So i'm doing CFD (Computation Fluid Dynamics) research on a typical cold-air intake. One item i need to know is the vacuum pressure that is seen at the throttle body. In essence, how much pressure is the engine pulling with? Anybody know these numbers?

 

nobody has any idea at all?

 

i think it all maters on the mods. but ive heard on VAFC it measures +1 at WOT

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spanishlude &raquo;</TD></TR><TR><TD CLASS="quote">i think it all maters on the mods. but ive heard on VAFC it measures +1 at WOT</TD></TR></TABLE>
Yup, and at idle somewhere around -550-600.

 

units???

thanks guys

 

at closed throttle there is about -11, -12 psig on the intake manifold side of the throttle plate. At WOT you should be at 0 psi, the +1 readings on the VAFC is just an error, well unless your running some kind of ram air,

 

I know the cars height at sea level plays a big role in the psi reading.

At sea level Atmospheric pressure is 14psi so I'd start from there, most sensible place to start on as then with the increase in altitude the pressure drops at a constant rate psi\altitude. (Youd have to research to find the rate)

I'd guess that the pressure read at the throttle body would be relative to engine rpm also, as a cylinder is in the intake stroke its sucking the air in right, so I'd assume the vaccume pressure would also be relative to rpm. Higher the rpm = lower the pressure.

If a CAI flows well there will be less resistanse hence a lower pressure over a stock air box.

 

thanks for all of your input guys, i'm doing a simple 2D model of an AEM CAI and i'm just going to use approximations of the velocity inlet and pressure outlet. If anyone is interested, i can post pictures of the velocity, pressure, etc. contours and gradients next week after im finished.

 

-550 to -600 mmHG if I remember correctly...

 

what is the 'mmHG' abbreviation short for?

 

mmHG = millimeters of mercury