2 stroke vs a 4 stroke

[jimmbo]

Would that apply for 2-4 strokes OB's running same HP while both run at its max wot rpm range with maximized props ?

Happy Boating

no it means the 4 stroke doesn't have the same low rpm grunt/hole shot/torque. Top speeds will be similar, but the time it takes to get there will be different.

 

[JimS123]

Surely, there is a difference in the torque / rpm/ performance curves for 2-strokes vs. 4-strokes. Maybe if you try to repower an old hull (that was designed for a lighter 2-stroke) with a new heavy 4-stroke, performance for some applications will suffer.

However, in my experience the current generation of fiberglass boats that are designed for and come from the factory with a 4-stroke exhibit awesome performance.

 

[jimmbo]

That's the first I ever heard of hulls being made for new heavy 4 strokes. 4 strokes generally have a weight penalty, added to weaker low rpm torque, and it shows in their slower acceleration.

 

[Scott Danforth]

nothing sounds like a ported 2-stroke at full song while your doing 90

 

[82rude]

You don't say what your looking for ,1.5 hp to 400hp?A ll I can tell you is my experience with my 60hp etec.Less emissions than pretty well every 4 stroke,(see emissions tests online),no smoke,great fuel economy,starts in less than 3/4 of a turn of the flywheel.Change lowerunit oil every 3 years or 300 hrs.Super quite ,even compared to my friends merc 50hp 4 stroke (approx. the same).Uses very very little oil on xd100 setting .Very great low end power .If were totally honest theres very few people that don't think THEIR outboard is the greatest.Me included.Till april evinrude has a 10 year warranty promo.As for weight saving etec,s are fairly heavy,right up there with 4 strokes.But their heavily built also with my 60 having a large gearcase which for me meant all my 90hp evinrude props didn't go to waste,which was a big bonus.When I bought my motor there wasn't a etec dealer around in my country so I bought mine in the U.S.A at considerable savings.Now we have a dealer less than 3 miles away who,s more than happy to help if needed with no jealousy involved that I bought elsewhere.As a matter of fact my friend just bought a new 2018 skandic 900 (ace) snowmobile from them and he,s selling me a nice evinrude barstool for cost .With all my bragging done id like to say id own a 4 stroke if need be ,I think their great also.I came within a wisker of buying a merc 60 4 stroke but at the time the dealer gave me a much better deal and warranty on the etec and he sold both brands.Mine has been mistaken for a 4 stroke many times out on the lake and at the dock.Lots of people are shocked when I tell them its a 2 stroke.My oldest running 2 stroke outboard a a 1939 22.5 hp opposed twin evinrude.

 

[Sea Rider]

That's the first I ever heard of hulls being made for new heavy 4 strokes. 4 strokes generally have a weight penalty, added to weaker low rpm torque, and it shows in their slower acceleration.

My apologies for bothering you fine boaters with my issues, plainly understood about 4 strokers having less or poorer acceeration, but nobody said if acceleration bettered with a top prop maximization revving towards max wot rpm range. If you compare acceleration between say 2-2/4 strokes 100 HP-OB's with factory delivered props, the 2 strokes OB should have better acceleration.

Ideal would be to knnow if someone has been through this prop maximization experience to know if solved his slow acceleration and it if was a day/night acceleration difference.

Happy Boating

 

[82rude]

Sea Rider,for most applications and for most motors bar a very few exceptions.,propped perfectly a 2 stroke will have better lower end grunt vs a similar 4 stroke propped perfectly.Now lets throw gearing into the equation.Darn, now ive messed up everything again.

 

[jimmbo]

Now lets throw gearing into the equation.Darn, now ive messed up everything again.

I really wonder how much difference gearing makes, once prop dia, and pitch are factored in.

Some examples I know of:

In the 60s Mercury inline 6s(80 - 125hp) usually had 2:1 and spun 13 in dia props(usually 15 to 21 pitch) while OMCs V4(60 - 90hp) had 1.15:1(23:20) gears, and spun 10in dia props(9 1/4 to 12in pitch).

One would think the long legged gearing and tiny dia props of the OMCs V4s would make for high top speed, and the higher numerical gearing and large dia props of the Mercs would make for stump pulling torque, but in real useage, the Mercs were the speed demons and OMCs were the workhorse motors

Another would be Mercury's 50hp with 2:1 gearing and 10 1/2 dia props(averaging 10 to 12 in pitch) vs. OMC 50hp with 2.67:1 gears and a 13 dia props(averaging 13 to 17in pitch).

Edit: Similar for the Merc and OMC 49 in 3 cylinder engines. Merc used 1.87:1, or a 2:1 gears and the same props as the merc 50, while the OMC used 2.42:1 gears and the 13 in dia props like the OMC 50 and post 1968 V4s

Now lets throw bore and stroke, connecting rod length, and number of cylinders in to really mess it up

 

[JimS123]

That's the first I ever heard of hulls being made for new heavy 4 strokes. 4 strokes generally have a weight penalty, added to weaker low rpm torque, and it shows in their slower acceleration.

In the olden days OB boats came without a motor. You put on whatever you wanted, or whatever the dealer carried.

Then came the golden age of the I/O. Few OBs were available. (Now before you get your nickers in a twitter, we're talking about runabouts and such, not tincans fishing boats that have always been OBs.)

Currently, the availability of Outboard powered boats is soaring. A few years ago you saw none at the boat shows, now every manufacturer has models equipped with a big 4-stroke OB.

Seems to me they did some design homework, because these oldie newbies seem to perform just fine.

That's what I'm talking about...

 

[JimS123]

My apologies for bothering you fine boaters with my issues, plainly understood about 4 strokers having less or poorer acceeration, but nobody said if acceleration bettered with a top prop maximization revving towards max wot rpm range. If you compare acceleration between say 2-2/4 strokes 100 HP-OB's with factory delivered props, the 2 strokes OB should have better acceleration.

Ideal would be to knnow if someone has been through this prop maximization experience to know if solved his slow acceleration and it if was a day/night acceleration difference.

Happy Boating

This prop maximization thingy is what I've done on every boat I ever owned since 1968. So, I know what you're talking about.

Last year I bought a brand new Boston Whaler equipped with a 4-stroke, SS prop, yada, yada. The motor is raised a few notches on the transom...from the factory. The performance is optimum - just look at performace curves, RMP, speed, etc.

Boston Whaler did the hard work for me. It performs better than the 2-stroke that I traded in for her.

 

[82rude]

Ive recently applied lemon pledge to my 2 stroke and it slides through the water and air much more efficiently than a carnuba waxed 4 stroke :laugh: Seriously I'm really not sure exactly what the op is looking for.The only outboar (new) id stay away from would be over seas Chinese stuff all other are pretty well proven reliable products.To bad we cant get the 90hp 2 stroke Yamaha,s like the rest of the world.But that's another subject altogether.

 

[GA_Boater]

Seriously I'm really not sure exactly what the op is looking for.

It would nice if he answered the questions. All we're doing since he asked is dilly-dallying around the never answered "What is the meaning of life?"

 

[jimmbo]

Ive recently applied lemon pledge to my 2 stroke and it slides through the water and air much more efficiently than a carnuba waxed 4 stroke

You need to get some of that stuff they used to market on the Infomercials 30 yrs ago. Where they would 'treat' a car hood with it, set it on fire and WOW! the soot would wipe right off leaving a brilliant shine. The stuff was called AURI

 

[82rude]

Actually ,honest to god in my Polaris service manual it actually tells you to use spray on furniture polish on the plastic..Their useto be a wax years ago called Prism that you applied then washed off with a hose.Im so anal about that motor it most likely has a few hundred coats of wax and is being weighed down,lol.I hope the poor op wasn't scared away or so much info all at once his head exploded.:lol:

 

[jimmbo]

up to you. I personally love the smell of a two stroke running at full song.

Yes, the sweet aroma of burnt TCW, brings back some great memories

 

[QBhoy]

All the above interesting.
4 stroke efforts should be commended recently with weight saving. The truth is that they are coming ever closer to the weight of 2 strokes. But as of yet, they still can’t compare for pound for pound power.
My earlier point relates to older boats from the 70’s 80’s and even 90’s which are rated for a 2 stroke weight motor of a certain HP. When 4 strokes weren’t even a thing. In my opinion one should never put an equivelant HP 4 stroke of equal HP on the transom as a direct replacement. That would be chancing it !

 

[82rude]

For an example a 2018 2 stroke etec 60hp weighs 240 lbs,a merc 4 stroke 60 weighs an unheard of porky 247.Four strokes have been on jenny craig the last few years.The only concern I might have is how the weight savings were realized.Was any integrity sacrificed?I believe my concerns are most likely unfounded or so I would hope so anyways.

 

[thumbnut]

The plan is to make outboards not financially feasible to repair when they are used up. Stockholders do not like to have their investments in stuff shortcut by us fixing..buying new creates profits. Just look at the price on a simple valve guide for a 2.5hp yamaha..its all about the money.

 

[Sea Rider]

..buying new creates profits..its all about the money.

Now imagine a Yam 4 strokes 150 HP-OB selling for 21 grand.....

Happy Boating

 

[82rude]

2017 150 Yamaha, 13 grand right on iboats.