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Discussion Starter #1
I have a stock restricted Australian bike which reaches claimed peak power of 38.3kw at 8k RPM. First Yamaha and new parallel twin, and still getting to know the bike after 4 months (thanks to Melbourne lockdown).

I'm sure I read somewhere, or maybe a YouTube vid that rev sweet spot is over 6k RPM. Mine seems happiest at 4-5k. At 6k it doesn't sound happy.

Does that sound right? Or should be a bit meaner with the throttle?
 

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My bike isn't restricted so I'm not sure if I can really compare mine to yours or not but I can run around at about 4000 or upwards of 7000 and it seems to be happy through that range and beyond. Sometimes having a "pipe" can confound the sound of the bike, making it sound like something is about to come apart when it isn't.
 

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Sweet spot is the range arount which the torque is near maximum. If you look at a dyno run of one you will see it in the torque curve. Here is an FZ07 run that Motorcyclistonline had used in an XSR700 article. they're virtually the same:

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The torque range is strong from 3000-7000 rpm, after which it falls off. I didn't do any calculations or anything, but the torque is over 80% of max through that entire range, indicating that the engine should near equally as strong through the range since torque is a measure of work capability.

Here is a chart I found of a reflash that showed original torque on one of the MT007 LAMS:

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They are only showing a range over 4000 rpm, probably because that is where the LAMS version drops off due to restriction. The unrestriction boosts the torque from there on up, hinting that the torque below there to be around the same as the unrestricted, showing that the LAMS actually drops off over 4500 rpm and gets significant after around 5000 rpm, reinforcing your feeling that your bike has its sweet spot around 4000 rpm. That would make sense. The restricted bike probably has the range from around 3500-5500 rpm losing 2000 rpm of strong pull compared to the unrestricted.

Most people tend to like lower rpm, thinking it is easier on the bike which is not really true. What is easier on the bike is running in the stronger power range, where the engine is performing most efficiently. Yours is at 4000 rpm, so if you like 4000-5000 rpm then run it there, if others prefer higher, their choice.

Key take away - if you want the bike to have the best capability to pull strong in an instant you should be reving around 3500-4000 rpm to have a strong pull. Plus for best mpg you should also be running in the most efficient range, 3500-7000 rpm (unrestricted), 3500-5500 rpm (restricted). Lower is lugging and not in the efficient work range, higher is also in a less efficient range, but obviously not lugging.
 

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Sweet spot is the range arount which the torque is near maximum.

Key take away - if you want the bike to have the best capability to pull strong in an instant you should be reving around 3500-4000 rpm to have a strong pull.
You put a lot of effort into that post, supported with dyno graphs.

Thanks KLX678, you really know how to help out around here
 

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I am not sure if the common nomenclature for "sweet spot" is what some owners would call a happy riding engine speed.
I have a restricted XSR too (although swapped the throttle plate for one that allows it to be fully open) and the best power is about 6500rpm, while for general riding I feel best keeping it at about 5000rpm. Some like to ride 60Km/h in 5th gear where I prefer to keep mine in 3rd gear in traffic and 4th when cruising in the city (speed limit).
Anything under 3800rpm and I think the engine is lugging and vibrates too much for my liking when opening the throttle a bit.
 

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I was really impressed with the new (not in production yet) Aprilia RS660 when I first read the article about it in Cycle World. Then, although it does sound like an impressive motorcycle, it is amazingly similar to our own XSR 700. Engine layout and capacity are very close although it is 30cc less in displacement. Supposedly it makes more power on top, but at about 2000 RPM higher levels and, torque pretty much the same. The only two things that really seemed like you'd expect from a tightly wound motor was a compression ratio of 13.5 vs the 11.5 of the XSR and 50mm throttle bodies vs. 32 on the XSR. Although it was suggested that it might cost upwards of $12,000 or maybe a little more, price is as yet a big ?. I'm still impressed with the performance of the MT07/XSR700 and after a year on the FZ07 and a couple on the XSR700. Having almost 50 lbs. ft. of torque on hand for such a wide area of the power band makes the XSR a true joy to ride. Yes, to go really quick and fast you have to grab some twist grip, but it doesn't take a whole lot and you're going about as quick and fast as you think is prudent. I've had quicker and faster bikes but at the same time, they were too quick and too fast to give real confidence in one's ability to keep things under control and safe. Power and speed is intoxicating and a good reason I got rid of my FZ09 was it was too much like a rocket that was always just waiting to get let out of the cage. The XSR700 is a bit more controlled and respectful, but still plenty to satisfy. I guess I'll just stick with the XSR and leave the RS660 to those who have more $ than me.
 

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Discussion Starter #7
You put a lot of effort into that post, supported with dyno graphs.

Thanks KLX678, you really know how to help out around here
KLX678, wow! You sir are a gentleman and a scholar.

This gives me comfort to nudge it to 7500 RPM when I cross over 1500km (still newbie). My take from this is not much point pushing above that, right?
 

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KLX678, wow! You sir are a gentleman and a scholar.

This gives me comfort to nudge it to 7500 RPM when I cross over 1500km (still newbie). My take from this is not much point pushing above that, right?
So I took the bike out again armed with knowledge provided by Dyno report kindly provided by KLX678. I went a little harder, staying in 3rd and 4th longer, and deliberately didn't use 6th on the freeway.

Surprise, surprise...bike responded fine. Cheeky little XXXSR !!
 
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