Quote:
Originally Posted by void_kp
as far as I understand (but can be wrong as I am new to these engines) it's ok up to 0.677 or even 0.700.
I'm sure some guru in the forum will have the answer
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The LS has a few features going for it which make lift in the .650" range completely reasonable, even for street driven engines. The biggest factor is weight - the lack there-of. The lightweight nature of the valve-train means we can run with so much less spring pressure than most other pushrod combinations. This makes the scrub-nose style rocker very viable.
The other major factor is the cam lobe design itself. This is a CRITICAL piece to making any valve-train live a healthy life. This varies between various manufacturers, but a well developed and tested cam lobe will keep the valvetrain smooth and stable, even with big lift and RPM.
I've put 20k miles on a .650" lift cam setup, and my rocker tips still looked great on inspection. Sure - any time you crank up the rpm, lift, spring pressure, you're going to see more wear than a factory engine would. That's a fair trade-off, we're looking for performance well above and beyond what the factory gave us, and so we're willing to accept we won't get 150,000 miles out of some of the more critical wear parts.
One other note, because it's like to come up, regarding roller tipped rockers. It seems like an obvious solution, right? Replace a sliding surface with a rolling one, less friction is always good, right? Well, in this case, no. There is no way to add a roller tip to a rocker without adding weight of the roller and axle setup to support it. This added weight comes at the worst possible point on the rocker, right over the valve tip where it creates the most additional inertia to control. The translation is more spring pressure to achieve the same stability at a given RPM. Now, we're asking more of a fairly light duty hydraulic roller lifter. It introduces more trouble than it's worth.
We spintron test our hydraulic roller valve-train setups into the 9000+rpm range, and we've never found anything better than the factory style rockers for those hydraulic roller applications. The Comp BSR Max Lift shaft mount system is proving to be a good option for retaining that OEM style rocker on a more stable platform - and would be my go-to recommendation for rockers on higher RPM combinations.