With a 325 whp Evo with stock IC and plumbing as example, if plenum (after TB) pressure is 20 psi, typically, what would be the pressure reading right before IC (turbo outlet), also before TB.

So basically whats the typical psi drop before and after TB, and before and after IC.

 

Guess I'll find out the old fashoned way

 

6 psi difference from turbo outlet, accross air to air heat exchange, throttle body, and finally the manifold

Turbo output is 31 psi while manifold is 25 psi (in air tight system)

I intend to use the turbo outlet air source to hold OEM BOV closed during boost (about 5 psi more force) through a 10 psi energized solenoid

 

Hmm... interesting. I saw some data from a turbo kit on a cobalt and at ~230whp, going through a front mount, the pressure drop from the turbo outlet to the IM was ~2.5psi.

Hmm... flow velocities are roughly the same (2.0L vs. 2.2L), pressures/densities are different (cobalt was at ~10psi manifold, 12.5psi turbo outlet). So about ~25% difference in densities. Eh, the stock Evo piping/IC is a litte restrictive, lol.

 

Two factors at play as for why the amount of pressure drop:

1. temperature - temp and psi are are proportional
2. Bernoulli's equation - sum of static pressure and dynamic pressure are constant - the smaller diameter turbo outlet increases the speed and pressure of air

This is why relative boost varies alot depending on where you tap, or whether using aftermarket manifold, and flow characteristics. It all boils down to the number of units of air is fed the engine and not allways psi

 

Did you calculate the value or attach a leaf blower up to the IC piping?

 

Ah, but PSI is a factor in density which is a variable in the reynolds number that in turn determines the boundry layer conditions eventually affecting pressure drop Flow velocity is the bigger factor though.

 

Actually considering the amount of restriction introduced by the lower IC pipe he might not be too far off. I still can't believe they went from like a 3" diameter to like a 2" on that thing.

 

My leaf blower died last spring.

Sorry, every posted test should include the procedure - here it are:

Procedure:

Test port 1 - compressor output
Test port 2 - manifold pressure via BOV port

Installed pressure guage (type that holds) to 20" 3/16"ID reinforced tubing tapped into OEM compressor outlet pipe nipple as test port 1 (MBC uses a tapped NPT port so this one is free) and then did 2 consecutive 2nd gear pulls (boost guage reads 25 psi).

Result: 31 PSI, 31 PSI

Installed same guage to spare NPT port tapped into BOV control/boost guage source and again did 2 consecutive 2nd gear pulls with boost guage hitting 25 psi.

Result: 25 PSI, 25 PSI

I'm not claiming this test to be scientific or velocity of air the main contributing PSI dropping factor, I'm just providing a down and dirty test result with unexpected results, for me at least.

The leaf blower question - I don't know if that would simulate real conditions enough (higher flow/pressure ratio)

 

Nice job. Yeah, a leaf blower wouldn't have the flow or power to effectively measure the pressure drop.

6 psi is pretty substantial. I would have thought that it would be only a few psi total. Seems like there should be some benefit to a more freely flowing IC and IC piping by reducing the pressure drop and therefore generating air that's not as hot and also by providing less backpressure from the turbine on the exhaust coming out of the motor.

 

Interesting result. Besides the temperature drop and variation in tube diameter, the intercooler itself is still mechanically restrictive and will result in a few psi drop from the friction between the air and the inner surfaces (which is necessary for a temperature drop).

6 psi sounds like a lot, but I'm comparing that with 10-12 psi supercharged applications that I'm used to.

 

Good theory with holding the bov closed by more pressure but you are forgetting one thing. The bov operates by the pressure difference. When the throttle blade slams shut the engine pulls vacuum which is usually goes to the port on the bov. This causes it to open because it has vacuum pulling on that end and pressure pushing on the valve side. The way you are planning on hooking it, you may never have enough difference to cause it to open because it will never see the vacuum from the engine.