I bought a 340 yesterday and guy said it came with a set of J heads and when I got it home and cleaned up I noticed it had one X and one J head. I know there is a difference in valve size and springs. but do they have the same size chambers inside? Because im going the have the valves and springs replaced anyways I was wondering if I had the valves upsized to 202 160 like the X would they be the same or would I need to find another X
Difference in X and J heads?
- Thread starter 79aspenrt
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bremereric
FMJ Body Moderator
Same size combustion chambers bigger valves in the X heads. They were the same casting.
Greg55_99
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Do J heads require a larger seat to fit the 2.02 valves?
Greg
Greg
bremereric
FMJ Body Moderator
Yep but they just mill them. I had a set of J heads with the bigger 2.02 valves street ported on a 475 hp 340 that I should never of gotten rid of.
Greg55_99
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Ah... So the answer is to mill out the existing seat of the J head and drop in 2.02 valves. I did now know that.
Greg
Greg
Early J Heads have 202 valve just like X. On our stock eliminator
stuff no flow difference between intake valves size(202 to 188) assuming stock ports.
The X heads average about 7 - 8 CFM more flow @ 400 lift than the J heads .
Also combustion chamber centering to block is much better on X heads.
I would prefer to have the same casting # head on my engine rather than different
ones for performance.
stuff no flow difference between intake valves size(202 to 188) assuming stock ports.
The X heads average about 7 - 8 CFM more flow @ 400 lift than the J heads .
Also combustion chamber centering to block is much better on X heads.
I would prefer to have the same casting # head on my engine rather than different
ones for performance.
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