Inliners International Forums General Discussion Hi Performance marine heads

Were any of the straight six heads used for Mercury Marine inboard/outboard motors supperior to car heads?

Merc did make some 8-port heads for the chevy ll four banger marine version, but as far as I can remember the sixes always were stuck with the stock 9 port (6-exh/3-int) configuration.

They were some 292s with Q-Jet intakes, but those intakes were made to deal with the water-cooled(or heated) exhaust manifolds.

I've wondered how they got 200hp from a 292 with just a 4bbl and cam.
If the head is stock(and the exhaust doesn't look like it is helping anything either) then I'm skeptical. You'd think it would take headers to get 200hp.

Tetotally stock 292s had 165 hp, to me 35 more hp with a 750 cfm carb and a diff cam dont seem unusual.

'57 283 car motors with 2 bbl had 170 hp, and with small 4 bbl, duals,and higher compression ratio, the powerpaks went to 220 hp (50 hp gain) also with no headers.

ok answered my own question sort of, mercruiser 165 I/O is a 250 I6 gm motor with 165 hp. from all the pictures I have seen it looks the same as the auto head. mercury used this motor from 1970 till 1981.

I am running a complete Mercruiser 165 in my 51 Chev , using the original head -- No apparent difference . Also the OFFY / tube headers / ps pump fit right on . Works great ! We cut the head .080 , 1:84 intakes , stock exh , unshrouded the valves , multi-angle grind , profiled the head bolt bosses and minor port matching -- Hope this helps -- DON