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Originally Posted by deruvian
Precisely. I really want to even out the lift on both of them.
And since the exhaust valves are open when the piston is rising, I do not wish to risk the life of the poor little guys. The intake valves are open when the piston is dropping, giving that diaphragm effect.
The one thing that I did want to ask, especially towards the technically minded (like Harvey  ), is if there are any other risks. For example, will the other internals have the appropriate threshold to allow another 1mm without breaking, binding, or stacking?
Do I need to worry about replacing other parts with the camshafts?
You know, the typical run-of-the-mill worries that come with any new performance parts.
Oh, yes, I also wanted to see if anyone knew the stock duration on the cams. Is it possible to measure it using the cam lobes? Per this thread, it appears as though the intake duration is 236 degrees, and the exhaust is 244 degrees. Just curious, really... because the service manual gives a value for the valve lift that doesn't appear to be true (per this thread), so who knows if the duration values are to be trusted either. |
I think the duration figures are right.
In increasing the lift, there are two ways to do it. First is to grind the cam lobe base circle to a smaller dia. This will increase the lift, but will also increase the follower clearance. For a small amount <1mm, the hydraulic lifter can take up the extra clearance. If more lift is required , a shim can be fitted under the lifter to take up the clearance.
To go to a larger lift the nose of the cam has to be built up with weld to increase its height and reground to the same duration profile. This then may have the nose of the cam hitting the sides of the lifter well, as it turns. This area can be ground away to clear the nose ok.
I have not looked at this engine to do this, and it would be best to let the cam grinder look at the head, to see how much clearance there is between the cam nose and the lifter well. Slightly stronger springs would be needed, but there is no point in using super strong springs, as they just stress the valve gear more than necessary.
As I have allways said if you are going to run an auto, you need to maintain the same duration figures. If you are running a manual and low gearing, and don't use low rpms, you could add more duration to pick up the power over 4000 rpms, you will lose a lot of the torque below 3500, but if you use the gears in the box to keep the revs up, the duration could be increased to about 256 degs.
Harvey.
