4 stroke vs. 2 stroke weight and power

[work in progress]

I don't know much about boating but I have been asking a lot of questions. Conventional wisdom seems to be for smaller boats use 2 stroke motors because they are lighter, more powerful, and cheaper. I am setting up a Carolina Skiff j16 which has a max hp rating of 40, which is what I will be getting. Yamaha doesn't make anything in 2 stroke between 25hp and 50hp, so I checked on the 40hp ETEC. (237lbs, +/- $5000) I just found out Suzuki makes a 40hp 4 stroke that I can get for $4800 that only weighs 6 pounds more, 243lbs. There goes cheaper and lighter. As for more power per rated horsepower, this dealer says the Suzuki should be close to a 2 stroke because it is fuel injected. I'm inclined to think he is not feeding me a line, because he is a Yamaha dealer as well and point blank told me the 40hp Yamaha 4 stroke would not be nearly as strong as a 2 stroke. I'm trying to be sure I don't wind up with too much weight, too little power, or both. Can someone help me here before I spend $5000 on the WRONG motor for my boat.

 

[rickdb1boat]

Re: 4 stroke vs. 2 stroke weight and power

The Suzuki motors are strong runners. It may not be quite as quick as the etec, but it will be close. It depends on what you like, 2 or 4 stroke. If you do alot of trolling, then I would go with the 4-stroke. If absolute speed is nessesary, then get the etec. Since recently going from many years with 2 strokes to a 4 stroke now, I would have a hard time going back. But those that have the etec say they wouldn't give them up either..

 

[QC]

Re: 4 stroke vs. 2 stroke weight and power

Well I am gonna open up a can of worms here, but there is no such thing as more power per rated power . . . Power is power, and the rating system we use in the US is called horsepower. Either they rate them conservatively, so they are actually stronger than they label them orrrrrrrr they are referring to the better acceleration characteristics of some 2 cycles orrrrrrr they are referring to the better power to weight ratio of some 2 cycles orrrrr they are referring to the misconception that 2 cycles are more efficient than 4 cycles because they fire every time the piston comes up. The fact is that the ETEC maaaaay be more efficient in some applications due to lower weight, but generally speaking four cycles are more efficient and again, power is power. If you want better acceleration, that may favor some two cycles, but not all . . . Top speed comes from horsepower and that too is a fact.

Today, I would buy a two cycle, either an ETEC or and Optimax as I love the idea of no oil changes, and I want to play with something different than I have owned in every other vehicle and boat except a weed whacker.

 

[JB]

Re: 4 stroke vs. 2 stroke weight and power

There is a lot of yakking about etec and other 2 strokes being "stronger" than equally rated 4 strokes, as well as lighter, cheaper, cleaner, quieter, able to leap tall buildings in a single bound, etc., etc. That may be "conventional wisdom", but it is wrong.

The amount of work 1 HP can do is fixed by math. It cannot be "adjusted" according to what engine it is applied to.

The rest is also mythology. Two strokes seem to perform better because they make sexy (or annoying, depending on your point of view) noises. In many cases the carbed 2 strokes are cheaper and lighter than similarly rated EFI 4 strokes, but they are also noisier, thirstier, dirtier, etc.

Many of the etec claims have been pretty well proven mostly irrelevant or outright incorrect.

That said, the Suzi DF40 is a great engine. So is the etec 40. I don't see either as being "better", whatever the heck that means.

 

[Scaaty]

Re: 4 stroke vs. 2 stroke weight and power

2 strokes will simply put out more "power" per pound of motor...less parts, less weight..but HP is HP..

 

[JB]

Re: 4 stroke vs. 2 stroke weight and power

I suppose that is true if the 2 stroke is significantly lighter, Scaaty. In many cases (not all, of course) that is only true if the 2 stroke is carbed. Many of the newer EFI 4 strokes weigh in pretty close to their DFI 2 stroke competitors.

 

[steelespike]

Re: 4 stroke vs. 2 stroke weight and power

In my limited research on Etecs,and various 4 strokes It appears that while the 4 stroke gets a marginally better GPH wot speed is generally slightly less
usually producing slightly less MPG.The other thing I've noticed is generally the 4 stroke runs as much as 500 to 1,000 rpm.higher at wot.
Even though they are quality motors when you run a motor with 4 times as many parts like that your going to have higher wear.Or for that matter on any engine piston feet per mile dictates a certain amount of wear.

 

[SkeeterBro]

Re: 4 stroke vs. 2 stroke weight and power

I work for a marine dealer, in sales. I get the oppertunity to run the same hull with diffrent motor's pretty often. We are a Yamaha dealer, so most of my experience lies with the Yammy! I recently deliverd 2 -ZX190's, one powerd with a 2-stroke 150 V-Max (VZ150TLR) and the other with a 4-stroke 150 (F-150TLR.) Both boats equipped and set up exactly the same. After demoing both boats (in the same day, same conditions) I found the 2-stroke VZ model had better performance in both hole shot and top end speed. Also better accelaration once on plane. If my memory serves me, i belive top end speed was 6mph higher on the 2-stroke. I know a prop change would help the 4-stroke get a better hole shot, but at the same time reduce top end speed.

Anyway, that's my story, and I'm sticking to it!

I think this 4-stroke vs. 2-stroke argument will continue unresolved untill the EPA shuts down 2-stroke production completly.

 

[JB]

Re: 4 stroke vs. 2 stroke weight and power

I think that is unlikely, Skeeterbro. DFI 2 strokes, and particularly the etec, are very competitive with EFI 4 strokes in emissions, which is what the EPA cares about.

Now, when and if direct injected 4 strokes and clean diesels show up in the market that may become a different story. Mercedes Benz has developed a new 4 stroke technology that they call a "DiesOtto" that runs both Diesel and Otto cycle, delivers Diesel-like torque and efficiency but starts and cruises on spark ignition. The twin turbo 1.8 liter example in the Frankfurt auto show delivers several hundred foot pounds of torque and well over 200HP.

 

[steelespike]

Re: 4 stroke vs. 2 stroke weight and power

I thought Otto cycle simply refered to a 4 stroke design.
Diesels can be either 2 stroke or 4 stroke.Are they running a 2 stroke diesel
and 4 stroke gas in trhe same motor?

 

[SkeeterBro]

Re: 4 stroke vs. 2 stroke weight and power

I belive you are rite on that JB. I don't see the DFI 2-strokes going away anytime soon. I think I have been conditioned to speak of 2-stroke technology as a passing thing. 90% of the customers I speak with on a daily basis are convinced that 2-stroke outboards will be outlawed by the year 2010!

 

[QC]

Re: 4 stroke vs. 2 stroke weight and power

Otto is spark-ignited, four stroke. Diesel is diesel . . .

 

[Scaaty]

Re: 4 stroke vs. 2 stroke weight and power

I suppose that is true if the 2 stroke is significantly lighter, Scaaty. In many cases (not all, of course) that is only true if the 2 stroke is carbed. Many of the newer EFI 4 strokes weigh in pretty close to their DFI 2 stroke competitors.

Yeah, thinking old (thats all I own..light 2 strokes). Last time I set foot in a dealer I was simply amazed at what a 4 stroke 10hp looked like...about the size and weight of an older 25hp! (of course the old 25 probably put out less than that anyway...)

 

[JB]

Re: 4 stroke vs. 2 stroke weight and power

Actually, what makes an engine an Otto cycle engine is intake-compression-combustion-exhaust with a spark igniting the combustion. That makes modern 2 strokes either Otto cycle or Diesel (compression ignition) cycle, just like the 4 strokes.

 

[QC]

Re: 4 stroke vs. 2 stroke weight and power

OK, I just did some further research as JB's contention had me thinking . . . Anyway, Otto (the man) very clearly worked on and kinda invented (1876)the four stroke cycle with spark ignition. Some guy I had not previously heard of, Dugald Clark invented the two stroke cycle in 1880. Rudolph Diesel invented the compression ignition engine in 1898. I cannot find anything that separates or identifies an inventor of the two stroke diesel . . .

 

[JB]

Re: 4 stroke vs. 2 stroke weight and power

Lots of adapting in modern engines. I think Diesel deserves credit for fuel injection, or at least direct fuel injection. Mercedes Benz first used it in spark ignition engines during WWII (BF109) and in the 300SL in 1953. I think Orbital was the first to direct inject a 2 stroke in the 50s. They broke a lot. Ficht might have been the first one to make it work in a production engine. Well, they put it in production engines;whether they worked is open to argument.

Now, MB's DiesOtto has "variable compression" and switches back and forth between spark and compression ignition depending on "engine demands", whatever that means. BTW, I also think that the DiesOtto uses two turbos in series, what I would call compound turbocharging. Maybe that is how they vary the "compression", by varying boost. Must be one danged sturdy little engine to make over 100ft/lb per liter.

 

[pine island fred]

Re: 4 stroke vs. 2 stroke weight and power

My experience only. 18 ft. ctr cnsl I hung a 115 yamaha 4 stroke. Am happy with the motor but wish I had gotten a 2 stroke of slightly lower hp. To much weight ! FRED

 

[Silvertip]

Re: 4 stroke vs. 2 stroke weight and power

The following post may help you or confuse you more than you already are.

http://forums.iboats.com/showthread.php?t=219751&highlight=Fuel+economy+study

 

[ron7000]

Re: 4 stroke vs. 2 stroke weight and power

Yamaha doesn't make anything in 2 stroke between 25hp and 50hp

um,

http://www.yamaha-motor.com/outboard/products/subcathome/11/home.aspx

--> http://www.yamaha-motor.com/outboard/products/subcatspecs/10/specs.aspx

I bought a 25hp 2-stroke last year. Go to a yamaha dealer and tell them to order you one. They probably won't have anything in 2-stroke on display because of the 4-stroke push, at least my dealer didn't.
portables are 2-25hp, midrange 50-90hp, hi-power 100-150hp.

if your planning on dropping cash on a brand new outboard, figure out what the max weight your skiff can handle on the rear with yourself standing back there then choose an outboard based on weight. That's all that really matters. The max hp rating is gay, especially with the extra weight 4-strokes are now in that outboard power range. I bought a 25hp yamaha, weights 106 lbs, the comparable 15hp 4-strokes which is my raft's max weigh 111 lbs on up. My neighbor got a 15hp 4-stroke evinrude for his 10-12' raft and wishes he went 2-stroke because of the extra weight and lack of low-end power. 2-stroke I think cost less than a comparable 4-stroke, it did when I bought my 25, vs 15hp 4stroke. I would certainly shop around and compare prices, power ratings, and weights. And if you're smart you will also look at displacement ratings to back up some of the advertised power ratings, especially between brands. I'm really happy i got my 2-stroke 25, it's very simple and very easy to work on and maintain. I think you should get a yamaha 70hp, or if you can get some ballast up front then get the 90hp.

yam 50hp 189 lb
yam 70hp 228 lb
yam 90hp 261 lb
yam 115hp 328 lb

merc 40efi 4-stroke 216 lb (jet drive = 267 lb)
merc 50efi 4-stroke 247 lb
merc 60efi 4-stroke 247 lb

once you get the yamaha and break it in, get a turbo prop

 

[Redneck]

Re: 4 stroke vs. 2 stroke weight and power

I have a 40hp 4 stroke Yammy, 2000 model. Slow out of the hole yes. I have it on a tunnel hull, and have a 3 blade SS prop from Propco coming tomorrow to try for an improved hole shot and to increase RPM. They say I am over propped right now, with a 10.5 X 12 stiletto SS getting 5400rpms.. I am going to a 12 X 10. It will be interesting to see what happens.

I love the quiet, starts easily, great gas mileage. Hate the carbs, as they will get stuck with the least little water or trash, and it's off to a cleaning. I have learned to watch the gas situation closely.

Top end is fine, about 27 mph by gps with 2 men and a load, on a Scandy White aluminum tunnel hull. It's a heavy hull, about 750lbs dry. Motor weighs about 200lbs with T and T.

I hope to increase top end a little and get better hole shot. I will post the results soon.