Ram air vs Low Drag?

[Fred2]

I watching the runoffs, I noted that the two top qualifiers were running what I would call "Formula Ford" type bodies, with small air inlets for the engine.

Cars such as the Stohr, Speads, Phoenix etc have what I would describe as a formula 1 type air inlet, with a big intake above the drivers head.

Does the big air inlet add drag, as I think it would?
if so,
Is the hp gain from the ram air greater than the drag that the intake produces?

Side pods are another think that I noticed on the Citation.
The car looked tiny compared to the big radiators on the F1 type bodies.

[Northwind]

Some of the cars use the high pressure air routed thru the sidepods. A clever idea but hard to package on some cars.

[starkejt]

I found it interesting that Bootz (DSR winner) had his intake opening pointing to the right rather than forward.

[Wren]

Just throw on a stock airbox and let it pull air from under the engine cover. It's cheap, packages nicely and gives the hit air from under the engine cover someplace to go.

[Fred2]

Just throw on a stock airbox and let it pull air from under the engine cover. It's cheap, packages nicely and gives the hit air from under the engine cover someplace to go.

Re routing the exhaust back into the airbox also pressurizes it, kind of like a turbo


From what I have read about in testing on m/c, in a well designed duct/airbox you would be looking at about a 10-15 HP boost at about 140 mph.

However,

If you have ever popped up from behind the bubble at 140mph, you would feel the air really slow the bike down, even without hitting the brakes.

So, is the extra power worth the extra drag?
(assuming that there is extra drag)

[starkejt]

[Wren]

Re routing the exhaust back into the airbox also pressurizes it, kind of like a turbo


From what I have read about in testing on m/c, in a well designed duct/airbox you would be looking at about a 10-15 HP boost at about 140 mph.

However,

If you have ever popped up from behind the bubble at 140mph, you would feel the air really slow the bike down, even without hitting the brakes.

So, is the extra power worth the extra drag?
(assuming that there is extra drag)

Go back and look at the pictures of Dixons car. Stock airbox sitting under the engine cover with no outside scoops or inlets to it. Works fine.

[Rennie Clayton]

DEI

Thinly veiled attempt to work in a human centipede reference?


Cheers,
Rennie

[Herman Pahls]

I had the impression that Brandon was force feeding his air box from the side pods.
What happens to the drag if we remove the ram air scoop on our engine covers (Phoenix) and leave the round roll hoop/hoops exposed above our heads.
Wind tunnel tests have shown that round tube has significantly more drag than an aero shaped tube.
I was considering cutting off the air intake on my Phoenix but fear I will not be able to quantify the change and then wish I had left it alone
Should we be fairing the exposed round roll hoops.
Have Brandon or the scoopless Stohr's faired there roll hoops?
Herman

[Fred2]

Thinly veiled attempt to work in a human centipede reference?


Cheers,
Rennie

Have you guys ever done any CFD to see how much drag the air intake creates?

(I like the centipede analogy)

[Fred2]

Go back and look at the pictures of Dixons car. Stock airbox sitting under the engine cover with no outside scoops or inlets to it. Works fine.

Hard to see where the air is coming in from.

With the top of the bodywork removed, it may be taking in ambient air from that area, or it may be plumbed to another area.

[Northwind]

Upon closer look at Brandon's Citation, I noticed an air duct that was located from the bottom of the seat to the intake of the airbox. I kind of wondered why Wren kept feeding him bean sandwiches all week at the run offs. It was the methane boost that gave him all the speed.

[starkejt]

So that's what the F in F-duct stands for.

[ASRF1000]

F'n A Baby!!!

[R. Pare]

Hard to see where the air is coming in from.

With the top of the bodywork removed, it may be taking in ambient air from that area, or it may be plumbed to another area.

Even tricker than that - he's pulling out air from slots just in front of the diffuser.

[Rennie Clayton]

Have you guys ever done any CFD to see how much drag the air intake creates?

Yes; there is a moderate amount of drag from an overhead air intake, but partially offset by the additional HP from ram air. Short answer is that there are probably other areas of the car that can / should be optimized before turning your sights on the air scoop.


Cheers,
Rennie

[Rick Ross]

For those that plan to test different types of air intakes, you could alway record the air pressure rise in the air box using a data logger, which would allow you to estimate the effect (if any) upon engine power output. There are some reasonably priced 5V analog pressure sensors on the market that should work with most data acqusition systems.

[Herman Pahls]

So Brandon reduces drag by not using overhead scoop but still gets pressure to his airbox.
I am sure he has calculated that an exposed roll hope has less drag than the typical scooped engine cover many of us use.
Is this the F-1000 look of the future?

[Wright D]

I have run a ton of cfd on this topic. It is obvious wich direction I think works as every Phoenix has had a under roll hoop ram air inlet.

[ASRF1000]

You also have to take into consideration the type of track you are racing on. Tracks like Road America where there are many long straights may favor the less drag scenario, but tight twisty tracks where mechanical grip is more important than the minimal drag that an overhead air scoop produces may favor the ram air intake.

If you were concentrating on one type of track you might focus on one or the other, but if you are running on tracks of various configurations its a difficult call. It is my belief that an under the roll hoop ram air inlet would work best (less drag but still ram air effect) best of both worlds scenario. But that's only my perspective.

Of course side intakes can be effective as well, but you have to take into consideration the flow of the air up and around the helmet. If you're not getting a clean, direct flow of air to the inlet, you've defeated the purpose of the ram air.

Its another thing I love about this class. There is not one correct and definitive answer to this question. It's the innovative part of this formula. Every engineer has his own theory, which is why you will see different approaches to the same question. Thank God this is not a spec class!!!

[urbanimports02]

i believe i have good insight on this subject as i have re-bodied the stohr now twice. on the first one, we shortened the first gen stohr intake 3" or so, and went with traditional side pods, and it all worked out pretty well the scoop is still over the roll hoop.
on the second, we went for a nice compromise, and went over the helmet, but kept the scoop/snorkel under the roll hoop but brought it through and angled it up so the tallest point is about 1.5" above the hoop(like 7.5" shorter then 1st gen) this plus cleaning up the cockpit sides and slightly narrower side pods yielded about 3-4mph over the other car with same wing configs(using data from when we ran the wings now on car 2 on car 1) this is as measured on the back straight at portland 141mph car 1, 144-145 car 2. i do not believe eliminating it would yield anything for us. the roll hoop and intake is very nicely faired in, which i do not believe the citation ever was faired in to this degree. i think that is something dustin is leaving out of his opinion as his are also nicely faired in. brandon has a lot more going on then his intake choice, and ran pretty similar times last year both ways. i think he found a very slight advantage for his car with his current setup, and that is why he is fast, he keeps tweaking all of the different systems on his car. it all adds up, but what works for him and his car may not be the best choice for you and yours.

[James Michael]

One question I had is how about overall lap time? Since it seems to be a trade off between low drag and more air into the engine, do you have a feel for difference in lap time. Thanks.

James Michael

[urbanimports02]

not sure we are experiencing a trade off in our case, we have 180 horsies gobbling up high pressure air that would otherwise be creating drag at the roll hoop, and spitting it out the exhaust right above the diffuser in our case, we have lowered the air scoop 7.5" compared to the original stohr and narrowed body work, so we see a huge drag reduction and 2+ seconds a lap quicker then last year, so yes low drag and good air to the airbox is good! our airbox is through the roll hoop instead of over it. as i have said, it all depends on YOUR setup. in our case, removing the air intake and placing it in a pod or otherwise would increase drag imho and reduce cool high pressure air to the airbox. not sure what brandon found, but his airbox was not faired in, and his roll hoop looks taller, so my guess is he found a drag reduction in HIS setup. in brandons case, it was fairly easy to test both ways, so maybe take that approach to your design. see the pic, taylor's helmet is still well below the intake, but the top of the car is 7.5" lower, best of both worlds.

[Fred2]

Thanks for posting the photo, I was wondering what the car looked like.

[James Michael]

Thanks for the info on the Stohr mod. I have the original Stohr with the tall intake. I would like to modify it but everytime I get out my hack saw, I have an anxiety attack and stop. Part of the problem is the roll hoop is just below the bottom of the intake so I don't want to cut off too much and expose the hoop. Your solution looks quite nice. I was thinking of even closing off the top altogether and getting the air to the engine via the oil and water cooler inlets but that's a long way for the air to travel thru ducting to the engine. With your mod, I would think you have a bit of a joggle to get the intake below the hoop and the inlet is smaller than mine now but probably is still very good for getting the air to the engine. Thanks.

James

[urbanimports02]

save yourself the hassle and just buy our body upgrade then you get the lower intake, WAY smaller side pods, improved cooling, more efficient diffuser, narrowed center body and shave 40-50lbs off the car! all that for FAR less drag. we have molds for every part of the car, and it is all vac bagged e-glass/epoxy (kevlar sides) with nomex honeycomb, very rigid and light. as for intake, for now we cut the top off the airbox snorkel, and feed it with a piece of 4" brake duct hose(overkill huge). the brake duct hose does the joggle very nicely. you can look in the front and see the filter element, which means nice straight shot. driver could feel it in his a$$ dyno we also moved the intake 2" forward to give more room for a smooth transition upwards. that car last year did 134mph back straight at PIR, and 145mph with new body, so while the intake was part of it, it was the whole package that made those improvements....

[urbanimports02]

there is also a possibility that once we upgrade the first prototype rebodied car we did to the new body, that we would sell the prototype body work. it would be a complete kit with light weight side pods and engine cover, undertray, radiator, mounts etc. this has the intake lowered about 3 1/2" with modified upper snorkel. we went further with the narrowing for the final product, so not as skinny, but much better then the original....this car gets compliments everywhere we go, looks sexy on track!

[James Michael]

Thanks Jesse, I might just take you up on that (PM sent)!
James