Help selecting Lm7 truck cam
02-24-2019, 01:23 PM
#42
02-24-2019, 05:11 PM
#44
How steep do you suppose the ramps of an aftermarket cam are, compared to a stock one? Valve springs control valve motion, by keeping them in contact with the cam (via rockers & PRs of course) at all times. The valves MUST NOT be allowed to bounce when some radical closing ramp drops them onto the seat; must prevent the valve from being "tossed" into space as the cam goes over the nose; a stock LS6 cam is NOWHERE NEAR as aggressive in those areas as virtually ANY aftermarket one.
How accurately are you setting them up?
Have you ever taken stock springs OFF of a motor - ANY relatively high-performance motor (not talking exotic here... just, not some sufferin' 6 or the like... a stock LM7 with the stock cam will do as an example) and replaced them with something that gives better valve control, and seen what a YUUUUUUUUUUUJJJJJJJJJJJE difference they make? Especially at the high end of the RPM range? I've seen a spring change result in a 700 RPM OR MORE increase in peak RPM capability.
Those are SINGLE springs. In other words, there is exactly ONE piece of metal keeping those valves from contacting pistons. You have 16 chances for that to go wrong. Have you ever seen what happens inside a motor when a spring breaks?
For the few ¢ involved and the many $$$$$ they cist when they go wrong, there are few places inside a motor that make less sense to skimp on.
There's AHELLUVALOT more to valve springs than just a "max lift" spec. Buy better ones.
Don't ever take them to their limit.
How accurately are you setting them up?
Have you ever taken stock springs OFF of a motor - ANY relatively high-performance motor (not talking exotic here... just, not some sufferin' 6 or the like... a stock LM7 with the stock cam will do as an example) and replaced them with something that gives better valve control, and seen what a YUUUUUUUUUUUJJJJJJJJJJJE difference they make? Especially at the high end of the RPM range? I've seen a spring change result in a 700 RPM OR MORE increase in peak RPM capability.
Those are SINGLE springs. In other words, there is exactly ONE piece of metal keeping those valves from contacting pistons. You have 16 chances for that to go wrong. Have you ever seen what happens inside a motor when a spring breaks?
For the few ¢ involved and the many $$$$$ they cist when they go wrong, there are few places inside a motor that make less sense to skimp on.
There's AHELLUVALOT more to valve springs than just a "max lift" spec. Buy better ones.
Don't ever take them to their limit.
02-24-2019, 11:30 PM
#45
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The Ls6 springs are a known quantity and we like the dampening by putting them closer to coil bind. They wont get out of shape. Other springs ok too, but Ls6 are highly developed.
02-25-2019, 11:30 AM
#46
There's a lot more going on than just the lift number is what RB04 is getting at. 570 on soft ramp rate lobe wont launch the valve the way a rapid ramp rate 5.70 or any lift lobe will. Valve control is incredibly important, if you start floating valves you not only lose power but it's hard on the valvetrain components too. The higher you rev comes into play too and most of us are going past the factory limiter setting, which puts a little more pressure on the springs to do their job (pun intended)
03-26-2023, 09:09 PM
#48
TECH Enthusiast
This thread is 4 years stale. Just beating Gatsma to the punch 🤣🤣🤣
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G Atsma (03-26-2023)
03-26-2023, 09:11 PM
#49
TECH Senior Member
AAAGGGHHH!! Beaten to it by that crazy Washington dude!!! LOL!!
How can I ever live this down.....
How can I ever live this down.....