swamp2 wrote: ↑Fri Mar 20, 2020 10:47 am
Hmmm... Well, if there's gains to be had from cam timing and it doesn't cost anything...
If you advance the intake cam ONE tooth clockwise Swamp, you will open the intake valve earlier during over lap, and close it earlier.
Opening it it earlier during over lap... or as the exhaust valve is closing and the intake valve is opening, will create a better scavenging effect. The existing exhaust gases .. or what is left of them at that point.... can actually HELP pull in the next incoming charge of air and fuel. Olbill... think of someone sitting in a car going fast, smoking a cigarette with the window cracked open. The smoke gets sucked out of that cracked widow faster as the car goes faster and that air outside the car is speeding by. I think some Italian brainiack figured this out back in the middle ages ? And something to do with carburetors and such ? Hehehehe !
Anyways... Advancing the intake cam will ALSO close the intake valve earlier after bottom dead center, trapping MORE AIR and fuel in the cylinder to compress.
If the valve were to close later .. . like stock ? There would be less of it. Why ?... because as the piston is moving back UP the cylinder and compressing the mixture FARTHER the cylinder before the valve closes, it is compressing that mixture over a shorter distance. There can be NO compression until the valve is closed. So you scavenge and cheat and pull in more air as the intake is opening at one end, then slam the valve shut earlier at the other end to trap it and compress it more . It ain't rocket science....
Result ? More air in there, more air to compress,more to light up ! More push on the piston as it is going back down on the power stroke. AND.. More twork ! How do you prove this all out ? Well... do a compression test both before and AFTER you advance the Cam . I bet you see about ... a 20 PSI increase if I'm remembering correctly ? But that is JUST at a "STATIC " compression test . The Engine is only cranking over at around 3 or 400 rpms . But as the rpm's go up and up and up and UP , that cylinder pressure with go up exponentially.