Old Bert,
Sounds like you are building a fine engine.
Have you read the May 1955 article in Hot Rod magazine about Frank McGurk's dyno test of several mods to a 261.
261 article in HRM One of the mods tested was changing from the stock 261 head, with a 6.75 compression ratio, to a 235 head, ported and milled 0.030" to give a 7.85 compression ratio. The torque at 3000 rpm went up about 7%; however, at 2000 rpm the torque only went up by 2%. How much was due to compression ratio and how much to porting? Theoretically, increasing the compression ratio from 6.75 to 7.85 should increase to peak torque by about 5.5%, indicating that the porting may have provided 2.5% boost at 3000 rpm, but hurt at 2000 rpm. With your increased displacement, there might be a little more benefit for the porting, as the engine will want more air. I have always felt that one of the major problems with the Chevy head design was the 90-degree turn that the intake flow has to make to get from the siamesed port to the intake valve. Just increasing the port diameter will reduce the velocity but it will not eliminate the turn.
Hoyt, II#922
