2 Stroke vs 4 Stroke Outboard motor mounts

[ebsail]

Originally Posted by coastalexplorer

Ebsail, Thank-you for your reference to Garelick, It seems like a recommendation?

Do you have the 71091 offshore model with a 15 1/2 " lift ?

Since I have a 25 degree raked transom I will have to make a wedge shaped transition to mount one, I have been considering making a foundry pattern and casting one in Aluminum.

Yup - I believe that's the model I have. I remember (I'm old) that the list price was around $400+ and the lift is either 14.5 or 15.5. I also had to cut a wedge, but I cut two wedges out of solid oak. One for each side of the bracket. Each wedge is 3.5" wide. I then epoxied the wedges and used butyl rubber under the wedges and bolts. For upper bolts, I used threaded rod as the lengths in bolts were hard to get in the two days I had available. Now as solid as a rock. A cast wedge would be even better, but make sure its thick enough not to bend or distort in any direction

[twelch1956]

Originally Posted by valhalla360

Assuming the same hp engine:

2 stroke has more torque particularly at low RPM where every other stroke being a power stroke makes a big difference. On engines with few cylinders it's also better at building up RPM, as you are getting that extra fuel converted to extra power quicker.

Once up to speed, assuming similar gear ratio and prop, torque will be similar as HP=torque*RPM

Agreed, turbo or super charged engines are whole different animals.

I agree, 2 strokes are usually much faster and run up the acceleration curve faster compared to the 4 stroke but, this can be offset by the stroke of the engine and number of cylinders. The reason four stroke engines vibrate is there is only one power stroke to four revolutions. In my opinion, horse power is horse power and weight is weight. Torque is what we are really dealing with here.

Just a bit of history! early engines were built with more cylinders in the auto industry to reduce the vibration. Usually the rich could afford the luxury of owning an automobile that did not vibrate so much say a 12 or 16 cylinder engine. Another device used to smooth out both types of engines is the flywheel. The problem became size and weight to eliminate vibration. Less vibration required a larger heaver wheel.

[Training Wheels]

[QUOTE=twelch1956;3201611The reason four stroke engines vibrate is there is only one power stroke to four revolutions. .[/QUOTE]


[emoji848] always thought 4 strokes had a power stroke every 2 revolutions.

[IslandInfedel]

2 stroke is for going fast and being loud

4 stroke is for everything else

For a dingy, Id go 4

[wingssail]

Originally Posted by a64pilot

Although it's been pretty much accepted that four stroke are heavier, that is changing, there are relatively light weight four strokes coming out now.

That is interesting. What new models of four stroke motors do yo know of which are size and weight competitive with two strokes?

[thomm225]

Four strokes are simply a better more efficient engine.

My old 2 strokes used to foul plugs regularly. With my 5 hp 4 stroke, I have changed the plug once in 9 years. I then saved the old plug because it looked fine.

And of course, the 4 strokes don't stink like a 2 stroke or blow oil into the water

[wingssail]

Originally Posted by thomm225

Four strokes are simply a better more efficient engine.

My old 2 strokes used to foul plugs regularly. With my 5 hp 4 stroke, I have changed the plug once in 9 years. I then saved the old plug because it looked fine.

And of course, the 4 strokes don't stink like a 2 stroke or blow oil into the water

Thomm225, What you say is undoubtedly true, but the four stroke engines have many more parts, are heavier, and many people I know think theirs are hard to keep running.

I have a 15hp Merc two stroke, which I love, it is light and small. It was made in Fond Du Lac, Wisc. I changed the plugs in it this July after 10 years since the last change (the motor is 20 years old). It runs better with new plugs, but it ran OK with the old ones also.

I've heard that new 4-strokes are coming out which are lighter and smaller. I wonder how they do it? I think A64 will tell us about it.

[Bill O]

Originally Posted by wingssail

That is interesting. What new models of four stroke motors do yo know of which are size and weight competitive with two strokes?

Suzuki came out w/some a few years back that were light weight, but were still a bit heavier than the 2 strokes.
Tohatsu more recently came out w/a 20 hp 4S that was ~2kg heavier (~43Kg) than the 18hp 2S. They reported the 18hp 2S to weigh 41 kg, but I've weighed mine and it's only 37kg.


In my book the 2S are still lighter, but are the new ones close enough/competitive weighing a few kg more?

[thomm225]

Originally Posted by wingssail

Thomm225, What you say is undoubtedly true, but the four stroke engines have many more parts, are heavier, and many people I know think theirs are hard to keep running.

I have a 15hp Merc two stroke, which I love, it is light and small. It was made in Fond Du Lac, Wisc. I changed the plugs in it this July after 10 years since the last change (the motor is 20 years old). It runs better with new plugs, but it ran OK with the old ones also.

I've heard that new 4-strokes are coming out which are lighter and smaller. I wonder how they do it? I think A64 will tell us about it.

Fair enough.

My 6 or so 2 strokes were all from late 1960's to early 1970's. I never owned a newer year 2 stroke.

I did though own a 4 stroke from the 1960's and was really impressed with how great it was on gas "mileage." I couldn't believe it actually.

It was this Homelite Bearcat .....just a little 4 cylinder, 4 stroke w/distributor cap, coil, etc. 55 hp. Like this one. All I had to do was replace the lower oil seal after I bought the boat it was on with trailer for $700.

https://www.youtube.com/watch?v=ccIDT7B3jHY

[wingssail]

Originally Posted by Bill O

Suzuki came out w/some a few years back that were light weight, but were still a bit heavier than the 2 strokes.
Tohatsu more recently came out w/a 20 hp 4S that was ~2kg heavier (~43Kg) than the 18hp 2S. They reported the 18hp 2S to weigh 41 kg, but I've weighed mine and it's only 37kg.

In my book the 2S are still lighter, but are the new ones close enough/competitive weighing a few kg more?

Tohotsu and Mercury both list the 15hp (and the 20hp) 4 stroke at 43-45 kg (91-95 lbs) They are 333cu. Displacement

The older Mercury 15hp two stroke listed in some countries is 35kg (77 lbs)
My old one (same motor) is 77 lbs, it is 262 displacement

That is 18 lbs diff, plus smaller.

They have reduced the weight by going to EFI, thus getting rid of the carb. plus they rev higher 6200 vs 6000

I appreciate the environmental benefit of 4 stroke motors, and they are quieter, but I love the simplicity of the 2 stroke, its smaller size and weight, and how well it fits on my dingy and the reliability.

[a64pilot]

Originally Posted by wingssail

That is interesting. What new models of four stroke motors do yo know of which are size and weight competitive with two strokes?

OK the venerable Yamaha 15 Enduro is considered by many to be the standard.
It weighs 87 lbs and that’s 5.8 lbs per HP
The Tohatsu 20 HP weighs 95 lbs and that’s 4.75 lbs per HP
The Suzuki 20 HP that I bought 6 years ago weighs 99 lbs 4.95 lbs per HP

Both the Suzuki and the Tohatsu make more power per lb of weight than the Yamaha Enduro 15, and I’m sure they burn much less fuel, and pollute much less too.

I sunk mine at Key West when a power boat passed me about 10’ away and his wake got me chine walking and threw me in. Motor came off the transom still running and went under, held by the fuel hose. I got it out and back into the dinghy and rowed to the boat, about an hour full of seawater. I flushed everything with fresh water, changed oil, go it running, but it ran poorly, changed plugs and it’s run fine since, changed oil several more times of course.

In six years it’s always run and all I have done other than changing lubricants and one impeller that didn’t need it, was those two plugs

[a64pilot]

God it’s been forever ago, but I was sponsored by Husqvarna of America and raced a WR250 Husky in hare scrambles in I guess it was 1974 or so, the Husky was about the best bike of its day. It weighed about 250 lbs if memory serves and made I think about 25 real HP or so.

My last dirt bike that I sold to go cruising was a 2008 TE-450 four stroke Husqvarna, it weighed 247 lbs, was electric start and street legal, meeting emissions etc. drop the cat convertor exhaust and weight was about 240 lbs and it made with the power up kit I believe 60 ish or so HP.
As much as I love old Husky, there was simply no comparison, the four stroke just made huge power, now it had four titanium valves and a complete titanium exhaust system etc. but power wise it was a monster.

Road Racing we called the four strokes Diesels, slow and heavy as Hell. That’s no longer true and hasn’t been likely for awhile.

Two strokes due to simplicity meaning inexpensive are good for chainsaws and a few other things, but that too will change, wait and see.

[wingssail]

Originally Posted by a64pilot

OK the venerable Yamaha 15 Enduro is considered by many to be the standard.
It weighs 87 lbs and that’s 5.8 lbs per HP
The Tohatsu 20 HP weighs 95 lbs and that’s 4.75 lbs per HP
The Suzuki 20 HP that I bought t years ago weighs 99 lbs 4.95 lbs per HP

Both the Suzuki and the Tohatsu make more power per lb of weight than the Yamaha Enduro 15, and I’m sure they burn much less fuel, and pollute much less too.

OK. Well my Merc 15hp two stroke weighs 77lbs and weighs 5.13lbs per HP so that ain't bad, (and I consider that to be THE standard).

I notice that the Tohatsu 15 HP 4 stroke is 95 lbs and weighs 6.33 lbs per HP

My previous motor, a Merc 25hp 2 stroke was 97 lbs and weighed 3.88 lbs per HP
The current Mercury/Tohatsu 25 HP 2 stroke is 105 lbs and weighs 4.2 lbs per HP

But bottom line, the new 4 stroke motors are better than they were when they first came out and improving. I reckon that in 10 years they might put out a 15hp 4 stroke which can match or beat my existing motor. They have not yet.

[MicHughV]

whoa.....I thought the whole move to 4 stroke outboards was to eliminate the gas/oil mixture required of 2 strokes...yes/no ??

This done to eliminate both air and water pollution caused by the oil mixture....yes/no ?

And..to obtain better fuel consumption....yes/no ??

Who can forget the clouds of blue smoke emanating from a 2 stroke?

The extra weight of a 4 stroke over a similar hp 2 stroke was really just all the additional bits and pieces.....valves, cams, etc, that a 2 stroke does not have, in addition to several quarts of oil now required inside the engine by a 4 stroke. It all begins to add up.

This is (was) particularly true of the earlier version 4 strokes as manufacturers basically took the existing architecture of their 2 stroke models and added the valve train components required for a 4 stroke.

Manufacturers have now fine tuned their 4 stroke engines a bit to bring them in line to the weights of the original 2 strokes.

It's just a work in progress at the moment considering the relatively short time the 4 strokes have been on the market......

Finally, there is the issue of the E10 gas mixtures sold today. Typically, marina's will sell non-ethanol fuel, but at a price. Non-ethanol fuel can also be found at some select gas stations, but many boater that launch their own boats often used regular gas, often with expensive repairs down the road.

It's not such a cut and dried thing......I have both 2 stroke and 4 stroke outboards in my outboard arsenal and like them both.

[a64pilot]

The 15 and 20 are the same motor as is common with two strokes also, so don’t take a top HP two stroke and try to compare it weight wise to a derated four stroke.
With the Suzuki even the 9.9 weighs 99 lbs, care to guess why?

But it’s really sort of irrelevant, unless you live in a Country that two strokes are sold legally, you can’t get parts for a newer one. Try it go to a US Yamaha dealer and ask them to hand you a piston for a 2020 Enduro. I bet they can’t even order parts.
So sure you can buy one when your in the Bahamas and bring it back, but good luck if it breaks and your not in the Bahamas.

The only advantage a two stroke used to have was weight, and that’s a big advantage, but it’s gone, and four strokes will continue to get lighter, but they start much easier, don’t smoke, are more reliable, can idle for hours, never foul plugs, and seem to last a long time.
They also use much less fuel, the little Zuki between 3 and 5000 RPM goes into “lean burn” where it doesn’t burn much fuel at all.