340 j heads?

Eventually I want to build my stock 360 into something a little more powerful. I always keep my eye open browsing on craigslist. I found a guy with 1971 340 J heads for sale. Im new to this whole scene and am trying to learn as much as possible. I can get the pair for under 100 bucks. Since Im new to this would any of you be able to school me on these heads along with any questions i should ask this guy about them?

Thanks,
Joe

Good heads with potential.
The intake ports have a lot of meat in them to modify, the exhaust side is touchy but does respond well to raising & straightening the roof.

Mine flowed just over 270cfm @.500lift

I'm not sure what year the cut off is but some J heads came with 1.88 intake and some came with 2.02 intake. Some others can tell you pretty easy.

varlo said:

Eventually I want to build my stock 360 into something a little more powerful. I always keep my eye open browsing on craigslist. I found a guy with 1971 340 J heads for sale. Im new to this whole scene and am trying to learn as much as possible. I can get the pair for under 100 bucks. Since Im new to this would any of you be able to school me on these heads along with any questions i should ask this guy about them?

Thanks,
Joe

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are those J-heads 1971 340 heads with a date code of 1970 or 1972 340 heads with a date code of 1971? If date code of 1971 I would check the size of the valves. Chrysler went with the 1.88 valves on 1972 model year through 1973 of the 340s. Not a big deal. It will just cost you a bit more to install 2.02 valves when you get them machined and cleaned up.

The J heads aren't going to have any more potential than the heads you already have on the 360. For under a $100 bucks that is a good deal for cores to rebuild then swap on but you can do the same work on the heads you have and get the same results.

dgc333 said:

The J heads aren't going to have any more potential than the heads you already have on the 360. For under a $100 bucks that is a good deal for cores to rebuild then swap on but you can do the same work on the heads you have and get the same results.

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yea. That too. Save your $100 and just rebuild your 360 heads. Leave the 340 heads for the 340 crowd.

What do x heads flow?

There is no real difference in the flow potential between and of the open chamber 340/360 heads. The X heads had 2.02" intakes but those can be added to any of the other heads.

posted in wrong thread....

green1 said:

What do x heads flow?

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My 68 340X heads when in stock form actually flowed a little less than a set of 72 small valve J heads I had. Just goes to show you that big valves don't always mean bigger perf. although they do have a little more flow potential when porting is done.

green1 said:

What do x heads flow?

Click to expand...

199cfm to 208cfm w/2.02 intake and 134cfm-149cfm exhaust around .450-480

fishy68 said:

My 68 340X heads when in stock form actually flowed a little less than a set of 72 small valve J heads I had. Just goes to show you that big valves don't always mean bigger perf. although they do have a little more flow potential when porting is done.

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So when you flowed your heads did they not have a valve job and were they the original valves reground? or did you take the heads off used and then flow them?

1wild&crazyguy said:

So when you flowed your heads did they not have a valve job and were they the original valves reground? or did you take the heads off used and then flow them?

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They were original valves but had new exhaust seats, guides and a fresh valve job by the local NAPA. How good the valve job was perf. wise is questionable. As you probably know a good perf. valve job alone is worth several cfm.

BTW: they flowed 209 max at .450 on the int. and 146 max on the exhaust at .550

I later did some porting and polishing on them myself (I'm an amateur, not pro) and had them flowed again (on the same bench) and got them up to 251 on the intake at .550 and 179 on the exh. at .600

The J heads I referred to was a set I sold to a fellow and BJR did the flow test on them. I don't remember the exhaust #'s but they were close to the X heads. I do remember the intakes flowed 215. I should state that it was a different flow bench but the atmosphere was real close to the same time each were flowed.

Oh yes,
I remember those heads they went to RamHi4X, they still had the 1.88 and 1.60 valves. On my bench and it's a bit stingy on flow and this is what they flowed, as gasket matched and bowl blended. I'm also adding a 675/318 head for a reference

lift.........Int........Exh...................318 head W/1.78/1.60 open early style
.100.......84.........79...................80..........78
.200......141.......115..................131........115
.300......197.......144..................190........155
.400......221.......188..................212........198
.500......238.......199..................214........204
.550......241.......203
.600......239.......207..................214........207

He was only using a mid .500 lift cam so I made the low lifts as strong as the heads would allow. With a gasket macth and bowl blending. The guides weren't narrowed or thinned.

This what the heads flowed as recieved, but like I said my bench is stingy.

lift........Int.......Exh
.100......78........71
.200.....125......105
.300.....188......127
.400.....209......137
.500.....221......140

1wild&crazyguy said:

199cfm to 208cfm w/2.02 intake and 134cfm-149cfm exhaust around .450-480

Click to expand...

BJ, your bench isn't as 'stingy' as mine. LOL, LOL. I get just about the same as wildcrazyguy. X, J, U they all go in the 199-206 cfm range as cast. Best ever for a stock 'J' casting on my bench was 212 cfm. all With the 2.020 valve and 190 to mid 190's range with 1.880 valves. But as has been stated before...we don't race flow benches or dyno's. They are just a tool. Always better to test the head on the same bench before and after. Not a good idea to get a baseline test on bench 'A' and make a mod and re-test on bench 'B'. Same thing on dyno's. I have seen one dyno show 625 hp and another give 578 hp..same engine..different operators, different dyno's/flow bench. Different correction factors ..i.e.... barrametric pressure, altitude, humidity, temperatures. Radius port entry's I've seen some shops NOT use these and that can absolutely destroy any repeatabilty altogether. Not to mention flow test pressure most shops give results @ 28" of depression. Some @ 25" . The small benches give results @ 10" and they convert that number to 28". Most car shops or hotrodders want results quoted @ 28" and most bike people use 10". Reason is the size of the benches. ALL of these factors contribute to the results. I have had heads on my bench that came out of 'BIG time' shops complete with flow sheets and NOT pull anything close to what their sheet shows. As much as 15% in some cases. Same head ...different benches. After a baseline, If I can show a 20% increase in flow, from my results then I know the head has definately been improved no matter what the other guys numbers say. NEVER test on one bench/dyno and retest on another after mods. As always JMHO..

Terry