Kpa vs. Boost reading

[Big Creek]

I think I know the answer to these questions but just want to make sure.

I just finished test driving my blower setup for the first time. I am turning the supercharger very slow at first until I get some other things dialed in and the intercooler mounted up.

At my elevation the normal kpa reading is 85. I have no actual boost gauge hooked up yet. My boosted kpa is 106. I assume if I had a gauge it would read 3psi (6.8 kpa per 1psi). Generally speaking, if I were at sea level would I then be reading 121kpa?

What if my intake system were not very efficiant and at my elevation my engine showed 78kpa at full throttle. Could it then be said I am actually building 4psi of boost at 106kpa?

Silly questions as it doesn't actually matter how it is measured but I just want to get my thinking correct.

Todd

[efahl]

Todd,

Your numbers sound right to me. I made a calculator up, just for you, so that you could calculate these numbers easily in a number of different units.

http://www.not2fast.com/turbo/boost_converter.shtml

What if my intake system were not very efficiant and at my elevation my engine showed 78kpa at full throttle. Could it then be said I am actually building 4psi of boost at 106kpa?

Yes, that would be the number you would use for pressure ratio calculations if you were trying to plot compressor efficiency on a map or something like that. I've got a blower calculator that back-calculates that number assuming you are supplying the pressure at the valve and the pressure drop across the intake system from the compressor outlet to intake valve.

Eric

[Big Creek]

Great calculator! Thanks for the link. It is in my favorites now.

Todd