bigTom

ok... due to the recent question involving compressor maps... i still have not figured out how to read these things... im sure many poeple here would also like to know...

anyone care to share?

Arturbo

So I dont have to type a long **** essay, what you could do is pick up the latest issue of SCC. They have a huge write up on compressor maps. Well, I havent read it yet but from scanning threw it earier it seemed pretty good.

art

Arturbo

BTW, the scammer thing I told you about eariler was a joke.

art

Ricehornet

From my understanding of them...
On the Y-Axis you have the pressure ratio
On the X-Axis you have air flow, i believe in cfm

Now, You have to calculate the values for the air flow of your engine at a specific pressure ratio . Then you would draw or imagine that data on top of the compressor map. The line you draw would porbably look like and angled feeler gauge with the section you measure with pointed down
. ________
/

Yeah, so now that line you drew is the engine's air/pressure demand. On the Compressor map you have various markings that resemble elevation markings on a topographical map. To read that, the area bounded by the loops have the efficiency of the number written on those lines that form the loop. The Center loop has the highest efficiency.

Now, what your trying to do i believe, is trying to get a compressor that has the surge limit (the left most line) that is ALWAYS on the right side of your car's CFM*pressureratio line. You want the most efficient compressor possible for your application.. SO a nice wide peak efficiency area would be nice, and the drop offs arent too steep, meaning it'd be better to have your boost line range from 75% to 65% and spend most of the time in the 75% area than to have a peak of 80% for like a moment and drop sharply to 70% and then all the way down to 55% ...The location of the peak eff. is important too.

Oh yeah if there are other numbers, the ones on the far right, those are turbine speeds.

Efficiency as you know is how well the compressor can pump/compress the air without heating it more than it has to mathamatically.
7X% appears to be the turbochargers ideal eff.

Intercooling will help make up for some of the crappy efficiency we get from the compressor, but supposetly SC only get 50% eff.

Im not experienced at reading them enough to pick a good compressor, but i believe i got the jist of it. I wonder if someone can actually integrate the function to get the virtual area so it would be easier to figure out the overall eff.

I hope this helps

PS - I didnt read the SCC article yet, they've been doing that SUCK SQUISH BANG BLOW series . (love that title). And i've read a few of them and they are cool. So i wouldnt be suprised if they did a nice write up on Compressor maps. I learned that compressor stuff from Darth Boost himself. I hope i made him proud


[Modified by Ricehornet, 2:23 PM 8/6/2001]

DoctorBob

Warning: my dumbass summary follows. I'm learning this as I go but the math all checks....

Check out the charts at http://www.majesticturbo.com/compression.html . Note that the density ratio chart is basically unreadable: if you're interested in tracking down real information, Corky Bell's book is good reading.

Target pressure ratio: 1.5 (7+smidge psi).
Resulting density ratio: 1.25 (at 60% efficiency), 1.3 (70%), near 1.5 (for mythical 100% efficiency intercooler).
My displacement: 1797 cm^3 = 110 inch^3
Redline = 8000 rpm
Volumetric efficiency = 0.8 (fudge / guess)

So for the cubic feet / minute equation CFM = ((0.5 * 110 * 8000) / 1728) * 0.8 * 1.25 = 255 CFM at redline. Given that I might intercool at some point, we'll call it an even 300 CFM at 8000 rpm redline and about 100 CFM at 3000-ish rpm. Since I'm literally at sea level (Rhode Island is about as close to wet as you can get), I get 1 lb / 13 ft^3, so my range of interest is about 7.7 - 23 lbs / min.

Going back to the charts, I draw a horizontal line at PR = 1.5 from air flow = 7ish to 23ish, making sure that I'm to the right of the surge limit and that I'm staying at high efficiency as long as possible. T3 60-trim charts look pretty good (see that site again); T04 charts look crappy (for my PR = 1.5 application), the line misses peak efficiency, hits surge, etc.

Blah blah blah. As you can see, I like to write, especially when I'm all wound up. The physics here is quite cool, too, but I'll leave that for another lecture....

Hope this helps.
--
"I'm not <U>that</U> kind of doctor!" Bob

Arturbo

That makes two of us that have learned from Darth Boost.

art