wcorey
Pinnacle OPE Member
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I've mentioned this somewhere before but didn't really generate any discussion about it...
Typical open port transfers are more or less a slot that feeds in a straight line right up from the crank case, so a slab sided piston is all that's required for efficient flow and windows are not only unnecessary but may even cause unwanted turbulence.
Where a typical closed port feeds from the side primarily through the piston windows and it would seem that a slab piston would inevitably impede flow.
That 42sp cylinder is open port and they seem to run fine with the factory slab sided piston but unlike most op transfers it's side fed like a closed port and would seem to me to be much more efficient running a 242 type windowed piston.
Typical open port transfers are more or less a slot that feeds in a straight line right up from the crank case, so a slab sided piston is all that's required for efficient flow and windows are not only unnecessary but may even cause unwanted turbulence.
Where a typical closed port feeds from the side primarily through the piston windows and it would seem that a slab piston would inevitably impede flow.
That 42sp cylinder is open port and they seem to run fine with the factory slab sided piston but unlike most op transfers it's side fed like a closed port and would seem to me to be much more efficient running a 242 type windowed piston.