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Greg Reimer 7376 · 07-04-2010, 11:05 AM

Well,from one 409 guy to another, does the term "straight up", etc. actually mean anything? The only relevant figure If you're assembling an engine, is the intake valve lobe center, which is specified on the cam card. If the cam is in the right place, all other figures are a moot point. The duration and overlap figures are nice to know and indicative of the torque and horsepower expectations of a given engine/cam combination,but have nothing to do with the intake valve lobe center figure. Usually, when building stocker motors, the rate of opening/closing is most critical at or about .125" lift, because that seems to be the point of the piston to valve clearance issue. It's worse on a 283 as opposed to a 350, because of the quicker piston movement because of the longer stroke.Sometimes it's necessary from that point of view to have to move cam timing back and forth a few degrees in order to achieve proper operating clearances. One fact that is invariable--the laws of physics in relation to colliding parts due to improper operating clearances are certainly costly to a racer's budget.

07-04-2010, 11:05 AM	#6
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,137 Likes: 172 Liked 719 Times in 220 Posts	Re: cam timing ? Well,from one 409 guy to another, does the term "straight up", etc. actually mean anything? The only relevant figure If you're assembling an engine, is the intake valve lobe center, which is specified on the cam card. If the cam is in the right place, all other figures are a moot point. The duration and overlap figures are nice to know and indicative of the torque and horsepower expectations of a given engine/cam combination,but have nothing to do with the intake valve lobe center figure. Usually, when building stocker motors, the rate of opening/closing is most critical at or about .125" lift, because that seems to be the point of the piston to valve clearance issue. It's worse on a 283 as opposed to a 350, because of the quicker piston movement because of the longer stroke.Sometimes it's necessary from that point of view to have to move cam timing back and forth a few degrees in order to achieve proper operating clearances. One fact that is invariable--the laws of physics in relation to colliding parts due to improper operating clearances are certainly costly to a racer's budget.