max lift on 243's? 241's?
#2
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I don't think you can simply determine a max valve lift. The duration of camshafts plays a role (a large one) when it comes to PTV clearances. I run a 232/234 .595 .598 112 LSA cam with 62cc 243's safely. Just an example.
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also I should elaborate that this would be a situation where the pistons do not have valve reliefs cut. That's the main thing I'm trying to figure out here. safest lift without cutting reliefs, if not the 100% max down the the .001" at least a solid number that is safe
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youre missing the point others were trying to make.
if youre concerned about cutting pistons, then that means your concerned about PTV (piston to valve) clearance.
and THAT means you need to be concerned about DURATION and LSA of the cam, not the lift.
duration and LSA play a far more significant role in PTV clearance than lift does.
it would help others (with more experience than I) to guide you, however, if explained more about the heads youre going to use.
stock? milled?
if youre concerned about cutting pistons, then that means your concerned about PTV (piston to valve) clearance.
and THAT means you need to be concerned about DURATION and LSA of the cam, not the lift.
duration and LSA play a far more significant role in PTV clearance than lift does.
it would help others (with more experience than I) to guide you, however, if explained more about the heads youre going to use.
stock? milled?
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Lift is wholly unrelated to piston to valve clearance (PTV), which is related to duration, overlap, and cam timing. The piston only comes close to the valves when it is at, or nearly at, top dead center (TDC). The occurs only twice during an engine cycle. It occurs once as the piston comes up on the compression stroke. On this stroke however, both valves are closed. The second time the piston approaches TDC is on the exhaust stroke. During the exhaust stroke the exhaust valve is open but is already retreating from its maximum lift as the piston rises. The piston can hit the exhaust valve if, and only if, the exhaust valve retreats too slowly. Under no circumstances however, can the piston catch the exhaust valve at its maximum lift.
On this same exhaust stroke, the intake valve is beginning to open (which constitutes overlap with the retreating exhaust valve). The intake valve, can hit the piston if it opens to soon and the piston is at, or nearly at, TDC. However, the intake valve will not hit its maximum lift until the piston is past TDC and is on the way down (the intake stroke).
Thus, the maximum lift of either valve is not a piston-to-valve issue.
On this same exhaust stroke, the intake valve is beginning to open (which constitutes overlap with the retreating exhaust valve). The intake valve, can hit the piston if it opens to soon and the piston is at, or nearly at, TDC. However, the intake valve will not hit its maximum lift until the piston is past TDC and is on the way down (the intake stroke).
Thus, the maximum lift of either valve is not a piston-to-valve issue.
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That makes me feel all warm inside. Have a G5X3 and I was worried about it and PTV.. Still gonna be cautions about it, but that's a relief that there's less chance or less likely that I'm going to have to fly cut since the MS4 is bigger.