Author: Bob in Michigan April 26, 2008 at 17:08:54 from 69.29.248.109
This is for Jim Honney and his question about cylinders getting hot in a circle track motor. The engine builder who balances my cranks showed me a BBC piston, it was #5 out of one of his motors for a circle track car. The guy ran the motor for a while and it galled up the piston after a while -- pretty ugly. He put in a fresh piston, and after a while the same thing happened, so something was going wrong with #5. He called his cam guru who said it sounded like they needed a 4/7 cam swap in the motor. With #5 and #7 being at the back of the motor and getting water that was already hot -- water flowing front to back from the radiator -- #5 was getting too hot. So they put another fresh piston in #5 and switched to a 4/7 swap cam and the problem went away. With the new firing order #2 & #4 fire in order but they are getting cooler water because they're at the front of the motor. I'm just repeating what he told me, but it DID SOLVE THE PROBLEM. Thanks for the posts -- I sort of figured that the 4/7 swap deal was mostly an advertising gimmick more than anything is you're not having any problems, and most drag cars don't worry about heating anyway. But I see Schafiroff Engines uses custom 4/7 swap cams in all of his BBC big cube (555 and larger) bracket racing motors, so if it does make 2 more HP and adds to longevity then people are going to want it. If you're paying $10K for a motor what's a few more bucks?
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