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YES, I know this is probly very basic knowledge but i seem to have developed a tumor and i need some one to imbue there knowledge onto me.

First, on a turbo's specs for the compressor and turbine what do the various numbers mean for example if there is a .50 A/R compressor and a .70 A/R turbine what do these numbers accumulate to? Fast spool?High HP? and also what does the (A/R) mean?
 

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Boostin' to the limit!
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ND_boost said:
YES, I know this is probly very basic knowledge but i seem to have developed a tumor and i need some one to imbue there knowledge onto me.

First, on a turbo's specs for the compressor and turbine what do the various numbers mean for example if there is a .50 A/R compressor and a .70 A/R turbine what do these numbers accumulate to? Fast spool?High HP? and also what does the (A/R) mean?
Someone correct me if I'm wrong, but the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing, correct?
 

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No One Ever Listens To Me
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A/R= Air flow Ratio

basically the higher A/R rating the more surface area meaning more power but with added time to spool...otherwise known as lag.

thats the SIMPLEST form of explaining i would think.
 

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In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end.


Ideal is wrong... A/R does NOT stand for Air Flow Ratio.
 

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Ckanderson said:
In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end.


Ideal is wrong... A/R does NOT stand for Air Flow Ratio.
A/R stands for area/radius. The area of a turbine's inlet scroll cross section (A) divided by the distance from the center of that cross-section to the center of the turbine shaft (R).
 
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