Turbo lingo??

Spindley · Post by **Spindley** » Sat Jan 06, 2001 8:29 pm

G'day all. This is a quote from the CB Performance catalogue - "The T03 is equipped with a parallel wall diffuser to maximize boost and CFM. Its equipped with a 4.5 A/R ratio turbine housing to provide low end torque and mid-range response."

What exactly is meant by parallel wall diffuser and A/R ratio?

Volkaholic · Post by **Volkaholic** » Fri Jan 12, 2001 10:54 pm

A/R = "A" is the ratio of the cross sectional area of the compressor outlet, "R" the distance from the center of the compressor to the center of the outlet. When they design & build turbos at the factory, they hold this ratio constant as the outlet spirals outward from the compressor. To calculate your A/R, measure the inside diameter of the compressor outlet D, then measure the distance from the center of the compressor wheel to the center of the outlet R. A = 3.14*D*D/4
A/R = the ratio of the two
IN GENERAL the higher the A/R, the more top end power you will get, the lower the A/R, the more throttle response.

Volkaholic · Post by **Volkaholic** » Fri Jan 12, 2001 11:01 pm

Oh yeah, a Parrallel wall diffuser is in the exhaust side of the turbo. Normally, when you bring the 4 individual pipes to the turbo, all 4 dump into a common area right at the turbo (like a 4 into 1 header). The parrell wall diffuser is just a divider that splits this in half. What the means is that instead of dumping 4 into 1, you dump 4 into 2, then 2 into 1 right at the turbine wheel. This keep exhaust gas pressure higher at the turbine wheel because the changes in cross sectional area are less sudden. I've never run one, but they are supposed to make a diffence.

Spindley · Post by **Spindley** » Sat Jan 13, 2001 2:01 am

That makes sense but what is the average A/R ratio? Where in the range would 4.5 be, high or low?

Thanks

volkaholic · Post by **volkaholic** » Mon Jan 15, 2001 6:51 pm

Are you sure you don't mean a .45 ratio, not a 4.5 ratio? I'm running .65. I did some looking around & the lowest A/R I saw was .36 & the highest was .86, not that other ratios don't exist, I just didn't see them. Good luck.

Spindley · Post by **Spindley** » Thu Jan 18, 2001 12:06 am

Here's the link to CB Performance's catalogue. I don't know if this is a missprint because its also word-for-word in the printed catalogue they sent me.
http://www.cbperformance.com/catalog.asp?ProductID=286

Mr. Turbo · Post by **Mr. Turbo** » Fri Feb 16, 2001 4:06 pm

Mr. Spindley,
A parallel wall diffuser is part of the COMPRESSOR or INTAKE side of the turbo, not the turbine/exhaust as someone said above. They are confusing this term with a divided exhaust housing, which is a completely different thing. the diffuser section is the area immediately surrounding the O.D. of the compressor on both the backplate and compressor housing side. The distance from the compressor wheel to the scroll section of the housing is normally very short, like 3/8 to 1/2 inch. In a parallel wall diffuser design, the backplate is a little larger in diameter and the section of the compressor housing which runs parallel to it is larger in diameter as well. Theoretically, this is more efficient as it gives the compressed air more distance to change its direction of flow as it enters the scroll section of the compressor housing. Hope that made sense to you.