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84 305 Mercruiser Block Questions

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71matador250

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"I am helping a friend with th

"I am helping a friend with the removal and repair of an 84 Model 305 that suffered from an internal water jacket crack in the intake valley. We are looking at purchasing a 350 short block kit, using a mild rv cam and using the 305 heads. Any thoughts from the sage inboard guru's please! Thanks Very Much"
 
"The 305 heads have smaller va

"The 305 heads have smaller valves(1.84 intake vs 1.94 intake), less air flow. you can have larger valves put in, if you have a little bit of cash get the comb bowls cleaned up a bit and the intake runner opened up a bit, can also port match the intake gasket to the head and intake.

while you have the head off at least do a valve job to remate the valve seats and keep the compression up. you want to keep the compression ratio around 9.0-9.5:1

depends on the RV cam there are LOTS of choices, you can call and talk to CompCams and CraneCams support for help picking, you'll need to know the type of Pistons and the part number of the heads and what you do/done to them, and the head gasket that you use.

Depending on what your pushing, I'd go for a 260hp-290hp Marine cam from a Marine Engine rebuilder, also think about Roller tip rockers, helps with valve stem wear and reduced friction, and the stamped steel ones aren't all exactly the correct ratio 1.5:1.

You'll probably want to stay with a low rise intake to maintain low RPM power, it'll flow plenty on the top.

What are you going to do for a carb ?

Keep in mind your power range is about 1500-5000 rpm with a WOT of 4200-4800"
 
We are considering going with

We are considering going with an Edelbrock performer intake and carb. The power curve would be from 3500 to 5000.When I get the heads off and benched I will get a close look. I really appreciate all the help.
 
"Got the engine out and onto t

"Got the engine out and onto the stand last evening. The block is stamped 5.7LG followed by the serial. I've got to clean the heads to get the head numbers. The oil water slurry is a real mess. Is there a chance with the 5.7L marking that this could be a 350 instead of a 5.0L 305? I realize bore is the chief differecnce. But I was suprised to see the 5.7L casting mark.The crack extended to the outside also so the block is scrap. I have access to several good 350 blocks, It could possibly save a wad of money."
 
""...repair of an 84 Model

""...repair of an 84 Model 305"

Now that you found the majority of the engine is trash; get a remanfgrd. vortec longblock drop-in 350. First check the condition of the floor, stringers and transom; may be full of rot and foam may be water logged."
 
"I checked out to be a 305, or

"I checked out to be a 305, ordered a 305 shortblock, perfomer cam and intake. Should have it operational by next weekend. I appreciate all the help and advice."
 
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