Originally Posted by Sierra977

Exhaust gas velocity is a critical parameter to engine tuning.

Exhaust gas velocity is one of the two controlling factors of the exhaust reversion wave. Smaller diameter tube has higher velocity given same exhaust gas volume. Length of exhaust tube is the other factor.

Exhaust reversion wave will scavenge combustion chamber IF reversion wave arrives at exhaust valve at correct time.

Exhaust reversion wave can be controlled by exhaust gas velocity and exhaust tube length.

Larger diameter exhaust tube comes into "tune" at a higher rpm than smaller diameter tube of the same length.

Practical applications are Ford "high-velocity" exhaust ports (read smaller area but higher gas velocity) and "long-tube headers" (again smaller diameter but longer length). Both applications increase low rpm torque values.

(We did this fifty years ago on the Can-Am cars)

Originally Posted by 98hotrodfatboy

If this helps. The two dyno sheets are identical build and dyno. The only difference is the pipes. The RB is 1 3/4 2-1 and the Python staggered duals are 1 5/8.

Originally Posted by Max Headflow

But not a valid comparison as one is SAE corrected and the other is Actual.. Also more to the pipe then just header diameter. Curve wise, I like the python better.