Aren't the 915 closed chamber and the 906 open chamber? The 915 should have significantly more compression ration, which might explain Dick B.'s enjoyment of them. I know my "Super Commando" 440 has 906s, but only about 9.25:1 compression. Turned out to be a blessing with some of the stuff they have passed out as fuel since 1970. _________________________________________________________________ Tired of spam? Get advanced junk mail protection with MSN 8. http://join.msn.com/?page=features/junkmail