270 Engine? 360?
- Thread starter Easy13
- Start date
MuckSavage
Scooter
<hijack>
Someone explain to me what 360 degree means? 270 degree? I kind of get it, but not really.
Someone explain to me what 360 degree means? 270 degree? I kind of get it, but not really.
Primary differences:
- location of crankpin journals (next to each other on the 360, 90 degrees (270 degrees) apart on the 270 crank. Pistons rise and fall side by side on the 360. As (for example) the right piston is rising to fire, the left is rising on the exhaust stroke.
Here's a Photobucket version of a powerpoint. Unfortunately it only runs thru the four slides, and has to be manually rerun, but this should show you how the 360 works.
http://s115.photobucket.com/albums/n...view=slideshow
- cam lobe positions are different
- timing:
360 has power stroke every 360 degrees of crank rotation
270 fires at 270 degrees, then at 450 degrees, 270, 450, etc, etc.
360 sounds like traditional British vertical twin
270 sounds (to me) more like a Ducati or Moto Guzzi
- location of crankpin journals (next to each other on the 360, 90 degrees (270 degrees) apart on the 270 crank. Pistons rise and fall side by side on the 360. As (for example) the right piston is rising to fire, the left is rising on the exhaust stroke.
Here's a Photobucket version of a powerpoint. Unfortunately it only runs thru the four slides, and has to be manually rerun, but this should show you how the 360 works.
http://s115.photobucket.com/albums/n...view=slideshow
- cam lobe positions are different
- timing:
360 has power stroke every 360 degrees of crank rotation
270 fires at 270 degrees, then at 450 degrees, 270, 450, etc, etc.
360 sounds like traditional British vertical twin
270 sounds (to me) more like a Ducati or Moto Guzzi
BlueJ
Blue Haired Freak
It's referring to how far apart in the 4 stroke cycle the two pistons are when the spark plugs fire. You probably already know that one full 4 stroke cycle means that the piston goes up (compression stroke) then the spark fires and the piston goes down (combustion stroke) then up again (exhaust stroke) then down again (intake stroke).
If the interval was 0 degrees, that would mean that both pistons rise and fall at the same time, and the spark fires at the same time on each side. If it was 180 degrees, that would mean that while one piston was up, the other would be down, and that one would have it's combustion stroke while the other was having it's compression stroke (or exhaust stroke, depending on which direction the 180 degrees is measured).
With a 360 degree interval, they both rise and fall at the same time, but as they each come to the top, only one fires - while one is in combustion the other is in intake, then they switch.
With 270 degree, they don't rise and fall together -- when one is all the way up, the other is only one quarter of the way up.
I'm not up on the *whys* of the different patterns, but I know that one major impact is on the sound. With a 360 degree interval, one of the cylinders fires with every turn of the crankshaft, and the firing interval is constant. So if I use dots to represent 1/4 turn of the crankshaft time intervals, and an L to represent when the left spark fires and an R for the right spark, the pattern over time looks like this:
L...R...L...R...L...R...L...R...L...R...L...R
etc. Notice that the time interval between firings is constant.
For the 270 motors, the pattern looks like this:
L..R....L..R....L..R....L..R....L..R....L..R
etc.
So the sound is going to be way different.
MuckSavage
Scooter
Excellent explanations, thanks all. I had a general idea, but that straightened it all out!
Nick Morey
Rocker
Look at hp versus torque of T100 versus Scrambler:
T100 - 67 bhp @ 7500 rpm
51 ft/lb @ 5800 rpm
Scrambler - 59 bhp @ 6800 rpm
51 ft/lb @ 4750 rpm
Bottom line: T100 - more high end power for maintaining higher speeds
Scrambler - more low end grunt for dirt roads and trails
T100 - 67 bhp @ 7500 rpm
51 ft/lb @ 5800 rpm
Scrambler - 59 bhp @ 6800 rpm
51 ft/lb @ 4750 rpm
Bottom line: T100 - more high end power for maintaining higher speeds
Scrambler - more low end grunt for dirt roads and trails
mikenva
Rocker
thats not because of the fireing deg. That has more to do with the cams they used in the 2 of them
Nick Morey
Rocker
my bad for jumping to a conclusion there mikenva, after reading up a little online it seems the primary advantage is two fold;
1. the push-pull effect of pistons firing along with the firing being 1/2 a stroke off sync causes a smoother inertial torque response at the crankshaft, especially noticeable at higher rpm's.
2. throttle response has a more direct feel at the limits of tire adhesion.
Here's a link that explains it somewhat better:
http://www.sense.net/~blaine/torque.html
1. the push-pull effect of pistons firing along with the firing being 1/2 a stroke off sync causes a smoother inertial torque response at the crankshaft, especially noticeable at higher rpm's.
2. throttle response has a more direct feel at the limits of tire adhesion.
Here's a link that explains it somewhat better:
http://www.sense.net/~blaine/torque.html
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