319-6291C heads on a 304?

[Slinwin8773]

Hello all,
1st post here. I recently bought a 1979 cj5 with a 304v8. A couple of months ago I found another engine out of a '79 jeep that was dissassembled, the block bored .060" over, mains align bored, and the crank polished. It came with new aluminum pistons already mounted to rods, an edelbrock performer intake, holley 600cfm carb, and the heads had been reworked and packaged in plastic to prevent rust. All for $400 (widowed barn find). I bought it and started buying up neccessary parts to reassemble it; hydraulic cam and lifters, hardened pushrods, arp head bolts, gasket set, valve covers, headers, etc. Well I finally started assembly this past weekend. I got the bottom end put together on Saturday and put the heads on Sunday morning. At that time I noticed that the rocker arms mounted on studs instead of the bridged rockers that I had on my engine. When I looked up the casting numbers (319-6291C) I found that these were early '70 heads from a 360ci with 51cc combustion chambers and larger valves (2.02 and 1.68 I think). The gentleman I bought this motor from told me that all the components were assembled and running at one time but everything I read says the block needs to be notched to keep the valves from hitting the cylinders. I guess my question is could the block being bored .060" over give enough clearance to run these heads? Can I put the rocker arms on and turn the motor by hand to see if the valves hit? Should I try to sell these heads and get some different heads that fit? Any advice is appreciated.

[tufcj]

Welcome to Bulltear!

If the block is bored .060", the 291C heads MIGHT fit without notching the cylinders. It will depend on the cam lift. The trouble is that the valve is so close to the cylinder wall, you lose all the benefit of the bigger valve because the air doesn't flow smoothly around the valve. Put a rocker on it and turn it over by hand. If you have hydraulic lifters, be sure to allow for "pump up".

The heads are probably worth $600-700. You might be better off selling them and putting the money into a set of 304 heads using 1.94" and 1.50" valves. I had a very potent 304 motor using that setup.

Good luck with your build.

Bob
tufcj

[Slinwin8773]

Welcome to Bulltear!

If the block is bored .060", the 291C heads MIGHT fit without notching the cylinders. It will depend on the cam lift. The trouble is that the valve is so close to the cylinder wall, you lose all the benefit of the bigger valve because the air doesn't flow smoothly around the valve. Put a rocker on it and turn it over by hand. If you have hydraulic lifters, be sure to allow for "pump up".

The heads are probably worth $600-700. You might be better off selling them and putting the money into a set of 304 heads using 1.94" and 1.50" valves. I had a very potent 304 motor using that setup.

Good luck with your build.

Bob
tufcj

Thanks for the reply Bob! Here are the specs on the cam:

ADV Duration (INT/EXH): 280 / 290
Duration @ .050" (INT/EXH): 204 / 214
Valve Lift (INT/EXH): .448 / .472
Lobe Centerline: 110
Power Range: idle-4500

So if I can turn the motor over by hand and the valves clear, would those heads (with losing the benefit of bigger valves) perform as well as heads with the 1.94" and 1.50" valves just due to the bump in compression ratio? This is my first engine build and although I've been reading everything I can find on AMC engines for months, I'm still not sure what's best for what I'm trying to do (mostly street - light trail), higher compression ratio and less flow or vice versa?

[Slinwin8773]

I got home and put two rockers on and spun the motor by hand. It turned over freely and I couldn't feel anything resembling a valve hitting the cylinder wall. If the valve hit the cylinder wall wouldn't I be able to feel it noticeably? Any help is very appreciated!

[tufcj]

That's a pretty mild cam. You may not feel the valve hit the cylinder wall. If the heads are already installed, swap one valve spring for a very light spring and see how much more the valve will open past full open on the cam. Generally, you want .100" minimum between the valve and piston, you can probably get away with a little less to the wall. Another option would be to view it with a bore scope thru the spark plug hole.

Performance would probably be a little better with the smaller valve heads, evem with the compression bump. The 291C heads give you about .5 to .75 bump in compression over the larger chamber heads.

Bob
tufcj