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Author Topic: random engine formulas  (Read 6479 times)
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whitehendrix
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« on: December 06, 2009, 05:57:08 PM »

chances are you guys probably already know these by heart, but this is my (weak) attempt to make a useful contribution...


Piston speed = stroke x 2 x RPM / 12

Port velocity = (bore^2/port_dia^2) x mean piston speed

CFM = 3456 / (C.I.D x RPM [max]) **this formula assumes 100% VE**

CFM = ( cid X .5 X Ve X rpm ) / 1728 (use 1.0 for 2 stroke engines)

Cubic inches =Cubic Centimeters/16.387

Injector sizing (in cc's) = (HP x BSFC x 10.5) / (# of injectors x Duty cycle)

Injector sizing (lb/hr) = (HP x BSFC) / (# of injectors x Duty cycle)

Max inj. HP (lb/hr) = (flow rate x # of inejctors x .Cool / BSFC

Max inj. HP (CCs) =  (flow rate x # of injectors x .Cool / (BSFC x 10.5)

Flow rate(modified) = (sq.rt of new rail pressure/old rail pressure) x old flow rate

BSFC = lb/hr of fuel / BHP

Fuel requirement = Horsepower x BSFC

Lbs/hr = HP x .5

GPH = Lbs/hr / 6

Pressure = V^2 / 57,600 (bernoulli's principle. v=velocity)


for turbo

Pressure ratio =Pb+Pa/Pa (pa= atmospheric (14.7), pb= boost)
PR=(14.7 + psi ) / 14.7

CFM = [(DxCIDxMAX RPM)/1728]xVExDR

CFM = L x RPM x VE x PR / 5660

Boosted CFM = PR x CFM

Turbine trim = [ (inducer^2) / (exducer^2) ] x 100


thats all for now. if i think of more, i'll put em up.
« Last Edit: December 06, 2009, 07:03:26 PM by whitehendrix » Logged
donpearsall
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« Reply #1 on: December 06, 2009, 06:15:52 PM »

Good info. Thanks for posting.
In the injector sizing formula, is that supposed to be BFSC, not BMFC?
Don
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whitehendrix
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« Reply #2 on: December 06, 2009, 06:39:04 PM »

that is something i will look into right now to confirm, as i honestly don't know that answer myself.
thanks for pointing it out though.
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whitehendrix
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« Reply #3 on: December 06, 2009, 06:41:40 PM »

yes. you're absolutely correct. thank you for the keen eye.
 correction in progress!
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Bob Ellis
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« Reply #4 on: March 27, 2010, 03:51:33 AM »

What does what when???.Can understand the formula's , But ya gotta speak English bro!
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