[70 340]

What is the difference, and what works better, X heads or J heads Pre 72'. Any help would be great.

[christer]

I got this answer from another board.

"the X heads were 2.02 intake and the j heads's were 1.88 intake both carried the same flow and the exhaust valves on both were the same size the j heads can be machined to take the 2.02 valves"

I do not know if it is true or not.

[christer]

I got the following answer from http://www.allpar.com/mopar/mopar340.html

"If you find the J heads at a swap meet, they could be either original 2.02 valve heads (1971) or original 1.88 heads (1972). If you find a set of 1.88 heads and want 2.02 valves, just take them and have them machined for the larger valves."

[dave-r]

Fit big valves to any 340/360 heads and they flow the same.

[Eddie]

And dont forget the 5.9 Magnum heads or even better is the lesser known '308' junkyard heads form 88-91 on 360 powered trucks that where throttle body injected but used the shaft mount rocker arms that oil through the block and shafts as the older LA engine heads. These heads have tall skinny intake ports that have excellent velocity. Most salvage yards dont know the potential of these heads and they can be had for about 100.00 a pair used or less.

[70 340]

Thanks for your help. So the X head and the J head should flow about the same but the 308 360ci heads are better. Would this be fair?

[Eddie]

For the most part Yes. As Dave has mentioned, properly 'prepped' they will all flow pretty good. A used set of heads re-conditioned with new one piece stainless steel valves, the factory used a regular steel two piece valve with the head and stem friction welded into place,(Scary huh), hardened exhaust seats for running hard on unleaded pump gas without having to worry about valve seat recession which takes many miles and heat to do this, new springs, valve seats re-ground, possibly new or re-sized guides, will add up quickly so the cost will almost be the same for a used set to a new aftermarket set. Head work is vital for a strong plant. The magnums will require oil through pushrods and lifters, but this is no biggie, they flow enough box stock for 400-450 H.P. as the 5.9 crate engines are producing this from the factory with a decent sized camshaft. It's easy to wrap up 2000.00 into a set of fully ported/prepped new or used castings, but remember you can do all this to a set of questionable used castings and they crack on the first outing and your day is ruined. New is always better! I really like the Hughes Engines Heavy Duty Magnum Head for LA or Magnum plants. It's cast iron head and a bit heavy but it's a decent price for 227 CFM flow,(enough for 475 H.P. with the right cam, and more available if ported, it's got dual closed chambers with a small chamber easy to build comp. with a flat top or mild ratio with a dished piston like the OEM design, hardened seats, high velocity ports), great street head! The '308' casting heads are almost 20 years old and will be harder to find in good shape, they were used only on fuel injected 360's truck/van chassis from 88-91 only. I used to have set, wish I still had em!

[Jimiboy]

http://neptune.spacebears.com/cars/stor ... cylhd.html

[Eddie]

Great info there thanks a lot JIMI!!!

[70 340]

Heaps of good info. Thanks guys