So, I had just dropped in a 5.0 HO into my old 81 that had a 351w. After some research here on the forums, I found that the 5.0HO and the 351w have the same firing order, while all other 302s had a different one. So Knowing this, when I pulled the 351, I numbered the plugs and wires, and left them connected on the dizzy end. Then I just transfered the cap over to the new dizzy. Well when I fired it up, it wasnt running very well and I figured it just needed timed. So I borrowed a timing light off a buddy and went to time it. I could NOT get it in, no matter how much I turned the dizzy, not even close. So I called my dad over and we putzed with it for a couple hours. We started to think I was 180 out. Well after a while we determined all was well there, but we still couldnt get it. So just before I dropped back and punted I decided to double check the firing order. Well it, should have been 1-3... ect. But it was 1-5... ect. So as it turned out the 351w I pulled had a 302 firing order. Once I changed the order on the dizzy it ran like a dream. So it appears someone had put a 302 cam in the old motor. I know it was rebuilt, but my question out of curiosity is why would someone do that???? Is there any performance advantage of running a 302 cam? Also, could this be why I always had trouble with the old motor? It also appears that they may have rebalanced the old motor to 50oz inbalance. After my curiosity struck me, I looked up the serial number on the 351's flywheel and it was off a 302. It ran for 5+ years this way. Very strange. I know it was a 351 as it had a edelbrock 351w performer intanke and larger main bearings. Any ideas why someone would have done all this? Just curious. The guy that put this truck together died a few years back so I can't ask him.

 

Could be any number of reasons, like maybe he put in the only parts that were available to him. The other thing I've seen is some of those engine rebuilding houses throwing mismatched parts together just to get them out the door. They end up in places like Pep Boys.

If I were to give him the benefit of the doubt, maybe he installed an after market cam. Most of those are made for the 302, with notes from the manufacturer saying you can use them in the 351 by changing its firing order. As for the flywheel, I would think it should work as long as it has the proper imbalance.