Improved high speed stability with front splitter/diffuser

[juicersr]

Finally got around to putting my front end back together after fixing all the damage done last year at track days and Turbopalooza, and decided to fabricate up an aluminum front protector/splitter. (sorry about lame iphone photos, but my digital was out of juice)



As you can see, the lip extends about 1/2" from the margin of the spoiler, and extends all the way around the sides as well. In order to secure it, my metal guy and i ran it centrally all the way back almost to the steering rack.

Finally took it out late last night for some deserted highway high velocity testing and WOW... the high speed stability of the car is dramatically improved. Whereas above 130/140 before the front would start getting a little squirrely, now it was rock stable. My first lesson in undercar aerodynamics was quite amazing

Is this increase in stability due to the small lip of the splitter, or the fact that there is less pressure/turbulence/cavitation of air underneath the front now that all the empty space behind the spoiler is 'blocked off'?

Anyone else have a similar experience with a front splitter/undercar 'diffuser?'

Will try to get some good pix of the underside later this week if anyone interested.

[rsrfan]

Would love to see the pics...

[drmatera]

Me tooooo

[Turboo934]

Justin : I've run a back splitter on mine, only 10" back. It seems to give front the glue it needs at high speeds. I discovered this on my 73 RRS but I did have 3" out front and more out the back side. How are you dumping the air flow to your front center cooler ? Looks great, have you thought about lexan covers for your lower lights.I've lost two sets, if you look at the 934 SPEEDSTER you'll see what I'm talking about.

[DDDD]

Hank at GT Racing sold me a RSR piece with the splitter lip around the front and it just makes the front end of the car stick like glue. He told me that the perfect splitter actually extends 3 inches forward, and that the regular 911 RSR piece he makes now extends 3 inches out. That seems like overkill for the street but you also track the car.

[JFairman]

Increase in stability would be a combination of the two and would work better if the front lip of the splitter stuck out a little farther.

If you have an oil cooler mounted behind the middle opening than air isn't going to flow out from behind it and then down under the car with the splitter extending back and the bottom sealed off back to the gas tank or steering rack like you described.

[DDDD]

You know you gotta paint that splitter black! It will look awesome.

[zeb930]

A splitter makes a huge difference in high-speed stability.. Currently running a 3 inch splitter that goes back to the tank area (Made of ABS-plastic = bombproof)

Had a glassfiber version earlier that got shot in a roadconstruction. Lost about half the splitter and immediately notices a degradation in high-speed stability..

[juicersr]

Originally Posted by Turboo934

Justin : I've run a back splitter on mine, only 10" back. It seems to give front the glue it needs at high speeds. I discovered this on my 73 RRS but I did have 3" out front and more out the back side. How are you dumping the air flow to your front center cooler ? Looks great, have you thought about lexan covers for your lower lights.I've lost two sets, if you look at the 934 SPEEDSTER you'll see what I'm talking about.

I guess i should post some pix of the underside, as the piece is really a 'T' shape that prevents flow directly under the cooler, but allows air flowing throught the cooler to vent out the sides where the plate is gapping. I was concerned as well about flow through the cooler, and this is what we came up with. Last night was balls-freezing cold (for us at least, around 30-32) so i cant really tell if the plate is going to interfere dramatically with flow through the cooler and thus running temps. Have to wait for the spring/ summer for that,

Rob, Christine was an inspiration for the Hellas, as i really liked how yours looked i got them two year ago, and had been on the fence about mounting, and with the front off for the last couple of weeks, and the night track experience in Florida at the end of the month looming, thought it would just bite it and do it.
Really dig the look.

Would definately be into covering them with some lexan... i saw them on the speedster, and it just makes sense, from an aerodynamic standpoint, protection, and i really am not in love with the 'Hella covers'. However, i still like the clean look of the factory 934 spoiler, and the speedster covers detracted from this.

[JFairman]

you could put something like a couple convex naca ducts or some louvers on the bottom of the splitter behind the oil cooler to suck air out of the flat area thats likely impeding some air flow from the back of the oil cooler now.

[juicersr]

Originally Posted by zeb930

A splitter makes a huge difference in high-speed stability.. Currently running a 3 inch splitter that goes back to the tank area (Made of ABS-plastic = bombproof)

Had a glassfiber version earlier that got shot in a roadconstruction. Lost about half the splitter and immediately notices a degradation in high-speed stability..

Damn Zeb, that thing would make sushi out of any road kill! U got me thinking i need to make a bigger one... and so it begins

Quad-D, yeah i was going to anodize it black, but not enough time before 'Winterpalooza'

[juicersr]

Originally Posted by JFairman

you could put something like a couple convex naca ducts or some louvers on the bottom of the splitter behind the oil cooler to suck air out of the flat area thats likely impeding some air flow from the back of the oil cooler now.

That's a really good idea Jim. I'll be curious if i see any difference in running temps down there at PBIR on the 26th.

[JFairman]

Yeah, and guess who you'll be meeting soon that has different size female molds for making NACA ducts..
Then cut the triangular holes and pop rivet them on.

[juicersr]

Originally Posted by JFairman

Yeah, and guess who you'll be meeting soon that has different size female molds for making NACA ducts..
Then cut the triangular holes and pop rivet them on.

LOL, the guys at G-racing could just pop her on a rack and and do it in like 15 minutes whereas it'll will take me all day Looking forward to seeing their shop.

[boxermania]

The splitter actually creates a venturi effect (Bernoulli) especially if it runs all the way to the pan, in essence creating a vacuum that draws the car to the ground.

Under normal conditions as the speed increases the air will fill any and all cavities under the car and create the opposite effect, lift, lightening the steering and making the car wonder.

Amazing how a little air management can improve handling and add little or no drag. Great job!!!!

[jimmcc]

Originally Posted by JFairman

you could put something like a couple convex naca ducts or some louvers on the bottom of the splitter behind the oil cooler to suck air out of the flat area thats likely impeding some air flow from the back of the oil cooler now.

"as the piece is really a 'T' shape that prevents flow directly under the cooler, but allows air flowing thought the cooler to vent out the sides where the plate is gapping"

Won't the 'T' shape allow for air flowing through the cooler to vent out the sides and into the wheel well area? That would negate the need for lower ducts and reduce the air flow underneath the flat bottom of the car.

Am I missing something here? Pictures of the bottom side would be helpful. You should know better than to leave questions.

The blocked off bottom is probably creating most of the change you feel. I have a AIR piece that accomplishes the same with a C2 Turbo setup (1980 vintage 930). I agree with the other posters that the lip should extend out further but what you are doing will help. Dull the leading edge if you move it further out as they make for neat shin skinners.

Good work and thanks for posting.

[zeb930]

Originally Posted by juicersr

Damn Zeb, that thing would make sushi out of any road kill! U got me thinking i need to make a bigger one... and so it begins

Quad-D, yeah i was going to anodize it black, but not enough time before 'Winterpalooza'

I would leave yours as it is, just make an exstension. That way you have a replacable (black anodized) piece that takes all the nicks and dings.. and you wont have to replace the section under the car..

Another idea is to block off the airflow behind the lamps (a little more drag but locks better) and also block the brake-cooling holes if they are not in use. The oilcooler airflow should evacuate ok to the wheelwells (if not naca ducts may be needed)

[JFairman]

You could also make it out of fiberglass or carbon kevlar composite if you have that hanging around.

Take a flat sheet of aluminum thats bigger than the piece you want to make and spray it lightly with mold release or wax. Even covering it with masking tape will work since polyester resin will not stick or go off in contact with masking tape.

Then lay 8oz. or whatever thickness fiberglass cloth you're using on the aluminum sheet and wet it out with polyester resin and a brush, adding layers of glass to get the thickness you want.
Then roll it with a fiberglass roller to squeeze the air bubbles out and press the layers of glass together and the excess resin to the top.

Then take a 6" or wider bondo squeegee and carefully wipe it over the fiberglass cloth while tipped at a slight angle to sqeegee out the excess resin. This will press the layers of glass together even more and wipe the excess resin out of the fiberglass layup and make the part stronger and lighter while leaving a nice uniform texture on the surface.
The other side against the aluminum sheet will be smooth when done and will be the smooth finished top side you see when screwed or riveted onto the bottom of the airdamn.

You can put pigment in polyester resin to color it so it doesn't need to be painted and it will stay the same color as it gets worn away if it bottoms out or hits something.

Then pull/lift it off the aluminum sheet that you used as a flat mold and cut and sand it to the shape you want.

The aluminum sheet is unharmed, the mold release rinses off with water, and it can still be used for other things.

[A930Rocket]

The car looks good! A splitter makes a big difference especially with a matching rear tail.

I use small bolts to mount mine and it takes about 5 minutes to install or remove. one day I'll convert to Dzus fasteners.

[juicersr]

Thanks for all your input guys. That's what i love about the board, the incredibly insiteful advice from everyone.

Well, i got to thinking about the whole flow past the oil cooler thing and when i got home from work, i looked again and saw that the flow was probably being impeded by my brake cooling ducts, so..... i took off the splitter and decided to cut off the lower part of the 'T' that was running rear ward. May have been anal, but with these cars, not paying attention to details will get u in trouble and the last thing i wanted was overheating issues with how i drive it.

Anyway, i then bolted it back up and took her out again, and much to my relief, i really didn't notice any difference from before... same great high speed stability but this time with peace of mind knowing that air was flowing unobstructed though the cooler.

Here are some pix of the underside after i chopped it. Anchored it to the two bolts holding the front A/c condenser bar.