Power of 2 Stroke v 4 Stroke?

SHRDLU

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Oct 31, 2002
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Re: Power of 2 Stroke v 4 Stroke?

This may add to the conversation. In general, internal combustion engines tend to be more efficient, on a specific basis (fuel consumption/power), when operating at or near their highest power setting. So, if you need 100 hp to cruise your boat under certain conditions, you will get better mileage if you use the smallest engine that will give you the 100 hp. If you have a 200 hp engine throttled back to produce 100 hp, economy will suffer.<br /><br />Now I have a question. Supposedly conventional 2-stroke engines built before 2006 will be grandfathered after that date. Only new engines will be required to meet the 2006 spec after that date. Should I trust the government? If I buy a new conventional 2-stroker now, am I absolutely guaranteed that the government will not outlaw it eventually?
 

JB

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Re: Power of 2 Stroke v 4 Stroke?

EDIT: I have deleted one post that was insulting and added nothing to the discussion.<br /><br />If there are further insults I will close this thread.
 

MIKE F

Petty Officer 1st Class
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Aug 30, 2001
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313
Re: Power of 2 Stroke v 4 Stroke?

JB,<br />When did you become a moderator? Congratulations I guess. :D <br />Going back to what AUGIDAWG said earlier, about the twin engine boat, with a Bomb and a Yamaha, I heard ( I believe from the Dusky people) that Bomb did that at last years Miami boat show. I forget if it was 2S against 4S or 2S against 2S but Bomb was doing that. Somehow Yamaha got them to stop that demo real quick though. ;)
 

blue.monkey

Seaman Apprentice
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May 22, 2002
Messages
34
Re: Power of 2 Stroke v 4 Stroke?

Going back to the original question,... at 6 dollars a gallon I would get a four stroke, just for the satisfaction of not lining somebody's pocket with tax dollars.
 

sloopy

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Jul 12, 2002
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2,999
Re: Power of 2 Stroke v 4 Stroke?

OK YIKES THIS IS BIG!!! <br /><br />Ok now....<br /><br />2 strokes fire very time the piston is near the top.<br /><br />4 strkes fire every other becuase it needs one stroke to push the exhust gasses out (it makes you wonder why its not called 1 stroke and 2 stroke) <br /><br />THAT extra stroke on the four stroke is it's tougre weekness.<br /><br />On the story about that 4 strokes can not get a boat on plane when side by side, is untrue, this is a boat with a prop that can slip, you can just rev up that way, then it will kick in. if you want a constant torque (notice that I spelled it right that time) look at some Jet turbine engines, in those engines as the RPM increases so does the torque..<br /><br />also most engines are geared and torque is useless, in calculation, also unless full torge of a two stroke is at full rpm, the four stroke can still get on plane just at a higher rpm...<br /><br />did I make myself cleare?
 

Forktail

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Re: Power of 2 Stroke v 4 Stroke?

Comparing outboards, either HP vs. HP or 2-stroke vs. 4 stroke, is almost impossible. No matter what type of comparisons are made, it's never apples to apples.<br /><br />First of all, outboards are sold based on a rated maximum power output. Not power output at idle, troll, or 3/4 throttle. Not power under the load of your particular boat. Not power trimmed, jack plated, or proped. Just max power.<br /><br />More importantly, HP is really a "false" measurement. HP is only a true function of torque and rpm, and it can only be measured by that torque and rpm. <br /><br />When torque and rpm are plotted on a curve, the area under the curve is called "work". So although some outboards may have equal HP in comparison, they will do different work. An outboard with a broad torque ranging over a large rpm band will do the most work. In fact a lower HP outboard may do more work than a higher HP outboard becasue it makes more torque over the entire rpm range.<br /><br />With that said, outboards of exact HP can have totally different torque outputs and operating rpm. For example a 225 HP 2-stroke may make its maximum torque in a very narrow band of rpm. Sure, it has the 225 HP, but only in a specialized area that we might want to use for racing, and not cruising or trolling. A 225 HP 4-stroke may make its maximum torque at a lower and wider band of rpm. This may not be a racing motor, but a very efficient cruiser or troller.<br /><br />Many other apples to oranges factors are involved in comparing outboards....<br /><br />Engine design. V-designs operate much different than I-designs. Although they may put out the same HP, I-designs usually run greater low end torque and lower operating rpm.<br /><br />Compression. Smaller displacement, higher compression engines may make similar HP to larger displacement and lower compression outboards.<br /><br />Operating RPM.<br /><br />Displacement.<br /><br />Fuel intake induction.<br /><br />Weight.<br /><br />Propping.<br /><br />And a biggy that everyone seems to ignore.....gear ratios!<br /><br />So identical HP ratings can mean totally different outboards. <br /><br />Lets not forget that inboards are 4-strokes. There is no way a 250 HP 2-stroke outboard will push a heavy 26' fiberglass V-hull as well as a 250 HP 4-stroke diesel. Why? Because the diesel makes almost 3 times as much torque.<br /><br />If I needed max speed and light weight, and want to save a few $$ the 2-strokes are awesome. But I don't need those things as much as I need maximum, overall enjoyment from my outboards. That's why I have 4-strokes. My own experience with 4-strokes vs. 2-strokes leaves no questions asked. :)
 
D

DJ

Guest
Re: Power of 2 Stroke v 4 Stroke?

Yikes'! <br /><br />So many opinion's. :( <br /><br />I should have known better. Stupid me! :eek: <br /><br />Help me, NEVER AGAIN! :rolleyes:
 

JB

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Re: Power of 2 Stroke v 4 Stroke?

Help me out, DJohns.<br /><br />What did they say? :confused:
 
D

DJ

Guest
Re: Power of 2 Stroke v 4 Stroke?

JB,<br /><br />It will be a discussion that will NEVER end. (Re; Yamaha price-US vs. Australia.)<br /><br />I've got too many irons in the fire.<br /><br />To each, his own-"may the buyer beware".<br /><br />See ya, you won't hear until we solve the 320 electrical problem.
 

StormRunner

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Sep 10, 2002
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Re: Power of 2 Stroke v 4 Stroke?

Interesting information here about power differences. Thanks all.<br /><br />JB, exactly what didn't you understand? And who is the they you are referring to everyone but you and Djohns?<br /><br />Djohns, sorry for your attitude and the comparison between this thread and another. I don't see that.<br /><br />Id like to know more about power of these engines.
 

Hooty

Rear Admiral
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Oct 2, 2001
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Re: Power of 2 Stroke v 4 Stroke?

JB edits?<br /><br />c/6<br /><br />Hooty
 

vinney

Chief Petty Officer
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Oct 29, 2002
Messages
437
Re: Power of 2 Stroke v 4 Stroke?

JB Thread see Nothing to do with boats SEMPER FI
 

JB

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Re: Power of 2 Stroke v 4 Stroke?

Hi, Runner.<br /><br />I didn't understand what points Sloopy and Forktail were trying to make. I thought maybe DJohns did.<br /><br />I wasn't flaming anyone. If anyone took it as that, I apologize. :) <br /><br />Thanks for the heads-up Vinney. Got it. :)
 

Forktail

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Re: Power of 2 Stroke v 4 Stroke?

JB, my points were right along the same line as yours.....comparing power ratings, horsepower, torque, work, and all the variables to consider when making side to side comparisons between different outboards. Given what you had to say, I didn't think it was that hard to understand.<br /><br />I'll try again, clearing up any confusion. I just don't like to get too technical here, but at the same time I don't want others to be mislead.
 

Forktail

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Re: Power of 2 Stroke v 4 Stroke?

JB said, "The horsepower rating of an engine is the maximum amount of work it can do at it's top rpm."<br /><br />Not really JB. The horsepower rating is not based on "work" at rpm. HP is based on Torque at RPM, where HP = Torque X RPM / 5252 (a constant).<br /><br />Torque and Work are not the same. Torque is a property that can occur without factoring in time or movement. It is only until that Torque is actually moved that Work occurs. For example, you can apply a Torque to a lug nut wrench, but there is no Work done until the lug nut begins to move. Work an engine can perform is better understood as the area under the Torque vs. RPM curve.<br /><br />" So, a 70hp 4 stroke and a 70hp 2 stroke, each running at it's top rpm, are pretty much equal."<br /><br />This is only true in a sense of maximum measured HP, or one point of Torque at one point of speed (RPM). More realistically overall performance of an outboard is measured by the ability of the engine to do Work. This Work includes the entire RPM operating range and how Torque is managed throughout that range.<br /><br />"Dealer's wrenches are in the habit of telling you what the dealer wants you to hear. I seriously doubt most of what you were told, particularly his tale about Yamaha warning that the engine would be damaged."<br /><br />It's a known fact that outboard engine damage can occur if the engine is being operated and lugged continually below its functioning RPM operating range. If you are running twins and one engine fails, it is highly unlikely the remaining single outboard can function at its normal operating range without lugging. Thus the suggestion to run throttled back. I would heed to the dealer's suggestion and the owner's manual.<br /><br />" Horsepopwer vs. torque curves vary greatly from engine to engine. In a 2 stroke, port timing and exhaust tuning make a big difference, as do cam profiles in a 4 stroke."<br /><br />This is why it is virtually impossible to compare engines. The variables are too many, right on down to propping and gear ratios. But this does bring out a good point in that 2-strokes do generally produce a more erratic and peaky Torque/HP curve. In order to obtain a flatter and more desirable curve on a 2-stroke, things like intakes, tuned exhausts, timing, and carburetion are carefully calibrated to fill in these dips in the curve. But there is generally a drawback on performance somewhere else since the 2-stroke is more dependent on these factors. <br /><br />Djohns19 said, " Horsepower is horsepower, and torque is torque. The differences are where these numbers cross each other, on a graph, and how quickly each one of these build and remain constant."<br /><br />Torque and HP will never cross at different places on a graph or dyno chart. This holds true whether it is an outboard engine, a lawnmower, or a race car. Torque and HP will always cross each other on a graph (be equal) at or very near 5252 RPM. Physics doesn't lie. If you experience a dyno chart where Torque and HP do not cross at 5252 RPM or begin crossing at different places, the information is a fraud.<br /><br />Also, peak RPM is always shown later than peak Torque on the curve. The usable power band is found between this peak Torque and peak RPM. This is why a broad Torque curve over a wide range of RPM will provide the most Work, and the best overall performance, efficiency, and economy.<br /><br />" Their reasoning, as I was told, is because they had a displacement advantage over their competition and it helped them achieve a better holeshot "feel". This was particularly true of the crossflow V-4's over the comp's. in line 4's."<br /><br />Displacement has little to do with Torque and RPM. It is how that displacement is used and designed. Many smaller displacement engines create more torque and power. This can be due to things like higher compression, longer strokes, and intake/exhaust/timing differences. Inline blocks almost always have longer strokes and many have higher compression than the V's. Thus the good Torque. The 4-strokes turn me on because they run higher compression, have longer strokes, and run at higher RPM. All things that make the "Work" and performance of the outboard more pleasurable.<br /><br />Here's a fun example:<br /><br />Suzuki's 50 hp vs. 60 hp.<br /><br />50 hp = T X 6500 RPM/5252 = 40.4 ftlb Torque<br /><br />60 hp = T X 5300 RPM/5252 = 59.4 ftlb Torque<br /><br />16.6% HP increase, but an amazing 32% Torque increase at max RPM. Guess that's why the gear ratio's are 2.27:1 for the 50 hp and 2.42:1 for the 60.<br /><br />There's a lot involved in comparing outboards……
 

JB

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Re: Power of 2 Stroke v 4 Stroke?

Hmmmm.<br /><br />Let us revisit 8th grade physics.<br /><br />Work: The application of force over distance.<br /><br />Horsepower. 550 pounds moved 1 foot in one second. (Force, distance and time.)<br /><br />Torque: twisting force. Measured as an amount of force applied to a radius. ex: pound feet or Newton Meters.<br /><br />Both your definitions and mine express these values accurately but in different terms, they do not contradict one another.<br /><br />The statement I challenged was that the Yamaha manual advised against running in on one engine. I said nothing about whether an engine could be injured by abuse.<br /><br />You are looking too hard for "yeah, but" (YABUT), Forktail. <br /><br />You, DJohns and I have said essentially the same thing: Any generalization about types and classes of engines will be incorrect most of the time. We have each explained why, but from different angles.<br /><br />I was confused by the tone of your post, which seemed argumentive. I didn't understand what you were arguing about.<br /><br />Are you comfortable now? :)
 

Forktail

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Re: Power of 2 Stroke v 4 Stroke?

No, not comfortable JB. <br /><br />I've always respected you here JB, but there was no argument in my response to ChrisE's original question, and I'm offended that you posted that there was. I tried to make my post as informative and unbiased as I could, without stepping on toes. I fail to see where it was argumentative or where I argue. I didn't mean for anyone to interpret it that way, at least until you brought it up. At least until you and Djohn responded with sarcasm.<br /><br />Coming from an Engineer and someone who has dynoed many engines, my second post clarifies and better states any misconceptions about some of the information given here. I realize no member likes their information corrected, etc. But that is the beauty of many opinions and a public forum. <br /><br />I guess it's bothering me why at first you were confused and didn't understand my post, yet now you say we said basically the same thing from different angles. Seems contradictory. It bothers me that you deleted a post and threatened to close a thread for insults and lack of discussion (whatever that post said), but yet allow Djohns and yourself to do the same. I thought it was inappropriate to bring up the Aussie thread, etc. It also bothers me that you need to ask me if I'm comfortable. What does that mean? And whats up with "8th grade physics" and "YABUT's"?<br /><br />How about we all get along and quit the childish games and repeated apologies (damage control)? This is a good thread with good information.<br /><br />With that out of the way, please simply understand the following....<br /><br />"Torque" is used when measuring HP from a rotating object, such as a crankshaft or propshaft on an outboard. "Work" is not. <br /><br />Torque is the force that produces rotation. Work is not. <br /><br />Work can not take into consideration a force over a radius, only Torque can. <br /><br />Torque, unlike Work, may exist even though no movement (distance and time) occurs. <br /><br />And finally, Torque is the correct and accepted property used when measuring HP in engines. We commonly call it "full load motor Torque", or "breaking Torque". <br /><br />Again, HP in rotating objects equals Torque times RPM divided by a constant 5252. Work can be used in finding the HP in non-rotating objects or non-outboard applications. <br /><br />Work is represented by the area under the Torque/RPM curve, from zero RPM and zero Torque to throughout the entire operating range. <br /><br />Hope this helps people here understand HP in their outboard a little better. It would be great if manufacturers would give us the Torque/RPM curve for our outboards. We could taylor fit our purchase for our particular need or use. Maximum HP ratings mean little other than how much power the engine puts out at a single point in the RPM range. I run my outboards throughout the entire RPM range, sometimes needing the most power down low, if I'm in a rough sea.
 

vinney

Chief Petty Officer
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Oct 29, 2002
Messages
437
Re: Power of 2 Stroke v 4 Stroke?

IM AN ENGINEER BY TRADE BUT MAKE MY LIVING IN THE BOAT BUSINESS. I LOOK AT EVERYTHING FROM AN ENGINEERING POINT OF VIEW. I WONDER WHY EVERYONE DOESNT LOOK AT THING THAT WAY. LOOK FOR THE CLUES. AS FOR JB WHY IS HE IN THE MIDDLE OF EVERYONE THOUGHTS. SIT BACK AND CHILL.WE DONT NEED ANY HAND HOLDING HERE. THERE OTHER FORUMS FOR THAT. SEMPER-FI
 

JB

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Re: Power of 2 Stroke v 4 Stroke?

Hmmm. It seems we both feel we have been contradicted, yet neither of us seems to believe we have contradicted the other.<br /><br />I don't think either of us intended to contradict, merely to have our point of view respected.<br /><br />The post I deleted said nothing about the subject of this thread, but included name calling. That sort of post will not be of any value to anyone and will be deleted.<br /><br />Now. This post, and your latest, do not deal with Chris' question, but our egos. If you feel it is necessary to continue, please don't clutter up the thread. Email me. jbshideout@aol.com.
 

Jacques321

Petty Officer 2nd Class
Joined
Jul 23, 2001
Messages
129
Re: Power of 2 Stroke v 4 Stroke?

Vinney, I disagree that 4 strokes need more maintenance. Prove it ?<br /><br />I think the general consensus is that the 2 strokes DFI offer slightly better hole shot,but regardless the strange thing is people are still lining up to buy 4 strokes for all sorts of good reasons.<br />More moving parts doesn't automatically mean more maintenance, I think that's irrelevant.<br />And most of us don't work for the DEA or Immigration or drive expensive fountain/Baja boats so that's why most people are adopting the clean, reliable quiet 4-stroke. In fact consumers are demanding them based on their great reputation.
 
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