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[matt]

Anyone able to explain how to read these, or check my poor turbo math
I'm interested to see because in looking for another kkk K26 a good KKK K27 has turned up and with my limited understanding of these turbo maps i think a K27 might work?
here are the maps:

and the K27


Heres my poor turbo math
Estimated pressure ratio is 1.54
Boost press req'd is .54 x 14.7 = 7.9psi
Density ratio 1.54(to the power of .28 )-1 x 550*/.75= 94 degreesF
intercooled desity ratio say 85% efficient thefore temp gain 94 x (1-0.85) = 14*F temp gain
Desity ratio intercooled 460*F+90*F/460 + 104*F = 97.5 = 2.5%density loss
intercooled press ratio = 200hp/130hp x 0.975 x 1.25 x 0.90 = 1.395
CFM 120cidx 5400rpmx 0.5 x 0.8Ev/1728 = 150CFM (stock engine)
Req'd Intercooled CFM 1.395 x 150 = 209 CFM
Turbo peak efficiency wanted around 25% higher than peak torque say 4000rpm + 25% = 5000rpm
new cfm = 139(stock) x 1.395 = 194CFM required
194/14=13.84 pounds per min ( to read turbo map)

Once you've picked yourself off the ground from laughing so much please let me know all the mistakes
I think these CFM figures are too high?????

Is 80% volumetric efficiency about right for alfa 4 cylinder (nord)
Can i use a drive power effiency of 90% for a turbo?
the K27 seems to be very efficient at 77% and 75%, more than K26?????

Thanks Matt

[Mats]

From looking at the maps it looks like the good old german boys have used real dimensions, i.e. Metric.
Have you taken this into account?

[matt]

Doh' thanks Mats
13.84 pound/minute = 0.1046286 kilogram/second?
I think..... so K27 not looking so good, is this the right thinking even though made to within 70% "island" of map

Whats regarded as the minimum practical effiency allowable when looking at all these maps? is 70% ok?

Thanks Matt

[Mats]

They also use dm^3 in ome formula, did you notice that?

[matt]

Mats i could only find a conversion for lbs/min to Kg/sec .......
but i have just bought another very good K26, so calculator and K27 idea will gather dust for now.....
If i work on a PR of 1.395 and .1 Kgs/sec this point on the K26 map its in the middle of the 72% "island" but the audi example is much higher at 5000rpm, sure its a 2.2 ltr engine(i think) but the map would indicate those things run 12 to 13psi boost and flow alot more air...is this the right interpretation??? or are my figures wrong?

[matt]

.....and on a side note is there any difference between KKK turbo's with a red or blue tag
are the red one's rebuilt or used on some jap cars??? as i've seen two advertised with red tags that where imoprted from japan?

any idea's?