just one more cam selection thread

Just another reason I do not like "one size fits all" cams
you notice how late motors with better exhaust may even use exhaust shorter duration than intakes
best to use head flows to pick durations along with all the rest of needed inputs
rule of thumb is early stock exhaust ports with stock manifolds and restrictive exhaust needs more duration- but even then not as much as some popular catalog grinds
late heads and headers do not need much duration difference but still need a different lobe
Best to calculate each lobe individually
the intake lobe has to match piston demand - which is none at TDC that's header pull-the intake is contoured to the demand- which is also stroke/ rod length related
whereas the exhaust is opening under pressure and wants to open quickly to bled down pressure - but not too early to lose expansion/ power/ mileage
Intake closes as piston is coming up and closing tries to keep intake gas flowing as long as possible without reversion
obviously full power rpm intake close curve is different than driving down the street mostly hardly any throttle opening