|02-23-2013 09:05 AM|
It's a dependable drive up to 300 hp, 'n still dependable over that, if the operator has self-control over his righthand...
in other words, skip the WOT jackrabbit starts, 'n yank back on the throttle if by chance ya clear the water, 'n catch air on a wave...
'n,... The thru-prop ain't so much the problem, but the open plenum exhaust manifods are the choke point in the exhaust flows...
The vortex created by the prop, actually helps pull the gases out...
'n, of course, a Worn out drive isn't dependable, regardless the amount of power applied...
There's No reason the OP shouldn't move forward with his Plan,...
383s are stuffed into boats, quite regularly...
If crussel would like a more Marine rated conversation 'bout this,...
Feel free to stop by iboats boatin' forums,...
There's many conversations there, 'bout this exact thing...
|02-22-2013 05:43 PM|
|troutman2||We still build that 5.7 engine w/ the same intake as the mercruiser in which is a Bosch injection set-up.|
|02-22-2013 07:40 AM|
|lg1969||Hey BadBehavior, That boat is sexy like a good women.|
|02-21-2013 03:15 PM|
|02-21-2013 11:44 AM|
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
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.
|02-19-2013 05:14 PM|
|02-19-2013 01:10 PM|
|crussell85||So... ... maybe just look into the 7395 cam and the stock vortec heads?|
|02-19-2013 12:03 PM|
|TMF Lindbeck||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|
|02-19-2013 10:24 AM|
|crussell85||Is this a bad out drive?|
|02-19-2013 10:18 AM|
|crussell85||Its a 2001 Volvo penta with the sx out drive.|
|02-19-2013 09:43 AM|
|vinniekq2||wet or dry? power required?|
|02-19-2013 04:41 AM|
|crussell85||Running the stock manifolds. The vortecs came stock on the 350 engine. Max rpm is 5000|
|02-18-2013 10:53 PM|
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
|02-18-2013 09:33 PM|
Boat Engine 383
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