427R Drive Ability

[olddog]

Originally Posted by blykins

Lift has nothing to do with how tame a camshaft is. You need to focus on durations and LSA. All of those work together to create overlap, which is the amount of time both valves are open at the same time. If both valves are open at the same time, no vacuum is being made. If no vacuum is being made then you have reversion. The OP’s cam has 88 degrees of overlap. Normally I would aim for somewhere around 65-70 with these engines while keeping the powerband the same. It’s just a lazy old lobe to keep guys from hurting valve springs and burning pistons up. Crate engine. Assembly line, universal....

An NHRA stock eliminator camshaft can be a very nasty mannered camshaft but in a lot of cases will only have about .400” lift. I can also grind a very docile cam that has .700”-.800”-.900” lift.

Well yes and no. The Chevy sbc guys have changed out their 1.5 ratio rockers for 1.6 ratio rocker for 50 years, or more, to get a bit more performance. It increases lift, but it also increases the 0.050" duration a tad bit, too. We all compare the 0.050" duration because it is generally accepted that nothing significant is happening below that. I read where they have actually measured the 0.050" duration before and after a rocker ratio change, but I cannot recall the actual numbers. It seems like it was a degree or two on each end for a total of 2 to 4 degrees duration change. It can be around 25 hp on a dyno. Nothing huge, more like a little, but never the less some change.

Now if you were to tell me that it is so minimal an impact on idle quality and low end manors that it is not worth the work to change out the rockers (let alone the cost), I'm totally with you. However changing out the rockers is a lot easier to do than changing a cam, with the engine in the car. So then the question would be, is a few degrees less duration going to make much of a change in manors? Theoretically going in the right direction, but is it insignificant?