I am running the 551's and really enjoy them. I had them installed in August. I have a 2001 FLTRSEI2 95" with stock heads, S&S SPO's, Arlen Ness Big Sucker and a PC III. I am running a canned map I got from dynojet over at vtwin forums. I find it pulls hard from go, I haven't adjusted the fuel pump function in the PC III yet. I haven't Dyno'd it either as I may do the heads this winter. It does as advertised, pulls strong from 1000-4000. I haven't been up past 5k and I can't tell of any drop off torque past 4k. It flies. Real world is I find myself speeding a lot more, getting on it when not necessary, doing burnouts and generally zipping in and out of traffic like I was riding my Sportster. Gas mileage has suffered also, but I think this is do to my inability to stay out of the throttle. Its kinda like riding an automatic, you don't have to downshift, but when you do downshift, you have a big **** eatin grin! Its (the torque) always on or always there. I wish I would have done it sooner. Now mine is a 2001 and S&S doesn't call it a bolt in due to the spring pressure. But they do bolt right in with no problems. I went with the gears also. Adios cam chain nightmare! I have not found any decrease in operating temperature.

I can say I am happy with it. If you want more zoom zoom you can go with the 583's or the 585's you just have to give it more revs...

 

The 204s have 8 degrees ground in advance. It doesn't raise compression, but it pushes the torque curve towards the lower rpm range. That 8* ground in advance, coupled with the relatively early intake close (compared to other performance cams) is why the 204 tends to hit earlier than similar cams like the Woods 6.

I think the 204 cams are best used at 9.7:1 static. You can run them up to about 10:1, but the tune becomes more critical, and at 10:1, other cam choices would perform better than the 204s.

 

I'm no expert, by any means, just a long-time hot rodder.

The amount of "ground in" advance is found in the relationship between intake lobe centerline and the lobe seperation angle. The SE 204 has a lobe center of 96* against a LSA of 104, or 8 degrees of ground in advance.

LSA is simply the angle between the intake valve centerline and the exhaust valve centerline. It's set when the cam is ground, and won't change no matter how you degree the cam. The intake lobe centerline is the position of the peak intake lift compared to the pistons top dead center. It can be changed by degreeing the cam in the engine. The cam card will tell you where the lobe centerline was ground, but that can be changed by advancing or retarding the cam on installation. If we install a cam with a LSA of 102 degrees and set the intake centerline at 102 degrees, the cam is installed "straight up".

If the cam is installed so that the intake centerline is greater than 102, the cam is retarded. If the cam is installed with the intake centerline less than 102, the cam is advanced. Advancing the cam generally gives you more torque off the line, but sacrifrices top end power. This is because overlap occurs sooner, the intake valve is open sooner and closes sooner. Advancing raises the cylinder pressure due to earlier intake closing. It's similar to the effects of running a shorter duration cam for building torque early. The downside is that more of the intake charge is pushed out the exhaust (earlier overlap) which reduces efficiency and makes less power.

Advancing the cam on installation isn't a way to fix a weak engine, and it isn't a magic bullet. Jamie at fuel moto had a thread recently where he demonstarted the effects of advancing a Woods 6 cam by 4 degrees. Basically, it didn't do much at all. It sometimes helps if you encounter exhaust reversion, and slightly modifying the valve timing can sometimes reduce the reversion. It's also useful if you're a little low or high on compression for the cam you're running. A good friend of mine taught me to set the CCP in a twin cam as close as possible to 190 psi for good off idle performance, but not so much that you run into detonation problems.

 

I am / was considering either an Andrews 48H or S&S 551 for two up riding with my heft.

When I did the calcs with either of those cams the CCP is in the 200+ range. The 551 of course take care of any starting issues but I would still have detonation concerns. According to some guy at S&S he was running 551 in a bike with 9.8:1 static compression without issues, but he autotuned, so who knows how much compensation was being performed.

Andrews specifically recommended that the 48H not be used with anything other than stock 96" compression. That early closes doesn't bleed off much static compression.

I am now thinking that I am going to use the Andrews 54H with 103" 10:1 which gives me corrected CCP right at 191.

 

Just did a 103 build on my 08 RG and installed the S&S 551 cams (EZ start). I've put 500 miles on it so far with a break in tune and the torque is awesome! I rarely rev past 4k and never cruise past 3k so this cam seems like it will fit my style well. I'm interested in seeing the difference between my stage 1 96 dyno sheet and this new build dyno sheet when I get er done. The only downside I see right now is that it runs hotter as I've gone into heat management mode in mid 60's weather. When the bike was a 96 stage 1 it never went into heat management mode, even in 100+ weather. But that is a manageable problem.

 

I was running SE204'S (as was BoogolooDude), Running a 103ci at 9.85
to 1 CR, 208# Springs, Zippers, SEPST, DYNO Tune, and a Crappy set
of non-tapered 1.75 inch Tru-Duals. Good power from 1800 to 4000, then Reversion from the Crappy Duals set in, and it would NOT turn above 4000. Numerous trips across the Dyno would NOT help (I Love the 204's and recommend them, it was the Duals at fault). I also had Hot starting issues, as my Harley dealer talked me out of CR releases, and it just wouldn't crank up when hot without grinding. etc. I'd added a Baker +1 pan, so the new S&S 2 into 1 into 2 pipes I bought would not fit. SO, I dug out my stock pipes to eliminate the reversion issue (wrapped w/ heat tape under the shields so my legs wouldn't roast), added the Kury heat deflectors, and slapped in a set of the S&S 551 easy Starts to eliminate the Hot Start issues (an inspection of my cam chest revealed extreme wear on the stock lifters at 7000 miles, as my friends are finding as well, so I needed new lifters ANYWAY, so I flew for the 551 cams too). My Buddy that runs the Dyno likes to do 4th gear runs (more realistic numbers), and spent around 3 hours dialing the 551's in. These numbers will be about 11% lower than what others get because of the Trike, Dyno and technique, but it yielded 75Hp at my Dual Posi-Traction wheels, and 93 foot-pounds, that held pretty solid to over 4100 RPM then tapered off slowly (remember, add the 11% and you're talking 83Hp/103Tq on a 2 wheeler in 5th gear). It'll idle down main street at 1000 RPM (No ****), and if you hit it, NO hesitation, barks 'em and it's GONE. NO hot starting issues. Here's how to make it run as cool as my Shovelhead or my Pan (well, almost): Add the HD Touring oil cooler, OR the JAGG Horiz. bottom mount OR larger side mount Oil Cooler, WITH the 180 thermostat. This will knock her down 40 degrees. NOW, buy and install the LaNale cooling fan (for LT 20 mph and at STOP SIGNS). Do a search on "LaNale" on this Forum, there is an article detailing a closley controlled test, at a stop, WITH the fan on, that measures Head Temp every 3 minutes, I believe. Instead of running up to 296 degrees and going into overtemp and COOKING your oil, it will NEVER get there (and if you forget to turn the fan on, it WILL recover from 296 degrees (correct me if my numbers are incorrect, anyone, I'm OVER 1/2 century Old). Anyhow, between the oil and fan cooler, you'll seldom see anything above 245 (212 mostly) oil temp, unless you're a Dumb **** like me and Tow a 700 pound camper with your geared down, Rivera clutched, tricked out Trike. And that really ain't a problem, IF you switch to synthetic and keep her rolling (or turn your fan on religiously). You'll LOVE the 551 cams. My Dyno Tuner got mine set up so it revs freely to 4700 (that's w/ stock pipes and BUB 7 Stealth Mufflers, the most restrictive ones out there, so I'm told). 37Mpg, It'll SPANK a stock 96", and w/out my camper & on the dirt (ie. Conesville),
I can do Broadies and Wheelies all day long, WITHOUT cooking my oil (245 most of the time during extreme abuse to 265 TOPS). I wouldn't give a plug nickle for the 583 cams, they're too wimpy, Get 585's if you can stand the loss of low end, or the 570's, now that's a MAN's Cam .

 

Great job explaning. I often play around with advancing or retarding the cams to taylor to a customers riding style. I read alot where guys never run above 4000rpm and I am hardly ever under 3000 so a cam I like would be horrible for someone else. Thats just me being a horsepower junkie that likes to ride in comfort...LOL

 

Two times you said that and two times you were wrong, in a technical sense. When you make a general reference to compression, you are referring to three specific criteria; static, corrected and cranking compression. A correct statement would have been to say that "cams don't increase STATIC compression".

While it is true that cams don't affect static compression, cams, specifically the timing of the closing of the intake valve, definitely affect what you refer to as "real world" or "running" compression AKA cranking compression as well as corrected compression.

Use any compression calculator and change the timing of the intake valve close from 42*ABDC to 25*ABDC and you will see a dramatic change in corrected and cranking compression. Those two criteria are much more important in selecting a cam for a build than static compression which remains the same regardless of the cam selected.