Boost And Stronger Valve Springs

[Scooby]

G'day guys;

some time ago there was discussion regarding the use of stronger valve springs when upping boost. the idea being that with standard spring tension at high boost the incoming air can slow the inlet valve returning to seat (for a millisecond of course) with catastrophic results. presumably this applies even more so when cams are used.

does anyone know at what boost levels stronger springs should be used?

regards

[StockyMcStock]

what engine, what springs, what setup?

there has been some conjecture that above 1bar on the R33 RB25DE head (softer springs) valve bounce can occur. other people have seen more than 350rwkw with standard valve springs in the DET heads.

[GTR32]

what engine, what springs, what setup? there has been some conjecture that above 1bar on the R33 RB25DE head (softer springs) valve bounce can occur. other people have seen more than 350rwkw with standard valve springs in the DET heads.

Hi Stocky;

as for springs

standard spring tension

and set up

at high boost the incoming air can slow the inlet valve returning to seat (for a millisecond of course) with catastrophic results.

i don't believe the power the thing makes is a consideration as it's the boost pressure that interferes, not the power. re valve bounce above 1 bar, i'm not sure i understand how boost and valve bounce are related?

[StockyMcStock]

i repeat, what engine? there are lots of factors here, like how large the valve surface area is and what the seating power of the spring is.

valve bounce is what you are talking about, where the valve doesn't seat fully because of large inlet pressures. other people call it "valve float" too.

[Scooby]

i repeat, what engine? there are lots of factors here, like how large the valve surface area is and what the seating power of the spring is.  

valve bounce is what you are talking about, where the valve doesn't seat fully because of large inlet pressures. other people call it "valve float" too.

Sorry should've said it's an RB26. But like GTR 32, I thought valve bounce and valve float are functions of insufficient seating pressure to cope with high revs. I guess the effect I'm talking about is a kind of float but not in the same way.

[StockyMcStock]

it happens more at high revs because of the need for greater airflow and hence, chamber inlet velocity. i don't know much about the 26 springs but i do know that people have made more than 350rwkw @ 20-odd psi using the standard springs.

[Scooby]

thanks Stocky, that's a good indication

[Bl4cK32]

remember rb25de has hydraulic lifters, and rb26 has solid