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Boat Engine 383

6K views 13 replies 9 participants last post by  bondo 
#1 · (Edited)
Working on getting a boat engine together. I have the rotating assembly for a 383. Scat 9000 crank, 5.7 rods, kb dished pistons with a d shaped cup 18cc. I have a set of L31 Vortecs sitting on the shelf but have been looking at the Gmpp small port bowtie heads. Chevrolet Performance Vortec Small Port Bowtie Cylinder Heads 25534421 - SummitRacing.com I am also looking at Chevrolet Performance LT4 Hot Cam Hydraulic Roller Camshafts 24502586 - SummitRacing.com for a cam that is suggested from a Marine Performance book that I have been reading. Not really sure what would have to be done to the stock vortecs to run that cam but if someone could throw me a link to a book or some good info. Another thought on a cam is Chevrolet Performance Hydraulic Roller Camshafts 14097395 - SummitRacing.com which I should be able to run with the stock vortecs. I'm don't have a target hp/tq number in mind I just want the boat to be fun! Great acceleration and good top speed. The boat is about 20 ft and weighs app 3,500 without passengers (typically four adults).

I'm not sure where the point of saying "it's pointless to go that much on a cam or heads because you still have the wet log manifolds which are staying.

I am also looking at an efi system from Marine: Affordable Fuel Injection these guys live about fifty miles from me so it will be nice for tuning and such. Just not sure if I want to go tbi or mpfi. I've heard tbi makes more torque? But mpfi burns more efficiently and will allow the engine to run smoother and last longer?

I know this isn't a boating forum but it's my favorite forum

thanks
 
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#2 ·
what type of exhaust manifolds are you using.some cams do not work well with wet manifolds. What rpm are you planning to run the engine at most frequently. How much horse power do you need to get the speed you require. or what RPM is your prop most efficient at? are you concerned about fuel burn or power ? I will likely try to talk you out of the vortec heads.
building a good/reliable boat engine costs more than a car engine
 
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#7 ·
There are many calculators on the Internet to figure your hull speed and the hp required to go a given speed in knots I would google for a hull speed calculator. I've found on my 16 ton 42" dive boat the first 7 knots ill need 60 odd hp but if I would want to go a additional 4 knots at 10 kt ill need a additional 400 hp. My leingth at the waterline and tonnage Re holding me back. For your little 20 ft'er you can really get going with little hp but you'll find a point whare it takes more than 100 extra hp to just gain a knot or 2. Basically what I'm saying is you can build a 350 hp engine and get a max speed of 8.5 knots or a 900 engine and go 12 knots in my case. What would be the better bang for the buck? Easy choice for me was a cat 3208 as opposed to a MAN with triple he hp and only going marginally faster
 
#9 ·
In my opinion that 7395 has too much duration for wet exhaust. You may end up with water reversion, and a no start in the water.you need to pick a marine performance cam or speak to someone that knows marine camshaft design. (Mike Jones Cam design, Denver NC)
 
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#10 · (Edited)
Here is the Ramjet intake for Vortec heads.


Merc marine intake for Vortec head use. Used on 305/350/383 marine engines, I run this in my 1997 Vortec 350 reg cab shortbox 2wd truck, runs much better than teh stock truck intake, and allows me to run any sized injector I wish(unlike teh stock truck intake)


Same marine intake next to Vortec truck intake manifold


Same intake in Mercruiser red



different angle


Here is the same marine intake with the upperplenum removed. You can see how the runner eopenings are across from the cylinder head intake port it feeeds. the cross ram runners are about 10" long from the opening inside teh plenum to the intake gasket flange.


Inside of Vortec 305/350 truck intake. Lots of injection debris impeding flow.


Scorpion 400 intake, it uses the same tunnel ram lower that is mentioned elsewhere in this thread.



peace
PAuly
 
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