Cylinder head question

[PerformanceAutoworks]

I have been asked about this head and doing a "build" around it by two different people on here already so I may as well post up what I have told them both via PM

Regarding the head - there is a bit of an issue with what you have told me already and that is with the oversized valves.
Oversized valves sound good on paper but unless the porting has been done to maximise the new size then they really don't give much benefit, what they do do though is create a lot of problems to overcome (depending on their size ie .5mm or 1mm oversized) and seriously limit the "size" of camshaft you can choose.
Your pistons WILL require pocketing work to the valve reliefs to get clearance for the bigger valves, not a major drama but time consuming work all the same - worth noting as well is that your stock pistons will also require (to a lesser degree) pocketing work if running stock sized valves with big cams such as Pro2s
The biggest issue with oversized valves is not the valve to piston clearance however, it is the valve to valve clearance at max overlap. You should be ok with the stock Type-S/ATR cams (again depending on valve size) but most "bigger" cams such as the superb Sk2 Pro2 WILL cause interferance between valves at overlap. There is a way around this to a certain extent by increasing lobe seperation at TDC but this also has negative effects on the overall cam timing event cycle. It will take some VERY careful dialing in of the cams and accurate measuring of V2P and V2V to gain any clearance at all let alone adequate clearance - not forgetting to factor in a safety margin.
Bigger valves generally are suited better for turbo builds where a lower lift but longer duration camshaft with less overlap is the key to power.
Like I said, this head and bigger valves can be made to work but it gets very close in there even with stock cams.

[damon]

Am not so sure I will be buying it as I carnt really be bothered doing the work needed, need to finish another project first. Thanks for the advice and information

[NafemanNathan]

I have been asked about this head and doing a "build" around it by two different people on here already so I may as well post up what I have told them both via PM

Regarding the head - there is a bit of an issue with what you have told me already and that is with the oversized valves.
Oversized valves sound good on paper but unless the porting has been done to maximise the new size then they really don't give much benefit, what they do do though is create a lot of problems to overcome (depending on their size ie .5mm or 1mm oversized) and seriously limit the "size" of camshaft you can choose.
Your pistons WILL require pocketing work to the valve reliefs to get clearance for the bigger valves, not a major drama but time consuming work all the same - worth noting as well is that your stock pistons will also require (to a lesser degree) pocketing work if running stock sized valves with big cams such as Pro2s
The biggest issue with oversized valves is not the valve to piston clearance however, it is the valve to valve clearance at max overlap. You should be ok with the stock Type-S/ATR cams (again depending on valve size) but most "bigger" cams such as the superb Sk2 Pro2 WILL cause interferance between valves at overlap. There is a way around this to a certain extent by increasing lobe seperation at TDC but this also has negative effects on the overall cam timing event cycle. It will take some VERY careful dialing in of the cams and accurate measuring of V2P and V2V to gain any clearance at all let alone adequate clearance - not forgetting to factor in a safety margin.
Bigger valves generally are suited better for turbo builds where a lower lift but longer duration camshaft with less overlap is the key to power.
Like I said, this head and bigger valves can be made to work but it gets very close in there even with stock cams.

[Chuffter]