Turbo maps?

[minicooper172]

I've just whacked a load of numbers into a spreadsheet I drew up, to calculate the size of turbos I need turbocharge my M30B35. It's all going well, and I've ended up with numbers near to what I expected. Now, how the hell do I read a turbo compressor map?!

[UweM3]

bet GeoffBob can help with this, he is clued up with that stuff.

[GeoffBob]

Thanks Uwe, that's kind of you to say. Sorry I got so angry the other day, I'm afraid I take things a bit personal some times.

Minicopper172, basically what a compressor map tells you is at what speed the compressor will have to spin (and at what mechanical efficiency) in order to flow a certain amount (mass per second) of air (read off on the x-axis) at a given pressure ratio (read of on the y-axis).

You need to think of a compressor as an air pump that, so long as it is pumping into something, will have a different (higher) pressure at its outlet than its inlet. If the pressure at the inlet is P1 (usually close to atmospheric pressure) then the pressure at the outlet is P2, where P2-P1 is called your "boost" pressure. The ratio of P2/P1 is what is plotted on the Y-axis of the compressor map.

Unfortunately, to use a compressor map to tell you how your engine will perform (how many horses it will make) you need to plot what is called a "load line" across the compressor map. This loadline helps you to determine how much air your engine will induct when the turbo gives it a certain amount of pressure, and thus how much fuel you must add, and thus how much hp you will make.

Now, read the first few pages of the Garrett turbo catalogue here to learn how to plot a basic loadline (given that you know some basic parameters about your engine) and then post up any questions you have afterwards.

Hope this helps for the time being

Regards
Geoff

[minicooper172]

Aah, thanks for that, that's starting to make a bit more sense. What a great find!

Thanks GeoffBob!