[BruceWilkie]

The turbine needs pressure and velocity. IIRC butlers 3000+ hp twin turbo 482 uses 2" primaries and merge to 2.5" at/near each turbo. Keep in mind methanol creates @ 14% more exhaust volume over gasoline. 3000 hp is ALOT of exhaust volume.

I think "too small" primary pipe would be if primary id/csa was less than minimum csa in the exhaust port. Heavier wall helps hold heat, thus exhaust doesnt shrink as much and lose pressure to contraction. Too big hurts spool and doesnt seem to add power.

Also keep in mind tuned length theory goes out the window when a turbo is on the end of the pipe. The turbine kills reflected wave.