The bb 915 head has the same intake port as the 906 head, but the exhaust port is unique to the 915. It looks very similar, but the short turn/floor is a little lower on the 915. It's a subtle difference.

I haven't had a 915 and 516 next to each other in a very long time, but the way I remember it is there are some subtle changes in the chambers between the two(but I wouldn't swear to that).

I meant to say the ports sizes at the gasket surfaces are the same on 915 and 906.

30+ years ago they were desirable and found on the 1967 big block motors...but now unless they have been in time capsule somewhere and are absolutely perfect in every respect needing no machine work there are better alternatives and they come in aluminum.

Combustion chamber volume on a 915 is approx 79-80 cc with no milling and no sunk valves. 516 heads are 84-85ccs.

Non-relevant fact: Back in the early '70s there were kits you could buy to convert smallblock chevy heads from straight plug to angle plug. It involved inserting a cast iron plug into the straight plug hole and then drilling a new hole at an angle. I cant remember if it had jigs or instructions for a Bridgeport.

Relevant fact: Most 915 heads came with smaller exhaust valves. Only the HP engine heads were supposed to get the larger exhaust valves. Some of the HP heads had the letters "HP" stamped on the end of the head.

Possibly relevant fact: To the best of my knowledge the first B/RB heads to use the smaller "peanut" plug were certain of the 213 "motorhome" heads that were used on motorhome engines and had extra cooling around the plug. I do not believe that these plugs were angled. They were called peanut because they used a 5/8" socket and tapered seat and the plug body wasn't much bigger than a peanut.

There were also 213 heads that had no extra cooling and used the regular plugs. I have a pair from a 2-barrel Newport.

Chrysler wasn't building collector vehicles, they were trying to stay afloat by shipping product. The phrase "never say never" applies. That's what makes this wing of the car hobby so much fun.

R.

If Ma ran out of a certain part, they would use whatever was left on the shelf. Seen it more than once.