[godot]

This is probably an ill-informed question, for I am still leaning about horsepower, torque, CAMS, etc.

With an EV46 CAM and a bunch of other upgrades, the ’99 Fat Boy is putting out 80 horses @ 5,500 RPM. However, my riding style is such that I am not ever at the range of RPM. At about 3,000 – 3,200 RPM, I am cursing between 90 and 100 MPH. This is plenty for me and I will probably never exceed it. So, here is the question: How can I “move” to 80 horses from the 5,500 RPM level to the 3,000 level? Is it as simple as changing the CAM to an EV27, for example, or is it more involved than that?

Thank you in advance,

[hotroadking]

Moving the cam to one like the ev27 is the correct way, the cam sets when valve events occur which basically set where the power curve will be for the motor.

[godot]

That is a logical answer. However, I've gotten so many contradicting opinions on this topic that I am still confused.

[VYBR8R]

Building an engine is a lot like cooking. Each ingredient you put into mix effects the total outcome. A few things you didn't mention is type of bike, other engine mods and your riding style. By changing exhaust to one that has more backpressure you will move your power curve lower in the RPM range and gain some torque, but will lose top end speed. By switching to an EV27 cam you will also lose top end but will gain bottom end torque which will make a bike quicker off the line. Give us the rest of the equation and I am sure you will get more than enough answers to either help you make your decision or completely get you confused.

[godot]

OK. Here is the rest of the equation:

- EV46 CAM
- Branch heads with stock pistons - 8:9.1/compression
- V&H 2-1 Pro Pipes
- Mikuni-42 carb
- AN's Big Sucker air filter
- SE's 6-speed-trany
- Crane's adjustable ignition module
- Crane's single fire coil

[CD]

Godot,

The qs I would ask is do you want to maximize low to mid range or, mid-high range?

Take a look at the following information.

Cam Open Close Duration Lift Overlap
V-Thunder
EV3030
In 16º 44º 240º .530 0º
Exh 44º 16º 240º .530

EV3040
In 17º 45º 242º .510 5º
Exh 50º 22º 252º .510

Andrews
EV27
In 20º 36º 236º .495 4º
Exh 44º 16º 240º .495

EV46
In 25º 41º 246º .495 8º
Exh 49º 17º 246º .495

Note the factor I added called "overlap" as it is a major player in the way a cam develops power. The profile of a cam dictates where and how much the power is made. Generally, a cam with the same exact gross lift can have the duration and timing events moved around to determine the power curve. Take a look at the EV27 and EV46 for example. Both are symetrical lift where the cam lobe gross lifts are the same. However, the duration and timing events are quite different. The EV27's duration is assymetrical with a shorter intake duration then exhaust, typical ofa torque cam. It also has a 4º overlap. The EV46 is a symetrical cam with all events being the same on intake and exhaust. However, note that the intake event is 5º sooner than the EV27 and the exhaust closes 1º later. This produces an 8º overlap. Overlap is an often overlooked part of the equation in determining what cam to use.
I was scratching my head trying to find a simple explanation of overlap and its effects when I came across this portion of a tech article.

"The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds"

This is one the best, yet simple explanation of valve overlap and it's effects I have ever read. Credit goes to http://www.newcovenant.com/speedcraf...camshaft/2.htm

With the combination you have you can flow some decent amount of air. In my opinion, an EV27 will not produce all of the torque and HP you are capable of. I would look hard at the V-Thunder 3030. It has slightly more duration on the intake side, .035 more lift and no overlap. The 3040 will produce a curve that is between the 3030 and the EV46.

[godot]

CD,
This is probably one of the best explanations of a CAM's role that I have ever read/heard. The link you provided is also great.
I will study it all very carefully.

Thank you!!