Why does anyone care to talk about the torque of a four stroke motor versus the torque of a two stroke motor? It is totaling meaningless without a transmission, the prop design and rpm of it is what will develope thrust and what is making it turn makes no difference. If 20 (thrust, same as lifting 33000lb(x20) 1 foot in one minute, or pushing it) ) horse will break your transom then 20 horse will break your transom. Doesnt matter if it is 20 horses, 20 horse two stroke or 20 horse four stroke or a 20 horse steam engine. I can understand wheight being a concern but that is never what the topic is.
four stroke
- Thread starter tkarasch
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I have not studied this situation in a while...however when I did it seemed that the torque on a 4 stroke 9.9HP was much greater than the torque on a 2 stroke 9.9HP.
The difference seemed to be enough to tear the motor clean off a boat if brought up to speed really fast.
Jack
The difference seemed to be enough to tear the motor clean off a boat if brought up to speed really fast.
Jack
HP vs torque
HP is Ft-lb/sec,or the units of POWER
torque is ft-lb, or the units of WORK
There is a very significant difference between the two. Mathematically I can get a VERY high power but if I only apply it for a short time it "does almost no work" The idea of a MW laser for a microsecond (high power) vs a come-a-long (high torque). Which one do you think is more likely to burn/pull the transom off the boat.
Another way I've heard it described is HP is a measure of the engine's ability to burn fuel while torque is a measure of the amount of intake air / cycle
To answer your question, apparently you and me.:dance:
HP is Ft-lb/sec,or the units of POWER
torque is ft-lb, or the units of WORK
There is a very significant difference between the two. Mathematically I can get a VERY high power but if I only apply it for a short time it "does almost no work" The idea of a MW laser for a microsecond (high power) vs a come-a-long (high torque). Which one do you think is more likely to burn/pull the transom off the boat.
Another way I've heard it described is HP is a measure of the engine's ability to burn fuel while torque is a measure of the amount of intake air / cycle
To answer your question, apparently you and me.:dance:
I used to have a go-kart. I had a 7hp 2-stroke and a 5hp 4-stroke engine to play with. I also had different sprokets to change the gearing. Several times I swapped these back and forth. The 4-stroke always gave me more pleasure just because it had more power sooner. The 2-stroke seemed like it made more power, but much higher in the rpm. For my cart, the 2-stroke would have been better with a gearbox. Also keep in mind this was years ago and the 2-stroke did not benefit from later exhaust technology. In the end I settled for the best of both, I put the Tillitson carb from the 2-stroke on a handmade intake manifold. That little Briggs would really go!
As far as boats go, I prefer 4-strokes in the marina. They are quieter than most 2-strokes, and they don't stink like most 2-strokes. However, I have the luxury of good gas. If I had to put up with the carb problems that many have posted about, I'd take the smell of a 2-stroke in a heartbeat.
Just my $.02
JerryA
As far as boats go, I prefer 4-strokes in the marina. They are quieter than most 2-strokes, and they don't stink like most 2-strokes. However, I have the luxury of good gas. If I had to put up with the carb problems that many have posted about, I'd take the smell of a 2-stroke in a heartbeat.
Just my $.02
JerryA
Four stroke motors will make more power/torque at lower RPM's that two stroke motors and do this with better fuel economy. Four stroke motors also have a wider powerband of useable power overall. Two stroke make their power in the higher RPM ranges and when geared with a system that keeps them in these higher RPM are quite hard to beat. Their drawbacks are fuel economy, noise and the smell of their burnt oil exhaust. They are also lighter in weight for their giver horsepower.
My main attraction to the four stroke motor was the lack of the burnt oil exhaust. I only use the motor when there is no wind and I hate having dirty exhaust all around the cockpit that comes with a 2 stroke motor.
Ray
My main attraction to the four stroke motor was the lack of the burnt oil exhaust. I only use the motor when there is no wind and I hate having dirty exhaust all around the cockpit that comes with a 2 stroke motor.
Ray
You carry less fuel with a 4 stroke than a 2. Although the 4 stroke is heaver than 2 stroke, the weight difference of the fuel is quite significant.
BTW why would you care if the 4 stroke is heavier. It is mounted on the transom. Fuel you have to find and lug on board.
BTW why would you care if the 4 stroke is heavier. It is mounted on the transom. Fuel you have to find and lug on board.
I like to use the comparison from the 2- Catalina-22's I've owned. My 1980 swing-keel C-22 had a Johnson 6 HP, 2- cylinder 2-stroke, hull speed took aprox. 3/4 throttle and the engine burned 3/4 gallon per hour. Our current C-22 wing keel MK-II with a 5 HP Honda pushes the boat to hull speed at just over half throttle, and motoring across to Catalina Island took aprox. 7 hours to cover the 33 miles and we used 1 3/4 gallons. So the same trip with our 2-stroke would have burned 5 1/4 gallons. The reduced noise and fuel consumption, and the lack of the pollution, personally, I would never go back, and the slight weight difference isn't enough to me. It's 4-strokes for me!
Don
Don
the newer 2-strokes with computer controlled direct fuel injection have gotten rid of many of the old problems smoke,inefficancy,narrow power band. my new nissan 50hp will run at 1500 rpm quietly all day burning just over 1/2 gph at 5kts. best part is starting,even after sitting 3 months it starts in less than 1/2 second every time.
Thing is, it is the shape of the torque curve that makes an engine feel “peaky” or not. Engines are rated for horsepower at a given RPM .. that rating says nothing about the operating rpm’s below the max.. The formula for Horsepower is:
Horsepower = RPM times Torque (ft pounds) divided by a constant, 5250 in this case.
So any 10 HP motor that is rated at, say, 7000 RPM will be generating 7.5 ft pounds of torque. Lets say you are running the engine at 4000, below max rated.. One engine may still be making say 6 ft pounds of torque which means that it would be capable of 4.6 hp at the lower speed.. the other engine might make only 4 foot pounds at 4000 rpm so it would be capable of only 3 hp at that RPM.. The torque curve is complex to manipulate in the design of an engine, and is a result of many factors like bore/stroke/displacement/ length of intake and exhaust runners, intake-exhaust timing, etc.. This is why engines with broad flatter torque curves feel more powerful.. because they can generate more power at lower RPM.. which may not be related to max power at all.. uuhhhhh never easy ..
Horsepower = RPM times Torque (ft pounds) divided by a constant, 5250 in this case.
So any 10 HP motor that is rated at, say, 7000 RPM will be generating 7.5 ft pounds of torque. Lets say you are running the engine at 4000, below max rated.. One engine may still be making say 6 ft pounds of torque which means that it would be capable of 4.6 hp at the lower speed.. the other engine might make only 4 foot pounds at 4000 rpm so it would be capable of only 3 hp at that RPM.. The torque curve is complex to manipulate in the design of an engine, and is a result of many factors like bore/stroke/displacement/ length of intake and exhaust runners, intake-exhaust timing, etc.. This is why engines with broad flatter torque curves feel more powerful.. because they can generate more power at lower RPM.. which may not be related to max power at all.. uuhhhhh never easy ..
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