Exhaust Pros/Cons for Slant 6

One other note is that 1-5/8 to 2-3/4” for the pipes from the Duals to the Y fives near identical performance as long as you have not done extensive head work with a huge cam and plan to make the power way above the RPM range where most 225s start to gasp for air due to the head. For a nice street motor with simple head improvements like oversized valves and just knocking out the lip right behind the valve 1-5/8” or 1-3/4” pipe is much easier to run down to the Y and has no performance impact and actually may make a tiny bit more torque down low due to the higher exhaust velocity and better scavenging effect. If you go smaller than 1-5/8" it will effect higher RPM performance and if you go larger than 2-3/4” the velocity drop will drop torque as the scavenging effect is reduced because of it.

This is based on a very accurate Performance Trends model Rusty and I have created. My Dart used 1-5/8” to the Y for an easier run and because I never run it past 4000-4500 RPM anyway.