A/R and cm2

Did some rubber molds of 2 Garrett housings GT47 A/T 1.27 and GT50 A/R 1.41 , and Holset 27cm2 for reference , and measured their area.

I got Holset at 26.8cm2 so accurate enough.

1.27 was 28.3cm2 so maybe 28 or 29 , calculated backwards R should be then ~87-90mm

1.41 was 30.6cm2 so 30 or 31cm2 , R ~84-87MM

Tried to measure Holset R , it is ~ 97 so that gives A/R about 1.1

Shows how stupid way to give housing flow capasity in A/R is , if you keep A same but make R bigger , it gives smaller A/R number even if it should flow more because better flow angle into turbine.

Wow! How do you have so much free time?

Got advice from my friend who is PhD of mathematics how to find centroid of that area. It is actually quite simple. So now 27cm2 Holset housing is about A/R 1.12

I'd always wondered what weird math was behind the A/R and cm2. Thanks for hte lesson.

joefarmer said:

I'd always wondered what weird math was behind the A/R and cm2. Thanks for hte lesson.

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When you calculate A/R you must convert everything to inches and square inches.

GT47 A/R 1.13 = 24cm2

if my exhaust housing is 14cm does this convert to .80 a/r ? sorry i am not educated on this.

MoparRiggan said:

if my exhaust housing is 14cm does this convert to .80 a/r ? sorry i am not educated on this.

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Hard to say , must find centroid and measure R.

I dont understand why A/R is given for users , it is only needed for housing manufacturing to get right shape.