RE: Tuned Pipe TH .75 - Tuning For Mid Range Performance?
Chris,
Extending the header and adjusting the system's length for the lower RPM, is virtually all that needs to be done.
If your Macs pipe is the 'Quiet' type, it is a cone-and-disk design, which has a wider range and is easier to tune.
The muffled pipe is more peaky...
Even the 'Quiet' type will need extending the header by 1.5-3", depending on how much lower the RPM will be.