OK, I guess my mis-understanding comes from thinking that the A/R of .81 on a 60mm turbo is still smaller than an A/R of .68 on a 76mm turbo; just because its on a larger turbo. I do realize that the 60 and 76 only refers to the compressor side. I already feel like the exhaust housing is too small on my turbo with the STS 60-1.

Is it always safe to compare exhaust side A/R's between turbos?

 

I'm not sure what you mean by compare exhaust side A/R's. I will say that it depends on the ratio of backpressure to boost pressure. You will always have more back pressure on the exhaust side than boost pressure on the intake but you don't want too much backpressure because then it means that your turbo, specifically the exhaust side, is a restriction and will hurt performance.

That being said, larger compressor sides produce more volume so as long as the turbine side is sized so that the backpressure is not greater than 1.5 times the boost pressure, then you are not restricting the flow too much for it to "choke out". Remember that efficiency is the biggest factor. If you can have a larger turbo get you the same volume of air with less effort and heat, it will equal more power.

 

I do realize all those points as well as basic turbo theory.

The thing I was trying to clear up is simply: if you have the two turbos mentioned in the previous post, how do the .81 and .68 exhaust housings COMPARE? Is a .81 always larger no matter what turbo you have?

 

Sorry, didn't mean to come across as insulting.

If you are comparing the same size trim wheels (Ptrim, Qtrim...) then yes, a P trim wheel that has a .68 A/R will spool faster than the .81 or .96 since it is smaller and increases the velocity of the air more. The .81 is always larger than the .68.

 

I know this thread is more "dead" but can someone explain more turbo theory to me. I cant find anything really