"J" heads advantage?

[Jonnyuma]

I found a pr of small block J heads for sale and I'm wondering if there's any performance to be gained over my stock '76 360 heads. For the price ($200/pr) I'm assuming stock 1.88" intake valves, although the ad does say they've been ported. Without an in-person look-see I have no idea how much actual porting has been done or if its a total hack job or not. But what I'm wondering is if these (assuming garden variety, non T/A) heads are any different and, more importantly, any better than my '76 360 smog heads. Any casting #s to be mindful of? Any telltales I should know about before I decide to go look at em? They are disassembled so inspection will be easy, but how complete of a valvetrain should I insist on for 2 hundo? I have to factor in opening up the intakes to 2.02, the valves themselves, and prolly new springs if the ones provided are generic or unknown.

Worth 2 bills? Or more like 60 bucks at the pick-n-pull?

 

[Cranky]

If they are early J heads (71 340), they should have 2.02 intakes....other than those, I wouldn't give 200 for them.....

 

[tallhair]

If they are early J heads (71 340), they should have 2.02 intakes....other than those, I wouldn't give 200 for them.....

The 71 360 had the same 2.02 intake valve J heads didn't it?

 

[Cranky]

The 71 360 had the same 2.02 intake valve J heads didn't it?

Couldn't tell ya....but most 360's came with a 2 barrel and I wouldn't think that those got 2.02 valves but I would think that the 4 barrel version would? On another note, the smaller intake heads might be a better buy these days because if the seats are worn, you could easily install the 2.02 valve in them and have good material to work with. Original 2.02 heads that need new seats ground could end up with sunk valves that were ground that way. Only alternative to that would be to install new seats and you really don't need to do that on the intake side so, to redo a set of the valve heads could get kinda expensive if they needed both intake and exhaust sides done.

 

[Jonnyuma]

So, as far as flow #s, chamber type and volume, there's not much difference? Cranky, even if they're the 2bbl units, wouldn't even a stock-ish rebuilt set of heads be worth a couple hundred bucks considering the parts and machine work? That question assumes a competent build with at least OEM quality parts. That, of course, gets away from my original question about a performance gain. So what's a good factory iron head to be on the lookout for? The early X or J with the bigger intake seats? Or maybe, like you said, the smaller intake side might be even better because of the likelyhood of cutting new seats. I ain't going racing, just always on the lookout for a bargain...you know how it is..

 

[62 Dart Convertible]

So are these J's rebuilt and dissassembled for inspection? If so and were done by a competent shop, surely they are worth the money. For mild street builds, most folks recommend staying with the 1.88" intake, nothing to be gained going 2.02", especially considering the cost to do it properly. I'm sorry I don't know if J heads offer any other port/chamber performance advantages over '76 heads.

 

[Jonnyuma]

I haven't talked to the guy yet so I don't know who did the machine work. That little chunk of "disposable" income just got spent doing the brakes on my DD pickup yesterday so that particular ship may have already sailed. But I'm still interested for the next time something like this rolls around.

 

[PoppaSmurf]

if your running stock 360 "587 heads" the answer would be YES, a noticeble difference ! if your running the 915's, or the 974's then the answer would be not much... but remember the "J" heads are becoming more and more harder to find, so they might be worth buying building and sitting on them,to sell or using them

and there are some very basic but very important difference between the 587 and the 915's/974's namely a flow increase of anywhere from 15 to 45% better flow with the later castings

Can you get the last 3 digits of your heads currently on your car, and more importantly the last 3 digits on the "J heads" ?

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and Yes the J heads do offer an improvement over stock 360 heads ESPECIALLY over the smog heads NON-swirl, biggest difference is the smoother softer radius, leading into the Valve pocket (intake) and a cleaner radius out of pocket on exhaust, there is also a difference in the floor and side walls of runners both on intake and exhaust that allow the J heads to flow anywhere from 25-30% better, and the X head even more so

If you happen to have the Mopar engine book take a look at the LA head design Edition 5 and up, pgs 74/75

 

[charger360]

i have a set here now, i don't bother with la heads anymore i sell j and x heads to the resto crowd. i run magnum heads on my la blocks it is a fairly easy swap with a huge improvement in flow and the bonus of a much smaller and more modern combustion chamber. if the j heads came off of a 360 they will have 1.88 intakes for sure. the difference in flow is there between the la style heads but it is not huge even a well ported la head will have trouble outdoing the exhaust port on a stock magnum head!

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Oh yeah the big worry with those heads would be valve seat shrinkage and guide wear. they are getting pretty old these day's. you may get lucky and find some low milage ones though.

 

[PoppaSmurf]

Charger360, well if you got a set of X's or J's and wanna sell em lemme know I'll surely take off your hands !!!!

 

[purplecharger]

Do not forget the O heads flow the about the same

 

[PoppaSmurf]

here's some interesting reading for those that are REALLY interested

http://www.hughesengines.com/TechArticles/7choosingheadsaluminumvsironwhichonesdoyouneed.php

I think I'll stick with my old obsolete cast Iron heads...

purple I would love a set of "O"...know of any around ..and for sale ??

 

[Meep-Meep]

I built a 340 back in the 80's and I think it had J heads. The core engine was out of a 73 Charger Rallye and had the smaller intake. We had a shop open up to 2.02" and I did a basic pocket port. Ports I believe are the same as early 340 heads (X heads?). Anyway, a hemi gring cam, LB4B intake, Holley 600 DP and headers this ran mid to high 13's in a 69 4 speed Dart. All that said, if your 76 heads have the same ports I'd say you can expect similar results. The big difference with the "smog" heads will be the air injection, which may have a protruding boss in the exhaust port. But a die grinder with a carbide burr will make short work of that.

I will add that there isn't much point in splitting hairs when it comes to factory iron heads of the B, RB and SB engines (340/360). Up to a certain performance level they can all be made to work well with some pocket porting and a proper valve job. Put those together with slightly more overlap, duration and lift and good things will happen.