Science Forums 2

[infamous]

Originally Posted by UncleAl

Good point! Consider a four-cycle four-cylinder engine doing a modest 3000 rpm. One intake occurs in 0.5 revolution. There is no more than 10 milliseconds to fill the cylinder, including valve opening and and closing. Nothing is running at equilibrium. With only 14.7 psi pushing the intake it is amazing anything gets in there at all.

Absolutely UncleAl; Things get even more critical at engine speeds of 8600 rpm. Cam timing and spring pressure along with reciprocating weight of valve train components become severely important. I use titanium intake valves to reduce valve weight along with special light weight solid lifters. Cam timing at 8600 rpm usually works better with at least 90 degrees of overlap. I have found that lobe separation of 108 degrees, and duration of around 300 works the best also. All these factors must work togeather to allow that 14.7 psi of atmospheric pressure to do it's job.