340 question?

[blueduster340]

What is the difference between the earleir 340s and the later low compression 340s?

[moparmotorman]

early 340's had X heads with 2.02 & 1.60 valves later 72-3 used the J heads with 1.88 & 1.60 valves. Early used forged crank and internal balance and late 72-3 used cast crank with external balance. Slightly different cam profiles. Those are the basic diffs, there are more i'm sure

[Clair]

I think also in 72, the manual trans cars kept the steel crank (I have one), but by 73 they were all cast cranks, with slight external balance, BTW. The only 340 with a funky cam was the 68-only manual trans application, and that cam was about 10* hotter on intake and exhaust duration, and had a little more lift. The rest of the 340's got the 68 auto trans cam, which was used on the E58 360's until the end of the E58 option.
Clair

[perfmachst]

hello, the 72-73, 340,s are 8.5 cr. with the 360 heads. 1.88 int & 1.60 exh valves. same cam specs as the earlier 340. and they are a very under rated motor. they can be made to go fast. with out 2.02 intakes. the 72 340's had steel cranks, last part of the year cast cranks were used and all 73 340's had cast cranks.

[blueduster340]

So would a simple change of pistons and x heads do the trick on bringing up the compression to where its at on the earlier ones?

[perfmachst]

yep, but why??? the 71 340 used a 915 head. the 68 to 70 used the x head only. the 68 to 70 used a avs carb. the 71 to 73 used a t.q. carb. the avs was flow rated at 625, the t.q. is 750. food for thought.