Felt like I got small gains out of
1) good tube up
2) muffler swap
3) k&n air filter (yes I know some of you don't like these)
4) power wire to advance the timing slightly
K&N filter information, this keeps coming up so lets look at some facts
as far as muffler swap goes you may gain 2/10 of a mile per gallon and .3 more horsepower but not much more
You really can't go by what manufacturers put out there trying to sell their junk.
Heres one such test and there are many many others every one K&N is on the bottom
Filtering efficiency is a measure of the filter’s overall ability to capture dirt.
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“Accumulative Gain” is the total amount of dirt that passed through the filter during the test.
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quoted from nicoclub.com