I do not know too much about those 6's, but are the cylinder head that bad flowing stock?
They have good size valves it seems.
I would think that what is mostly holding back the engine from RPM,ing is that the camshaft specs are short on duration.
A 300 Horse 350 10:25.1 SBC cams specs are I: 212, E:222 @ .050" .
I do not think GM would even put a camshaft with those specs in a 250.
But, I could be wrong, we need to find the actual specs of duration @ .050". There should be some info out there somewhere. Or get it cam doctored. I am just thinking it's mostly the cam holding it back.
Found this just now. "The camshaft had .400 inches of lift and 228 degrees of duration " Duration at what though?
Sprint engine: .438 inches of lift and 244 degrees of duration
sprint” produced 207 bhp at 5200 rpm and 228 lb-ft of torque at 3800 rpm. This “spirited” six-cylinder was also capable of revs to 6500 rpm and beyond.
I thought the high compression Sprint engine was a 230 CI? Or did they make a 10.5:1 250 CI sprint?
Any who, If it was a 230, & you are using the sprint camshaft in a 250 CI engine, most likely the engine will not make the same RPM, should be a little less.
So it says it could rev to 6500 RPM, but at 6500 RPM it would make less power.
This is a 67 Sprint now displacing 255 CID. The head has SS valves installed as well as hardened valve seats and bronze guides. The cam is 260 duration with .465" lift at the valve. (slightly larger than the factory H grind) The Headers are Clifford Shorty type. The engine makes power to 5000 rpm then drops off. We revved the engine to about 5500 rpm."