Quote:
Originally Posted by 98nbmz
Boost doesn't matter so much as backpressure. A car with a more efficient turbo system (less backpressure) can actually get away with less spring.
As an example 20lbs of boost going through the intake isn't going to effect anything when the valve is on the seat. When the intake valve opens you have flow into the cylinder and pressure is trying to equalize between the intake and the cylinder. As you reach intake valve closing the compression cycle starts and pressure in the cylinder immediately eclipses pressure behind the intake valve.
On the exhaust side however you may as an example have 40psi backpressure. As the exhaust valve is closing your intake valve starts opening (overlap) and there is still 40psi on the back of the valve but little pressure in the cylinder to balance it. At this point you can bounce the exhaust valve causing a drastic loss in rpm/power.
For the hyd roller stuff that's going to see 20psi boost I usually run a spring with around 400lb/in rate so I can get 200lbs on the seat and 425 or so over the nose. Seat pressure is what's important here.
That is very generalized and like anything else should be decided on when selecting the rest of the parts for the combination. I can say with certainty that 918's will not be enough for a turbo LS1 that will see 20psi boost
Taken from ls1tech, maybe itll help
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So the cutouts not staying open might be the issue?