MARINE INBOARD VS. REGULAR SMALL BLOCK

Kmodi9 · #1 08-24-2006, 03:57 PM

what is the difference between a regualr small block from a car/truck and a marine one? Thanks!

1bayouboy · #2 08-24-2006, 04:04 PM

the basic blocks are the same as far as I know......
however, the gaskets are marinized as are the electrics
to prevent sparks that could ignite fuel vapor (alternator,
starter, distributor, ignition).....and the air intake uses
a flame arrestor for the same reason. Things like power steering, seawater pumps, remote oil filter kits are somewhat different too.....

nestorpr · #3 08-24-2006, 04:33 PM

The camshaft and intakes are also different since the power curve for an engine used in a road vehicle and one used in a boat are completely different.

Kmodi9 · #4 08-24-2006, 05:18 PM

thanks!!!

does anybody know what rpm range an inboard 23 wants to live at?

also any opinions out there or carbs vs. efi?

Miles Offshore · #5 08-24-2006, 10:20 PM

wot should be 42 to 4800 rpm's. i cruise mine at 3 to 3200 rpms for optimum fuel /speed - i have a friend with a 350/320 efi on his formula that really honks. I have a 350/270 carbed that does well also. Gary (Knot working) on this board also has efi and his boat runs right along as well.

oldbluesplayer · #6 08-25-2006, 11:25 AM

a couple more things - first - I'm gonna guess we are talking about the ubiquitous 350 chevy small block -

if that's the case, the basic 350 block comes in two versions, the difference having to do with the number of bolts holding the crankshaft bearing caps in place - they are what is referred to a 2-bolt, or 4-bolt, mains. The 2 bolt mains are the common car variety blocks. The 4-bolt mains are used on the heavier trucks, and the high output motors like the Corvette - these are also sought after by drag race guys, as they are much stronger.

To my knowledge, the blocks that are diverted to marine industry use up front, ie. that go to Mercruiser et al, are all 4-bolt mains blocks, to provide increased reliability - the typical boat useage does place a higher continuous stress level on a motor - cranking along at 3000 to 4000 rpm for long periods under load, where the average car use would be floating along at 2000 rpm, under a lighter, rolling resistance, loading.

Also, for the 350 small blocks, depending on the vintage, as these have been around for half of forever, there are a variety of heads available, depending on carburated, or FI, and these contain different configuration intake and exhaust ports, and often different sized valves, from each other - the high output Corvette motors, for example, use different heads than a sedan or station wagon motor.

Along with all that is the already mentioned camshaft differences, and the marinized electrics, starter, distributor, etc.

hope that helps some.

Bill

Kmodi9 · #7 08-25-2006, 12:14 PM

we are indeed. it is a crusader 310 i believe and it is going to get looked at in the next few weeks by my buddy who should be chiming in here.......

additonally we are going to put a 383 in it in feb. which is why i was asking about the differences.

any opionions on a 17/15 3 blade vs. a 16/15?

thanks!

wendell · #8 08-25-2006, 03:19 PM

I hang with kmodi.

We're thinking about building a 375hp 383 stroker for his 23cc. If any one has any experience with hot small blocks in these boats, feel free to chime in. I know of a Silver Hawk with a 377 that seems to go great. The two boats are very similar so it should be a decent indication. Again, any info or advise would be great.

oldbluesplayer · #9 08-25-2006, 04:46 PM

are you guys building your own, or gonna buy a crate motor ?

I think I'd call Summit Racing, they do crate motors, tell them what you're doing and ask for a 383 stroker done up as a marine engine, specify a block with 4-bolt mains - though I think all their strokers are done that way anyways - that would be the fastest best trip to that end result.

Bill

RUSTYNTABATHA · #10 08-25-2006, 04:49 PM

Your going to have to be very carful when building engines that out of the norm for a boat. your cooling capacity is reduced on boats due to engine enclosure and open or closed water systems. The hot rod motors you put in a car are not the same as the hot rod marine engines. My father-in-law built a 383 stroker for a searay and i tryed to tell him to call in for outside help, but son-in-laws opinions arn't much good apparently...... he should of asked for help.. you can't use standerd rv cams in marine aplications. Ask for as much imput as you can get from marine mechanics. Remember no is always free.