Chryco,this was posted on a set of J heads a while ago on ebay.I was just wondering how much of this is true?The flow comparrison chart I negleted to save.
Mopar Small-Block HP J-Casting Cylinder Heads!
Maximum factory power for your small block... at NO RESERVE!
Just clearing out parts left over from a stroker project that ended up going a little wilder than planned (meaning W2 heads)... what's being auctioned here is a pair of the famous 1970-71-only 340 head castings. Casting number on these heads is 3418915, but they're commonly known as "J" heads.
This pair of castings was factory-machined for 2.02" intake valves... a trick used only in 1970-71. Casting dates on these heads are 2330 (August 21, 1970) and 2510 (September 8, 1970). These are REAL 340 heads--notice that where the "360" designation is normally cast, the 6 is missing, leaving only "3 0". Real 2.02" J-heads are the only heads so cast. These are the heads so desired for performance use. The intake-port flow is virtually tied with the famous 894-casting 340 "X" head, but their exhaust ports outflow any other factory LA casting (see flow chart below). These are an excellent upgrade for your small-block performance project.
These heads will really wake up virtually any small-block, though 273s require a bore notch to clear the 2.02" valves (and 318s benefit greatly from the same process). These are a great swap for early 360s and small-valve 340s. I bought these heads as a complete set, and as such, they had valves, springs, etc. The springs were a little tired, so I dumped them--but I had the valves cleaned up and checked. The intake valves are all in excellent shape (I wouldn't hesitate to use them) and the exhausts are usable but I'd probably replace them. I will include the valve-spring retainers but some of the locks were cracked (you should always buy new anyhow)
Both head castings have been beadblasted and magnafluxed, and neither head is cracked or damaged in any way--all threads are good, no marring or warping was found. Of course, they sat more than 5 minutes, so they started to rust a little, but it will bead-blast right off. There is typical pitting between the center exhaust ports on both heads--but it doesn't cause leaks or any other problems. The valve seats are fine --just lap 'em and you're done, though for unleaded use, you'll probably want to have hardened exhaust seats installed.
Your heads are the key power-makers for your small-block Mopar... why screw around with inferior heads from a 318 or 273, or even the mediocre "587" or "345" casting 360 heads, when a pair of good "J" heads is still affordable?
Thinking about those fancy Edelbrock heads? Keep in mind that all else being equal, aluminum makes less power due to heat loss... and no, the weight difference doesn't make up for the power loss (it's that much). Simple engineering principles at work.
Also, Edelbrock heads can't be ported any further than either X or J heads, because it has the same limitations (factory-style valvetrain) as the OEM castings! The Edelbrock design is nothing more than a slightly-port-matched J head, cast in aluminum.
So, if the flow is the same and the power is less, why waste the money?
