Kaptain Krunch
Pro Junk Collector
Re-Read his post, he said torque is what you really want to know, meaning HP really doesn't matter as much as people think, its just a number to help people understand power.
cc to HP
- Thread starter fowler
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Re-Read his post, he said torque is what you really want to know, meaning HP really doesn't matter as much as people think, its just a number to help people understand power.
devino246
Official DIYGK Chem Nerd
my mistakeRotore
Teh SPIK
how?
Kaptain Krunch
Pro Junk Collector
gear it down.
Kenny_McCormic
Kartless....
Displacement and power have almost nothing in common.
This is a 5hp engine, makes just as much power as a Briggs flathead.
http://www.youtube.com/watch?v=2nGCxJPsXY4
Here we have a 25hp gasoline engine bigger than the lawn mower you typically see a modern 25hp installed in!
http://www.youtube.com/watch?v=k_yev9fqUzo&feature=related
This is a 5hp engine, makes just as much power as a Briggs flathead.
http://www.youtube.com/watch?v=2nGCxJPsXY4
Here we have a 25hp gasoline engine bigger than the lawn mower you typically see a modern 25hp installed in!
http://www.youtube.com/watch?v=k_yev9fqUzo&feature=related
How about a 5 HP Fun Power, 136212 series?
sideways
Unfinished projects king.
sideways
Unfinished projects king.
Horse power is torque over time. It is measure (calculation really) of how much power the engine has and how fast it can put it out.
The formula is, HP= (Torque * RPM) / 5252
So an engine with 1 ft*lbs of torque spinning at 5252 RPM will have 1 HP.
Displacement is loosely attached to HP, since displacement affects torque. More displacement the more torque you can achieve since torque in an engine is a function of pressure over the piston's travel. It's a complicated integral taking into account the pressure at ignition and the changing pressure as the piston moves down, increasing volume which decreases pressure. Typically, the more area your piston has and the longer crank travel you have, and the longer you can keep the connecting rod perpendicular to the crank shaft, the more torque you will have.
Horsepower is all about how much torque you can produce each power stroke, which is a function of initial volume, piston surface area, how far the piston will travel, and how much fuel you are burning, and how fast you can get your engine to produce power strokes. This is where motorcycle engines, especially crotch rockets, get their power from, they red line above 10k rpm usually.
This is in a perfect engine, engines are not perfect, and there are a lot of variables involved, more than I know about and can think of, that affect its performance. So the above is to be taken in a general sense, not as a gospel.
So, if you see a 150cc engine with more HP than a 300cc engine, the 150cc engine is probably capable of turning more RPM's than the 300cc engine. They are going to show the maximum horsepower attained in tests, and they will usually show you at what RPM this value was attained. The 300cc engine will produce more torque, but it won't be turning the shaft as quickly. If you got the 300cc engine and the 150cc engine spinning at the same RPM, the 300cc engine would likely be producing more horsepower, assuming no mods.
The formula is, HP= (Torque * RPM) / 5252
So an engine with 1 ft*lbs of torque spinning at 5252 RPM will have 1 HP.
Displacement is loosely attached to HP, since displacement affects torque. More displacement the more torque you can achieve since torque in an engine is a function of pressure over the piston's travel. It's a complicated integral taking into account the pressure at ignition and the changing pressure as the piston moves down, increasing volume which decreases pressure. Typically, the more area your piston has and the longer crank travel you have, and the longer you can keep the connecting rod perpendicular to the crank shaft, the more torque you will have.
Horsepower is all about how much torque you can produce each power stroke, which is a function of initial volume, piston surface area, how far the piston will travel, and how much fuel you are burning, and how fast you can get your engine to produce power strokes. This is where motorcycle engines, especially crotch rockets, get their power from, they red line above 10k rpm usually.
This is in a perfect engine, engines are not perfect, and there are a lot of variables involved, more than I know about and can think of, that affect its performance. So the above is to be taken in a general sense, not as a gospel.
So, if you see a 150cc engine with more HP than a 300cc engine, the 150cc engine is probably capable of turning more RPM's than the 300cc engine. They are going to show the maximum horsepower attained in tests, and they will usually show you at what RPM this value was attained. The 300cc engine will produce more torque, but it won't be turning the shaft as quickly. If you got the 300cc engine and the 150cc engine spinning at the same RPM, the 300cc engine would likely be producing more horsepower, assuming no mods.
Further, for those videos, imagine how much HP those things would have if they were turning a couple thousand rpm, instead of less than probably 150.
This is why a two stroke engine is superior (in terms of power) than a 4 stoke. A two stroke puts twice as many power strokes as a 4 stroke does in any given amount of time. A two stroke will have twice as much horsepower as a 4 stroke of same displacement, all else being equal.
This is why a two stroke engine is superior (in terms of power) than a 4 stoke. A two stroke puts twice as many power strokes as a 4 stroke does in any given amount of time. A two stroke will have twice as much horsepower as a 4 stroke of same displacement, all else being equal.
But naturaly a 4 stroke will have more tourqe then a 2 stroke of the same displacement....
I don't see why it should. Enlighten me.
fowler
New member
because a 2 storke is very unefient in using its power and a lot of the power is lost so although 4 stroke only has 1/2 as many power strokes each is a better use of the expansion
Oh I see. The two stroke would still be better unless it is so inefficient that the 4 stroke is able to produce twice as much power the 2 stroke produces.
Then there is also weight and complexity to consider. A two stroke is more light weight, less complex, and has fewer moving parts. I still think a 2 stroke engine is far better than a 4 stroke, all things considered. The only reason they aren't used as much is because of emissions, which is worse on a 2 stroke because of the burning oil.
modelengineer
Lord of the noise
A 2-stroke will generally have more torque than a similar 4-stroke at high rpm
yeah at a rpm that the 4 stroke can not reach and maintain reliably.. 4 strokes have the tourqe down low were its usefull.
Yes they can. Redlining your 4 stroke at say 7,000RPM is in "reality" 14,000RPM (in the 2 stroke world). It's a 4 stroke, so /2.
Two strokes are limited by the shape and port timing of their exhaust port. Very abrupt steep bumpy torque curve. Four strokes are extremely broad... great torque down low and up top.
Four strokes can make badass power up top... and still be reliable. Briggs and Clones were built to be reliable in their STOCK form. Obviously won't be very safe doing 6,000RPM on a stock rod and springs.
alright that does kinda make sence there i didnt think about that
modelengineer
Lord of the noise
No,
rpm doesn't measure how many times it fires, it measures how many revolutions the crank does. a 4-stroke spinning at 5,000rpm is going the same speed as a 2-stroke at 5,000rpm.
The 4-stroke however is only firing 2,500 times per minute, whereas the 2-stroke is firing 5,000 times per minute.
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