OK guys, here is the deal. I took the 428 out to change heads and rebuild tranny. I found a "scalloped" piston top in one of the cylinders that was fouling because of the valve seals/guides. OK no big deal, get another piston. Except, the existing pistons are down in the hole about .100........Hmmmmm. OK. order another, same P/N,(1138) and it's about .100 taller from pin to top and has 4 valve reliefs....I'm trying to figure what and why, mostly WHY. Called KB tech guy. The ones in the motor have lathe marks in the dish! And no valve reliefs like the replacement? Tech says they never machine the dish, so these have been cut! Now the question, is this a "fix" for small chamber 390 type heads? (BTW the rod #s and length is correct for the 428). The heads that came off are C7AE-A, w/ horseshoe shaped chambers, the replacement heads, C8AE-H are "as cast" chambers. Is this something any of you have seen? I'm debating buying 7 more vs cutting the new one to match.......But, I can't help wondering if this was done for a reason, like CR reduction..........Any help would be appriecated............Ray

Edit....Screw it, ordered 7 more "uncut".....Now I know why this engine has always turned the pipes black, no quinch...........

 

sounds like the right decision to me.

 

Damn with the pistons being 100 thou in the hole and dished to boot...you probably could have started it by pushing on the fan blade....LOL

RJ

 

This engine seemed to have plenty of power while towing. I guess now I'll be buying alot of rear tires. All I can figure the original builder had thought of turbo and/or supercharging. According to tech guy at Silvolite the comp ratio was in the 8. something that far down......should be about 10. now......Wierd deal, and I've never heard of anyone doing that unless the were adding some kind of boost, BUT they're CAST pistons!!!......aMP

 

Are you sure there is a 428 crank in there?

 

Yep, 3.98...Well, I measured 4.0, close enough. the 390 is 3.78, so it aint one of those. And the rods are 428s as well.........Someone cut the pistons, plain and simple...........aMP