Anyone have the basic formula for determining final compression ratio when engine is under full boost? I am not looking for exact figures with altitude corrections etc. Just ballpark basics.
Thanks Conner

((boost psi / 14.7) + 1) x motor compression = effective compression.

I take no credit for this - just came accross it. Does it look right? I'd guess motor compression = static compression? Not sure...

Here's a calculator that includes altitude correction - just plug in the numbers:

Calculator

Frank

Thanks Frank: I had seen that and used it. However i am not convinced of its accuracy. thats why i want the formula to work out myself.

Thanks DOT. Is something missing from that formula? I am having a problem making it work.
Conner

I got it to work (I think), as I came up with the same numbers as the calculator Frank posted. I put in the following:

8.5 : 1 static compression ratio
20 PSI boost
0 ft. altitude

So pretty much, ((20/14.7) + 1) x 8.5
((1.3605) + 1) x 8.5
2.3605 x 8.5 = 20.06
20.06 : 1

Again, I'm not sure if this is correct but it came up the same as the calculator.

Conner -

Now just what the heck are you up to? <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank

Frank: this is a project that i have been working with my son-in-law on for some time now. Without going into details, this is a compact stationary engine used for a specific purpose that must produce a lot of ponies at specific times. This is a one of a kind implement in which he has applied for a patent . We are going to install a positive displacement blower which is also unique and basically modified for this application. Just want to be sure i am dealing with facts so that we can determine proper static compression, drive pulley diameter etc.
Conner

Sounds interesting - I'd like to see the details when it's done.

Frank