Cylinder Head part number help on 7.4 mpi

boatrboy

Well-Known Member
Oct 3, 2006
1,839
Orange, CT
Boat Info
2006 340 Sundancer
Engines
Twin 8.1 Horizons with V-Drives
I am looking at replacing the heads. My casting numbers appear to be 10141279 which seems to match up with some sites selling refurbished heads. The new mercruiser p/n for the whole assembly is 938-802743 from the parts look up.

What I am wondering is what would be the difference from the earlier mark V heads - p/n 14092360.

Thanks for any input you could provide.
 
There could be different part numbers for a bare head and a fully assembled (with valves and springs) head.
 
stick with the vortecs - smaller cc to match your pistions - the "360" heads will lower your cr too much
 
stick with the vortecs - smaller cc to match your pistions - the "360" heads will lower your cr too much
Thanks - is there some website showing the dimensions you are referring to?
 
I don't have a link, but just google the casting number along with "combustion chamber volume" and it will come up - the 279 heads have a fast burn, heart shaped combustion chamber IIRC 110cc and the 360 heads are 119cc open chamber
 
I don't have a link, but just google the casting number along with "combustion chamber volume" and it will come up - the 279 heads have a fast burn, heart shaped combustion chamber IIRC 110cc and the 360 heads are 119cc open chamber
Thanks
Are there any differences in marine heads vs automotive heads? I realize the gaskets are stainless, but the heads themselves?
 
What if the numbers match up but one head had CM6. And the replacement has CM4. Are the heads interchange?
 
Mark IV heads will fit a Gen VI fine with the correct gaskets. You want to be conscious of the chamber volume. These boats already have only 8.5:1 compression which is very low. If you put on a set of heads that have a larger volume, like from a Mark IV, you'll lose a ton of compression if you don't put in dome top pistons. This will kill your power.
 

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