There is word that the R32/33 RB25DE valve springs are slightly softer than the RB20/25 springs.
Apparently this causes valve bounce over 15psi which generally occures at 6500rpm.
17psi valve bounce begins to occur around 5500rpm.
The higher the boost the earlier the valve bounce.
This causes the lifters to pump up which then makes the car idle lumpy until the lifters bleed back down.
I am unsure if this is a rare occurance where the valve springs have started to go soft or another issue regarding the valve spring tension when the valve is fully closed.
I have also heard a roumer that some stocker CA18DET's running high boost have this issue also. Fitting heavier valve springs fix's the problem. Any 1 care to confirm that for me?
I will find out with my RB25DE head soon as it uses the stock valve springs BUT the head has been rebuilt and all tensions checked etc..
Another bloke Darren also bought the same head as I & had his head rebuilt at the same place/time as I. He had to have his valves shimmed due to the valve spring tension not being great enough when the valves are closed. Mine were fine. I'm not sure 100% the exact terminology so don get picky on me.
As I said i'm not 100% as i've onyl heard of a few people having this problem.
Any one else care to share any problems they have had with the 'possibility' of the NA valve springs being softer than the T springs?
Still nothing like quite like a Jap Car.