Prop question for SHO 225

[BassinLA13]

Recently went from a 25P Mercury Tempest A45 (flung an ear) to a newer A47 - the hole-shot & top end (71.5) are the same but the RPM's on the A47 max out @ about 5600 (can't get it higher) whereas the older A45 reached 6000.

Any ideas why ? No motor adjustments etc. made between prop swap.

Thanks

[21XDC]

http://www.bbcboards.net/showthread.php?t=1083717