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Turbo ? cm vs ar

curtis

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May 4, 2003
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Clarksville TN
Google sucks if I type in ar vs cm I get a million racing videos and chemisty formulas dealing with argon and measurements of gases...

Ok ar is area radius yadda yadda

ar picture click me

Cm is usually 6 or 7 or 18 or whatever bigger the number larger the housing size.

I've never seen a real comparison and all my knowledge on the subject is in ar ratios

What is the relationship between the two?
Lets say you have a .48 T3 garrett is that comparible to a 6cm. But how far is it off.

Then lets say you see a 30cm on a big ass dumptruck in a coal mine is that 30cm equal to a 1.36 or 1.5 or 1.7 /ubbthreads/images/graemlins/dunno.gif

All of this is good to know.
I've owned a 14b then went straight to a garrett in a t3 .48 and a T3 .63 and a bullseye .55..... the .63 Garrett pulled harder than any up top. Then I stepped to a s362 schwitzer/borg warner but the turbine wheel dwarfed the garrett and of course with a .80 compressor in a grown ass man size turbo was no comparison to any of the Garrett's I owned. I've now sold the schwitzer and have bought the new. There's not alot of info on these things so hope someone that knows understands the question I'm asking.

I can't go any further in detail the new turbos is the top secret. /ubbthreads/images/graemlins/devil.gif I do know the compressor in a small housing has made 650 to the tires on a dsm so hoping for a little more out of this behemoth.
 

Andy_S

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MHI Turbine housing areas:

6 cm2 = 0.41 A/R
7 cm2 = 0.49 A/R
8 cm2 = 0.57 A/R
9 cm2 = 0.65 A/R
10 cm2 = 0.73 A/R
11 cm2 = 0.81 A/R
12 cm2 = 0.89 A/R
14 cm2 = 0.97 A/R
15 cm2 = 1.05 A/R
16 cm2 = 1.13 A/R
17 cm2 = 1.29 A/R
19 cm2 = 1.37 A/R

These are mhi to mhi, not mhi to garrett. They rate them from slightly different points. What those points are, I couldn't tell you.
 

curtis

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Clarksville TN
Thanks Man
 

GVR-4

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Apr 22, 2002
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Asheville, NC USA
A/R (read "A over R") is the ratio of the cross sectional area of the turbine housing volute over the radius from the center of the trubine housing to the center of that cross sectional area. A picture is easier to understand than a description with words. I'll look for one.
 

GVR-4

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Apr 22, 2002
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Asheville, NC USA


I realize that this is simlar to your photo, Curtis, but this one shows that the ratio is consistent despite where on the turbine housing you are taking the measurements.

I'm still learning, but as far as I can tell the A/R is used to tell how restrictive the turbine housing is. Curtis, I'm not really sure what you are asking as far as how A/R relates to "cm." What do you mean by "cm?"
 
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curtis

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Dave
Aspod hit it dead on.
I wanted a close approximation of x ar = y cm
 

Dialcaliper

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Jun 22, 2007
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Mountain View, CA
Curtis,

I think you are getting confused because the two measurements are actually independent, and describe different aspects of the housing. Aspod has all of the right A/R's for the mitsubishi turbine housings, but that's because they only have one A/R for each size (or more like a narrow range of A/Rs). (actually, not true, because they have different lines of housings - TC05, TD05, TD05H - same size wheel, different A/R. Some of the larger housings have bigger A/Rs like TE or TF, and it gets even more complex with the Evo 4+ turbos that have similar A/R's but different throat areas - Just like the T3 vs T4 difference, but with less drastic changes in size)

The cm^2 that you see on mitsubishi turbines is actually the smallest cross sectional area at the throat of the turbine, right before it opens up and hits the wheel. This tells you a bit about what the velocity will be going into the turbine. That's why you hear variable vane turbines referred to as "variable area turbine nozzles"

A/R is a measure that tells you about the "compactness" of the nozzle volute. A lower A/R housing has a gentler spiral that, in general, keeps the air velocity up as it hits the turbine blades, spinning it up faster. This also means that because the passage is narrower relative to its longer length, it does not flow as well (think long skinny tube with high velocity but higher backpressure, like a N/A exhaust)

A higher A/R is a tighter curve, but with higher cross sectional area - this means higher flow and lower backpressure, but the air slows down more before it hits the wheel (think like a big turbo exhaust).

The important part is that you can technically have any A/R with any throat area. In practice, there tend to be solutions that work better for a given size and purpose of turbocharger, but you'll still find subtle differences in A/R vs throat area combos between turbo brands depending on what size compressor it's matched with (and what boost levels the compressor is intended for)

Garrett housings are always a bit of a compromise, since they tend to have standard housings across multiple sizes of compressors - they make up for it by providing a choice of A/R ratios though. This is why a T3 and T4 housing with the same or similar A/R will flow completely differently (the T4 will have a larger throat area, but have the same A/R because the housing is simply much larger.

At the same time, MHI tends to have housings that are much more optimized for one or two compressor sizes - which means they tend to be pretty good for the intended turbine, but end up performing less well than the Garrett when you start mixing and matching housings. The side note is that we only ever use the largest A/R turbines from Mitsubishi (the TDXX and TDXXH series - the TCXX are smaller A/R housings of the same or similar size - faster spooling but worse for flow). Also, when you port a turbine housing, you are basically changing the A/R ratio by increasing the area. The reason you get better spoolup from porting is that the higher A/R performs better at higher flow and boost pressures. Up to the stock boost level, the turbine will spin up slower, but above that, the lower restriction wins out over the higher velocity because it gets too turbulent (it works exactly like head porting - there's an optimum "mach number" that results in the most efficient flow)

In the diagram above, imagine the T3 as a turbine that starts at A2 and terminates at A6, and the T4 as one that starts up at A1, but ends at A5 - same A/R, different throat area.

Sizing turbos is complex simply because there are so many different independent variables that affect the performance.
 
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Andy_S

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Shithole Wisconsin
^Thus why I stated it was an MHI to MHI measurement. Thanks for the clarification on the Garrett measurements compared to MHI. Holset uses cm^2 like MHI also. Are they measured in any way similar to what was already mentioned?
 

The 12cm^2 holset turbine housing has individual volute areas at various angles originating from the hub very similar to the 6cm^2 14b turbine housing. There are two volutes and thus a 12cm^2 measurement.

. . .This is all from my personal observation and measurements.
 
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if u can answer this question i wounld be gratefull my turbo on my evo 6 has stoped working since the police impounded it it is like they turn it off the car were fine befor now it makes a whizzing sound and the bearings is fine can u help me
 
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