318 with 340x heads sluggish

d5667 said

now put those heads back on a 340. Just about anything can be achieved with enough money and time.the problem here was not enough research in the beginning. Now we are throwing more money at it_-no point!318-340-360 completely different engines from the factory but mix and match? Lots of research needed or spend lots of money.

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Did it all the time. Put the best factory heads on, good valve train to match, good intake and Carb, open up the exhaust, and away you go. Doesn't matter if it is a MOPAR, Ford, or Chevy. Do you think 22 cubic inches is gonna make a difference? Same stroke, same rods as a 340, 7 % increase in displacement? Really?? I've run J heads on a 273, cammed right with a 71 TQ, it was killer. He already has the heads.

I agree with you about the OP combination. I never ran someone else's combination. There are too many unknowns. Good ring seal? Good valve job? Where is the timing mark at TDC? What cam is in there and where is it installed? Let alone everything else you guys are pointing out. I'm just not going to buy the 340 X head theory. It is in the combination, and what rpm you want to run at. As you said, you can't just throw a bunch of parts together and expect them to play nice. Any poor machining, or any bad part, let alone a bad combination, can cause the outcome described by the OP. I've seen it over and over again.