Photo of a H2 Cam compared to 04.5 stocker

Max lift has no impact on Piston-To-Valve issues, only duration & LSA. At max lift the piston is near the BDC. Cam duration and LSA (Lobe Separation Angle) are what you need to look at. For a given intake/exhaust duration as the LSA decreases two things happen - 1. Overlap increases (or becomes less negative) and 2. PTV clearance decreases. For a fixed LSA, increasing durations has the same effect. LSA is a number that basically "falls out" of a properly designed camshaft when selecting your Valve Closing & Opening Points (IVC, IVO, etc.) based on where you want your power band, etc.

For example:
180/180 .550/.550 cam would have no PTV issues
220/220 .350/.250 cam would

banshee said:

Max lift has no impact on Piston-To-Valve issues, only duration & LSA. At max lift the piston is near the BDC. Cam duration and LSA (Lobe Separation Angle) are what you need to look at. For a given intake/exhaust duration as the LSA decreases two things happen - 1. Overlap increases (or becomes less negative) and 2. PTV clearance decreases. For a fixed LSA, increasing durations has the same effect. LSA is a number that basically "falls out" of a properly designed camshaft when selecting your Valve Closing & Opening Points (IVC, IVO, etc.) based on where you want your power band, etc.

For example:
180/180 .550/.550 cam would have no PTV issues
220/220 .350/.250 cam would

Click to expand...

Well put. Thanks for the good write up. The question of more duration decreasing clearance is appropriate to the conversation. It may take the cam designer to determine any clearance issues with higher ratio rockers and its benefits with the use of higher than stock flowing head at higher lift rates. Higher ratio rockers would add lift at peak of cam but add very little to lift on the outer edge of duration. Thanks again.
:Cheer:

03kbcobra said:

Well put. Thanks for the good write up. The question of more duration decreasing clearance is appropriate to the conversation. It may take the cam designer to determine any clearance issues with higher ratio rockers and its benefits with the use of higher than stock flowing head at higher lift rates. Higher ratio rockers would add lift at peak of cam but add very little to lift on the outer edge of duration. Thanks again.
:Cheer:

Click to expand...

If the stock rockers are like 1.5:1 or so, if you add high ratio rockers that are 1.7:1 (persay) it would improve lift at all amounts of lift throughout the entire duration of the camshaft lobe not just at full lift. It would be "chasing" the piston down faster and also be "slower" coming back up. Atleast that is what I think but I have had SEVERAL drinks.

:Cheer:

You're right Muddin. With a higher ratio rocker every lift would be 1.7/1.5 X original lift (if you went to a 1.7 ratio from a 1.5 ratio). They basically add a percentage of lift everywhere but add no duration. Higher ratio rockers can be an okay way to add flow, but there are more downsides IMO. Because the ratio is higher they accelerate the valve faster and allow it to come back to the seat faster which adds valvetrain instability and valve bounce if the spring can't control your new ramp rate. Coil bind of the spring along with potential accelerated valve guide wear due to side loading the valve (different wipe pattern) are other big concerns. Like mentioned earlier, for the cost of a set of rockers it really makes as much sense to install a cam that has the lift ground in.