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  #16 (permalink)  
Old 08-26-2013, 01:04 PM
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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

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Old 08-26-2013, 07:25 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
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?
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Old 08-27-2013, 05:23 AM
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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







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Last edited by engineczar; 08-27-2013 at 05:38 AM.
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Old 08-27-2013, 09:39 AM
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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
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Old 08-27-2013, 11:50 AM
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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.
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Old 08-27-2013, 11:59 AM
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Quote:
Originally Posted by BobBoat View Post
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?
This cam is used a lot of boat engines.It doesn't look very good on paper,but,it performs well.Provides a very flat torque curve out to 4500.has a pretty much smooth idle in a 350.A little lope to it in a 305.it's also easy on the valve train.You can get off Ebay ,(new pullouts) for $99 to $120.
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  #22 (permalink)  
Old 08-29-2013, 05:17 AM
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If I was building a performance 350 marine motor with vortec heads that would not be the cam I would use
in it. it is not a "Bad" cam, just not the cam I would use .

I'd be more inclined to use the cam from the 350 ZZ4 crate motor (208-221 112 .474 .510)
or the GM LT4 "hot cam" 218-228-112 .525" w 1.6 rockers .491" w 1.5 rockers
Of the GM Hyd rollers these would be my choices.

I'd look at the Crane hyd rollers for this for max perf from a 350 or 383
(222@.050")
I believe Crane cams HR-284-2S-12 IG (109831) is the same cam or near identical to the cam used in the Merc 5.7L Black Scorpion ski boat motor.
You can build a simiar carbed version of this motor using reworked Vortec heads or bowtie vortecs 9.4:1cr RPM hi rise dual plane , this crane cam
and a marine 750 cfm Holley carb and the good magnum ex manifold and thru the hull ex.
Howards has a similar cam for this.
It builds a good hi perf 355 for your purpose. needs 92 octane.
Use the V6 thunderbolt spark box or aftermarket spark. as the V8 merc ign box is rpm limited.

These cams need thru the hull exhaust and the good magnum manifolds . The thru the drive exhaust is restrictive.

For a 350+CID the 1.47:1 or 1.50:1 drive is prefered.
If you are stuck with the 1.65:1 drive the (350) engine needs to rev higher and the prop has to be dialed in
May need a custom prop (money) to get it right.
But it can be done.

A 383 will not like the 1.65 drive at all.

Note: watch your compression ratio. Both a 350 or a 383 need a (-12cc or -18cc) dished piston w/ 64cc cylinder heads
keep it under 9.6:1 Ya it matters. Excessive cr is not your friend in a marine motor.

Either motor version built with a flat top piston and a 64cc head will probabily need 94+ octane gas.
Crap gas will not work.
If you are going to run crap gas keep the cr low.
If you are going to run 10:1 cr on the water plan on bringing your own gasoline (94+ octane)

Last edited by F-BIRD'88; 08-29-2013 at 05:47 AM.
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  #23 (permalink)  
Old 08-29-2013, 05:50 AM
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So the first thing to do is decide what fuel will end up in the tank of the boat.
Ya it matters
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  #24 (permalink)  
Old 08-29-2013, 05:57 AM
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If you want to build a 355 or a 383 with flat top pistons use a head with a 72cc combustion chamber.
(based on a O decked block)
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Old 08-29-2013, 06:04 AM
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GM GMPP camshafts #12370845 and #12370846 are other good cam choices
in a HYD roller for a hi perf 350 or 383 boat motor.
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  #26 (permalink)  
Old 08-29-2013, 07:58 AM
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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
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  #27 (permalink)  
Old 08-29-2013, 08:03 AM
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Quote:
Originally Posted by BobBoat View 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.
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,...
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  #28 (permalink)  
Old 08-29-2013, 08:08 AM
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This is for the most part absolutely true.

But a freiend here built a "horsepower" 355 ( it made just over 500hp on the dyno on methanol) and ran
it on Alpha drives ( actually they were twin 355's. @6700-6800 rpm.
These 355 were radical, not your typical "boat motor"
Yup used to spit the oil out of the drive LOL. So ya had to refill it every once of a while.
But the Alpa drives never gave up. Yes there was no doubt increased wear.
But it ran and ran and ran and went like hell. Your mileage will vary.

The 9.4:1 350 motors I layed out cruise real well at 3000-3500rpm... run real good at 4800-5000-5200rpm
and run fine flat out around 5500-5700rpm (short WOT blasts) Peak Horsepower
A lot of it depends on how you prop it. And how much prep you do the the heads for power.
Very good overall durability of bothe the motor and the drive as long as the alpha drive is not all used up already before you start.
You will get a good service like out of it. As stated if you do a lot of WOT running abouve 5200rpm
keep an eye on the oil level in the drives.

A radar gun and a few props to try out will show you where the engine wants to run. And what makes the boat go the fastest.
From these tests you can then prop it to keep the engine rpm down a bit if you want.
The difference in boat top speed is not that much, until you are racing a bud side by side for grins.
Then it matters. So just throw on the "race prop" for that day.

Last edited by F-BIRD'88; 08-29-2013 at 08:17 AM.
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Old 08-29-2013, 08:22 AM
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Olnolan: This is anoth3er reason I like the low cr 355 with the little 142 roots blower combination.
You can and will make a ton of power @5000rpm and a ton of torque.
We did this combo on a Scorpion just like the poster's boat.
That one also ran and ran and ran on a Alpha drive.
It was a lot of fun. It ran the fastest with high boost (8-9 psi) and high octane gasoline ( 110 mixed with 94 )
for short blasts. in this tune up the max rpm was around 5700rpm flat out...Short drag blasts.....

But ran real good all day long on modest 6psi boost and proped to run around 5000rpm WOT. on 94 octane gas.
good boat top speed, pump gas, good fuel consumption and rpm for the boat speed.
So two different tune ups. Depending on what you wanted to do with it that day.
fuel octane choice/blower boost-pulley /prop choice

Its hard to beat supercharged power. The ability to dial the power/speed up or down as you need it, is one reason.
A lot lot lot of power and torque at moderate rpm is another reason.
The supecharged 355 eats up any N/A 383 and the Alpha Drives seem to take it.

Last edited by F-BIRD'88; 08-29-2013 at 08:40 AM.
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Old 08-29-2013, 09:03 AM
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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
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