Calculating Pressure Ratio

[SkullingAxe]

Im just making sure i got this.

I do this 2 ways depending on what im tuning for... If im tuning for while in Vacuum I first convert my Ambient Pressure to in.Hg. since vacuum is messured in in.Hg

So for with an Ambient pressure of 14.5psi (What mine is locally) that is 29.5 in.Hg. I used the calculator on this page. Pressure Units Online Converter

Once i know what my Ambient is in in.Hg i then subtract my gauge reading (lets use 16) from the Ambient.

29.5 - 16 is 13.5.

Ok, now to get my pressure ratio. I then Take 13.5 and divide it by ambient.

So 13.5/29.5=.458

Now for calculating it for When im in boost i do it a much simpler way.

I leave everything in PSI.

So i take my gauge reading (lets say 10 psi). And add it to my ambient.

So 10+14.5=24.5

I then take 24.5 and divide it by ambient to get my pressure ratio.

So 24.5/14.5=1.67

Equations as Follows

Calculating Vacuum. (Convert Ambient psi to in.Hg)
(Ambient-Gauge reading)/Ambient

Calculating for Boost (leave in PSI)
(Ambient+Gauge reading)/Ambient

Am I correct? I believe so however im making sure.

Bryan

So

[nemiro]

your pressure ratio is simply manifold pressure / barometric pressure. Pressure Ratio is always relative to your conditions.

[Nick Chestnut]

Quote: Originally Posted by nemiro

your pressure ratio is simply manifold pressure / barometric pressure. Page Ranking is always relative to your conditions.

He means Pressure Ratio not Page Ranking....

You can't type "P" and "R" together on these forums or it comes up as "Page Ranking".

[nemiro]

Bizarre. I didn't even notice that. Will correct in a minute.

[SkullingAxe]

Yeah,

I understand what pressure ratio is. I was just double checking to make sure my math was correct. I'm pretty sure it is but its always nice to double check things.

Bryan

[JANNETTYRACING]

Quote: Originally Posted by nemiro

your pressure ratio is simply manifold pressure / barometric pressure. Pressure Ratio is always relative to your conditions.

You also have to take in to conderation Pressure drop across Air Filter

[nemiro]

Perhaps technically, but all we are concerned with is what is in the intake manifold. The pressure drop across the air filter and the pressure drop across the intercooler is all used to determine turbine speed.