Mercruiser 350 MPI rebuild
#11
Very good advice on letting the machine shop source the parts. As long as they are familiar with Marine Build engines he will set things up based on experience and more likely to stand behind work if they know the parts he put in instead of a mix mash of parts. Some things just work better together.
Where are you? If you ask you certainly will get recommendations on shops familiar with Marine builds.
Where are you? If you ask you certainly will get recommendations on shops familiar with Marine builds.
#12
Registered
Most of those flat top pistons with 4 valve reliefs are about a 5-6 cc "dish" for the valve reliefs. Unless I am doing my math totally wrong with a 1.560 compression height the piston will be about .020 down in the cylinder. That combined with a .050" gasket and the 64cc Vortec heads gives you a compression ratio of just about 9.5 to 1 ? I guess as long as you are ok with 93 octane fuel then it should work.
#13
Most of those flat top pistons with 4 valve reliefs are about a 5-6 cc "dish" for the valve reliefs. Unless I am doing my math totally wrong with a 1.560 compression height the piston will be about .020 down in the cylinder. That combined with a .050" gasket and the 64cc Vortec heads gives you a compression ratio of just about 9.5 to 1 ? I guess as long as you are ok with 93 octane fuel then it should work.
#14
Registered
Many years ago, I had "260 Mercruiser (350 non Vortec GM) in my 23 ft Wellcraft. I removed the engine around 250 hours and installed brand new GM Vortec heads, different valve springs, a mild flat tappet Comp Cam around 212 / 218 @ 0.050. New Edelbrock intake, roller rockers, timing chain, HiPo Mercruiser exhaust manifolds, and kept the stock flat top pistons with 4 valve reliefs and never even removed them. I calculated around 9.3 compression and was concerned as well, since I think I used the stock Mercruiser head gasket. I started at 32* total timing and 89 mid grade. It gained 9 mph and I switched from a 21 Mirage to a 23 Mirage and it turned that prop to 5100 rpm. Later, I put the timing back to 30* total and ran a few tanks of 87 octane and could not detect any detonation or pinging. I went back to 89 for safety and ran the boat like that 8 years, no issues, sold it to a friend and he has had it with no issues for 5 years.
Last edited by kornegle; 09-18-2024 at 10:54 AM. Reason: Had ttrouble posting and did a check