Well... Once again I waffled and am back to a 103" project (from a 103" > 96") with 204's. Like Boogaloo, I will also be adding SE 1.725 rocker arms to the equation. I will also have some mild head work done, primarily concentrating on a nice valve job with 1.90 int/1.61 exh and intake bowl contouring. HOPEFULLY it starts in about a month as I have all the parts....

 

Can anyone explain the basic difference between the 204's & 255's on the 103? Been looking at a Limited, & the dealer is pushing the 255's.

 

By stage one I mean seac, cobra slipons and pc5 or tts.

 

I can't explain the difference, but judging by the op's numbers, I had to add performance heads and pistons to equal his numbers with 255 cams.

My tq comes on sooner, but dives sooner as well. The op's combination seems really good overall.

Dennis

 

what is the advantage of using the 1.725 rockers over stock with the 204 cams...how about the +4 degree gear in a 103 with 204 cams...thx

 

gotcha. Yes, the 204 cams will work in a 96 with stock heads and stock compression. Your set up would be just fine.

SE255s will be a little snappier at the lower rpms than the 204s, but the 204s have 24* more duration, which will carry the power band further into the rpm range and produce higher overall numbers.

The 255s were designed to make torque in lower compression motors. They have an intake valve close of 25* ABDC, which is 5* earlier than stock cams. They open and close the intake valve quickly, which increases dynamic compression. The early intake close limits duration, which is why they tend to start falling off earlier than other cams. As your engine spins faster, the amount of time the valve is open gets shorter and shorter, until you reach a point where there isn't enough time to properly fill the combustion chamber.

The 204 cams are a little more conventional, with an intake close of 34* ABDC, which is 4* later than stock. It's still very early compared to most performance cams, and the 204 cams also have 8* of ground-in advance, which will enhance low rpm torque. Some guys think the 204 cams are too "small" for the 103 motors, but I've never quite understood that thinking. They are very comparable with the Andrews 37 and Woods 6 cams. In fact, the SE204 is essentially an Andrews 37 that's been advanced 4*.

Any cam is better than stock in the 96 motors, the stock cams are so bad. The stock cams have minus 8* duration, which is there for one reason: to cut down on emissions. You close the exhaust valve before you even start to open the intake valve, which eliminates any possibility of unburned fuel to escape with the spent gasses. Unfortunately, it also essentially eliminates exhaust scavenging. Normally, a little overlap is added, and towards the end of the exhaust cycle, the tail end of the exiting gasses will pull in the fresh charge in a suction effect. This can have a dramatic effect on power production, the faster you can fill the combustion chamber, the quicker you can close the intake valve and start compressing the charge.

Now, with the 96 motors, the moco has done some performance work for you. They increased displacement by 8 cubic inches, and did a bunch of head work. This should have resulted in a nice jump forward in performance, but they then strangled the power by putting catalytic converters in the exhaust and designing cams with no overlap and very short duration.

So when you pull out the smog cams and install even a mild performance cam, you get a big jump forward in performance. The cams in the 88 inch bikes weren't nearly as bad as the newer cams, but the head design wasn't nearly as good. That's why a cam swap in an 88 inch motor doesn't have quite the effect as it does in a 96. The moco has given us a pretty good set of heads to work with, all we have to do is plug in a mild performance cam and go riding.

 

thanks boogaloodude, very informative post and has gotten me thinking i'm thinking too much about which cam and i should just get off the pot and pick one.....

 

you got a strong runner there. no wonder you're happy.

 

Based on your post, you obviously know what you're talking about. I have a 2011 FLHX with the 103" motor option. Mod's to date, D&D FatCat 2 into 1, SE Super Tuner, Roland Sands Open Air Breather. I'm not sure if I want to mess around with a heads/cams/TB upgrade or just the cams. Do you have any input on the the 2011 103" motors.

Thanks!

 

Great Numbers with the 204 ~ A buddy of mine put 255's in his 10 FLHTK and the numbers were a little lackluster in my book.. I may have to look into 204's for my 10 FLHTK ~ already have autotune, PCV, and jackpots on the bike with the K&N...