Please define "runs out of steam"
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Road Master
Joined: Jul 2010
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From: Bellefonte PA
Please define "runs out of steam"
I am driving myself nuts researching cams and this seems to be the go to catch phrase to describe any given cam's shortcomings. Example: "Pulls good but runs out of steam at 4500 rpm. What exactly does this mean? What happens at 4500 rpm? How much real world riding is being done at 5000 rpm? I don't have a tach on my bike so I don't know for sure what rpms I'm cruising at but I would think that if it pulls to 4500 or 4800 or whatever that ought to be plenty for a street ridden Harley. Especially a heavy one. I'm not trying to be a smartass, I just wonder if these criticisms are kind of irrelevant when you're talking about a mild bolt in cam. Please share your thoughts.
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From: SoCal
I usually compare "running out of steam" to "still making noise but not making power". And for me the real world does include revving above 5000 rpm. But my engine does not have a mild bolt in cam either. This is why they make many different grinds of cams so you can find a set that fits your wants and needs.
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From: Bellville, Tx
Runs out of steam refers to the rpm at which the horsepower curve drops dramatically. A cam that puts out a lot of torque on the bottom end will often not breath well enough at higher rpm because the valves do not open as much as a cam designed with high lift and duration for max hp at 5500+.
My personal taste leans to more torque for a street bike, high horspower is a real kick on the strip but not used much in average riding.
My personal taste leans to more torque for a street bike, high horspower is a real kick on the strip but not used much in average riding.
2nd Gear
Joined: May 2011
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From: AZ
Runs out of steam refers to the rpm at which the horsepower curve drops dramatically. A cam that puts out a lot of torque on the bottom end will often not breath well enough at higher rpm because the valves do not open as much as a cam designed with high lift and duration for max hp at 5500+.
My personal taste leans to more torque for a street bike, high horspower is a real kick on the strip but not used much in average riding.
My personal taste leans to more torque for a street bike, high horspower is a real kick on the strip but not used much in average riding.
Have to agree, I learned the hard way that street cams and strip cams aint the same. I'd look at the cams that make most of their power between 2-4k...
How hard does your bike accelerate in any given rpm band? Get out on the road, and set the bike in 3rd gear at a steady 2000 rpms and peg the throttle. Does the bike jump forward? Or are you waiting for the cam to come on. Then do the same at 3000 rpms, then 4000 rpms and 5000 rpms. How hard your bike accelerates from the different starting rpms will tell you whether you're on the cam, or off it. Just because your bike will run to redline, doesn't mean it's making a bunch of power in the upper reaches. Do you accelerate harder by staying in the throttle, or by upshifting and dropping the rpms?
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Road Master
Joined: Jul 2010
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From: Bellefonte PA
Scott, I'm going to assume these builds you're referring to involve quite a bit more than a simple bolt in cam.
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absolutely, that build would not be described as "running out of steam".
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Road Master
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From: Bellefonte PA
I read some stuff on the Nightrider site about cams and some of the characteristics that will determine whether or not a particular cam makes good low end power. What aspects of a cam design can you look at on paper to know when it runs out of steam? Or even how to get an idea of the whole effective rpm range of that cam.
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From: Boca Raton, FL
Seat of the pants (also called the Buttometer)
runs out of steam = the point when you are at wide open throttle and the bike is pulling you back and off the bike and then that shifts and starts to relax and the suspension levels out
on a dyno its easy to see, but seat of the pants is basically that, the point at which you no longer feel the bike pulling hard and you should shift to the next gear
runs out of steam = the point when you are at wide open throttle and the bike is pulling you back and off the bike and then that shifts and starts to relax and the suspension levels out
on a dyno its easy to see, but seat of the pants is basically that, the point at which you no longer feel the bike pulling hard and you should shift to the next gear