Another problem with Al barrels is the sleeve is an interference fit. I personally know two guys who have had the sleeve slip in use. Not good! These were from different suppliers...one from Left Coast Racing and the other from Norvil. I wish they had a better reputation, for the benefits norbsa mentioned above. 5 Franklins is a lot of $ for a product that could potentially wreck the motor. I'm not racing so I'll stick with cast iron.