Cylinder heads on '77 Mercruiser 888 (302)

[roemere]

Would these likely be 302 heads or 351 heads? I just assumed 302 heads, but someone told me they often used the 351 heads on these....how can I tell which I have?

 

[SloBurn]

"The most merc did with the 302 was a 225 inboard that had a 4bbl. It's not hard to build your 302 to 230hp and many of the 888's have the better flowing 351 heads".

Pasted from another forum, so it looks like the 351 heads will have a higher HP rating.

http://forums.iboats.com/forum/engi...board-engines-outdrives/46330-merc-302-vs-351

 

[roemere]

This seems to confirm what I have heard/read, that many 888's had 351 heads....how do I tell which heads mine has? I may need to replace one and I need to make sure I don't mix the two...

Also, I have seen some 351 heads listed as "marine" heads. Do I need "marine" heads, or will automotive 351 or 302 heads work? What is difference between automotive vs marine heads?

 

[Ten Years Gone]

edit

 

[roemere]

Thanks!

 

[OnTheReel]

All 888's used a 351 head that was drilled with smaller diameter head bolt holes to fit the 302. These heads are specific to the 302 marine engine. As I recall the casting number is still normal 351, but even if you replace your heads with ones of the same casting numbers (from say...a car), you'll need adapter washers to mount them. These washers can be bought at racing part suppliers.

 

[roemere]

Thanks! The adapters/bushings are the only thing I will need to use auto 351W heads on my marine 302?

[edit]: And I use the 351 marine head gaskets, correct, not 302 head gaskets?

 

[roemere]

All 888's used a 351 head that was drilled with smaller diameter head bolt holes to fit the 302. These heads are specific to the 302 marine engine. As I recall the casting number is still normal 351, but even if you replace your heads with ones of the same casting numbers (from say...a car), you'll need adapter washers to mount them. These washers can be bought at racing part suppliers.

Since these 351 heads with the smaller head bolt holes were special heads for the 888 would they say 351 or 302? Pulled the heads off of my '77 Mercruiser 888 and they definitely say "302". So are these actual 302 heads or the special 351 heads?

If they are in fact 302 heads am I better off replacing them with 302 heads or 351 heads?

 

[KC_Sundancer]

Since these 351 heads with the smaller head bolt holes were special heads for the 888 would they say 351 or 302? Pulled the heads off of my '77 Mercruiser 888 and they definitely say "302". So are these actual 302 heads or the special 351 heads?

If they are in fact 302 heads am I better off replacing them with 302 heads or 351 heads?

The important thing with the heads is that the port size and shape match the ports on the intake manifold.
If you wanted to change heads, the intake may have to be changed too.
I personally would stay with the 302's and have a performance head shop "polish and port" the intake and heads for the improved performance.
Also as someone else noted the marine head gaskets are sometimes different that automotive.