Hello all, I have a 68 XR7 J code car with non original motor. I pulled a valve cover off and instant sadness. Stamped 2V. I have been keeping my eyes open for the correct 4V heads and a pair popped up on ebay for $300 plus shipping so I pulled the trigger. My question is, what should i use for rocker arms, springs and such? My car is not a speed demon but it sure was fun to drive with the 2V heads oh and I should add it has a 2.79 rear end. (I was told that’s a lame rear end) also has a.c. Please let me know how I should rebuild the heads but I don’t want to over do it for this car its just a fun cruiser. thank you for all your help.
What do you have for a camshaft profile? The valve-train needs to work together as a system. The valve spring rate, rocker arms etc… needs to match up to the camshaft.
Good questions that I dont have an answer. I just wanted to rebuild the heads and throw them on. I have the springs and rockers on the 2V heads that I think I can get that info (maybe). But I thought the only things that made a J code was the heads and the carb. Now I think its more than that.
What makes a 302 motor a J code?
Did the 4V heads come with valves and springs, If so, then just re-build them and bolt them on, if not then that is a different can of worms.
The J code uses heads that unfortunately have too much compression for today’s gasoline. You are probably better off using the heads that you have unless you want to start buying fuel in 55 gallon drums. A performance improvement can be had by going to Edelbrock aluminum heads, or any number of other mods to the existing heads including bigger valves, porting, better valve springs, headers, intake, carburetor and / or gears, camshaft, etc.
they did not come with the valves and springs 
really? premium fuel would not work? If that’s the case I will sell them to someone that wants to do that.
True, the premium fuel that we have today is not good enough to prevent pinging with the J code 302-4V heads. They have some of the smallest combustion chambers ever used on a small block Ford. I was unable to stop the pinging on my 302 with those heads and unleaded 92 octane. Aluminum heads like Edelbrock can be used with today’s fuel.
When the car was new leaded premium was 100 octane. Not many places that you can buy that today.
Thank You, Im not sure what I will do with them now. I wish I would have asked the forum before I pulled the trigger on buying them.
289 4v and 302 4v have similar cc . If you already have them aren’t there some choices for octane boost that can help or tuning? I know the unleaded gas which has been around for decades requires hardened exhaust seats. I guess wanting to keep original is a goal for many.
I agree. I would put the correct seats, valves and rockers in for today’s fuel. Not the end of the world if I have to carry a bottle of octane boost on a trip. I would for sure do that. But the problem that I might be facing is deeper. I thought the only thing that made a J code a “J code” is the carburetor and the heads. Now I have heard that the pistons might be different. I don’t want to rebuild the heads the right way just to find out that the valves would hit the pistons. Does anyone know if the pistons in a J code are standard 302? If I find out that I need to change pistons in the motor I have then I would build a fresh motor. So the new question is: Can I rebuild the heads and put them on with no problem??? 
Don’t get scared off by the compression ratio. I’ve been daily driving my j code for the past 15 years (well over 80,000 miles) on premium fuel (91 octane) at 12 dig advance without any problems. Of course, I drive like an old man and generally stay well below 3k on the tach. But my point is, the j code heads are perfectly streetable. Just rebuild them and bolt em on.
What I found out on a trip from Dallas TX to the CCOA Nationals in Concord, CA in 1996 was that no matter which brand of octane booster I used it had no effect whatsoever on the preignition, which was worse when going up hills and worse still with the AC on. Again, this is my actual experience, not some theory. I tried several octane boosters including 104+, Moroso, and Real Lead. The results were always the same, no matter how much the cost of the booster or the claims on the container, it pinged like crazy. Retarding the ignition caused loss of power and overheating. This was a trip of about 4000 miles in every kind of terrain in all sorts of weather conditions.
You can compensate for the small combustion chambers using custom dished pistons. This would be the ideal solution to be able to use the original heads, but it would cost perhaps $600 for custom forged pistons versus $200 for ordinary cast rebuilder grade pistons.
Yes, 289 HP heads are similar in chamber size. A 289 has less swept volume so the compression ratio is lower.
Royce,
Just because you had a car that didn’t run right, doesn’t mean they all will. I agree with Yorgle I also have good experience with J code engines running just Hi test gasoline.
J-code here as well, never had any pinging on premium fuel. I know the block is matching numbers and the heads are 4V, but beyond that I have no idea of the history on the motor.
My local Sunoco gas station sells 110 octane leaded and 100 octane unleaded racing fuel, neither is cheap ($9.99/Gallon), but it’s cheaper and easier then buying drums of it. The sign on the leaded pump, says “not for street use” (or something to that affect) but nobody ever busted me when I pulled my car up to it and filled it up (not like there’s a line of cars at these pumps! ;-)).
Now my 351 4-V seems to run fine on the 93 octane Premium fuel I (now) use, but I suspect the compression ration (10.7 to 1 I believe) is probably less then the 302 4-V you have.
Jay
Given my studious attention to detail and utmost care in assembling that particular engine I would have to submit that you are sorely mistaken. Perhaps you own a J code that does not have proper valve seal, or you have an engine that was built with sloppy ring seal. Or maybe the engine builder did not hone the cylinder walls properly. Or perhaps the engine is simply worn out. In any case your engine is not making the same cylinder pressure if it doesn’t ping on 92 octane with the timing set to factory specs. That means something is wrong with yours, not mine.
My engine was rebuilt to the highest standards, although mostly stock. One deviation I made was to use stellite valve seats, stainless 2.02 / 1.66" valves, and bronze valve guides. Pistons were .040" oversize cast Clevite brand, and we used a Speed Pro Plasma Moly ring set. Intake and exhaust manifolds were stock but were vatted and baked to remove any trace of rust or carbon. Camshaft was a Melling stock replacement cam, nothing special.
I stand by what I said!
Royce, what were you actually running for initial timing? I believe the owners manual calls for only 6 deg initial advance- but I’ve never seen anyone actually run one that far retarded. I can get by with 12, but like you said, it’s probably because I’ve been losing compression over the years. Could the .40 over bore on your motor be a factor? Distributor advance also comes into play- was yours stock?
A 0.040 overbore would make a small increase in cylinder volume that would increase compression slightly. Given that, I have had similar issues with a fresh stock built J code (but then the best gas here is 91 octane with alcohol bringing up the octane rating). Adding alcohol effectively leans out the mix so I did have to re-jet to run richer. I also had to flip the mechanical advance to limit total advance while allowing me to run more initial advance. I also believe that altitude and temperature plays a role.