Quote:
Originally Posted by wayner
Speaking for myself, I don't know where the threshold is but from what I understand the main safety net for compression is twin plug heads.
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We run 10.5: pistons using single plugs and the engine runs quite well but we also have S cams fitted.
I am not sure about what problems will occur due to running a higher compression with a 'softer' cam such as a 964.
Plug shrouding due to a high domed piston is a much bigger problem with the 2.0 litre where increasing compression much beyond 10.5 tends to reduce low end performance.
2.0 litre single plug race engine don't seem to get much beyond 200 hp and have poor low end performance.
The shallower chamber used in later engines is a little more forgiving and at 10.5:1 works quite well without twin plugs.
It would be good to compare single plug 9.5:1 and 10.5:1 engines to see what happens to the Torque behavior.
The pin offset is also interesting and I would be keen to find a table of different pin offsets with regard to bore and stroke combinations.
If I have understood correctly an offset pin will reduce the inertia loading regardless of the direction of the offset.
The thrust, however, will be different from side to side depending on the direction of the offset.
I guess most piston manufacturers believe that the inertia loading has the most importance as the thrust will change depending on which side of the engine is considered.
As far as I know none of the 911 pistons are 'handed' and I wonder if this is worth considering?