What do you stand to gain or lose by changing the size of your turbo flange? T3, T4, T6 etc?

 

volume of the turbine housing

 

How does that affect peak power and spool?

 

Your A/R (Area/Radius) is the relationship between the area (size) of the inlet of the turbine housing and the radius of the center of the snail where the turbine wheel inducer sits. As the size of the inducer increases, ie, bigger turbo, you need to be able to increase the area of the inlet of the turbine housing. Going with a bigger flange allows for that. T25, T3, T4, and T6 are just standardized sizes. Using a smaller A/R increases the exhaust velocity going across the turbine which increases how quickly it will spool, but the trade off is less ability for total flow which gives you less top end power. Higher A/R is the opposite. Remember though, the A/R is a ratio, not a size. A 1.06 A/R on a GT35 T4 might still have less total volume in the snail then a .95 A/R on a GT47 T6. However, there will be no difference in total volume between a 1.06 A/R T4 and 1.06 A/R T3 on a GT35. They will both flow the same. Of course, you can't actually get a 1.06 A/R T3. The T4 flange is your most versatile flange for the RX-7.

 

I'm cognisant of A/R ratio's. I am not, however, aware of the exact relationship between flange size, spool, and peak power.

I have been lead to believe it is not as simple as small=spool and large=power