ptuomov wrote: ↑
Tue Oct 29, 2019 8:25 am
3V Performance wrote: ↑
Tue Oct 29, 2019 8:04 am
The problem is how do you account for EVO and remaining cylinder pressure and that changes with VE and rpm. That with added deflection induces un calculated valve velocity.
I’m not worried about EVO event in terms of exhaust valve bounce. The pressure is higher in the cylinder than in the port, the valve has been closed for a while, and the camshaft is trying to open the valve. I think that the valve and lifter are going to stay on the cam lobe reasonably well at that point. This is a DOHC with hydraulic direct acting bucket lifters, so I am thinking it’s pretty rigid and it’s not going to spring load the valvetrain the same way as a pushrod system. Is that a safe assumption?
I’m specifically worried about the EVC and valve bounce related to that event.
List out the components in the valvetrain and determine where your assumption is valid and where it might not be.
Is the cam really stiff or does it flex?
How thick is the bucket face? How thin is it where the cam first contacts it?
How many bits between the bucket face and the valve pad? (EDM a lifter bucket to look at its guts)
Bulk modulus of the oil?
Stiffness of the spring retainer?
All these stiffnesses are in series so the net stiffness is softer than the stiffest component in the system.
You also mentioned increasing rpm. So, F/a= dynamic mass. This comes in handy if making lumped mass estimations due to a lack of component inertia properties.
Match your new dynamic mass with the current dynamic mass and see if your linear assumption is proper.
Tangential acceleration increase will probably be a pretty significant factor in determining spring seat pressure.
You allude to knowing what variable will trigger exhaust valve float in the current system. How do you know that?
Did you just keep turning up boost until it you lost power on the chassis dyno? Was it exhaust valve float, lifters or ignition?
What's the drive pressure at the higher boost level?
Anyway, figuring out your requirements from two directions and comparing results is better than only looking at one method, in my experience.