As stated above, the greater the duration, the longer the valve stays off it's seat. For an exhaust cam it's benefit would be keeping the exhaust valve open longer allowing the piston to expel more exhaust gas.
For a forced induction setup, I would increase the cams duration slightly and would pay attention to the lobe separation angle and intake centerlines. The wider the angle between cams the less over lap at TDC, the narrower the angle between cams the more over lap at TDC.
Top Dead Center - end of the exhaust stroke and beginning of the intake stroke
lobe separation angle - the angle between max lift of intake and exhaust cam
intake centerline - the angle between TDC and max lift on intake cam
Here are some intake centerline figures I use on my 2T-G
(intake cam* - exhaust cam*)
low end gain
108* - 112*
mid range gain
106* - 110*
high end gain
100* - 106
my 2 cents
fonz
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