Oldskool84

Is there a such a thing as TOO much lift?

TripDeuces

No, unless of course you start hitting the piston dome with the valve.

MDchanic

When putting an engine together, it is possible to have too much, too little, or just enough of absolutely anything.

The trick is to have just enough of each thing, so that it all works together.

- Eric

ps: factors influencing degree of lift:
Mechanical limits of the combustion chamber (as George said - you don't want to introduce the valve to the piston)
Mechanical limits of the valvetrain
Limits to how quickly the cam can lift the valve, related to the laws of physics (ramp speed).

Oldskool84

Roger, thx.

TripDeuces

I wasn't even thinking of the stock set up. There's a limitation there.

joe_padavano

Actually, yes, and not just because the valve hits the piston.

Keep in mind that the cam lobe must have a shape that can accelerate the lifter, pushrod, rocker arm, and valve from closed to fully open and back about five times every second at 5000 RPM. The higher the lift, the further those parts must travel from closed to fully open, thus the quicker the acceleration and the higher the loads. A larger diameter valve at lower lift with the same total flow will be preferable to a smaller diameter valve at high lift for this reason. Bottom line is that you should use the smallest lift possible to achieve your power goals.

MDchanic

Check your calculator, Joe, you're off by an order of magnitude.

The lobe has to open the valve 42 times a second at 5,000 RPM.

Otherwise, yeah, what you said.

- Eric

joe_padavano

No, actually I'm off by the number of cylinders. I divided by eight because I was incorrectly thinking about CFM-like calculations. DOH!

42 is correct. I thought my number was awfully low. Sorry about that.

rcrac3r

Sure. In my build I had to swap out the stock pushrods & pedestal rocker arms for shorter pushrods & adjustable roller rockers because of the camshaft I chose to put in.

oldcutlass

I don't believe it was required to change all your rockers and push rods for that cam. I believe you chose to as the stock stuff would have worked with it.

cutlassefi

That's not necessarily true. That cam was obviously ground on a different base circle than the original. Typically there is enough room on a cam with the stock base circle to add a bit of lift before you reach the limits of the cam journals but yours was apparently different. That coupled with possible mods/changes to your heads is what most likely necessitated a valvetrain change.