pistons in merc 420's


G

Gearhead2

New member
Hey y'all I just took the port side motor out of my 357. Thats a whole other story. Anyway i see that she has .030 over pistons in it. Is this stock from merc? I'm trying to do some research but, I'm not having any luck. I know i didn't have them put in, and i bought it from a dealer so i have no feedback from the previous owner. Any input? Thanks
 
every mercrusier i've seen apart,has been standard bore size. she's no virgin! 420's are a real reliable motor though.
 
The 420's are a 454. I read a thread from powerboat mag that said the 420 and the SC525 were the same motor. Exept the 420 lacked the B&M 174 blower. Anyway Maybe mine have been tweeked a little more than i thought. Sweeeeeet.
 
Yup that is sweeet! I sometimes wish i would have gotten big blocks :-\ OR ;DMaybe just put together some stroker small blocks ;D
 
I found a conversion chart on car craft of hot rods website. cant remember which. Anyway a 454 bored .030 is a 468. Your are right Cuda. I also found out that the 420 comes with standard pistons.
 
are both motors 468's? if they are don't worry those 454's are the best motor mercruiser ever made in my opinion. the 425 was the same other than intake valve size was increased from 2.19 to 2.25.
 
Yes they are both 468's. I took the heads off today because i was curious. I figured it was worth the cost of some new gaskets. It was actually fun to work down in the engine compartment with only on mill in there. I wonder what the horsepower rating is now. They are .030 over and have gill exhaust. Maybe 450?
 
make sure that the valves are all the same size. i knew a guy who had a 357 and when he took off the heads, one set was 2.19 intakes and the other was 2.25. but this thing was no virgin either.
 
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