In a number of places I’ve read references to 4 stroke engines being more powerful than 2 stroke. I thought that 2 stroke engines were more powerful but less fuel efficient. Might people have said this because 4 stroke engines typically have more cylinders?
As for as powerful… one more than the other… I would say that is in the HP rating.
I just bought a new fishing boat with a 60 HP, 4 stroke EFI, 4 cyl Mercury. I love it, sooo quite, smooth and sooo fuel efficient! I have a 80 HP, 2 stroke, 3 cyl Yamaha on a party barge that has been a great motor but no one can talk/hear while it’s running… also it drinks gas/oil!
Also last year bought a new Bombardier ATV with a 4 stroke, love it!
I think 2 stroke motors will soon be a thing of the past. For sure in boat motors for they soon will not be sold in the USA.
IIRC its a HP Vs torque thing.
2 stroke gives more horses per cube because each cylinder is getting used twice as often - but the power-band is really limited because the whole induction and scavenging process only works properly at one particular speed.
It’s a power to weight thing. A 2 stroke is generally much more powerful for its weight when compared to a 4 stroke. The power band is usually at a higher rpm as well. Most applications seem to be heading towards 4 strokes, but I think it will be a long time before you find them on something like a chain saw or a weed trimmer.
From here: http://science.howstuffworks.com/two-stroke1.htm
“Two-stroke engines also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination of light weight and twice the power gives two-stroke engines a great power-to-weight ratio compared to many four-stroke engine designs.”
Disadvantages of two-strokes listed here: http://science.howstuffworks.com/two-stroke6.htm
This brings up another question:
What are the main variables that contribute to “where the power is” within a range of rpms?
A simple question that takes an entire semester to explain it properly. Essentially, most rpm-dependence of bmep is directly a result of how the volumetric flow works going into and exiting the combustion chamber. This is one reason why peak torque on an NA car is typically at a much lower rpm than the peak power - volumetric efficiency generall decreases as the rpms increase. And as the curve of volumetric efficiency falls off as rpms increase, there comes a point at which an increase in rpms does not yield an increase in horsepower.
A long time ago I posted a giant post on this, but can’t search for it.
Another issue w/ 4 stroke is they don’t like to run inverted due to the oil pump and sump. 2 stroke doesn’t really care. Not a big issue with outboards, and for that matter weed trimmers, but chainsaws and the like might be run at any angle, and still favor AFAIK 2 stroke.