Bizarre rust hole on BOTH heads on SAME EXACT exhaust port

"I have an 88 BAJA with a 7.4

"I have an 88 BAJA with a 7.4 gen IV mercruiser, bravo 1 with thru hull exhaust and square port heads. On both heads there is a rust hole about the size of a dime in the exhaust port. If you lay the heads on a table with the ports facing you (manifold side) its the 3rd port to the right. SAME EXACT SPOT, SAME EXACT HOLE!! If you look into the port it is right where it turns downward. The ports have extensive surface rust damage on the part that separates the exhaust gas and the water. The front and rear ports are PERFECT and the 2nd ports to the right have a little corrosion. My wild guess is that it is some kind of galvanic corrosion. Does anyone know where to get a set of square port gen IV heads?"

"Merc PN: 938-883491R1

Ins

"Merc PN: 938-883491R1

Insert the PN above in the "engine parts" search box. For the price of a pair of remanfd. heads, you might as well cough up the rest of the money for a remanfd. longblock."

Has anyone seen this before? S

Has anyone seen this before? Since its the same port on both heads it would seem to be a fairly common problem. And does anyone know how much power I will lose If I put on standard "oval" port heads versus the rectangular hi- perf ones I have now?

"Thx for tip guy, but I cant a

"Thx for tip guy, but I cant afford OEM parts, and if I could I would most likley get aluminum aftermarket ones."

"How much duration in your cam

"How much duration in your camshaft? Is there a heat crossover through the intake manifold? It could affect exhaust pulsing. I had a 5.7 with 218 degrees exhaust duration @.050. I had rust in the two center exhaust ports on both sides. Reversion at idle was drawing water back through the exhaust elbows and letting it drip into the exhaust ports. With any amount of lope at idle you need to modify your elbows so that the water that drops over the outlet from the channel at the top is dropped further back. I was told you can add stainless steel trays to the top channel to extend it about 6 inches, top only. This allows the air being pulsed back in through the exhaust to not have water in it.
You might look into wet headers or other high performance exhaust designed for cams with overlap. Stock Mercruiser exhaust was not designed for high duration camshafts."

"WOW, awsome answer James. I j

"WOW, awsome answer James. I just got boat so I am still learnin specs about motor, It is the 365hp magnum version and I dont think the cam was changed. The exhaust is in pretty bad shape so I will replace as soon as budget allows. I couldnt afford the hi-perf heads, so Im goin to have to put the "oval port" heads on for now. I can get 1 set of hi-perf heads for what 3 sets of oval port heads cost. THX"

"Hi Larold. had the same thing

"Hi Larold. had the same thing happen with my 1991 502. only knew i hade a problem after i tried to start it after being stood for about a month and it would,nt turn over, got a socket on the crank pulley and got it to turn but bent a push rod as the exhaust valve had sized in the head. finish up doing a complete rebuild. new heads from Dart, rebore, crank grind, mains and rod bearings, circ pump, therm housing plus other stuff, cost me a fortune as i had all the stuff shipped to Spain from America but what a difference, even tried welding the old heads but still porous. good luck"

"Ouch, Yea im going thru same

"Ouch, Yea im going thru same process. I had to downgrade to oval port heads due to cost. I think i lost about 30 or 40 hp. I will put the hi flow heads on next season and possibly a stroker kit also. Either a 502 or maybe even 572. By doing most of the engine work myself, minus machineing, I was able to rebuild engine and buy heads for about $2000. Just the hi flow heads were almost that much. This was an ebay buy so it has MANY more hidden problems than your average boat. So far I have had to buy Carb, dist, fuel pump, sea water pump, rocker arms, pushrods and thermostat housing (he said all this stuff was there) and I am now in the process of replacing stringers that the motor bolts to (arrrrg) they were completely hollow ie the fiberglass around them is perfect but there is NO wood inside. when i pulled motor, I left mounts "bolted" to the stringers, the mounts just fell off when i lifted the motor. But all this aside I should have it done inna week barring any further suprises. not sure about outdrive yet since the motor was half taken apart and full of water when i got it. THX and good luck."

"Sound the transom down low!!!

"Sound the transom down low!!! "