Big 2 stroke
Originally Posted by nerobro
No, twingles are a special sort of twins. They share a combustion chamber with two pistons that run up to it. Twingles are necessarily parallel twins, parallel twins are not necessarily twingles.
Twingles were also usually two strokes.
What you’re feeling on the different motorcycles is an effect of tuning, not engine configuration. There are some 4 cylinder bikes that make massive low end torque (look at the Bandit 1250) and some singles that make all their torque at high rpm (look at any motorcross bike).
If you grab a few dyno plots, you’ll see that displacement makes torque, and the state of tune of the engine determines the RPM that torque happens at. The amount of torque is dependant on the engine technology. For a given displacement that is. Side valve is the lowest, over head valve is better, four valves are better than that. Engine cooling too.
Air cooling is the lowest, oil cooling is better, water cooling is better than that.
Ive owned a Yamaha XJR1300, loads of grunt but nothing compared to the Honda XR 500 4 stroke, CR 500 2 stroke and Kawasaki KX 500 below idle RPM snap.
i loved coming around a hard dirt hairpin turn close to home in 3rd on my XR, the engine bucking about to stall at below idle rpm and just cracking a umph of throttle and the rear end would sweep out gracefully into an almost full lock slide. The CR was even more potent but would go down to way below idle under load without bucking like the 4 stroke.
the KX was angry. I saw it in a shop in NW Miami. The salesman said a guy bought it for his son and brought it back after 4 rides saying it will kill his son.
Because I rode it on the streets in Antigua I put the largest front sprocket and smallest back sprocket available. I even put multiple cylinder base gaskets about 3 millimeters thick to lower the compression and machined a weight for the crank mounted ignition rotor, in an effort to tame it down
i used to stop it on a gravel road, click it up to 4th(of 5), bring up the rpm to between 1/3 and 1/2 and dump the clutch. She would spin the rear and sweep the rear side to side while accelerating from a standstill.
at just about 20 mph in top gear, I would push down on the front end to compress the forks and on the rebound wack the throttle wide open pull up on the bars and throw my weight back and she would almost effortlessly rotate up to 11 o’clock. That’s not far above idle rpm, without using the clutch.
The ’69 BSA 441 shooting star I owned did not snap like the dirt bikes above probably because she had a heavy flywheel. She would pull very low without bucking like the XR. I remember riding slowly in a narrow slippery paved footpath and was surprised how she would so effortlessly spin the rear wheel when I eased out the clutch to move out at a walking pace.
And that is with max finesse with the clutch and throttle, but the torque at tick over combined with the heavy flywheel was almost unstoppable.
imho as grunty as the 1300 is there is no comparison in the below idle snap of these big singles I rode. I don’t think they make bikes like that anymore probably because those with smoother, less torquey power deliveries make much better lap times.
coupling the cranks of 2 KX 500s, or any of these for that matter, and firing both jugs together would yield a serious torque monster, IMHO.
March 17th, 2013, 12:40 AM
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