Swapping out a 305 for a 383.

StevNimrod

Petty Officer 1st Class
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Dec 13, 2008
Messages
343
Re: Swapping out a 305 for a 383.

All very good information! Great post.

Thanks.

Good luck with your effort to explain physics. Reminds me of freshman physics and the professor spending the entire first lecture telling us how important it was to "forget everything you think you know about physics." Nobody listened; first exam average was something like 19%.
 

TilliamWe

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Dec 21, 2004
Messages
6,579
Re: Swapping out a 305 for a 383.

I'm running an Alpha Gen 2 behind my 383 and haven't had any drive problems in two years.

Consider a good intake manifold + carb. You're feeding 78 more cubes.

I went from 350 to 383 and now can cruise at about what what I was getting WOT. I use more fuel at WOT. Significantly more fuel. It's nice to have the extra power, but you might get tired of filling up every week if you run WOT often.

Overall I'm satisfied, but it's hard to say if I'd do it again if I knew then what I know now. It's a little more complex than just picking up "free" HP. I know of quite a few around here that are stuck with stroker powered small and big block boats they can't sell at half price because people get scared about prices at the gas pump.

Also keep in mind that compression ratio tends to get high quick with strokers and shops use various means to keep in down (dish pistons, pistons down the hole some borderline obscene amount, big cc heads). I ended up with big dish pistons to keep my ratio down using 64cc Vortec heads. All stuff you might want to find out from Jasper or keep open the possibility that you may end up at a local machine shop depending on how detailed you want to get.

It's for all these reasons that I recommend going to Mercruiser and buying one of their 383MAG MPIs. Yes, they are very expensive, but they are complete, drop in, and turn-the-key motors with fuel injection and approx 325hp at the prop.
 

DaNinja

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1,407
Re: Swapping out a 305 for a 383.

It's for all these reasons that I recommend going to Mercruiser and buying one of their 383MAG MPIs. Yes, they are very expensive, but they are complete, drop in, and turn-the-key motors with fuel injection and approx 325hp at the prop.
I'll have to look into a Mercruiser replacement again. Last I looked, it didn't look like the numbers worked for a old lil' Ray.
I'd never get the costs out of the boat. Still worth another look, though.
Maybe I would recoup more of that cost than I would a less expensive Jasper?
Hmm...
 

QC

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Mar 22, 2005
Messages
22,783
Re: Swapping out a 305 for a 383.

Maybe I would recoup more of that cost than I would a less expensive Jasper?
Define "recoup more of the cost" . . .

Resale? Fuel? How? Not being argumentative but helping you think this through.
 

DaNinja

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1,407
Re: Swapping out a 305 for a 383.

Define "recoup more of the cost" . . .

Resale? Fuel? How? Not being argumentative but helping you think this through.
More resale, I think. Tough sell spending $4K on a motorless old SeaRay.
I think it's still well below they resale price after a repower.
I'm not even bringing fuel consumption into the equation with the "Budget Master".

I also have to take into consideration that it's "her" boat and she runs it without me sometimes.
That steers me to a milder upgrade.

Yep, thinking it all through with a head full of equations now.:D
 

QC

Supreme Mariner
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Mar 22, 2005
Messages
22,783
Re: Swapping out a 305 for a 383.

I'm not even bringing fuel consumption into the equation with the "Budget Master".
Good. You'll never make a legit argument either way. Fuel is not the reason to do this, or not to do this. Resale is slippery as well. Do it only because you can afford it, and you love the boat. If not, sell and buy something else.
 

oops!

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Oct 18, 2007
Messages
12,932
Re: Swapping out a 305 for a 383.

lol....when i get home....im gonna read this whole thing !
 

DaNinja

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Re: Swapping out a 305 for a 383.

Good. You'll never make a legit argument either way. Fuel is not the reason to do this, or not to do this. Resale is slippery as well. Do it only because you can afford it, and you love the boat. If not, sell and buy something else.
Even without the math classes, I think as this gets closer that I'll probably split the difference and go with a 5.7 like we have in the Starcraft. The admiral is comfortable with either boat and I don't need to add a specialized motor into the equation.

Funny sidenote....
Today, on a whim, I stopped at a national brake service place to get the truck brakes inspected. The staff was great and I learned a bunch from the mechanics. I learned enough to probably save $250 and do the brakes myself.

On the way out, with truck keys in hand, I joked, "Thanks guys, now if you could just drop a 383 Stroker in my broke SeaRay."

Without batting a eye, the manager and mechanic started punching numbers on a calculator. I thought they were just messing with me.

It turns out the mechanic and manager build hot rod jet boats and they were thrilled about dropping a 500hp motor in our SeaRay. Not a chance they'll touch the lil' Ray with a motor like that, but it was funny that I found another boat mechanic during a fluke stop at a brake shop.
 

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: Swapping out a 305 for a 383.

I have feel like i have read the entire internet on this subject and have come to a few personal oberservation's If you plow around at 2500 rpm most of your boating life you need a traditional boat cam. If you run between 3 to 3500 at crusie you need to upgrade your cam or you can if you wish....most boat cams are setup for that 1000 to 2500 rpm band...safe but old tech and who cares.

Think of a boat motor like its a indy car long term motor and set it up for the rpm band your going to run...long term thats where the moneys at. Personally im setting my cam and valver trian to come alive at 2500 i curise at 3500prm and have fun at wot from time to time. I have also lightned my valve train and a few other things along the way...Tinkering is a blast...:eek:
 

GLENN M

Petty Officer 1st Class
Joined
Aug 14, 2010
Messages
204
Re: Swapping out a 305 for a 383.

Bubba, static friction takes more force to overcome than kinetic friction. And for every force there is an equal and opposite force in the opposite direction. If you understand those two concepts, then you'll realize why hammering the throttle from a standstill is so hard on an outdrive.

Glenn, sorry, you are not correct. A 400 has a 4.125 in bore with a 3.75in stroke. If you reduce that stroke to 3.48 (350) you are left with a 372. A 383 has a 4.03 in bore with a 3.75 in stroke. Using the formula for volume of a cylinder "Pi times Radius squared times height", you'll see how it all works out that a 350 (4in bore 3.48in stroke) is 359.67 cid, a 6.2 (4in bore 3.75in stroke) is 376.8 cid, a 383 is 382.47cid, and a 400 is 400.7 cid.

so i said 350 4inch .030 over with 400 crank is 383 um so are you,i said400 block 350 crank is 377,you say 372.oh i guess iam wrong i forgot to add .30 over.so a 350 is actually 360
 

DaNinja

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Re: Swapping out a 305 for a 383.

20.5-305=0
20.5-305+383= +10
20.5-305+350= >5<10
That's the way my math is falling out.:D
Purely hypothetical, though.
 

StevNimrod

Petty Officer 1st Class
Joined
Dec 13, 2008
Messages
343
Re: Swapping out a 305 for a 383.

QC brings up a good point in that you really have to think and feel this through from a variety of angles.

What might be important as a consideration to us might not be to you, and vice versa. Some things that might be considered (even if only in passing):

-Fuel (There are a bunch of boats where I dock that aren't run more than few times a year because the owner can't afford to, but didn't know that at the time of purchase. Gas prices are volatile; you might have to hedge).

-Resale (This repower might leave you upside-down. If so, how far upside-down are you willing to go? That's between you and the Financial Department; start bribing early, do so often.)

-Cash flow (Liberal application of bribery often yeilds desired results. For what it's worth, avoid using analogies involving shoes that aren't worn or purses with tags still on them when the phrase "wasting money" is used to thwart progress. But, it's typically less costly to do it right the first time than it is to do it twice. And it may be that all of the viable options mean you seriously have to consider getting a completely different boat and parting out or selling what you have. There are still a bunch of great deals out there.)

-Length of season (At least for me, it was hard to justify certain options given our five month long boating season. YMMV.)

-Power (It's easier to run at 3/4 throttle than it is to run at 8/4 throttle. If it's there, you can control how much you use; if it's not there, it ain't there. You've giving it all she's got.)

-Desire (The emotional aspect of the whole deal. You want the XYZ because you want the XYZ and won't be convinced otherwise, like the package it comes in, the stickers, it being a turn-key, the boat deserves it, it'll help you sleep better at night, it's got safety features and since she goes out by herself her safety is top priority, or whatever.)

-Ability (If you decide you want to try your hand at building all or part of the engine. Depending on what you think of your mechanical abilities/desire to learn, and what she thinks of them, be prepared to offer a clever response if safety comes up.)

-Warranty (There something to be said about knowing it's right because you did it and went the extra mile to make sure it's right. There's also something to be said about dealing locally with someone who has a reputation for standing behind their work; they might have a bad day and it happens to everybody, but it's typically easier to make it right when you can do a face-to-face. Even still, there's something to be said about a warranty book with impressive looking terms from a big corporation. Just be sure to read the fine print on limited liability contracts since there are places out there offering contracts with no questions asked.)
 

StevNimrod

Petty Officer 1st Class
Joined
Dec 13, 2008
Messages
343
Re: Swapping out a 305 for a 383.

so i said 350 4inch .030 over with 400 crank is 383 um so are you,i said400 block 350 crank is 377,you say 372.oh i guess iam wrong i forgot to add .30 over.so a 350 is actually 360

No, a 350 is actually a 349.8, which would get tiresome to say. Bore it 0.03 over and you've got 355.1 ("355"), take it 0.04 over and you've got 356.9 ("357"), push your luck and take it 0.060 over and then you get 360.4 ("360").
 

GLENN M

Petty Officer 1st Class
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Aug 14, 2010
Messages
204
Re: Swapping out a 305 for a 383.

No, a 350 is actually a 349.8, which would get tiresome to say. Bore it 0.03 over and you've got 355.1 ("355"), take it 0.04 over and you've got 356.9 ("357"), push your luck and take it 0.060 over and then you get 360.4 ("360").


not according to poster i was replying to its 359.8.myself i happen to be more on your figures side of the post,i also like short stroke engines keep piston speed down.i always build 377 ci engines,less bottom end tq easier on drive:rolleyes:
 

GLENN M

Petty Officer 1st Class
Joined
Aug 14, 2010
Messages
204
Re: Swapping out a 305 for a 383.

Bubba is right on this on. An engine will not produce maximum torque and horsepower at a low rpm. Thas why racers use stall torques in their cars to get to the rpm range where they start makeing power. But in a boat I would assume that The effects of torque will be less after the craft is moving. That is unless the operator is running say 20 and floors it. And we never do that. Well hardly ever.

an engine makes max hp at max load and max rpm,depending how and what parts tq could be max any where,an engine will only produce the amount of tq it needs
 

proshadetree

Lieutenant Commander
Joined
Jul 19, 2008
Messages
1,887
Re: Swapping out a 305 for a 383.

Now Glenn, I dont care if it is a boat or a car or a lawnmower, all engines will rev past their max horsepower level if not governed to do so. Max horsepower at the crank will vary dependent entirely on the load. Check any dyno sheet ever regardless of the manufacture max horsepower will not be at max rpm. I have never seen a engine produce max horsepower at exactly the same rpm as max torque. If you have ever run any car it will pull hard up to a point normally close to max horsepower level then fall off even though it still is gaining rpm.
 

GLENN M

Petty Officer 1st Class
Joined
Aug 14, 2010
Messages
204
Re: Swapping out a 305 for a 383.

Hmmm, so you build a 383 stroker so you can run 75% throttle all the time? Why do it if the plan is to never use it? Just go with the 350 it had in the first place. Sorry but I still have to say WOT at low RPMs (below 3000) does not put near the strain on the drive as WOT at high RPMs and anyone sticking a stroker in their boat did it so they can use it. Lets do the math again.

2500 RPM at say 200 lb ft of torque (95 HP) -- 3000 RPM at 225 lb ft of torque (128 HP) -- 4000 RPM at 250 lb ft of torque (190 HP) -- 5000 RPM at 300 lb ft of torque (285 HP) 5500 RPM at 300 lb. ft. (314 HP)

You can plug in about any engine torque curve you care to but the results will come out the same. Rising RPMs even with a perfectly flat torque cure (not possible with an internal combustion engine) increases the load on the drive as the RPMs climb.

Think of it this way. Lets say you have an engine that develops 200 lb. ft. of torque at 2500 RPM. That gets you about 95 HP. The drive could sit there and do that forever without a problem. (Not true of the engine, it would probablly burn up.) As I said, the math is what it is and every manufacture uses that math when they design a drive and rate the maximum torque/HP. (Same for the design of any gear box and thats really all an out drive is.)
-300hp x5252 divided by2700rpm=584 lbft 300hp x 5252 divided by4600rpm=343 lbft 300hp x5252 divided by8000rpm =197 lbft 300hp x 5252 divided by 1591 rpm=991 lbft thats how i was looking at it,and i think i was wrong boats are differant thanks for the lesson
 

86 century

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Sep 8, 2009
Messages
986
Re: Swapping out a 305 for a 383.

What about the external balance of the 400 crank.
 

DaNinja

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Messages
1,407
Re: Swapping out a 305 for a 383.

QC brings up a good point in that you really have to think and feel this through from a variety of angles.

What might be important as a consideration to us might not be to you, and vice versa. Some things that might be considered (even if only in passing):

-Fuel (There are a bunch of boats where I dock that aren't run more than few times a year because the owner can't afford to, but didn't know that at the time of purchase. Gas prices are volatile; you might have to hedge).

-Resale (This repower might leave you upside-down. If so, how far upside-down are you willing to go? That's between you and the Financial Department; start bribing early, do so often.)

-Cash flow (Liberal application of bribery often yeilds desired results. For what it's worth, avoid using analogies involving shoes that aren't worn or purses with tags still on them when the phrase "wasting money" is used to thwart progress. But, it's typically less costly to do it right the first time than it is to do it twice. And it may be that all of the viable options mean you seriously have to consider getting a completely different boat and parting out or selling what you have. There are still a bunch of great deals out there.)

-Length of season (At least for me, it was hard to justify certain options given our five month long boating season. YMMV.)

-Power (It's easier to run at 3/4 throttle than it is to run at 8/4 throttle. If it's there, you can control how much you use; if it's not there, it ain't there. You've giving it all she's got.)

-Desire (The emotional aspect of the whole deal. You want the XYZ because you want the XYZ and won't be convinced otherwise, like the package it comes in, the stickers, it being a turn-key, the boat deserves it, it'll help you sleep better at night, it's got safety features and since she goes out by herself her safety is top priority, or whatever.)

-Ability (If you decide you want to try your hand at building all or part of the engine. Depending on what you think of your mechanical abilities/desire to learn, and what she thinks of them, be prepared to offer a clever response if safety comes up.)

-Warranty (There something to be said about knowing it's right because you did it and went the extra mile to make sure it's right. There's also something to be said about dealing locally with someone who has a reputation for standing behind their work; they might have a bad day and it happens to everybody, but it's typically easier to make it right when you can do a face-to-face. Even still, there's something to be said about a warranty book with impressive looking terms from a big corporation. Just be sure to read the fine print on limited liability contracts since there are places out there offering contracts with no questions asked.)
I appreciate that input and all the others. All of those are being factored into my decision.

I don't think my upgrade go past a 350. One of the factors driving it is upgrading a boat to the point where it is unusable to the wife.The "Texas Belle" is her baby and I'm not always here when it's taken out. I think we'll split the difference and go with the tried and true 5.7L.

Thanks for all the inputs and math classes!:D
This place is great!
 
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