SVTeeshirt

So it was to my understanding the only thing stock valvesprings would limit is my RPMS, recently i got into a well lets call it a conversation about how stock valvesprings could limit the amount of boost i could run as the incoming air could lift the valves? Maybe boost pressure keeping the intake valves open? Probably not? lol.

I've decided to keep stock (01 cobra heads) for now get the car on the road and slowly build ported 03 cobra heads .w blower cams and all the works.

enlighten me.

Stevecooper

From what In understand its not really the "boost" pressure thats the problem its the cylinder pressure. Adding supercharger will greatly increase cylinder pressures and could open the intake valve if the pressures are too great for the spring to overcome.

SVTeeshirt

hmm, good to know, anyone else have experience with this?

Tim99GT

+1. I have personally never experienced this but have heard the same things. Running high boost will increase cylinder press which might be too much for the stock springs. Possibly causing them to not shut completely or to stay /"stick" in the open position. This is why you would need to upgrade to "stronger" springs with a higher spring rate. The new stronger spring woulfd then be able to overcome the high cylinder press and successfully open and close the valves.

Sxynerd

My buddy Eric (Doughby4.6) is running 19lbs though a T trim, stock springs/heads and 262ah NA cams. (555rw) 2.9"RR pulley and 10% OD Balancer.

nickmckinney

Boost is in PSI so take the surface area of your intake valve(s), multiply by the boost pressure, and that is the amount of valve spring pressure you are loosing. A turbo car also looses pressure on the exhaust valve. How much is too much? Too many variables. Its always wiser to run more spring pressure than not enough especially on the seat.

Eagle2000GT

I'm a bit skeptical. If true this must have something to do with the overlap otherwise the cylinder pressure would hold the valve closed.

Frostbitten

ive heard about this also. a couple people told me that a turbo car will float the exhaust valves on stock valve springs. So when I built my motor I had the heads ported out and at the same time I had a fresh valve job done with brand new manley nextek springs and comp high load retainers. Finished it up with a fel-pro MLS head gasket and arp head studs. Still using stock cams and im telling you this thing feels smooth in the upper rpm's....

SVTeeshirt

well looks like we'll see lol.

highpsi04

That makes no sense. Higher cylinder pressures will hold the valves shut. I have heard of turbo cars floating the exhaust valves because of backpressure but I have never heard of valve float due to boost.