a slight plow v. the impossible adding of mat'l - I don't always think everything completely thru hahahaha)

http://i.a.cnn.net/nascar/.element/img/1.0.../22/cot/COT.pdf

Thanks for the link. That definately helps. I can make that.