Track Tac

Air Flow

alvin l nunley

alvin l nunley

Site Supporter
I have no way to prove this, but I believe this is how it works. I believe the white line represents the pressure differential boundary between the vacuum in the carburetor and the surrounding air pressure. The farther you get away from the carburetor, the lower the pressure differential difference.

Assuming I'm right, the more contaminated the filter becomes in the high flow area, adding resistance to flow, the farther the red lines would move from the carb opening. Moral; keep the filter clean!
filter air flow 1.jpgfilter air flow 2.jpg
 
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Al that is just basic physics. Correct. Now for cleaning the air filter. that my friend is just common sense! backed up by physics.
Al think about this
An engine is about 12.93 cu.in in displacement
At 5,500 rpms
It would fill the cylinder 2750 times per minute.
Assuming 100 % volumetric efficiency. That would be 35,557 cu.in of air fuel mixture. or 2963 cu. ft. of air.
What size carb would you need to provide that much air.
 
One Fast Kat said:
An engine is about 12.93 cu.in in displacement
At 5,500 rpms
It would fill the cylinder 2750 times per minute.
Assuming 100 % volumetric efficiency. That would be 35,557 cu.in of air fuel mixture. or 2963 cu. ft. of air.
Click to expand...

OneFastKat ---

12.93 x 2750 = 35,557 cubic inches/minute

35,557 / 1728 = 20.57 cubic feet/minute

PM
 
The problem is, we do not race engines with 100% volumetric efficiency.
A more reasonable amount may be closer to 85% - 90% in the open classes. The blueprinted and spec classes are sorely worse off.

For years, guys have tried coating, filling, etc their air filters on stock class engines to move the air in a specific way (ie shield it to windage, funnel, etc.) If the air filter is more than sufficient in size, then the extra area can be used to shape and direct the air entering the carb (which, or course is illegal.) For a while, it was pretty common for guys to paint shellac or even use hairspray on the inside of the front side of the air filter pleats. Not easily detectable without removing the filter in the tech barn, and even then I suspect many slipped through.


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Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
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alvin l nunley said:
"And how much", good question. My question; and how would you measure when enough is enough?
Click to expand...
Interesting Question!!! But exactly to the point. If we had a system that would actually pump more air than we need! Then we would still not have enough. Fuel injection with blower or turbo charger.
But then you still a an industrial engine designed to turn 3500 rpm and would not handle the horsepower that it would deliver.
3 types of racing engines. Fast, Cheap, Reliable. Pick one. Sometimes in the open class now it is reliable if it lasts the entire race. Once. How far do you go.
I built a monster last year. It blew the entire top end of the engine Off. Last lap. But it was really fast.
Some Racing engine, run over a 30 lb ambient.. boost from the supercharger. That would put them over 100 efficiency .
But we are still only racing, in most cases the cheapest industrial engine available on planet earth.
 
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