Valves hitting each other or piston, limits?

[NOSferatu]

Is it possible to give any rule of thumb (is that correct way to say) for how much lift and degrees an engine can take without modifications to pistons?

Engine would be 130TC based with Regata 100 pistons, 130TC head gasket and standard valves.
I am upgrading camshafts, but I want to do it without lifting the head off the block.
Could it accept 11,1mm of lift?
I have heard that TC suffers more often from valve to valve contact, but is that because of incorrect timing or what?
How can I check that there is enough clearance that valve to valve contact doesn't happen?

[Guy Croft]

About 10.5mm of actual lift and 3.5mm lift at tdc actual is about the limit in my exp without the need to pocket the pistons deeper. The problem is mainly the inlet valves because they are 1-2mm closer to the pistons anyway. One trick to reduce the lift at tdc is to shift the inlet cam timing to a later point from say 110deg FL after TDC to 112.
As for hitting valve to valve you will be OK on those valves, the problem really only comes with 45/40 combos.

The problem with higher lifts like 10.8 + is that you might not get enough safety clearance between the spring coils at full lift and the vibration they experience with non standard cams at higher speeds can cause them to fracture. I reckon 1mm is the absolute minimum and 2mm is better. I can't check this for you.

GC

[NOSferatu]

Thanks! This makes me to reconsider this procedure.
Valve springs would be ok, as those are custom picked by a professional and spring loads measured for cam specs.
Those cams are actually what originally were intended to use with this engine.

This is the curve of cams, lift is metric units.
Curve has some unsteady spots because of my poor measuring methods.