Ok after lots of carfull thought I think ive pretty much given up on the idea of machining the STK pistons for valve pockets to accept the S cams. Just going on the intake valve at overlap it has almost 3mm extra lift so with the extra duration this will likely be more at 10-20 degrees before and after TDC. I doubt with pockets that size there would be enough thickness left on the crown.

So now im left with the choice of what CR to run on the JE'S. should I go 10.5:1 and twin plug or stay safe with 9.5:1 and run single plug. Theres obviously a cost element here but im also concerned with what happens if a plug lead fails and your twin plug becomes single plug. What sort of difference would 9.5:1 and 10.5:1 give in terms of HP all other things been equal with the addition of twin plug obviously on the 10.5:1

Steve

I believe you have over thought the valve pocket issue. There is plenty of thickness to machine a CIS piston for "S" cams. If there wasn't I would not have suggested it.
As for the performance difference between 9.5:1 and 10.5:1 all things being equal I would doubt you would realize a 12 % increase in overall HP.
The compression and twin plugging will afford you more snap in the lower RPMs.

Hi Henry

Just been back and read your original post, id overlooked that you said you have been doing this for years, so in that case it is still an option for me. Do you have a set figure you machine the recesses to or do you re-measure on every engine you have done this on?

BTW the barometric cell arrived today Thanks

Steve