Please make sense of this

[FastRthenU]

Now I have heard many ppl say great things about the 50trim wheel. So I went and found a map for it. Im a little new to reading these things. I kind of understand but not full what it is telling me. Can someone tell me what this map is saying. thanks

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[XTurboSpYderX]

On the compressor flow map, the horizontal axis represents the amount of uncompressed air entering one turbo in lbs. per minute... as a guestimate you can say that one Lb. of air could potentially equal 10 flywheel HP. The vertical axis represents the amount of air compression that occurs inside the compressor... the formula for ploting a number on that axis is: (x+A/A), with x being Psi of boost ran and A being one atmosphere, or 14.7. The curved lines with labels at one end (113,707... 120,418... etc.) are the rotational speed (in rpm) of the compressor wheel. The elliptical curves with labels such as 78% represent the efficiency of the compressor.

The main point of using a compressor flow map is to determine if the compressor part of a turbocharger is sized properly for your engine. In order to do this, you need to know the aprox. Psi. and HP numbers you are shooting for.


so... if you are shooting for 290 +/- 15 crank HP at 17 +/- 2psi of boost... then this could be a good turbo... all other variables must still be considered, altitude, ambient temp, supporting mods on the car... that sort of thing...

did that help at all?

 

[FastRthenU]

Still a little shakey on it. I know how to figure out the psi. presure x 14.7 -14.7= But how to i know where to plot the point on the graph to see how much air it is flowing?? at that psi?

 

[XTurboSpYderX]

Originally posted by FastRthenU
Still a little shakey on it. I know how to figure out the psi. presure x 14.7 -14.7= But how to i know where to plot the point on the graph to see how much air it is flowing?? at that psi?

1) the equasion is X+A/A... not X+A-A... that would just be X

2)with only one value you would have a line, not a point... you would draw a line, horizontally across the grid...

3) you would use said line, not to find out how much air is flowing at a given PSI, but at what speed, and efficancy the compressor is working at any given rate of flow, whilst compressing it TO aforementioned PSI.

 

[FastRthenU]

I didnt say the equation was x+a-a=. I said it was presure x atmospheric - atmospheric =

so 2.00 x 14.7 - 14.7 = 14.7 1 bar is this not correct?
or 2.60 x 14.7 - 14.7 = 23.5 psi

Iam I doing this wrong? sounds right to me. If i do it your way which is presure + Atmospheric / Atmospheric =

so 2.00 + 14.7 / 14.7 = 1.136 ???
or 2.60 + 14.7 / 14.7 = 1.176 ???

so are you sure im wrong??

edit Ok i see what your saying. But when I put that equation on there i knew it was for just presure. Im so confused

 

[XTurboSpYderX]

I appologize, I should have made my equasion more clear...

X = PSI you intend to run

A = 1 atmosphere (1 Bar) (14.7)

so the equasion for 18psi of boost would be:

(18+14.7) / 14.7 = 2.2245

I hope that helps a little more...

you have the same equasion, but you are working it backwards with a grid point as your variable...

 

[FastRthenU]

Now that i have the anwser to the equation. What does that mean? 2.2245? What does this number represent? What do I do with it? I still dont know how or where to plot it on the graph.

 

[DrZiplok]

That gives you a horizontal line across the graph; draw it at the 2.2 point for simplicity's sake.

Now you can tell a bunch of things about that compressor at 18psi boost. For example, it won't make 18psi below about 20lb/min because you run into surge. Peak efficiency will be between 28 and 35lb/min at that boost level, and will fall off sharply at about 40lb/min.

The SWAG given above (10hp per lb/min of fuel) is "good enough" to say that you can reasonably expect to make 300-350 horsepower at the crank at 18psi, but above 400 and the turbo will be running out of puff.

You could also sneak up the graph a bit to see what sort of room you have to increase the boost; for example if you go up to 2.5 the compressor doesn't start suffering until you get to 44lb/min, netting you perhaps another 40 horsepower at the crank.

For a lot more of this, check out the math in Corky Bell's book. He discusses compressor maps and a bunch of other stuff in enough detail to get you into a fair amount of trouble.

 

[FastRthenU]

so how do ppl go so fast and make such good power on this turbo. If its only good to about 350 to the crank?

 

[XTurboSpYderX]

it is only good to about 350 at 18Psi. if you bump the boost... and tune it properly... it is good for more than that... especially if you use an EBC with several preset boost levels...

 

[DrZiplok]

You can go awful fast on 350hp, especially if you cut your weight and learn how to drive.

The 10hp number is also pretty damn "approximate". What the map does tell you is that over about 45lb/min this compressor really starts to suck, no matter what boost you're running.

It's up to you to work out how much fuel, how many RPM, etc. you can run to consume that much air. Nitrous adds an entirely new dimension to the equation if you care to go down that road as well.