73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Macj1983 on May 15, 2013, 12:10:28 pm
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What are the differences in a motor for a boat then for a car
Its a mercury marine motor looks real clean to me
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One big difference is that it will have a torquer camshaft in it, which is actually pretty good for use in a truck or street rod, or even a daily driver. My buddies all use marine camshafts in their street rods, and my truck is out at the shop getting one right now.
Not sure of the other differences, but someone here should know.
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Marine camshafts are typically designed to help the engine run at high RPM for long periods of time not really good for street use. It's OK to use a marine engine in an automotive application provided the rotation is correct. It's typically not OK to use an Automotive Engine for Marine applications without modification. If your intent is to rebuild it and use it in a truck it should be fine.
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Uh, you have that exactly wrong. Marine camshafts are ground to provide high torque at low rpms. Often called a marine/rv/truck camshaft. Marine and high-torque street camshafts are basically one and the same. See this discussion on iboats.com.
http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/marine-camshaft-differences-231217.html
or this item as an example on Comp Cams site:
http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=12-300-4&Category_Code=
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I believe the blocks are normally "high nickel" which is desirable for a performance build.
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Cam seems little small or its it just me? I have the 260h and it rocks for a daily. Got it cause any bigger and mpgs go way too south...
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Depends on what you want. The torque curve of the 12-300-4 in a 350 with the 76cc heads starts at 300 ftlb at 1000 rpm and peaks at 380 ftlb at 3100 rpm. That's a heck of a lot of torque in the rpm range that most people drive in the great majority of the time. The early intake valve closure gives decent dynamic compression even with low-compression heads, while the late exhaust opening retains the charge longer for better mileage. You can go to a "bigger" (longer duration/higher lift) cam, but at the expense of greater overlap, later intake closure, and earlier exhaust opening, which moves the torque curve up in rpm, gives lower dynamic compression, which hurts low end torque, and gives lower gas mileage. You will get more horsepower, but you will get it at higher rpm, the torque will come on at higher rpm, and there is a gas mileage penalty.
Note also that the penalties for a bigger cam apply more with less displacement, so a bigger cam on a 454 is a different question than a bigger cam on a 350. Also, the dynamic compression issue is not a problem with high-compression heads; there it actually helps by reducing knock at low rpms, allowing more timing advance. It's almost like having variable compression.
There is so much variety in cams available, you pretty much pays your money and takes your choice. But a marine/rv/truck cam in an otherwise stock 350 has a lot to be said for a street rod or a daily driver around town, including a smoking hot hole shot.
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Actually, the only difference is piston to cyl wall clearance between the two, boat motors use the lake/river for cooling so the block don't get as hot as it does in a vehicle so the expansion rate is not as high, pistons however get just as hot and expand the same amount which make for tight clearances and could possibly sieze up, clearance is .001-.002 more in a boat motor. Cams are for whatever the application needs.