Help with Valvesprings and valve float. Noob
The motor that the dyno sheet I posted belongs to came to me because the owner was unhappy with the power, and rpm capability.
It hadn’t been on the dyno before, but the owner said it basically wouldn’t go over 5100, which was confirmed with a chassis dyno test, where the power fell off a cliff at that point.
I swapped it over to a solid cam and shimmed up the valve springs from 115 on the seat to 130.
Other than longer pushrods to fit the new solid cam & lifters, the rest of the valvetrain remained unchanged.
As you can see by the sheet...... no problems at 5100 anymore.
I'm sure the rpm problem was improved due to the solids, but it wasn't because the lifter was bleeding down. On the contrary, it was pumping up. When the valvetrain becomes unstable, it opens up clearance. That's when the hydraulic lifter, which is under preload, does it's job and pumps up to close that clearance. Now the valves are held open because the lifter can't (and shouldn't) bleed down fast enough to recover, and the motor hits a wall where it won't rev anymore because the valves are off the seat. That's the only purpose behind an anti pump up lifter. Set it at or near zero preload, and the motor rpms better, similar to a solid. The problem with a hydraulic, is that eventually you will hit the springs natural resonant frequency and instability will occur, even when the geometry is right. A solid will drive through it, while a hydraulic will pump up and shut down. If a hydraulic could handle higher spring pressures, then the resonance would move higher in the rpm range and the engine would never see that rpm. Unfortunately, that isn't the case, and that is why a high performance engine is ALWAYS a compromise to some degree.
My point is, if the geometry isn't addressed first, the additional spring pressure is only a short term fix, because the additional stress will weaken the springs prematurely, and you now have the rpm problem all over again.
For an aggressive
[email protected] iron emissions headed 360 to pull clean through 6000 with only a stock replacement lifter @.040" preload, 1.6 rockers with corrected geometry, and a cheap single spring, it had to be stable. Prior to the correction, it was popping like a Honda on a two step at 5200. There was nothing fancy in the heads to improve rpm either. 2.02" and 1.60" stainless valves with 3/8" stems, steel retainers, and 5/16" x .080" pushrod. IIRC, the valves weren't even undercut. The testing was done the same day on the same dyno, with nothing changed but the geometry and pushrod length. Was it still making power at 6000? No, but it needed to shift at 5800, so we gained 600 useable rpm just by getting the geometry right.
Again, I'm not saying it doesn't need more spring. It at least could use the springs being shimmed another .045" IF it is at a true 1.800" installed height now. But, imo springs are the second place to go, and lifters are third, unless you are planning a new cam combination anyway.
