jon928se

Mark

somewhere before you posted a pic of the windtunnel testing derived external pressures on a 928 - that will give you the optimal place to locate "into the rad" vents and "out from under the hood" vents.

IIRC the "out from the hood" vents are ideally located about 1/3 of the distance from the nose to the windshield.

HTH

PS it was probably in a thread about Dr Nicks Orange GTS engined track car.

WallyP

Extensive wind tunnel work at Ford shows that the air flow thru the radiator is "stalled flow" at 18 mph, regardless of road speed. You might not need as many openings as you think.

Fabio421

Damn, very subtle. I like it alot. I didn't even notice those vents at first. I think I'm going to mod my front bumper cover on my Code Red widebody and also incorporate the hood vent in order to facilitate additional air through the intercooler. Nice find Brian.

mark kibort

This is false. Also, similar information has been posted regarding fans. I have prove that racing, if i dont use the fans, I get HUGE overheating. One fan is better and both are used on hot days and drops my racing temps to mid range, with Average lap racing speeds of 85mph.

The faster I go, the more the tufts started to point up, even against flow. you cant stall flow there is a pressure drop across it, but no stall until supersonic flow.
Ill even put on some pressures sensors to the hood vent to show the flow is increasing with speed. this is nothing new most all race cars have huge vents at the front and rear ofthe radiator, directing flow through the radiator the faster you go, CERTAINLY the greater the air flow. at the race track, I start to overheat during caution laps or in traffic. the faster i go, the more air flows through the radiator. Now, does this air end up under the car or out the hood vent. That is an easy thing to prove.

I only took pressure measurements to make sure there was a differntial pressure change at the opening. I can take more readings to show what happens with hood venting.

mark kibort

There is a reason i put the hood vent on. it works, i routes air from the nose , through the radiator out the hood vent with amazing efficiency. (vs releasing under the car)


Ive already done the hood vent. it was done near the same time as the orange car discussion. I posted pictures of pressure readings, tuft tests, and other information. yes, the distance is right around wheel center forward about 1 foot on the hood.

https://rennlist.com/forums/928-foru...d-vents-4.html

mark kibort

it wont work, unless as you say, you were able to tilt the radiator forward and thats still in the high pressure zone partly. You want the air to go though the radiator and out the hood vent. the only thing my system now is lacking is proper ducting and a larger opening. I think the larger opening might help a bit. the picture above shows the sweet spot of vacuum on the hood. right above my #19 racing number

mk

ptuomov

A dumb question:

Aren't stalling and choke different things? Stalling to me means that the laminar flow separates from a surface. Choking to mean means that flow is approaching sonic velocity going thru a restriction, which makes it more and more difficult to push air thru the restriction any faster. I am sure that these two are related in some subtle way that I don't understad.

So, is the air going thru the radiator stalling or choking or flowing free or what?

White Lightnin'

Mark, it's a race car... not a concours trailer queen. So, tilt the radiator forward; build focused ducting in front and behind the radiator and use a hood already made for it. Additionally, the airflow over the hood and those slats will creat a vacuum and help pull air through. The additional room from where the radiator used to be will afford some creative fresh air induction...

mark kibort

I agree. that is right. my point is that you would want to hit the sweet spot of the lower pressure zone which is where my vent is today. I could make it 2x as big and have some nice ducting like the ferrari, and that would work great.
edit: correction. the hood you show would work with a lot of work! the radiator would have to be all the way forward to the edge of the hood latch and then you would want a more gradual release of the air upward, which would be near my vents now.
That radiator movement and modification would be a tough mod. But you are right.

also, air isnt "pulled" out, its pushed out. symantics I know, but vacuum does nothing, pressuer does everything.

That was my only point.

mk

mark kibort

Yes, choke is when there is no flow. all air passages have flow and associated pressure drops across them. BUT, if you raise the pressure, the flow increases. you are also right about stalling. stalled wings still have air flowing over them, but it might be turbulent. . you dont get a restriction with increase pressure, until you approach supersonic speeds. our radiators flow up to 100s of MPH no problem. sure, not the flow you would get if it wasnt there, but still it flows. it has a pressure drop associated with it. you can measure it and predict its flow at any speed.

bottom line, this is a common way to get downforce. injest incoming air through an inlet vent and vent the air to the hood so it doesnt end up and ADD to the air under the car (bad because thats the high pressure zone and that creates more lift).

ever notice nascar vents? they can pull off tape to make the inlet larger or smaller. larger more cooling. less aerodynamic, smaller opening, more aerodynamic. nascar air flows under the car. but i bet this changes at some point in the future.

mk

WallyP

"This is false. Also, similar information has been posted regarding fans. "

Mark,

I have no desire whatsoever to get into a never-ending Kilbort pissing contest. Perhaps you would like to explain to Ford that the multi-million dollar, fully-instrumented wind tunnel tests that they and Emprise Corp did at Lockheed were worthless...

Wally

mark kibort

There is a good chance you or someone misinterpreted the results.

I have another data point I just thought of. you know our dual fans., when they are off , they are not spinning at low speed, but did you know they freewheel at highway speeds ? And , if you go 120mph, they are going so fast, they make a loud howling noise? I can get a rpm for you based on BEMF if you want. Just because ford spent a lot of money on wind tunnel time, doesnt mean what they found pretains to us. we also dont know what they found. you are translating. could something be lostin the translation? If what you are saing is true, then past 18mph, my little electric cooling fans should be able to pick up air flow. kind of like an animometer, right.

How about this. Im drving to the track this friday AM. Ill put a volt meter on the electric fans and as they spin they will generate a voltage. If the voltage from spining goes up from 18mph, will you believe that there is air flow at faster and faster speeds?? (my s4 fans are manually controlled so i can make sure they are off for the test)

Ill bet you any amount of anything that there is more air flow through the radiators at high speed than at low speed.

ew928

Ford's wind tunnel surely isn't obeying the laws of the racetrack.
They should have just bought a few spools of wool and not have wasted all that wind tunnel time.

mark kibort

Also, why did they use the term "stalled flow" that really pertains to axial flow compressors, and such.

Its pretty obviously that wallys information might not be talking about stopping flow. maybe they were talking about their cooling fans stalling, but flow continues at higher speed no doubt. I dont know, i didnt see the study.

see :
http://books.google.com/books?id=S6H...esult&resnum=5

White Lightnin'

Sure, I am not an Aerodynamic Engineer -but this is what I had in mind for that hood. You only need to move the radiator, open up the slats you want to and create the ducting...