Calculating turbine housing A/R ratios

[chaloux]

Okay, my head is about to explode. I understand how to calculate a/r according to everything I can find online. you calculate the cross sectional area of a point in the volute and measure the radius from the center of that point to the center of the turbines outlet, and then divide a/r. BUT, when I use my numbers, my outcomes make no sense.

A/r = area/radius

To expand on that, it shouldn't matter where you take these measurements on the volute because as area decreases, so does radius.

But when you actually figure out your values, the area is so much larger than the radius that it simply doesn't come out as a decimal point. So wtf am I doing wrong. It seems simple enough but I know I must be missing something.

Ie. 1600mm2 / 80mm. Clearly not a decimal point such as .63 or .82

This is all stemming from my supposed .82a/r housing being physically smaller than my .63a/r (two different manufacturers). Now that SHOULD be okay according to the calculation, because if the volute area stayed the same but radius decreased, a/r should increase.

But the equation doesn't make any sense. Someone shed some light on this PLEASE.

.63 left, .82 right

[chaloux]

Well shoot. I need to figure out what this housing is. From what I can tell turbonetics offered an 8cm^2 and a 10cm^2 housing. I see two numbers there that someone could easily mix up with .82a/r...

[speeding-g60]

you would solve one riddle for me when you figure this out, but moreso in relation to twin scroll or divided housings.

but my riddle is easier i think.

how does a twin scroll A/R number coincide or correspond to an open scroll A/R? IE: .63 open is equal to .xx divided?

[bradyzq]

1600mm^2 = 2.48in^2
80mm = 3.15inches

2.48/3.15= 0.79

Methinks it's all about the units chosen.

Kinda like when you try to figure out why torque and power don't cross at 5252RPM, then you realize the units are kw and Nm...

[loxxrider]

Yep, you've got a unit problem.

Aaron, that relationship would vary from one turbine housing to another depending on size. There isn't a fixed number you can just multiply by or something. That's because the role the center part (the part which splits the opening) plays in the equation is reduced as the size increases.

[speeding-g60]

BW 1.25 divided T4 = ??? open?

[loxxrider]

One thing I just thought about Aaron... I think you're thinking of 1.25 divided T4 = ?? open in terms of spool (I was talking in terms of size I guess)... there is no way of calculating that which I know of. 1.25 divided = 1.25 T4 in terms of area vs radius obviously, but that means nothing if you don't know more about the problem.

[chaloux]

Lol. Dang. Didn't think units mattered but I guess so! I'll convert my measurements and recalculate.

[chaloux]

Awesome. .63 calculated out to be .64 (measurement discrepancy) and the Turbonetics housing came out to .78

So I'd say it's in the .8 range.

Use it? The price was right - essentially a free swap.