Lower compression ratio, presumably because the 261 motors were for the larger trucks, oil trucks, dump trucks, school buses, equipment that was run at low rpm, but needed some torque to do the job, not horsepower. Both pistons are flat tops. Then there is the 261 head, there are two of them that were used, can have combustion chamber volumes of 86cc and like 91 or 92 cc which resulted in an advertised compression ratio of 7.0 but most times was actually lower then that. The 56-57 motors with the 848 heads were advertised at 8.0, and the 58 and up were advertised at 8.5. Now I have never measured a 56-57 head and compared it with a 58 and up head to see if the difference is in the combustion chamber or maybe in the machining of the block or some slight difference in the compression height of the pistons for the .5 bump in compression.
Last edited by Dragsix; 07/04/2019 2:35 AM.
