Never ran a stock 346 but I'd say they'd be in the same ball park. 346 turns up more rpm
However I do not own a closed port 55 but the standard 55 has some ass to it
Owned both and I'd say no way. Tree for 6 all the way.
Ballpark maybe but if you are timing cuts, 55 loses. Closed port is very very close the the open port. Very marginal difference between the two.
"In the ballpark" being a relative term, I'll say that a cp 55 is closer to an op 55 than to a 346. 55 is also heavier.
Might be a little closer modded.