Pounds of boost?

[Sinister Angel]

I was thinking, wouldn't the boost pressure depend on the size of the engine you are running? Pressure is created by resistance, so wouldn't a turbo or a supercharger install be rated by CFM of air it can push? Just wondering.

 

[ROADWARRIORSVT]

Yes, you may order a S/C kit that has a 10# pulley on it. On a stock motor, it may produce 10#. If you P&P the heads, add big LTs. etc, boost pressure will drop. Does'nt mean you're making less power right. So power can't be measured by boost numbers. Wit hthat same 10# pulley, the S/C is still pumping out the same amount of CFMs. Thats what its all about.

 

[Sinister Angel]

Yeah, see, maybe it's just me, but I like hearing static numbers, IE, CFM, isntead of numbers that can change, like boost pressure. Does anyone have the equation for figuring boost pressure based on air flow and size of the motor?

 

[Jimmysidecarr]

It's a little more complex than that unfortunately....a given displacement engine will.."ask" for a certain amount of air at a certain rpm, and forced induction will stack up the air resulting in elevated boost pressure....but even though a 331/5.4 will ask for the same amount of air, because of the variables in air path, there can be restrictions which could cause higher boost.....
example....
picture a 5.4 lightning w/ stock pulley puts out xxxx pounds boost...put the same blower and pulley combo on a 32v Navigator motor, (assuming pistons were changed to same comp ratio) two things will happen...1 you will see less boost....2 you will see more power...the air path into the engine has been staightened and enlarged, so more air got in to make more power but it didn't "stack up" so you see less boost..
sorry I tried to make that as short and simple as I could....

 

[Sinister Angel]

Damnit, I need some classes for this shiz.