V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

[sikpupy]

Thing is, after my first 1k boat money was stolen by my GF and my other 2 boats just stolen, I have left a few 4cyl motors, a V8 drive and a V6 drive for my 3.7 mercs. Now that I am dead broke living by myself, the only option I have for a boat is one that has no engine and or drive, thats the cheapest option I see in the forseeable future.

If I was to use my V8 drive first, to save my V6 drive, how would that work out? I know the V8 drive would put a load on the engine, but, I was thinking I could go down in prop size? I dont do a lot of water ski-ing, just cruising. Dropping down in diameter would theoreticly keep the loading down but also be spinning faster. Keeping that in mind, would it be feasable (not desireable) to be able to use my V8 outdrive?

 

[180shabah]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

What are you saving the "v6" drive for? Do you plane on destroying the first drive?

The 3.7's were pretty torquey for 4cyls and used the same ratio as the v6's.

It sounds like money is going to be an issue, so why not ditch(sell) the 3.7 while you still have a chance. get a v6 or v8 and sell the other drive. It may not sound like the best plan right now, but in the long run you will be much better off.

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

I like the idea of a compact 4 cylinder engine thats light weight compared to an iron block. Eventually I want to put an aluminum head on it too. Yes, and, also, torquey is what I also like about the 4, plus less gas putting around. The final nail on the head is the fact that the 3.7 is a closed system, in love with that idea!

Since I have the engines and all the amenities that go with it, no need to waste a summer trying to sell them when all i need is a boat and a weekend. If I run across a good deal on a V6, I would buy it and trade it out.

Going with my drives I have, yes, I do plan on destroying the first drive. I am a novice boater and have no idea what lurks at the places I have not been too yet. Until I get to them and boat around a little to become familier with my surroundings, I know I am going to whack my first outdrive and kill it sooner or later. I would rather it be the V8 outdrive than the V6 out drive i just rebuilt.

Man, admin, why you put it here? No one is going to read this here and it is not engine related!

 

[180shabah]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Do a little research on that 470 and you might not be so excited about it.

They were a great concept but the execution was not so hot. Funky stator charging system with water cooled votage regulator, leaky cam seals that allow engine coolant onto the cam, zero tolerance for high temperatures, etc. etc. etc...... none of these are good reasons to "love" the 470.

The "high power" versions put out 190hp, at the crank, which is roughly 160 at the prop. 155hp at the propshaft is the low end on a 4.3, they are capable of up to about 230hp before you start to sacrifice durability. Thye only weigh a little bit more, are of a conventional design and parts are readily available. The SBC's weigh 100lbs more than the v6 with power potential upt to about 300hp.

As for the closed cooling system, that is an option on any marine engine. It was, however, required on the 470's because of the aluminum block.

Do whatever you want, but your infatuation with this frankenstein engine is likely to cost you a small fortune trying to save your new love from extinction.

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

I have studied it quite a bit. Delco alt to take care if the stator charging system, make sure you have a 4" heat exchanger and not 3", steel sleeve on cam snout to fix groove if there IS one (most have one) and prestones coolant lube to help the cam coolant seal stay lubed.

V6 or other I would have less interior room, more gas useage, $800 plus to get a closed cooling system for it, more weight (has to be at least 100lbs more), more HP = more gas used per rpm .....

They both have thier pro's and cons. Since I have the engines, like i said, finding a boat with a blown setup would be my cheapest option. I have $1500 to drop on a boat if I want, but, if I dont have to, why would I want to?

 

[droptheline]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

they didnt put the closed coolant system for no reason. do some research on that motor my friend, and run with what little money you sell the whole package for and get an inline 6 or v-8 steel block, if you want to stay on the water versus the trailer in the long run for the least money, this is the way. believe me, alot of us learn the hard way!

 

[45Auto]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

All excellent reasons to keep producing the 470 - oops, wonder why they discontinued them ..............

 

[Bondo]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

I would rather it be the V8 outdrive than the V6 out drive i just rebuilt.

Ayuh,... I Agree that using the 470 is just plain ole NUTS....
But,...
If you Do,...
The differences in the outdrives is in the Upper Units,.... The Lower units are the Same...
So,...
Use the V6 Upper unit to get Closer to the gear ratio you need...
Then you can Wack either, or Both lower units before you need to buy another 1...

 

[180shabah]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Well it certainly sounds like you really understand the shortcomings of that engine. If you are still comfortable proceding, then I say go for it. You are definately in the right place for assistance along the way.

Couple quick things, make sure that the "delco alternator" is marine rated and not the $30 special.

More hp does NOT equal more fuel consumed. It only has the potential to use more fuel. Any boat with the same load, in the same conditions will require a "set" amount of power to achieve a certain speed. It doesn's matter if that power is prodeced by a 4cyl at 4300RPM, a v6 at 3500RPM or a v8 at 2800 RPM. The difference in fuel consumption at a set speed will not be noticable. There are variables that I do not account for, like the weight difference between engines, engine efficiency at the different RPMs required to reach our set speed above, etc.... Without a flowscan (which ain't cheap) you will not see the difference. Higher available power WILL equate to higher possible top speed(doesn't mean you have to go that fast, but is available of you need it), faster planing time, especially as the load is increased (either onboard or towed) and better speed control when in "rough water" trying to maintain minimum planing speed.

Don't know wherre you are located, but budget boats in Chesapeake, VA always some project boats. Even has a couple of 470 powered ones that he ahs been sitting on for 3-4 years. Probably willing to deal at this point. Check thier website, and remember if it has engine/drive in it, they may be willing to seperate and sell the hull only.

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Thanks shaba, thats the answers i need. I know i dont have the best made engine around, but, I have enough of them that I could easily get through a summer if any and or all problems arise. All the haters probably just got big repair bills that left bad tastes in thier mouth for the 470. I belive it was a GREAT concept but they did not have head gasket technology back then and or much experience with aluminum blocks. A lot of the honda engines have/had open decks like the 470 and push blowers on them. they also used matching aluminum (for thermal expantion compatability at the least) heads. Now, if the 470 just had a slightly better water pump design.... I was even thinking of using an external pump off of the crank but I am just not in the mood to get too exotic right now, maybe in the winter?

 

[180shabah]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Good luck, and keep us posted on your progress.

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Bondo:
Swapping lower units is an option....


Are you sure about that 180shabah? You ever looked at the cars at the lots with the stickers? The 4-6-8 cylinders all have differant MPG. Now, albiet thats a car and were talking boats, not sure if it is the same apples to apples.

Still, no one answered my question, lol. could I use a v-8 drive on a 4cyl engine with a small prop? If so, what prop pitch and diameter should I use not to load my engine any more than the v-6 drive, and, what kind of performance (loosly put) should I expect?

 

[Bondo]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

could I use a v-8 drive on a 4cyl engine with a small prop? If so, what prop pitch and diameter should I use not to load my engine any more than the v-6 drive, and, what kind of performance (loosly put) should I expect?

Ayuh,... My Guess is,... You'll need a 9" or maybe an 11" pitch prop...

 

[45Auto]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

All you have to do is change prop sizes by the ratio of the drives. For instance, if the V8 upper is a 1.47 Alpha, and you're going to put it on a 4 cylinder that originally had a 1.94 Alpha, then you have to change the prop pitch as follows:

Original 4 cylinder prop pitch x new drive ratio/old drive ratio = new prop pitch

For example

19" original x 1.47/1.94 = 14.39" new pitch (easiest to find a 15" pitch prop)

Reason this works:
Original setup - motor drives the boat 19"/1.94 = 9.8" per engine revolution
New setup - motor drives the boat 15"/1.47 = 10.2" per engine revolution

(10.2 - 9.8)/9.8 = .04

Means new gearing and prop is 4% higher than original setup.

Since we used a 15" instead of a 14.39" pitch, it is now the same as the original 1.94 drive with a 19" x 1.04 = 19.76" pitch. In other words, so close you won't see any difference.

I have a 16' Mark Twain with a 2.5L (120) that was given to me. Upper half of the sterndrive (Mercruiser #1) crapped out. The original upper had 1.98 gears and a 19" prop. I replaced it with a 1.50 geared upper off Ebay for $27.

So I needed a 19" x 1.98/1.50 = 14.39" new prop pitch, just like you will.

I replaced the original aluminum 19" prop with a stainless 15" prop off Craigslist for $50. The boat runs just like it always did, you can't tell any difference.

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Thats awsome, thats exactly what I need, thank you soooo much, I owe you a beer or two.

 

[Bondo]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Ayuh,... I ain't gonna argue your math,...
But,...
I'm telling ya,.. It Don't work that way in the water,... Been there,.. Done that...

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

Care to enlighten me on some tweaks needed to add to the formula to make it work for curiosity sake? I will end up seeling the V-8 drive anyways more than likely, but, in case i just want to throw it on the boat and go, would be nice to know.

You also say "been there done that". What were your results?

 

[slasmith1]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

that is the math if your boat runs in a test tank. However in the real world it doesn't account for the reduced surface area of the prop and higher speed of the prop, both of which will increase cavitation and slippage.

 

[Bondo]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

You also say "been there done that". What were your results?

Ayuh,...

I put a 1.50:1 drive on a Good runnin' 140hp,....
The Smallest prop you can buy that fits the drive is a 15" pitch....
With it,.. 2800rpms was Tops...
Sooo,...
I took a jigsaw,+ trimmed a Full Inch off the ends of the blades,.... Still 2800rpms....
When I put the Right drive on,.. Everything was back to Normal,.. 4600rpms...

The Math above doesn't take into account available Horsepower, nor Torque available....

Do whatever you Want,.... But that won't work....

 

[sikpupy]

Re: V8 Merc outdrive on a 4cyl boat, time to experiment - opinions..

You took a jigsaw to the blades????? Man, even "I" would not do that to experiment, i would have just given up!

Cool, thats why i ask and ask. I never know what stories I will discover. It beats me wasting time and what not, plus, I get to see said results of finished tests, lol. I am always intrested in test results instead of "naaa, cant be done" comments. Call me a stickler or whatever.....