The 76 YZ250, less torque than a briggs and stratton lawn mower below 3k, above it only able to riden by the very brave or very mad, preferably both, off then on, all of it . If you managed to not be spat off the back of it when it came on the pipe you ran the risk of being gelded at the first obstacle by the air fork reservoirs.
Low end torque. good grief.
apollo11,
Jun 24, 6:56pm
The least peaky 400 4 that I had was the VFR. I had a bit of a blast on a mate's RG400 2 stroke. Similar peak power to my VFR but more torque and at a lower rev band too.
tygertung,
Jun 24, 7:06pm
OK, 1980 Yamaha TT250 Max Torque 14.4 ft lb at 6500 RPM. At the same RPM a 1978 YZ250 is putting out 21.94 ft lb
More torque, same RPM despite being a considerably smaller engine.
ronaldo8,
Jun 25, 7:57am
If you think 6500 rpm is "low down" I can't help you.
Let me remind you of your assertion.
"you can't beat that low down torque"
ronaldo8,
Jun 25, 8:02am
Yeah, that detail seems to have conveniently slipped through the cracks in the reed valves and been shot straight out the tail pipe.
Much smoke out the tailpipe.
ronaldo8,
Jun 25, 8:07am
at 5500 rpm. ahem
"you can't beat that low down torque"
absolute_detail,
Jun 25, 8:33am
Outboards with the same displacement the 2 stroke has way more low down power than the 4 stroke
ronaldo8,
Jun 25, 8:42am
what rpm ? spinning a prop in water is a very different load case to engaging a clutch in the drivetrain of a static vehicle. The prop only presents significant load when its spinning fast enough to do so.
absolute_detail,
Jun 25, 8:56am
Just have a look at the videos on youtube. A boat setup with twin outboards, one a 200hp 2.8l 4 stroke the other a 150hp 2.7l 2 stroke. One engine tilted out of the water and only the 2 stroke has the low down power to get it on the plane
ronaldo8,
Jun 25, 9:07am
This thread is about two strokes in bikes, not boats. Its apples and oranges. When you let out the clutch on a bike that clutch is not slipping, hopefully. A prop in water can still spin regardless of the boat moving or not, like a slipping clutch.
The bike either has enough torque to move off or it stalls, the boat just doesn't move or moves very slowly, but its doesn't stall from lack of torque. Its only once the prop is spinning fast that the load is there and anything happens. That's not the "low down torque" we are talking about in relation to bikes.
At 0~1000 rpm of a bike at low speed, stalling or not, in a boat you are just trolling along if moving at all. Completely different.
absolute_detail,
Jun 25, 9:57am
It proves that the 2 stroke has more low end torque than the 4 stroke.
Who the hell operates an engine at 0-1000rpm? You are comparing apples and bananas, if I let the clutch out on my xr250 it stalls the same as the crm250. The crm has more torque than the xr down low. The crm has a lighter flywheel than the xr so it is easier to stall, that has nothing to do with the amount or torque produced just the lack of inertia
ronaldo8,
Jun 25, 10:46am
The heavier flywheel has everything to do with higher torque, because torque is force x distance, and inertia is energy/force stored in mass. It doesn't matter were the energy comes from, it doesn't have to sign its name, it just has to be multiplied by the distance its acting through, the diameter of the flywheel, to make torque.
Your XR250 is very oversquare as I recall, a buzz box, hence the flywheel to compensate, even more than your CRM, and unlike for instance a Harley engine, very undersquare with huge torque per rpm.
ronaldo8,
Jun 25, 11:13am
Here's a simple question for, does the tuned pipe on your two stroke work the same throughout the engines rev range and just how important do you think that pipe is to the engines performance.
bumfacingdown,
Jun 25, 11:46am
"You can't beat that low down torque " So far no evidence of this greater low end torque
absolute_detail,
Jun 25, 5:53pm
So why cant the 4 stroke outboard get up and going when the 2 stroke can? Wouldnt be because the 2 stroke has more low down power than the 4 stroke would it
tygertung,
Jun 25, 6:17pm
Yamaha YZ250 30.6 foot-pounds force (41.5 N⋅m) of torque at 7,500 rpm
Yamaha YZF250 YZ250F made its peak 18.5 pound-feet of torque at 8,500 rpm
So the 2 stroke has way more torque, and at a lower RPM
ronaldo8,
Jun 25, 8:05pm
I have to wonder if people dont understand the difference between power and torque.
Two strokes make most of there power at high rpm, not all, there are some exceptions like big industrial ones but for motorbikes just look at the expansion chamber, if you understand what it is and how it works you know this fact. Its tuned, tuned for max efficiency at where the bike is designed to run thats exhaust scavenging and compression timing at a tuned frequency, and its not low rpm.
A 30 hp two stroke makes peak power higher in the rev range with its flow dependant timing than a 30hp 4 stroke that is relatively flat with its non rpm dependent timing. They both make the same power, guess which one makes more torque at low rpm .
ronaldo8,
Jun 25, 8:17pm
FFS . displacement is irrelevant,.you may as well pick 2 with the same wheel size to compare. Why do you think smaller displacement 2 strokes race larger displacement 4 strokes? Do you think race officials are just biased?
They try to match power class.
ronaldo8,
Jun 25, 8:37pm
You have to be taking the piss, noones this dim.
"You can't beat that low down torque and the rush of power as the engine comes into the most efficient area of the rev range"
Waiter! I want to eat my cake and have it! I demand to see the manager!
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