The length of the pipe in the stock configuration is longer than it needs to be in most cases. If you
would like to increase the power in the upper rpm range you will need to shorten your header length.
This is done by removing and shortening the section of straight pipe between the exhaust header and
the 45 degree fitting. Remove ¼ inch sections at a time and retest. Continue shortening this header
until you get what you are looking for.
A word of caution, these engines only produce so much power. You cannot expect to just keep
shortening the header length and it will continue to rev higher. There is a point where the port timing
of the engine just will not allow it to rev any higher and on these motors is probably a good thing or
we would blow them up.