Still a newbie and have only riden a few bikes besides mine. Gonna be doing a 107 kit in the spring and have been doing lots of research on it.

I think I am gaining an understanding of dyno charts, and the impact of various cams on preformance. What I don't get yet is what this feels like when riding. Suppose I go with a cam that comes on later in the rpm range, i.e., more tq in the mid and upper rpms; how does this effect for example slow speed manuvering: (like the ride like a Pro stuff I have been practicing)? Will it more difficult to slip the clutch or do a "slow race" depending on the cam and/or displacement or is all that remaining the same.

Education appreciated!

Benny

 

Until a more expert person comes along ( and to keep the thread from falling from the front page), heres my experience:


the cam profile ( valve lift height, duration of that lift, speed of the lift ( ramp) and overlap- time duration when both valves are open) will cause a peak of power within an RPM range.

cams are chosen for this power peak depending on the weight and gearing of the vehicle.

as you touch on, a performance cam may reduce low speed "manners"--- extreme cases are the top fuel cars where at idle the motor bounces all over--- and launch happens at 4000 rpm, as there is little power at the low rpms

the variable valve timing technology on many current cars alters the valve timing to provide better power throughout the rpm range.

the difficulty with motor design is that they have to provide good power/efficiency and emissions at all rpms
This is why the chevy volt is cool, the motor runs in a narrow rpm range and powers a genny which powers the electric motors

mike

 

cams are just one part of a quadratic equation when it comes to getting power when you want it at certain rpm's or conditions.

The exhaust system design, how the heads are ported, ignition curve and cams all have to be chosen as a package to get the most efficiency.

Ask any old school Chevy guy about intake manifold runner length, header tube length, compression, cam profiles ( lift, duration,ramp, overlap) ignition timing and how they all relate.

If you have pipes that are designed for low end torque and cams that are designed for mid range power, and heads that are so restricted on the intake you can't get the gas into the engine, nothing is going to work as intended.

So don't focus on the cams, look at how the different components will work with each other.

 

Thanks. I hear what you are saying about making the packge work. I ave stage 1, Jackpots, and pcv. Will a more aggressive cam reduce low speed manuvering or is this a non-issue. For example, suppose I went to a 103 and went with a 204 versus a 255. Will the increased torque in midrange in the former versus lower end torque in later--effect ease of very slow manuvering when slipping clutch, etc?

Appreciate this may be a dumb question; but from what I am learning the "manners" of the bike has something to do with when the power comes on. I am strongly considering a FM 107 build with Woods 555 from FM this spring.

 

As far as low speed maneuvers, IF the cam has an effect, it can also be tuned to be smoothed out as well with manipulating the spark timing and fuel injection. I haven't seen the question asked before, but it's a legitimate one.

I'm sure you'll be just fine.

 

I would suggest not- valve timing has such a huge effect on motor performance that electronic controls cannot restore "lumpy" low speed operation.

It is correct that retarded ignition timing can give better low speed operation, the older models had manual timing advance controlled on the left grip, which allow the motor to move bike and rider at very low speeds turning about 600 rpm.


Mike

 

I would amend my statement to say it can be adjusted, but not smoothed.

Please provide information on left grip manual timing advance. I've never heard of this.

 

My thoughts: Unless you get really radical on the build and design a drag motor ( as mkguitar indicated,) you'll still be able to navigate parking lots without the motor hic-cupping or generally misbehaving.

Its when you leave the parking lot you'll have to let the revs climb a bit more before the cams 'come on' and you can accelerate briskly. ( You'll still be able to practice your slow speed maneuvers.)

 

The manual advance lever was mainly used for starting the engine and eventually correcting the octane value of gasoline; this would slightly rotate/shift the 'base' plate where the points were fixed to the engine block.
The centrifugal ignition timing cams mounted on the camshaft added a timing offset to compensate the effect of the speed of rotation that increases the compression temperature inside the cylinder as the engine speed increases. It was a fairly simple approach at the time and I remember using only one spark plug that had a glass isolator to visualize fuel combustion color.
For setting the optimal full open throttle between 1,500 rpm and 5,000 rpm I used to tune my timing advance controller by grinding the little wings/masses or by changing the springs. In my early days we only had mechanical stopwatches to evaluate speed gained by our tuning, and people were quite happy with that. It was a nightmare to modify your vehicle successfully in one go a few decades ago.

Today you have a wide offering of cams, air cleaners, exhaust systems, clever bits and pieces that fit everywhere and 'do everything' but you still need to clearly define your need, choose and match the parts you will use knowing how they interact otherwise you're going into a never ending cycle of frustration. Money matters are kept aside of course because the pleasure of riding doesn't only depend on the number of horsepower you have: it's often related to the person sitting behind you.

 

The question in this post is something that I am also curious about. Specifically, let's say I put in cams that start to make good power at 2200 rpms. Assuming all of the components are a good match to each other, and the bike is properly tuned, what does the bike feel like between idle and 2200? How will it compare to the way it feels in its current stage 1 setup? For the record, I am talking about bolt in cams with no sort of headwork or anything.