adequate and severe duty boat use is opposite,,,,
The 383 will make decent power at a lower RPM setting than a 305.
What do you "need" for power?
Build the engine to live in a harsh environment(boat)
Pick a power level and buy the best quality parts that give the engine the ability to perform to your needs

 

Is buying a vortec truck engine from a salvage yard a good way to start even if it needed rebuilt?

 

The biggest advantage of the Vortec block is that it is provisioned for a factory roller cam (as opposed to your flat tappet cam block now). The roller cam is better for power production (valves open and close faster adding power in at all RPM ranges), and it is not susceptible to wiping a cam lobe like a flat tappet cam does with modern oils.

The 383 makes more power due to more cubic inches. The ratchet analogy is not correct. The only real reason to upgrade to a 383 is if the original crank is shot and needs to be replaced. The other reason is because you want a 383 and have the money to build it. Now days 383's are common and you can get a complete rotating assembly for cheap (Eagle and Scat offer these, but again, they are cheap and you get what you pay for).

 

Not being much of a boat person, had to look up that Scorpion model and found that it came in a variety of lengths and model types - mostly dang big. From what I could see, a 305 in something that big, and I have to assume it is a pretty big boat, would make it a real slug. OK and moving along, what do you really want to do with this boat? Just make it go faster or add reliability? Then you get into how it's propelled. Installing a mega sized motor with 50-200 or more % more horsepower and torque in front of an out drive or even a shaft drive that was built for something around what a 305 puts out is a quick way for a boating disaster and from my little bit of experience with boats, very expensive. Then there is the added feature of higher gas consumption. Again drawing on my limited boating experience, have found that marinas tend to be legally stealing you blind for the 'convenience' of having a fuel dock and extra long hose just to help your wallet get lighter. There are several pluses for a later car based engine - you can use unleaded gas, add fuel injection and be able to buy most parts at a NAPA store. Oh and one more consideration - direction of engine rotation. Some marine engines rotate opposite a normal car. This means at least a different camshaft, distributor and starter and maybe a few more parts.

OK - all the negatives are over, and if you have a fat enough wallet, everything in the boat is or can be reasonably fixed, modified or replaced - go for the biggest that will fit in that hole and have a great time!!!:thumbup:

 

thanks for the replies guys. I talked to the guy atmy local salvage yard and he doesn't have a complete vortec engine. I then went to my local machine shop and talked to him and he has a block that is a 2 bolt 1 piece rear main and a4 bolt 2 piece rear main. he said the four bolt block would work with all the stuff from my 305. oil pan, flywheel, etc. he said the crank out of my 305 won't work on a350 due to balancing issues, Is this correct? He also said if I am going to buy heads he would suggest a set of gm vortec heads and a edelbrock performer intake but wasn't really sure on the cam. am I headed in the right direction?

 

You ARE headed in the right direction!! Engine rotation: make sure you are building a motor with same rotation as whats coming out. Some transmissions will change rotaion of the engine. Reverse rotation requires different crankshaft, camshaft, and rear seal. Distributer and oil pump should stay the same as the cam still goes clockwise due to geared timing set.
Check your oiling system, many Chris Crafts used a flexible oil pickup hose that was prone to collapse with age. This may have been your reason for failure in the first place. SBC pump failure is uncommon. I HAVE see the housing break off the cap and Pickups fall off, drives break, and relief valves hang up.

 

so how do I determine engine rotation? how about camshaft selection? I read a few articles online about cam selection and I think I know less about camshafts after almost two hours of reading than I did before I started. the guy at the machine shop was also kinda lost on cam choices. He said he knows how to select camshaft just doesn't really know if a boat engine needs to be all torque or not.

 

You should spend a couple minutes or hours and google "how to build a sbc boat motor".
A bunch of interesting topics surface.
Way different than building your typical street motor.

 

reread my post

 

talking about the drive: if a new larger/ more efficient engine was installed and the prop remained the same it wouldn't be any harder on the drive than the old engine, would it?

I don't plan on racing the boat anytime soon. The majority of what we do is float in the lake and get sunburnt. It gets to expensive to fly around the lake all day. Maybe twice a year we get the two person tube out and tow it around the lake.

This is the best picture of the boat I could find.

 

talking about the drive: if a new larger/ more efficient engine was installed and the prop remained the same it wouldn't be any harder on the drive than the old engine, would it?

I don't plan on racing the boat anytime soon. The majority of what we do is float in the lake and get sunburnt. It gets to expensive to fly around the lake all day. Maybe twice a year we get the two person tube out and tow it around the lake.

This is the best picture of the boat I could find.

Ayuh,.... Talkin' 'bout yer Drive Bob,... What drive is it,..??

'n yer ole 305, is it a 2bbl. carb, or 4bbl. carb,..??

About what Vintage are We talkin',..??

Dependin' on yer answers,...
Yer most likely, cheapest, easiest way to satisfy yer Love,(the Wife, not the boat ) is to plunk down yer cash at yer local Chevy Dealer, 'n buy a brand new pickup motor from GM,...
Either the 350, or their 383,...
Just the Long Block motor, with tin,...
They come with brass core plugs, 'n composite head gaskets,...
The cam is plenty close enough to do what you need,...

You'll be able to use most of the accessories from yer ole motor(dependin' on yer answers)...
You'll need an Intake, 'n probably an Electric fuel pump kit,... Marine uses an O/P shut-off switch,...
'n a standard Chevy Flywheel,...(14", dependin' on yer answers)

Lookin' forward to yer answers to my questions,...

 

If all you do is sunbath in it, don;t need to go faster which will burn more fuel then don;t replace the 305 with a engine that is bigger or more powerfulJust replace the 305 with another 305. Get a used 305 and install it. use the accessories from your old motor on the new Used one.
If you do replace the cam in the new 305 get a mild short duration cam.
not more than 204deg in 214 ex on a wide 112+ LSA.
It will do everything this boat needs to do for you.

I'm not to concerned with fuel mileage, the gas seems to be the cheaper part of boating. I said something to my wife about getting a used engine and she didn't seem to interested. She said we do enough boating that a new engine seems to be the right path. we talked abouanother 305 and she said " ask them guys about building a bigger engine with more power, because the kids are getting older and are gonna wanna go tubing eventually." The boat didn't care much for a two person tube before so we just don't do it that much. if we had more power we might use it more. with that being said.....
Would you suggest the same camshaft if it was in a vortec 350 engine? I was also doing some googling and seen that a few guys are running the gm performance 7395 camshaft Chevrolet Performance Hydraulic Roller Camshafts 14097395 - Free Shipping on Orders Over $99 at Summit Racing my buddy was telling me this would be a bad camshaft for a boat, I don't know why he says that he just says because it would be.

Would you select a different cam profile if I was going to use a roller cam?

 

if you repower with another engine your drive gear ratio needs to change. personally I would recommend the upgrade to a 260 hp 350 and matching drive. however I don't thinktheres anything wrong with the 305 you have. I would rebuild the engine you have and add a few upgrades. 305s run good in boats other than the plastic timing chain gear they used on your engine. those always fail. if your 305 is the 200 hp version, find a 4 barrel intake and carb and you now have a 230hp 305 and you don't have to change your drive gear ratio. if you have the 230 already then rebuild that engine the way it is. keeping the engine you have will put you back on the water much cheaper than a repower. whatever you do, don't buy a used running engine match because your timing gear will fail and you will be back at square 1 almost guaranteed. fix the issues that your engine has and it will live a long long time. plus a 311 CI runs a good bit harder than a 305 would. plus a .040 overbore 305 can use l31 vortec 350 heads and not too much valve shrouding and you will love it. roller timing chain new distributor gear and oil pump and some +.040 flat top pistons and that cam f-bird suggested is a reall good runner...I built one and its a great engine very fuel efficient.

 

Bob, Give Mike Jones a call at Jones Cam Design. He is very knowledgable and familiar with boat engines. He does cams for many different applications including Jersey Skiffs, Cracker boxes and Hot Rods. He knows what "water reversion" is unlike the tech guy I spoke with at Comp Cams.
He will hook you up.
Richie

 

Bob, Give Mike Jones a call at Jones Cam Design. He is very knowledgable and familiar with boat engines. He does cams for many different applications including Jersey Skiffs, Cracker boxes and Hot Rods. He knows what "water reversion" is unlike the tech guy I spoke with at Comp Cams.
He will hook you up.
Richie

watch what cam you have or put in there. seems reversion is only a factor to the boat owner not the cam company. i mean that. reversion could hydrolock the engine, worst case blow a rod through the block or light case scenario it will rust your exhaust valve and seats and compression will be down after a couple seasons. also chine walking is very dangerous and overpowering a boat is the one way to get you ejected from your boat. usually whene you get ejected, unless you have a tether cord your boat will turn hard around and go in tight circles at whatever speed you were at at the time of ejection, around where your floating in the water. that would be some pretty scary stuff. i see your wife is leaning tward a new engine but you cant buy a "good" choice built 305 engine in a crate. just stockers. but a 305 can make good torque if you build it with flattops .040 over pistons and vortec l31 heads. or even 081's would work well and you wouldnt have to buy an intake to match the heads. your q-jet would need a little tuning but your ignition will work great and drive ratio would be fine. that will save you some money and get you going a good bit better than the old power plant. i love a 305 and have relied on em for years glad to hear you wouldnt mind keeping a 305. i recomend you go .040 over and make it a 311 but either way a 305 is good. wont set the world on fire but there small displacement and high torque is a appreciated at the pump and they are super super reliable probably because they dont run as "hard" as other engines. if you have the old log style exhast then throw them in the scrap pile and get some newer header style upright manifolds from the late 80's early 90's alphas. they work very well on a 305 even through the prop. the prop while spinning, actually pulls exhaust from the engine like a vacume so once rpms are established thru-hull exhaust doesnt do anything for a 305 compared to thru-prop. its those crappy log manifolds holding the exhaust back. loose em.

 

The thing with most boat engine cams not used strictly for racing is the overlap. Overlap is the amount of time both valves are open at the end of the exhaust stroke going into the intake stroke. Having both valves open at lower RPM's gives the outside water an easy avenue to enter the motor either through reversion or the water backing up when slowing the boat down.

That being said look for cams with wide lobe centers (112-114) or mathematically low overlap numbers (less than 60 degrees @.006 lift)

Also if building a boat engine remember to use water resistant materials like brass freeze plugs, stainless ringed head gaskets, and stainless fasteners.

Here is an online calculator to figure out overlap:
http://www.wallaceracing.com/overlap-calc.php







*

 

ChrisCraft

Bob, Those are some sweet boats. As mentioned by others here, seems to me that you need to determine what gear ratio you have in your outdrive to make a good decision on which engine to use. You could have a 1.5:1 or a 1.65:1 depending on which 305 you have.
If I were in your shoes, I would size the engine according to the drive ratio to avoid having to spend additional cash to get the gears changed to match the engine. If you have the 1.65:1 set, I'd recommend staying with a replacement 305. If you have the 1.5:1 set, then I'd be tempted to go with a replacement 350/260 and enjoy some additional top speed with little more than a prop change and still be able to snatch some tubers or skiers out the water.
Fact is that if you put a bigger cam in a 350 or put a 383 stroker engine with a decent cam, then you have to start upgrading the intake and exhaust systems to allow the engine to breathe better and the costs really start climbing.
Ask me how I know. My 20 ft. Eliminator Sport Cruiser 406 SBC
Here's a chart on the Alpha 1 outdrives;
Seiler Marine - Mercruiser Gear Ratio Chart

 

Going to respond from a v-drive boat guy. Just please be careful to not put too much power in a boat that the hull was not designed for. I have seen it before with disasterous results... Sounds like your not going too crazy, but certain types of boat hulls were designed for specific duties and speeds.

 

Alpha 1 Stern Drives

I'm not sure if the OP is still here, he has stopped responding. Just for information for future readers of this thread, I wanted to point out a fact about marine propulsion. A V-drive, direct drive, jet pump, or a stern drive all have their RPM limits.

When it comes to an Alpha 1 stern drive, the outdrive has an RPM limit of 5000 RPM, better longevity at less (4800). One of the reasons the drive is limited is because above 5000 RPM the centifugal force of the spinning ring gear in the upper gear case will sling all the oil off in a vortex allowing the oil to cling to the case and run the ring and pinion with less than enough lubrication and cause failure.

With this fact in mind, engine power building practices should focus on building max power below 5000 RPM. Does no good to put huge heads and huge cams designed for high RPM power, when you start exceeding 5000 on an Alpha 1 you will destroy it soon or later.

This is one of the reasons you see so much difference in opinions about horsepower building in boats. Engine horsepower/torque/rpm limits have to be matched to the propulsion system being used. Nolan

 

A blower would be sweet

I have given thought to a small blower, it would make some nice power right where you need it.

However, I've tryed to remain conservative with my lil Alpha 1.

I spent boatloads of money(pun intended)on an old piece of junk OMC 800, blew it up countless times. I finally did a total transom rebuild and converted mine to the Mercruiser Alpha 1.

A little history on the Alpha drive; Mercruiser ran this drive with different power plants up to a 365 hp 454. When the warranty work started costing them alot of money they realized they had pretty much found the HP/Torque limitations of the Alpha with the BBC. Thats when the Bravo was born, built to take the brutal torque of the BBC.

I wish I could have afforded a Bravo drive for my boat, but at the time a complete Bravo was more than double the cost of an Alpha. I've got a 502 Mercruiser I could drop in it now but it would likely twist the Alpha into a pretzel.

Without giving away all my secrets, the best way to build a high performance engine for a stern drive is too; 1)realize the torque limitations of the outdrive. 2) Try to utilize engine components around achieving the most torque and horsepower you can get on the chart @ 5250 where the two cross. If you have to make a compromise between the two, always go with the package that makes the most torque in that 5000 rpm window. Nolan

 

sorry guys I'm still here. for some reason I'm not getting emails telling me sometime has replied. I'm at work right now but will definitely reply tonight. you guys are amazing,I am very happy to have all the help.

 

how much would a build like this cost?

 

the blower build definitely is interesting. maybe I'll make my way to Canada after retirement and hire your for a consultant during the build . but for now I think we are going to go with a regular engine. I did some looking at the drive today and I seen it has 1.65 stamped on it. I hope this won't be a lost cause or a deal breaker. I am interested in some advice about building the engine to use this drive. but also, Is it expensive to change the gear ratio to a preferred/ better ratio?

 

I can agree with everybody about how much fun a blown boat can be,, but they can and WILL be very expensive if you think you have to have that throttle on the floor too much
I had a 18 Ft Pantera jet with a Blown 383 small block chev, and 2 other motors , (all 3 were blown latterly),,,,all within a 3 year period,, pretty expensive boating,, but on the other hand,, you don't have to run them full bore all the time,, its just so much fun to go fast,
I no longer have a boat,,,:thumbup:

Bill

 

When you get it wide open and all trimmed up only about 6" of the back of the boat's hull will be in the water at all
@ speed.

And if you are lucky, you wont encounter the "fun" (terror?) of chine walking at 60 mph with many You Tube vids showing that experience.

 

I just happened to be talking to a co worker Friday and I was talking to him about my boat. When I told him that I'd really like to get a Vortec engine and rebuild it he said his brother was talking about scrapping his 98 Chevy 1500. So he called his brother and just so happens he still had the truck. His brother told him it is a vortec 350 with 250,000 miles. After work I went over to his brothers house and looked at everything. Didn't hear the engine run but he said it ran fine when he parked it but it's been sitting for a few years. So for two hundred bucks,I pull the engine then haul the truck to the scrap yard for him the engine is mine.

I plan on a total engine rebuild. So I am building a vortec 350 for the boat. Would still like suggestions on building this engine now that we know for sure of the size.

 

take the engine apart and see whats good?

 

Keep in mind, if your current motor is the 2bbl version, than going to a 350 will require a new outdrive leg because the ratios are off. It's 1.65 vs 1.5 for the 350. I wouldn't be surprised if your 1984 boat has a 1983 stern drive which is not an Alpha. What are your S/N's? They are forward compatible as in you could put an Alpha leg on an "MR" drive but not the other way around

 

I'm not changing the drive. If I go to a higher pitch prop with the lower ratio drive then it should be accomplishing the same thing, right?