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Now using the equation from the Mach .55 Hp flow loss :
FPS = ( bore * bore * stroke * rpm * .00353 )/ ca
ca = port area
ca = 1.41 sq in ( 1.34 * 1.34 * .7854)
stroke = 2.677
piston speed at max torque ( 5500 rpm) = 2454 fpm
Plugging in the numbers:
FPS = ( 3.622 *3.622 * 2.677 * 5500 * .00353) / 1.41 = 483.57
I'm trying to reconcile a couple of formulas to figure port flow in fps.
I'm porting my Ducati's 2 valve heads and trying to figure out flow speeds in various parts of the port.
The formula I've been using I got from Kevin Cameron's book "Sport Bike Performance Handbook" as follows:
Take the ratio of the port dia to bore dia and square that. Multiply that by the piston speed in ft per second. This gives average velocity. Plugging in some numbers:
(bore) 3.622/ 1.34 (port dia) = 2.70
Square that = 7.31
Piston speed at max. torque in fps. = 40.898
40.898 * 7.31 =298.96 fps a not unreasonable port speed.
Thanks Larry.. how about 379.4534 fps. I think it's based on diameters. If you figure what sized circle = 4.115 sq in , it comes out to 2.228969359 dia.
A lot of numbers after the decimal, but you need them to get 4.115.
4.687/ 2.228969359 = 2.047646458
2.047646458 ^2 = 4.1928560
4.1928560 * 90.49999 = 379.4534275 fps
Does that sound more realistic?
You're right, the engine peaked at 7000 and that probably explaines why
the last 3 lifts remained flat on the flow bench - .350-.400-.450". Valve lift is .460".I do have a bench I built to do this. I have made a U shaped probe but it's not a pitot. Does the static input of the pitot have to be at the very end?
Can somebody help me tie these two formulas together
I forgot to ask.... what is the math for mach number to theoretical VE?
Larry
Interesting reconciliation of different calculations. How accurate is the data generated through this link:
http://www.wallaceracing.com/machcalc.php
And how do reconcile the calculation of mach indexes using valve diameters and lift, on the one hand and as is done in the above link, and cross sectional area, as you have explained, on the other?
Sorry, didn't realise VE was one of those questions.
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