Just curious.

Lets say it is three inches thick and six inches wide.
Frontal area is 16 square inches or .1 square foot.
Drag factor of one.

Half sea level density at 14,000 feet roughly. 0.0013 times 200 MPH ^2 
or 52 pounds per square foot dynamic pressure or about 5 pounds
of drag at 200 MPH at 14,000 feet.

200 MPH is about 300 FPS so HP is 5 pounds times 300 FPS or 1500 
pound feet per second or almost 3 HP out of the prop. If he is 
down to half of sea level HP or about 90 engine HP. Figure a 80% 
prop eff. That is 72 HP out of the prop. So 3 HP would be a about 
a 4% loss in  HP out of the prop and about 5% out of the engine.
5% of 180 HP is 9 HP. That's a lot.

As a check let's say his over all RV4  equivalent flat plate area 
is 2.5 square feet. Total drag would then be about 125 pounds. 
Another 5 pounds of drag is 4% more drag. Lets check 125 pounds 
drag at 300 FPS is 68 HP out of the prop. About right.

IMHO I think you should streamline it Tracy.

BTW IMHO I think your collector pipe dia. is on the small side.
I think you should go up to three inches and you would get
more HP or even better BSFC and MPG.
 
Paul Lamar
 
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