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Discussion Starter #1
anyone wants to hazard a guess at the highest comfortable cruising rpm? one at which would be able to cruise at all day long without stressing the engine.

when i ride with others of the same model, they almost always seem to be cruising a lot faster than i am. i just feel that noise the engine makes at sustained rpm of 5000-5500 may be a bit close to red line for comfort. i've read some mags that says the 650 is spose to be able to hold 150 all day long. can she really?

the 400's seems to take to 140km/h quite well.
 

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Putting 'stress' on the engine is really a relative term ... some may be comfortable with a certain rpm, and others not. Needless to say Suzuki places the redline there for a reason to address the more "aggressive" population of riders.

The mags are probably right that the engine will be able to handle 150KPH (just under 100mph) 'all day long.' Needless to say, most riders probably wouldn't do that not just for the stress, but the safety issue as well.

For me, a cruising speed of about 60 to 80mph (100-125kph) feels just fine, and I wouldn't be worried about the stress on the engine as much as my personal safety at higher speeds.

Hope that helps...
 

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crusing rpm

I believe both machines red line @ 8,500 rpm. crusing 65-70mph @6,000 rpm on the 400 would seem to be more stressful than crusing 65-70 mph on the 650 @ 4,000 rpm. I would think if 6,000 rpm is fine on the 400, it would also be fine on the 650. The only difference would be the speed.
 

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Discussion Starter #4
ok migz123... i can see the logic about the redline bit. never thought of it that way.

i spose i fall into the 'not comfortable' category. considering the engine's under the body work and i've got a fitted helmet, i can still hear a bit of a din, i'm imagining if it was a naked scoot, it would probably be pretty noisy.

has anyone here dealt with the diesel sound yet?
 

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relaxed RPM

Putting 'stress' on the engine is really a relative term ... some may be comfortable with a certain rpm, and others not. Needless to say Suzuki places the redline there for a reason to address the more "aggressive" population of riders.

The mags are probably right that the engine will be able to handle 150KPH (just under 100mph) 'all day long.' Needless to say, most riders probably wouldn't do that not just for the stress, but the safety issue as well.

For me, a cruising speed of about 60 to 80mph (100-125kph) feels just fine, and I wouldn't be worried about the stress on the engine as much as my personal safety at higher speeds.

Hope that helps...
I find cruising at 4,000 RPM most comfortable and gives the best mileage. In fact to make life easier I added a black arrow with the point facing down on my 4K mark. I made it from black electrical tape. It makes it easy to see at a glance.
 

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Engine stress vs. RPMs

lMechanical stress is related to RPM squared, i.e. doubling the RPM quadruples the stress.

One can compare relative stress by comparing RPM squared at various engine speeds.

IF an engine is redlined at 7500 RPM the square is 56,250,000. At 5500 RPM the square is only 30,250,000. Comparing the numbers, the stress at 5500 RPM vs. 7500 RPM would be the lower divided by the higher.

Keeping is simpler, drop the last four zeros from each number and divide 3025 by 5625 to get the fractional ratio, in this case, about 0.537. At 5500 RPM the engine is stressed only to about 53.7% of what it would be at 7500 RPM.

This comparison does not take into account the efficiency, just the relative stress. It does suggest that an engine redlined at 7500 RPM should be capable of sustained running at 5500 RPM easily.

I've often heard that an engine performs most efficiently when operated at the RPM where maximum torque occurs. Don't know that figure for either 400 or 650 Burgmans, but it might be available from the specs. Doing the math for max. RPM vs. RPM at max. torque would show the relative stress at the most efficient engine speed. Now if the traffic would clear so you could drive at that speed easily.

Just a thought.

Ray Nielsen, in Minneapolis and sitting out the warm weather.
 

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Hi Ray - this question is arising from my English major mind:

Is all 'stress' bad (as in wearing down an engine)? Meaning that lower stress is better than higher stress? If an engine is designed to withstand a certain maximum threshold of stress, does it care about RPMs that are below that threshold? I guess the heart of the question is, if I cruise at 5500 rpm vs. 4000 rpm, am I shortening the life of the engine (or accelerating it's need for maintenance)?
 

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That's the beauty of the eCVT - just enjoy riding and keep your eyes on the road - the bike will look after itself.?
 

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(most commonly cited numbers, gathered from the web)

Maximum HP & Torque ratings for the '400:

pre-'07 400 (385 cc):
  • 32.0 HP @ 7600 RPM (22.1 lb·ft)
  • 23.6 lb·ft @ 6000 RPM (27.0 HP)
'07+ 400 (400 cc):
  • 34.0 HP @ 7300 RPM (24.5 lb·ft)
  • 26.8 lb·ft @ 5800 RPM (29.6 HP)

Maximum HP & Torque ratings for the '650:

early models (2003 to ???)
  • 50.0 HP @ 7000 RPM (37.5 lb·ft)
  • 39.8 lb·ft @ 5500 RPM (41.7 HP)
later models (??? to 2014)
  • 54.0 HP @ 7000 RPM (40.5 lb·ft)
  • 46.0 lb·ft @ 5000 RPM (43.8 HP)
 
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