I've spent a lot of time over the last couple of months looking at cams for a project 103 that I was building, and all those notes and scraps were just scattered all over - so I finally sat myself down and organized it. The SE 103 kit is a little unique in that it has significantly higher compression than the stock 96 or even the CVO 110, and that plays a part in how cams relate to it. It occurred to me that there seemed to be a lot of info out there for 96ers and 110s, but I felt like I was really scrounging for useable info for a basic 103 build without headwork. Maybe some of the rest of you might have the same goals as me, and maybe I could save you some time by sharing, so here it is.

This is an Excel spreadsheet of a bunch of different cams for my 2008 Ultra. This was the criteria:
1. The motor is a standard Screamin Eagle 103, with the included air filter backing plate and a K&N gauze filter. I also installed some relatively quiet Supertrapp SE mufflers and a 1.7kw starter for the added compression.
2. I did not want to do head work or change valve springs and all that stuff. I'm going to drive it, not drag race it.
3. (Related to #2) I'm not as obsessed with dyno charts as a lot of people seem to be. It's clear to me that a dyno chart tells me what a bike will do at wide open throttle in 5th. And it only tells me what MY bike will do at wide open throttle in 5th if I have the exact same components and tune as the dynoed bike; which, since a lot of dyno guys seem to be in competition to see who has the biggest numbers, is rare, because (refer to #2) I'm not really interested in spending another 800 bucks on headwork. Besides, unlike everybody else (it seems), I'm not really spending a lot of time driving around at WOT in 5th... actually, I'm a whole lot more interested in the rare post where someone talks about what it was like to ride his modified bike - sound, throttle response, feel.
3. The cams in the list all fit '07 up Twin Cams, and '06 Dyna.
4. I like compression. So all the cams chosen have an intake closing of 42* or less.
5. (related again to #2) I'm okay with a lift up to about 555 thousandths. I don't want to have to change the springs or relieve the pistons, and I don't want to wear down the valve train in 15,000 miles.

Okay, so that's it. Here's an average bike with low maintenance criteria, and we're looking for a cam that produces substantial low to midrange torque, but doesn't fall on it's face at 4500 rpm like the SE255s that came with the kit. If you have criteria like that for your bike, you might find the attached spreadsheet useful. I'm not making any recommendations here, or even showing any actual performance numbers, just organizing a bunch of cam data, and if we understand a little about cam design, we can make some (basic!) assumptions. Here's the assumptions I make:

1. The earlier the intake closes, the higher the static compression (combustion chamber pressure, or CCP) will be.
2. Longer, and earlier the exhaust opening will make the bottom end feel softer and the top end feel stronger.
3. Overlap is a funny thing. Overlap allows the exhaust pulse to create a suction that helps draw the intake charge in past the intake valve, but that is as much a function of timing as duration. We can't just say that more overlap creates a top end engine. Where the overlap starts and ends will determine where the suction occurs, at different rpm, and has a lot to do with fluid dynamics. Jeez, that's starting to feel like high school calculus to me.
4. Lift is a good thing, up to a point. It's obvious that if we had two cams with the exact same timing, but one had more lift, the cam with more lift would outperform the cam with less lift - to a point. A cam with too much lift has to accelerate, stop, and accelerate back down again, so too much lift becomes a liability with stock springs when the valves start to float (not close all the way) at high rpm. Also, with no headwork done, the throttle body and inlet tract can become the limiting factor at higher rpm. So I limited my choices to cams with .555 lift or less, all of which will work with stock heads (but would certainly improve on the top end with head work)

The chart:
Excel is not an accepted format on the forum, and the .pdf file was too big, so had to compress the file. You may have to download it and extract it, then print it out, and tape it together - that's what I did.
The valve opening and closing is laid out in a linear fashion, exhaust opening to exhaust close, intake opening to intake close. To keep the sheet from being 4 pages wide, I "compacted" some of the columns to eliminate the unimportant areas. Keep in mind, because of this, the lines are not to scale, and the minor differences in timing are exaggerated.
The cam names are listed on the left, followed by lift and overlap, separated out so you don't have to add up all those numbers. That data, plus the degrees across the top are "frozen" on the spreadsheet, so you can move the lines around to get them closer to the labels and see what you’re looking at.
On the top right are CCP numbers calculated for the different intake closings - remember, this is just for a standard Screamin Eagle 103 Stage III kit, which starts out with about 10:1 compression. These numbers are probably pretty close, as the chart shows 207psi for a 25* intake close, and that is exactly what I get from my motor now with the 255s in it.
For those of you working on the same kit, I put the stock 96" cam at the top of the chart (that’s what we started with), and the 255 that you got with your kit second, so if you've ridden with either one of those in the bike, you might be able to draw some comparisons.
Remember, there's no data here for ramp or lobe angle, and there's probably 4 or 5 other factors that affect cam behavior that I don't even know about - but it may be useful to have all these cams that fall under a streetworthy build all in one place. These should all make good drivers, and at the very least, you've got a bunch of data to further confuse the issue!

 

An Andrews 26 is a shoe-in at the OE compression of that 103.
Scott

 

It must be a long winter up there..

 

I'm with Paul; long winter, too much time on your hands. No need to reinvent the wheel on cam choices for a 103, just look at dyno charts and replicate a build that produces the power curve you want. Yeah, that's another useful thing about dyno charts.

Use a compression calculator and see which cams will produce a corrected CR in the 9.0-9.3 range, or if more adventurous, in the 9.3-9.6 range depending on your tolerance for compression, local fule and local tuning capabilities. Additonally, keeping cranking compression under 200 psi, say closer to 190psi.

See which cams meet that criteria and start looking at dyno charts and select the power curve that best suits your riding style.

I wouldn't say headwork was a waste of money but would agree that you don't need it to build a good runner. You would at least want to use a .030" head gasket and CC the heads so you know your baseline for the above calculations.

Not knocking your chart, just a differernt way to look at it.

 

Ha ha... yep, waaaaay too long

 

Not to nit-pick ... but, thought this worth mentioning ....

In the second series of numbered paragraphs, in paragraph #1 you say: "The earlier the intake closes, the higher the static compression" ....

Definitionally, static compression is the measured compression ratio ... corrected or dynamic compression ratio will depend on valve timing events ....

* * *

For the general interest and information of forum members, I've posted some of my data on the thread linked below ... check it out ....

https://www.hdforums.com/forum/dyna-...-and-data.html

 

Ah! Another analytical data collector! Nice to meet you, and good input.

 

For the general interest and information of forum members, I've posted some of my data on the thread linked below ... check it out ....

https://www.hdforums.com/forum/dyna-...-and-data.html[/quote]


Surfor,

That's a great post, and really makes me reconsider the benefits of swapping out the SE255 that came with this 103 kit. Although, I understand that cylinder temp is an issue with the 255s, and going to an Andrews 37 may help with that while still retaining the bottom end.