Originally Posted by papifun

so u saying a stock 2011 HD with Power Pak option (103) with just SE204 cams, True Duals and Stage 1 AC would would tune to numbers in 85HP 105TQ range ?

Originally Posted by Tek74

I was reading the below recent thread on adding Cams to a 2011 HD with a 103 PowerPack. Im picking up a 2011 RGC with Power Pack in late February, and the only mods I know that I'm doing for sure are V&H Monster Rounds exhaust, along with V&H Air Cleaner and Fuel Pack. But its sounding like adding Cams might be a good idea at some point if I want to maximize power output.

Originally Posted by 07FLHT

I'd say forget the V&H Fuel Pack & get a tuner that can be more useful when/if you ever decide to do the cam swap.
www.fuelmotousa.com

Originally Posted by boogaloodude

A cam swap for a 96 or 103 motor makes a lot of sense, mostly because the stock cams are so bad. The moco has done a bunch of work for us in the last few years. The 06 and later heads flow much bettter than the earlier ones, the increase in displacement adds torque across the entire rpm range, and the closed loop fuel injection system can bring both increased performance and better fuel economy. On the other hand, catalytic converters in the exhaust will rob performance, and the stock cams are designed to reduce emissions, not boost performance.

The good news though, is that a simple cam and header swap will boost performance in a big way, more so than with the earlier 88 motors. The 88's had better cams and no cats, but less displacement and a less effective head design.

Guys get hung up over one cam spec or another. When I was a young hot rodder, we were all about duration. It's human nature to want the biggest bang for your buck, and it's tempting to push a bigger cam in your motor than it needs. Adding too much cam is one of the most effective ways to make a fast bike slow. Generally, too much of anything in a cam will hurt low end power. Your cam manufacturer will have recommendations for the proper compression ratio for any given cam.

I'll try to keep my remarks brief. Your starting mechanical compression and cam selection must be considered as a system. You're starting with a fixed static compression, which is (roughly) the amount of air that your cylinder holds compressed into your combustion chamber. Your static compression starting point along with your cam's design will determine what your dynamic compression will be. Your cam has four main valve timing points: Intake valve open and close, and Exhaust open and close.


Lets start with the piston on it's intake stroke. In a performance cam, your intake valve opens before top dead center, and towards the end of the exhaust stroke. This period of time when both intake and exhaust valves are open is called overlap, and the exiting exhaust gasses help pull in the fresh charge in a siphon type effect. Stock cams eliminate the overlap period, because the EPA doesn't want any unburned fuel escaping with the exhaust gasses. The stock cams open the intake just after TDC.

Your cam's intake valve closing point determines the rpm band your best performance occurs. Because your camshaft intake valve closes after bottom dead center, you don't start compressing the fuel charge until sometime after the piston starts upwards on it's compression stroke. A early intake close results in greater cranking pressure, which builds early torque. Higher rpm motors need a cam with a later intake close to insure all the fuel possible makes it into the combustion chamber. The faster the motor spins, the quicker the valve opens and closes, so a longer duration is needed for high rpm power. Ideally, you want the intake valve to close exactly at the point where air stops flowing into the chamber, but that point changes with rpm, so a cam has to strike a balance. Shorter duration cams are designed for low rpm and early torque, long duration cams are designed for high rpm motors and peak horsepower. An early closing cam would generally be considered as closing at 38 ABDC or earlier. A mid closing cam at 38-45 or so would shift the torque curve up the band by a few hundred rpms, and peak horsepower would also increase. Unless static compression is increased, response off-idle will decrease somewhat. Also, later closing, longer duration cams are more effected by exhaust design.

Back to intake opening, briefly. All cam design componants are a balancing act. Open early and the exiting exhaust gasses can pull the incoming charge into the combustion chamber. Open too early, and some of the exhaust gasses can back into the intake manifold, slowing the intake pulse velocity, and contaminating the fresh charge. It also hurts fuel economy if more unburned fuel escapes with the exiting gasses. A late opening intake will result in smooth operation at low rpms, and better throttle response off idle. Early means more overlap, less throttle response at low rpms, rougher idle, and poorer fuel economy. You want your intake valve to open early enough to where the valve is open far enough to flow max CFM at the same time the piston is traveling at max velocity.

Exhaust opening. Probably has the least effect on performance of the four open/close points. However, if you open too early, you decrease torque by bleeding off cylinder pressure that's still pushing the piston down. It does have to open early enough to provide enough time to scavenge the cylinder. Late opening helps low rpm performance by maximizing burn time and keeping pressure on the piston. Too late and you suffer pumping losses because the piston has to work harder to push out the spend charge. Too early, and you hurt the bottom end, but help the top end. Most cams split the difference, with stock cams tending towards a later open.

Exhaust closing: close too late and you hurt the bottom end. Closing late increases overlap, and is similar to opening the intake too soon which can cause reversion up the intake manifold. Close too early, and you might not evacuate all the spent gasses, and the residual burnt fuel will dilute the fresh charge.

As a motor spins faster, all the opening and closing points need to be pushed out to allow sufficient time for the various functions to occur.

Most street engines benefit the most by a cam with moderate specs. Not too early, not too late, not too much.

Three more things, quickly. Lobe seperation angle (LSA) is the angle between the middpoint of the intake and the exhaust lobes on the camshaft. Generally, a tight LSA (98-103) produces a narrow, early torque curve, and a wider LSA (104-108) broadens the powerband, and develops more power late. Lift: more is better generally. As long as your valve springs can handle the amount of lift, and you don't bang the valves into the pistons, opening the valves as much as possible is a good thing. The primary downside is increased wear because of the higher stresses put on the valvetrain. Even though your heads only flow up to a certain amount, opening the valves beyond that generally increases the amount of time they are open during the max flow period. Finally, duration. The faster the motor spins, the longer the valves need to be open. Short duration cams (under 220*) tend to build torque early. They can usually be bolted in as a stock replacement and will return moderate gains across the entire rpm band. Mid duration (220-240 or so) start moving into the mild performance arena, but will still work with stock compression and exhaust. Move up past 240 or so, and the cams will generally work better with other induction, compression, and exhaust modifications.

Originally Posted by atrain68

Hey Boog,
I think you scared off the OP, but this is a damn good explanation!

Originally Posted by papifun

was just doing some reading and seems the SE204 cams as per catalog are only for pre 07 motors... any input ?

from SE catalog

Part # 25149-00
Fits ’99-’05 Dyna, ’00-’06 Softail and
’99-’06 T ouring models