Hey Tom, good job on the formula! I had went about it a little differently
though but with the same, I hope, results!
I developed the following:
Inlet Area (in sq) = (Disp * RPM *VE) / (MPH * 2112)
Where: Disp is engine displacement
RPM is RPM at which you want to run
VE is volumetric efficiency of engine (1 if you don't know)
MPH is the at which you want to run in MPH
2112 is a combination of conversion factors)
So, an example... my car, 306 CID, 200 MPH, 6250 RPM, .8 VE
Inlet area = (306 * 6250 * 0.8) / (200 * 2112) = 3.622 in sq.
This provides for an exact balance of the engine needs. I would use a
volumetric efficiency of 110% to account for some ram air effects, however.
This is an interesting equation because the slower you go the larger the
scoop. I think this means that when testing on the dyno that you need a
large plenum and inlet. Tom, does your equation do this also?
Unfortunately, adding a scoop or the inlet adds some drag to the car, but
if confined within the frontal area envelope, shouldn't add much, if any.
Neat stuff, this!
mayf
At 10:50 AM 2/11/00 -0800, Thomas E. Bryant wrote:
>Group,
>
>I hope that I can explain the formula where it makes sense and is useful
>to you.
>
>The idea is to calculate how much air the engine requires while covering
>a mile. The cubic inches of air is then converted to square inches by
>dividing by 1 mile. This gives you the size of the opening in the scoop.
>Naturally this is not absolutely accurate because of the variables,
>volumetric
>efficiency, wheel slippage, etc.
>
>The size of the column of air 1 mile long can be found by working
>backwards from the distance covered (mile) divided by tire
>circumference, equals the number of revolutions the wheel makes
>multiplied by the gear ratio to calculate the revolutions the engine
>makes while covering the distance, divided by 2 (since it takes 2
>complete revolutions of the engine to complete the firing cycle for all
>cylinders) multiplied by the cubic inches of the engine equals the cubic
>inches of air pumped. Now divide this by the distance (mile) and you
>have the size of the opening.
>
>Here is the formula for my engine geared for the Lakes:
>
>Mile (63,360") / tire circumference (86") x gear ratio (3.18) / 2 =
>1,171.41 x engine size in cubic inches (304) = 356,108.64 cu. in. / mile
>(63360") = 5.62 sq in.
>
>I have put this formula in the computer so I can plug in gear ratios and
>cubic inches and get instant results.
>
>The higher the gear the smaller the size of the opening needed.
>According to Tom Burkland, if the size is right for the engine, baffles
>are not needed inside the scoop because the pressure is equalized to all
>cylinders. He also said that it is wise to oversize a bit, to allow for
>going through the gears, since the calculation is for top gear.
>
>Tom, Redding CA, #216 D/CC
>
>
L.E. Mayfield
124 Maximillion Drive
Madison, Al. 35758-8171
ph: 1-256-837-1051
http://home.hiwaay.net/~lemayf
lemay@hiwaay.net
Sunbeam Tiger, B9471136
Sunbeam Alpine Bonneville Land Speed Racer,
'66 Hydroplane Drag Boat (390 FE)
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