Cam Advice?
Road Master
Joined: Dec 2006
Posts: 832
Likes: 0
From: NC foothills
I would suggest getting a cam like SE 255 or S&S 510 that pulls best between 2000-3500 RPM. I pulled down the data log of all the hours ran on my bike over the last year and i was really surprised how much of the time was spent between 2000-3000 RPM and how little was spent at 5000 RPM. And this was on a bike that i routinely run the crap out of.
Ultimate HDF Member
Joined: Aug 2008
Posts: 5,413
Likes: 17
From: eastern oklahoma
thabull, i agree, i'm thinking of the 255's myself for that exact reason. sure you could get more hp etc at higher revs than you'd actually use, but numbers ain't everything. torque is. low end torque from off idle to 5k if even that high. i think the 255's would fit the bill. bikerboys i think is the site where they have some great comparisons. it may be spelled biker boyz. that gives detailed information, comparisons etc. i don't mind spending money, but i want the best bang for the buck, that's why it's best to study before buying, and why we're here reading in the forum, for me anyway.
Tourer
Joined: Mar 2008
Posts: 435
Likes: 2
From: Alberta, Canada
Something that is always overlooked in a discussion about which cam is best is the fact that you have 6 (possibly only 5) gears on your bike. You also use a wider range of RPMs than you might think - you do stop at stop signs, you do ride in traffic, and you do ride in town at town speeds, right? Even on highways, unless you only ever ride one road, and there is no traffic, you can't say all your riding is at 70 MPH. Throw in some wind and some hills and luggage/passengers and you see that your bike needs to operate in a variety of RPM ranges.
Now when you use all the gears, you are using a lot (maybe not all, but a lot) of the RPM range your bike was designed for - say 1800 to 5000 RPM. BTW, if you say you only use the 1800 to 2500 RPM range you are lugging your bike badly at times (See above, hills, wind, etc.). What is needed is a cam that produces the widest, and flattest, torque curve possible, not a peaky torque curve. Remember 2-cycle motors? They had a very narrow power band that peaked in the upper RPMs. This made them gutless if you dropped down to lower RPMs. You needed to rev the crap out of them and shift often to keep in the usable power range.
Flat, wide torque curves will give you greater overlap in the available torque as you run your bike through the gears. I've attached a highly accurate and detailed illustration to show what I am referring to. Obviously I'm kidding, and NO, I am not trying to compare any particular cams or brands! Each gear and it's range of RPMs is shown on the horizontal axis. Torque is shown on the vertical axis. Note, I have exaggerated the torque curves to make my explanation more obvious.
Recently another thread contained reference to a magazine article that said if you want more torque just downshift. Everyone assumed this to mean rev your bike higher for all your riding. What I think they meant is, stock H-Ds produce good torque but the curve is narrow than most riders think so you have to downshift more often to stay in the power or to get into the power to pass. You can see that with a wider torque curve you don't need to shift as often to stay in a usable torque range (Shown by the skinny horizontal lines in my drawing.). While it is possible for a peaky cam to produce more low end torque (Actually - reach it's torque peak earlier.), it also runs out of torque earlier so you have to shift more often, which seems to be counter to the reasons people give for wanting a cam that produces more low end torque at lower RPMs. The skinny vertical line is intended to show how the peaky curve may produce more low end power earlier than the flat curve, but because of the wider power band, this is only an issue at very low RPM - like when leaving a stop light. Just rev it a bit higher and it's a non issue.
And "Yes" you can choose a cam that is too big just as easily as you can choose a cam that is too small, but we're talking about low end torque here so I think going too big is not as much of a problem in this discussion.
Bottom line - If you choose a cam that produces a flat torque curve in conjunction with your bikes other components (intake, mufflers, gearing, etc.), you will be much happier with the results than if you pick a cam based solely on it producing it's best torque in one range (e.g. Low RPMs).
Just my 2 cents.
Now when you use all the gears, you are using a lot (maybe not all, but a lot) of the RPM range your bike was designed for - say 1800 to 5000 RPM. BTW, if you say you only use the 1800 to 2500 RPM range you are lugging your bike badly at times (See above, hills, wind, etc.). What is needed is a cam that produces the widest, and flattest, torque curve possible, not a peaky torque curve. Remember 2-cycle motors? They had a very narrow power band that peaked in the upper RPMs. This made them gutless if you dropped down to lower RPMs. You needed to rev the crap out of them and shift often to keep in the usable power range.
Flat, wide torque curves will give you greater overlap in the available torque as you run your bike through the gears. I've attached a highly accurate and detailed illustration to show what I am referring to. Obviously I'm kidding, and NO, I am not trying to compare any particular cams or brands! Each gear and it's range of RPMs is shown on the horizontal axis. Torque is shown on the vertical axis. Note, I have exaggerated the torque curves to make my explanation more obvious.
Recently another thread contained reference to a magazine article that said if you want more torque just downshift. Everyone assumed this to mean rev your bike higher for all your riding. What I think they meant is, stock H-Ds produce good torque but the curve is narrow than most riders think so you have to downshift more often to stay in the power or to get into the power to pass. You can see that with a wider torque curve you don't need to shift as often to stay in a usable torque range (Shown by the skinny horizontal lines in my drawing.). While it is possible for a peaky cam to produce more low end torque (Actually - reach it's torque peak earlier.), it also runs out of torque earlier so you have to shift more often, which seems to be counter to the reasons people give for wanting a cam that produces more low end torque at lower RPMs. The skinny vertical line is intended to show how the peaky curve may produce more low end power earlier than the flat curve, but because of the wider power band, this is only an issue at very low RPM - like when leaving a stop light. Just rev it a bit higher and it's a non issue.
And "Yes" you can choose a cam that is too big just as easily as you can choose a cam that is too small, but we're talking about low end torque here so I think going too big is not as much of a problem in this discussion.
Bottom line - If you choose a cam that produces a flat torque curve in conjunction with your bikes other components (intake, mufflers, gearing, etc.), you will be much happier with the results than if you pick a cam based solely on it producing it's best torque in one range (e.g. Low RPMs).
Just my 2 cents.
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