Air pressure @ 100 mph?

[racer189]

Has anyone done any testing or know if a an engine will see an increase in air pressure at the carb with a drag style scoop mounted on it at 100 -105 mph in an open engine cockpit (marine race application)? We are considering trying a dragster style scoop instead of our normal K&N oval air cleaner - twin carb set up. I contacted Harwood and they hadn't done any testing at all, so they had no data to help me. As well, they weren't much help in helping to determine which scoop design would work best for our application.

The engine is a max effort 366 SBC with about 750 hp, twin carb, sheet metal intake.

We were just wondering if anyone had any info to help us decide before we needlessly spend $500-700 on a scoop, only to find out that there is no difference.

Any help would be appreciated. Thanks in advance.

[MadBill]

Any reasonably well designed scoop will convert 100% of the air's kinetic energy into a pressure which increases as the square of the speed. At 100 MPH, this would be 0.176 psi, or ~ 1.2%, thus ~9 HP on a 750 HP engine. e.g., because of the squared factor, it would be 0.7 psi/4.8%/36 HP at 200 MPH.

[F1Fever]

there are some formulas to determine the scoop hole size but I've misplaced them. the lower the speed the larger the hole. at 200 MPH it's amazing how small the hole has to be to achieve the best air flow vs aero drag. I'll see if I can find it.

I didn't find the page I was looking for but this is in the right direction, I'll look again soon .. http://www.racecarbook.com/articles/airscoopsize.shtml

[racer189]

Here are some pictures to give you an idea of the application.

http://www.shutterfly.com/progal/album. ... 40f03e1568

And videos

http://www.youtube.com/watch?v=31MG0lW3uQA
http://www.youtube.com/watch?v=IMlw9bcv ... ed&search=
http://www.youtube.com/watch?v=XIj0mmzTg7Y

[Stan Weiss]

Any reasonably well designed scoop will convert 100% of the air's kinetic energy into a pressure which increases as the square of the speed. At 100 MPH, this would be 0.176 psi, or ~ 1.2%, thus ~9 HP on a 750 HP engine. e.g., because of the squared factor, it would be 0.7 psi/4.8%/36 HP at 200 MPH.

How does air density factor in? If you are running at 5280 feet is the PSI lower but the percentage increase stay the same?

[jacksoni]

This might help also:

http://www.landracing.com/index.php?opt ... view&id=22

[Bucky1]

I have a friend who did some testing on his dragster a number of years ago. He tried several different shapes of scoops, with no real progress. Finally, out of frustration and humor, he turned the scoop he was using around backwards and made a pass. Didn't make any difference. Just about anyhing you get from extra ram effect is lossed by air resistance slowing the car down.

[tommurphy73]

A better idea might be to try to measure pressure at different places around the boat. There are probably areas that are at higher or lower pressure because of the aerodynamic design of the hull and engine covers then put the air intake at the highest pressure point.

Regards
Tom

[Eric68]

I think the key is to try pulling air from a place that is already high pressure so you do not create additional drag on the car. For example, a cowl induction.

I played with a ram air setup on my Camaro that had two 4" tubes that got air from two holes on either side of the radiator. It added about 1 MPH to my trap speeds, but I later abandoned the setup because it was a pain to get at the carb for tuning and was tough to route the tubes around accessories.

FWIW

[Cfin]

I don't think I have seen a scoop used in marathon racing? I would think the risk of it injesting water would probably out-weigh any gains you may get, especially around 100mph??

[Pete]

I was thinking the same thing.

In a marine application keeping the intake clear of water would be my first design priority and whatever gains could be made from the intake design adding power is a bonus.

Cheers , Pete.

[racer189]

I don't think I have seen a scoop used in marathon racing? I would think the risk of it injesting water would probably out-weigh any gains you may get, especially around 100mph??

Injesting water is a concern and when we run head to head with other boats, we run a regular K&N filter with a shield. However, some of our competitors run a scoop when they are making a solo timed run, and of course it's difficult to determine if it's giving them any improvement in performance.

[blackbeered]

Seems to me the size of the air scoop would come into play, no?

A 4" x 10" rectangle would grab 2,444 cfm while a 2" x 10" half that. And the carb would see the difference, no?

[JC565Ford]

I have a friend who did some testing on his dragster a number of years ago. He tried several different shapes of scoops, with no real progress. Finally, out of frustration and humor, he turned the scoop he was using around backwards and made a pass. Didn't make any difference. Just about anyhing you get from extra ram effect is lossed by air resistance slowing the car down.

20 years ago F1 cars had a slit at the back of their scoops to allow air to pass thru to reduce the drag. If I recall correctly the cars (at 800 hp back then) got about a 20 hp boost at 300km - 186 mph = 2.5%

[MadBill]

Seems to me the size of the air scoop would come into play, no?

A 4" x 10" rectangle would grab 2,444 cfm while a 2" x 10" half that. And the carb would see the difference, no?

No. Apart from being so small that it chokes down the flow, the size of the scoop doesn't matter, only the speed and air density.