Carb Air Scoop?

[Veefan]

Does anyone have a good source of an air scoop for the carb intake of a formula vee? I've seen a few cars with one that is pop rivited to the top body just behind the drivers head which is low enough to stay within the rules.

Thanks.

[FV80]

What do you mean by low enough to fit within the rules? I am not aware of any rules that limit the height of any bodywork. Also - FYI, almost all of those scoops have a primary function of feeding air to the oil cooler. You don't want to RAM air into a Vee carb - you won't be able to jet it - just get it 'cool' air and allow the carb to suck it in.
Steve

[Veefan]

Wow this early in the morning, I feel like I'm back in school being lectured by a teacher

2008 GCR
"C.9.B The rear bodywork shall enclose the engine by surrounding it from a point no higher than the lower edge of the intake manifold and extending from the front of the engine to its rear on each side. " Not sure what that means... but since I've never seen a Vee with a scoop above the roll bar, I figured, must be a rule out to prevent it.

Just looking for a scoop to get some cold fresh air to the carb...

Thanks

[Dietmar]

VF:

What that means is that you MUST run rear bodywork. It does not say that there can not be any openings in this bodywork.
Ducting is also described in the GCR
Hope that helps
Dietmar

[FV80]

...from a point no higher than the lower edge of the intake manifold ...

What this means is that the bodywork must go to at least <b>DOWN TO </b>the bottom of the intake. There is no limit on the upper (height) of the bodywork. I have seen several over the years going above the roll hoop - but not many. Jim Vaseff in SEDIV is running one now (or will be, when he gets his car fixed).
Steve

[Dmclellan]

The trade off for an air scopes is increased horse power verses increased drag. At 80MPH or 7000 FPM the air velocity pressure is about 3 inches of water or 0.108 PSI. For a 10" x10" air scoop assume a Cd of 1 (WAG) that's about 11 pounds of force. Force times velocity equals horsepower, so if all my conversion factors are correct thats about 2.5 HP. 2.5 is the break even point for 100 square inches at 80 MPH. Will the air scoop increase horsepower more than 2.5 horsepower? At lower speeds the drag horsepower is less, but so is the ram air effect of the scoop.

Does the carb jetting need to account for the increased 3 inches? A quick search of this website quoted 116 CFM at 28" for a FV Carb. Would you want carb set up for a higher pressure for a FV engine running a scope? What about an air filter pressure drop? Does any of this really matter with a FV engine?

[Veefan]

Wow, I was just looking for an air scoop.

It all sounds good, but since the scoop I'm looking for is directly behind my helmet, the drag exists scoop or no scoop. I'd only be catching the residual, cooler air, flowing around my helmet and dumping it into the carb.

[SR Racing]

It is highly unlikely you will get enough boost to offset the aerodynamic costs. Just make sure it is getting as cool as air as possible.

Does the carb jetting need to account for the increased 3 inches? A quick search of this website quoted 116 CFM at 28" for a FV Carb. Would you want carb set up for a higher pressure for a FV engine running a scope? What about an air filter pressure drop? Does any of this really matter with a FV engine?

With boost or non, the carb will still provide proper a/f ratios. (assuming it is jetted right in the first place.) (at least to any reasonable limit. If you can get 10lbs of boost all bets are off.
116cfm at 28" is a VERY good carb. But there are some out there.

[Chris Robson]

I'm probably out of my league with regards to Vee info, but a 10 x 10 airscoop for a Vee sounds huge. Assume a 5 in. diameter circle air inlet with a 1/4 in. glass surrounding it. That's about 24 in sq. not 100. Add another 10 in. sq. for scoop "holder". Also, the Cd is less than 1 because you are "swallowing" the air, not deflecting it around a 100 in. sq flat plate. You'd probably end up with < 3 lb force or about
~ 1/2 HP @80.

Don't know how jet sizes are for the carb but maybe one about 10% bigger in area might be good. Not sure the jets are that fine.

Justs my thoughts, as an "outside observer"

[SR Racing]

Also, the Cd is less than 1 because you are "swallowing" the air, not deflecting it...

If you "swallowed all the air, you would have zero boost. To achieve boost you will have pressure and thus aero drag.

You'd probably end up with < 3 lb force or about ~ 1/2 HP @80.

If you mean 3 lbs of boost, it would be MUCH more than 1/2HP. It would be in the 5 to 8 HP area.

Don't know how jet sizes are for the carb but maybe one about 10% bigger in area might be good. Not sure the jets are that fine.
"

You would not want to change the jet at all, assuming you were in the 13:1 area at ambient air. If you did get 3 lbs of boost (I don't think so), you might want to re-jet slightly to richen the a/f only to limit spark knock at peak torque.

Jim

[Chris Robson]

...I think we are talking about two separate concepts. I will bow out of the discussion as I have re-read the post and see that the discussion is centered on the initial air inlet, (scoop) not where/how the air is introduced to the engine.

Sorry for the confusion.

Chris

[neilcox]

The scoop on my Protoform is a very nice bolt on piece. It supplies cool air to the carb AND oil cooler. You might try to contact Dave Green.

[Veefan]

Thanks, do you have a phone # or e-mail address.

Thanks again!

[RacerGeek]

Protoform Race Cars 607-739-7345

[jpetillo]

Also, the Cd is less than 1 because you are "swallowing" the air, not deflecting it...

If you "swallowed all the air, you would have zero boost. To achieve boost you will have pressure and thus aero drag.

Actually, I believe that Chris is right on this one. With no scoop, you have a negative pressure at the carb throat. With a scoop, if you have zero pressure at the throat, then you are swallowing all the air and potentially no drag from the scoop inlet, and you have higher pressure than without a scoop, so you have boost. There will be drag from other parts of the scoop, though.

About the Protoform scoop, does anyone have a picture or web link? I'd like to see it.

Thanks, John

[Veefan]

[ external image ]

I think this is a Protoform scoop...

[jpetillo]

Thanks. I dug through some of my pictures and found some of Protoforms with that shaped scoop. I saw the bottom half of the inlet - the part behind the helmet - blocked off. Is that typical?

[SR Racing]

Actually, I believe that Chris is right on this one. With no scoop, you have a negative pressure at the carb throat. With a scoop, if you have zero pressure at the throat, then you are swallowing all the air and potentially no drag from the scoop inlet, and you have higher pressure than without a scoop, so you have boost. There will be drag from other parts of the scoop, though.

Yes. You would be getting a "boost". If it were designed so that it captured the exact amount of air that the engine was using at that RPM and car's speed. The measured boost (like with a boost gauge) would be 0. But you are correct it woud be a differential pressure. The gained HP, would be some fraction of the engine's pumping losses. I stand corrected.

A better/best way to acheive "boost" is by using air pressure that is already there. Like most racing stock cars. From the rear of the hood off the windshield. Not sure how to do that well on a Vee though.

[neilcox]

Thanks. I dug through some of my pictures and found some of Protoforms with that shaped scoop. I saw the bottom half of the inlet - the part behind the helmet - blocked off. Is that typical?

yes. that opening cools the oil and supplies the carb very well.

Neil

[Dmclellan]

I think the scoop likes great, but
The air scoop does not sallow the air; the scoop deflects the air. In this case down which means lift and drag. The scoop must accelerate the air from rest to the speed of the car and then deflects it down. If the air passes through the oil cooler, the low pressure behind the car sucks the air through the oil cooler and out of the car. The air that is sucked into the carb goes out the exhaust pipe and provides some thrust in the opposite direction to whatever direction the exhaust points, but all the work done on the combustion air is done by the engine. The air must flow in behind the scoop, because the air that was in front of the scoop is inside the car and can not flow back to behind the scoop as it would for a fin with the same frontal area. The Cd of the scoop is probably less than 1 but greater than zero. In order for the scoop to do what you want- blow air through the oil cooler and passed the carb- it has to do work.
You can't break the Laws of Thermodynamics. In engineering terms:

1. THERE IS NO FREE LUNCH.
2. Rockets are faster than jets.

If I had a F1 budget I could do some CFD runs, then put a couple FV in a wind tunnel and I'd know if any of my analysis is correct. I still wouldn't go any faster, but I’d have a lot of fun the computers and wind tunnels.
My oil temperature looks OK, so I don't need a scoop. Keeping the oil temperature in the correct range is much more import than the scoop’s drag increase or lift that probably has less effect than tilting your head.

[Veefan]

All this info is great, except I just pulled out all my photos from last years runoffs and except for a few cars... everyone had carb/oil cooler type scoops. Ok, so yes, many of the cars were Protoforms or Vortech's which come with scoops... I'm pretty sure that if scoops were a bad thing and created more drag then they are worth ... many of the national guys would remove them.

[Dmclellan]

I didn't say a scoop was a bad thing. I said that basically anything dragged through the will create drag. If a scoop is need to cool the oil, the drag doesn't matter.
I still woluld ike to know how much a scoop could improve engine performance. Does 0.1 pounds of boost matter?

[Larry Bradley]

Several years ago, I took a 90degree exhaust pipe and adapted it to the carb top, and over the top of the roll bar.

Direct ram air.

We took a pressure reading with a 100" of water gauge.
Driving on the long straight at Gratten, reading the "boost" at about 100 mph was so low that between needle bound and eyeball bounce I can't even claim I got 5 inches of water. I think 409 inches is one atmosphere.

The only down side was after lifting for the corners there was a hesitation on acceleration.
Like the accelerator pump was not rich enough.

Also having an air filter presented a problem. I opted for having an air filter v a ram induction.

And I never saw anymore RPM or change in lap times.

Larry

[Kartgraphix]

Several years ago, I took a 90degree exhaust pipe and adapted it to the carb top, and over the top of the roll bar.

Direct ram air.

...
Also having an air filter presented a problem. I opted for having an air filter v a ram induction.

... never saw anymore RPM or change in lap times...

Gaining a ram air effect is much more complex than anyone guesses. Simply piping air into the carb throat with an elbow will produce little or no real result, as their is no collection of volume greater than the throat size of the carb itself. This causes jetting issues, float bowl pressure problems, and enough air leakage to insure nothing actually results.

On modern sport bikes, and powerful sports cars, ram air induction with air filters are du-rigor. In drag racing, we found that using a carb plate sealed to the under side of a scoop was step one - pressurizing the whole carb, not just pushing fast moving air into it. Next is to design a scoop that funnels a large area of high pressure (read slow moving) air from a large opening into an area of smaller capacity, thus creating a compression space. Next, the differential between the volume entering, and the volume of the cavity, must exceed the engines air flow (induction) or there will, again be no compression, thus no positive compression. Scoops simply pointed forward, with a helmet stuck in front of it, in fast moving air, that is not sealed tightly to the carb base... will not produce anything more than cooler air flow than it would get from the engine bay... nothing more or less.

Oh yeah, aerodymics are like header designs. A design that works at the "design" speed is likely to produce minimal results at lower speeds, and may even loose effectiveness at higher speeds. If the ram air box volume creates too much pressure, a sort of pressure bubble fills the box, eventually acting like a plug to the scoop, at which point the airflow goes around the opening, and the pressure inside stabilizes - possibly at less than one atmosphere. This creates all sorts of strange symptoms where the car suddenly loses power, slowing, then the bubble collapses, the car races or lurches, then slows.... salt flat dudes run into this, and fight the balance. My theory would be to apply a small "gate" to regulate positive pressure at some level by allowing the excess pressure to escape. Some use a variable opening in the scoop, or more sophisticated designs that use aero forces in other ways to prevent the problem - beyond what we mear mortals might contemplate.

I have not seen one FV yet with a scoop design that is anywhere near producing positive pressure or ram effect. The Lazer has a huge inlet placed at a good height. Yet, its not sealed off, and the drivers helmet in its opening will create a larger and larger airflow around it, and around the opening at high speeds. I;d be surprised if it actually didn't have a negative pressure problem at the highest speed, drawing hot air from under the cowl, where higher pressure from the slower moving air exceeds the faster moving air around the opening itself.

This subject is way more complicated than it looks. A good intake for this class is one that provide fresh air to the intake with minimal drag. This too is more than it appears, but is at least more intuitive... sort of.

[FM4SOLO]

That makes more sense than anything else I've read. Makes my solo vee with a simple open top tail with exposed air cleaner much more effective than I'd thought. Thanks.