My experience with fast rate hyd cams is...... The lifters collapse more than "normal" on the opening side, and when the rpm reaches the point where lofting starts to occur, the lifters "pump back up", and if there is any appreciable preload, the valves hang open, and the power drops like a rock.
More spring pressure just exacerbates the situation.
What is required to get this type of cam to turn any real rpm are lifters with extremely tight internal clearances, and a very low quantity of oil below the plunger(limited travel), so enough spring pressure can be used to properly control the valvetrain, without worrying about how much collapse the added spring pressure brings.
Lobes that use longer, slower ramps have less of a tendancy to collapse the plunger on the opening side, so that's one plus if you're trying to achieve a higher rpm, plus the slower overall action requires less spring load to maintain control at any given rpm.
My personal experience is, I have never gotten any fast rate hyd cam to rev very high....... In any brand of motor.
I'll admit, I have zero LS or Gen3 experience though, and those platforms seem to not suffer from this situation as much as the old school stuff does.
Thank you and BRADH for the input. This conversation couldn’t have been more timely. I have an XE cam in my car. I just switched to a different set of heads with different valve springs and when I’ve taken it out to dial it in, at around 5900 rpm or so, the car feels and sounds as if it’s breaking up a little. I had no issues before with my old heads and springs; everything was smooth up to 6300-6400 (as high as I’ve ever revved it). The valve train noise sounds louder than what it was with the old heads and springs too.
In regards to it breaking up at higher rpm, I’m not saying there isn’t possibly something else going on because I’ve only had minimal time to mess with it but, the cam did come to mind. I added about ¾ turn of pre-load when adjusting the valves this time; next year when good weather comes back, I think I’m going to go to a half turn.
The car has always performed well with the cam but, I cannot stand the noise it makes. It always sounds like something is wrong but, every time I’ve adjusted the valves or had things apart for whatever reason, there is never any issues. The noises are variable too (sometime I’ll have X ticking and or ext. but, sometimes I don’t). Again, I don’t think anything is wrong but, it drives me nuts. I’ve got probably around 2000 miles on the car and 15-20 passes. I’m going to keep plugging along with this combo but, when I freshen the thing up, I will definitely be going with a different cam.
FYI- Not that it was apples to apples given I re-curved my distributor at the same time but, I changed from 4.10's to 3.73's and picked up a tenth and a half in the quarter.
