Measuring boost back pressure

subcom said
Test 2:
Everything else the same, just dumping the exhaust before muffler with the 3" cutout.
Boost: 7psi
Back Pressure: 12.9-13.0
View attachment 1716233031 View attachment 1716233032

Significant difference. You need one of those exhaust valves that open with boost pressure so you can bypass the exhaust.