These are actually 71 2.02 Js but they are the same casting as an X head so I’ve been told.
The knowledge I gained from this series is unbelievable. I had no idea that air would flow like this through a head. Also see David Visard’s YouTube channel for more good information on porting. He is also working on the mission impossible buildup, doing the rotating assembly mods. Really good stuff.
Yep, if I had the choice, port the J’s and sell the x’s to a restorer.
Xs are fine keep em. everyone on the web is a racer so keep that in mind. They will say xs are junk to buy aftermarket aluminum. If I were racing id do that. the most I have in race parts is a single plane intake and a 750 holley, maybe my 3 91 rear could be considered race but it came that way from the factory. The xs in my opinion work with the positive deck height pistons for that original early 340 compression ratio. Js are late 340-360 heads and some TA heads were J castings. Some say Js came from the factory with 2.02s but a book i have says they were all 1.88s. X heads were all 2.02s. X heads are collector pieces for a correct resto they are great. Js are also great and it is said they flow much better with 2.02s.
agreed i do beleive the thing wiith either head is for compression to run the positive deck height pistons but then again on todays gas 9.5 to 1 may be ideal.
I personally have two sets of factory 2.02 J heads. Only came that way on late 70 blocks that were built for early 71 model cars.
What is the indicator to you that they are factory? I have a set of 2.02 Js that when i took them apart, the intakes were knurled while the exhaust valevs have wear, that indicated to me the 2.02s were added later. Now I have to have guides installed but oh well that's the gamble on 50year old parts. I have heard about factory js, but I do know punching the 1.88s to 2.02 was common practice. This was when the 1.88 valves sunk and new seats needed ground. i suppos emy point is unless its early 1972 right now, and I am tearing into a 340 with js that is 1 year old how would we know? I took my info from a book that has been around since the 80s I dont mean to spread bad info. But i suppose it doesnt matter .its 2023 who really cares about any of this. this is why Uncle Tony gets away with his BS daily. I know what I have you know what you have,at the end of the day thats all that matters. What I have is, 1 set of x heads...2 sets of js one with 2.02s, one with 1.88s... I also have a complete LA 318 collecting dust. When someoine actually convinces me that a 318 LA smog engine is worth dumping money and tome into I may open it up till them, Ill wait for someone to offer me stupid money for it...
