Finding blow off valve pressure
 

Ive read and read about turbo theory and compressor maps. On top of this im about 2.5 years into a 4 year mechanical engineering degree, and I still cannot figure one thing out.

Boost pressure is always measured at the waste gate, so off the exhaust gas. But how do you know the pressur of the intake air in the charge piping going into the motor. Sure this can be read by the map sensor, but id imagine youd want to know how much pressure your going to be building before you get there.

You could calculate the intake pressure from the pressure ratio accross the compressor * atmospheric pressure, but how does the pressure ratio vary with boost pressure?

im lost...

Re: Finding blow off valve pressure
 

ive thought about this before.

like external wg's. your o2 sensor isnt reading all of the exhaust gasses. sure, it should be the same, but you know, its the logic behind it

and, you're dumb.

boost pressure is measured via intake side, but regulated exhaust side ;)

Re: Finding blow off valve pressure
 

---- whats with all the math lately,

its simple, boost + enigne = massive burnouts

Re: Finding blow off valve pressure
 

for the math guy...
if you are not moving in your honda and you do a burnout and only one wheel spins your speedo will read say 140km/h.
how fast is that tire spinning?

Re: Finding blow off valve pressure
 

44mph

Re: Finding blow off valve pressure
 

ok so im dumb, but answer me this

Exhaust pressure of say 10psi, makes for an intake manifold pressure of how much?

Re: Finding blow off valve pressure
 

plan and simple.. ---- maths

Re: Finding blow off valve pressure
 

what are you talking about? boost pressure isnt measured off the exhaust gas. the wastegate has a vac line going to the pressure side of the compressor, which sees the positive pressure in the charge pipes/IM. nothing is reading or measuring the pressure of your exhaust gasses...
refer to above...

Re: Finding blow off valve pressure
 

He said it best. The wastegate just controls how much exhaust flows through the turbine. More exhaust = faster spinning of turbo = more boost. Now the wastegate is controlled by boost pressure on the compressor side. when it sees say, 7lbs of boost the actuator opens the wastegate some to let aditional exhaust bypass the turbine, this hold the boost pressure at 7lbs.

The blowoff valve will only go off when the intake manifold pressure drops (vacuum), and the throttle plate closes infront of your boost pressure. That is why a vacuum line goes to the BOV, it opens in vacuum when the boost in the charge pipe pushes it open.

Help any?

Re: Finding blow off valve pressure
 

280 km/h