A/R and wheel trim relations

[marleyskater420]

How come there are 56mm wheels in .7 A/R housings, and we use 63mm wheels in .63 A/R housings?

Does this mean that overall,the 56mm cant flow as much as the 63mm wheel, but the 56mm fills more air in the housing, which helps "make up" for the smaller wheel, by flowing more air?

Someone please explain in depth how the A/R and wheel trim affect overall flow. Also please explain how the turbine side limits this flow.

In great depth please.

 

[turbo2nr]

If you had two turbos the same, except the a/r was .63 for one turbine housing, and .85 for the other, then:
The smaller turbine housing will spool up faster (lower RPM) but will have more exaust back pressure at higher RPM (less HP).
The larger housing will need a higher stall converter to spool, but it will have less back pressure at higher RPMs and high boost. The bigger the A/R, the more efficient the turbo becomes, but with a trade off.

Bigger displacement motors can get away with even larger A/R. Some big deisel engines have an A/R over 1.1

A book titled "turbochargers", by HP Books describes a lot of good stuff.

A/R can be applied to any housing, either the turbine or the compressior cover.
I forgot exactly how to measure, but it goes something like this.

Take the distance from the centroid area of housing, and measure to the center area of the nozzle and divide by the measurement of the centroid area of housing to the outer edge of the widest part of ther housing's inner cavity. (how big the housing is compaired to the nozzle, which is the big hole the exaust enters the turbo.)

Two different size housings can have the same A/R....How you ask? Well maybe one has a 2" opening at the nozzle, and the other has a 3" opening. then the outer diameter of both will be in the same percentage in relation to the nozzle for it. One will be 50% overall larger in size than the other, but with the same A/R ratio.

This is not 100% correct, I'm pulling this info from my dusty brain, but it is pretty close.

 

[marleyskater420]

Originally posted by turbo2nr
If you had two turbos the same, except the a/r was .63 for one turbine housing, and .85 for the other, then:
The smaller turbine housing will spool up faster (lower RPM) but will have more exaust back pressure at higher RPM (less HP).
The larger housing will need a higher stall converter to spool, but it will have less back pressure at higher RPMs and high boost. The bigger the A/R, the more efficient the turbo becomes, but with a trade off.

Bigger displacement motors can get away with even larger A/R. Some big deisel engines have an A/R over 1.1

A book titled "turbochargers", by HP Books describes a lot of good stuff.

A/R can be applied to any housing, either the turbine or the compressior cover.
I forgot exactly how to measure, but it goes something like this.

Take the distance from the centroid area of housing, and measure to the center area of the nozzle and divide by the measurement of the centroid area of housing to the outer edge of the widest part of ther housing's inner cavity. (how big the housing is compaired to the nozzle, which is the big hole the exaust enters the turbo.)

Two different size housings can have the same A/R....How you ask? Well maybe one has a 2" opening at the nozzle, and the other has a 3" opening. then the outer diameter of both will be in the same percentage in relation to the nozzle for it. One will be 50% overall larger in size than the other, but with the same A/R ratio.

This is not 100% correct, I'm pulling this info from my dusty brain, but it is pretty close.

Oh ok, so the A/R is basically a area/ratio, right? So you divide the housing size by the nozzle which is exits, and thats your A/R? So the housing has nothign to do with wheel trim?

So could you have a small wheel turbo with a big A/R flow as much as one of our big wheel turbos with a small A/R?

Like there are import turbos Ive seen that give motors 200+hp at 9psi, and say they flow over 65 lbs/hr and the boost comes in at 3k rpm. How can this be? Does it mean they have a large wheel with a smaller housing, so the wheel will still flow lots of air, but since the housing is smaller, it will spool up quick and it will loose top end power?

 

[turbo2nr]

Don't get too deep into thought about compairing different motors with different compression ratios and turbos. Just stick to one car for now. Bigger A/R= more flow and more lag.

Bigger trim wheels=more flow and more lag.

Those are the main variables that change with turbo design.

 

[marleyskater420]

Originally posted by turbo2nr
Don't get too deep into thought about compairing different motors with different compression ratios and turbos. Just stick to one car for now. Bigger A/R= more flow and more lag.

Bigger trim wheels=more flow and more lag.

Those are the main variables that change with turbo design.

So a small wheel trim and big A/R means it will flow a lot of air, but it is still limited by the wheel trim?

The wheel ultimately desides how much it can flow, right? Like a 63mm wheel in a .63 A/R will flow more than a 56mm wheel in a .63 A/R, right?

Or can it balance out? Like a 63mm wheel w/ a .63 A/R will flow as much as a 56mm wheel with like a .82 A/R. Although the 56mm turbo will take forever to spool,but regardless, they will still flow the same?