confused about compressor maps

[cow]

Ok.. I was looking at compressor maps for a couple of turbos and I am kinda confused. I calculated the flow of a KA to be about 19 lbs/min (does this sound right?). Then I figured at .8 bar it would be like 30 something, I don't have the numbers in front of me. Anyway, when looking at the compressor map, do I use the 30 lb number to match with the pressure ratio? I think that's right but i'm not sure. If this makes no sense I'll try to clarify later. :\

Thanks in advance.

[lessthanjakejohn]

Yes, you use the x=30 y=pressureratio.

Go over 30, Up pressure ratio.

[huguetpj]

I think this might help

http://www.geocities.com/hugue...n.htm

[cow]

Yeah, I have read maximum boost and I was using the methods described in it. I just noticed that using boosted and unboosted numbers produced 2 results that both were very efficient, but for different turbos. Anyway thanks to all..

[cow]

By the way that is a great website, thanks huguetpj

[huguetpj]

No prob... thanks for the compliment:pface

[C-Kwik]

Pedro, You look to be on the right track on your site except for one thing. It looked like you plugged in 85% VE in all your figures. Motors tend to have a VE curve that varies with RPM. Variable cam set-ups tend to have flatter VE curves. But since a KA's torque drops off so dramatically after 6000 RPM, your CFM calculations may be on the high side at 7000 RPM. I didnt see any notes regarding cam changes or headwork, so I assume a stock KA's characteristics. Just something you might want to consider. My rather conservative estimates for 1 bar of boost puts airflow just above 30 lbs/min last time I did the calculation.

[huguetpj]

C-kwik... thanks for the inputs, and yep the head was stock when I did the calculations and purchased the turbo. Since I'm rebuilding it now I'm gonna do a mild port and polsih.

But since VE cannot be calculated theoretically, I used an estimated value all through the RPM range. Hope this doesn't affect my selection much... :pface

[C-Kwik]

Well, while it can't be calculated, you can make an educated guess. Figuring that most DOHC motors make anywhere from 85-90% VE, use a number in this range at the torque peak. Then kind of work backwards and calculate what torque would be at that that RPM with 100% VE. Using this as your base torque I'd use a dyno chart to determine torque levels at the RPM points you want to plot. Then calculate the percentage of difference between the base torque figure you came up with, and the torque on the dyno at that RPM. That percentage should be somewhere along the lines of the engine's VE. There are certainly other factors, and this is by no means totally accurate, but would be a better reflection of VE than using some arbitrary number all the way across the board.

[huguetpj]

good info. I'm gonna make a note of that one... thanks