"Getting On The Cam"

[jaudette3]

OK, I'm starting the day with what is probably a really stupid question.

I took a friend for a ride in my '73 2.7 S the other day and pointed out how things changed when we crossed 5,000 RPM. Told him that they were different beasts once they got on the cam. He's a retired doctor, not a car guy, and his response was, "Isn't the cam always working? It's an inanimate object, how can it be on the cam or off the cam?".

Well, he *is* a doctor, so I'm used to speaking slowly and using simple terms.

However, I discovered that I only have a vague idea, in technical terms, of what changes occur in the running of an engine when it gets on the cam. Is it a kind of optimum condition reached in terms of the duration of the valves opening and closing? Can someone provide a technical description of what happens?

Thanks,
John Audette

[kenikh]

Is it a kind of optimum condition reached in terms of the duration of the valves opening and closing? Can someone provide a technical description of what happens?

Yes. "On the cam" is when intake gas speed and engine speed hits its optimum for torque production when the car goes on cam. This is when overlap and lift are ideally suited to that engine speed. As long revs are increasing faster than torque is falling off, you will have a rising HP curve. Thus the car is on cam from the torque peak to the point revs rise slower than the torque falloff.

[Chris Tallon]

Who knew Kenikh also had a PHD? Nicely done Doc.

CT

[Zeke]

Who knew Kenikh also had a PHD? Nicely done Doc.

CT

Indeed. The more power designed into the high RPM range is done so at the detraction of usable performance in the lower ranges. Some tractablity has to be retained for street use, but one can still feel the kick of a high lift, long duration camshaft as it gets into its designed performance RPMs. To me, it's realy cool that the modern day engine can have varible cams and variable intake designs to spread the best performance throughout the range.

But we like our old fashioned S motors that "get on the cam" at about 5K. That having been said, I'm planning a motor with E or Solex grind cams with fairly high compression and bigger ports. I'm hoping for a little more grunt from, say, 4K. I find that easier to drive in the twisties when it doesn't go flat on power below 4K, or nothing at all at 3K.

The answer to your question, John, lies in the high lift, long duration aspect. That, and a carefully designed overlap of the valve timing which serves well in the high RPM, high flow period of an engine's operation. In turn, high overlap causes rough idle and compression loss at low RPM. That's about as technical as you wanna get until you start reading about header design and intake design.

[Homemade 911]

First time I hit the "on cam" sweet spot in my racecar, I was just exiting a fairly technical corner (At Buttonwillow, I think)...gawd, what an experience THAT was!

It was a "virtual turbo" rush: nothing, nothing, nothing, then WHUMP! "jaysus, now what %#&^ do I do!?"

I don't think I've shifted the thing below 6500rpm since...

I just love the little motors...

Cheers
Thom Kuby

[kenikh]

But we like our old fashioned S motors that "get on the cam" at about 5K. That having been said, I'm planning a motor with E or Solex grind cams with fairly high compression and bigger ports. I'm hoping for a little more grunt from, say, 4K. I find that easier to drive in the twisties when it doesn't go flat on power below 4K, or nothing at all at 3K.

To say that I have been getting a bit obsessive about cams and gears lately is an understatement. I'll merely say that I have a very good memory for reciting the brilliance of others.

Milt, I'd recommend a few other cams if you want 'E' torque and ideal HP numbers. The Mod-E, Mod-Solex and Mod-S cams come to mind. Faster lobe ramps means more air flow like a high overlap cam, but without the overlap (and subsequent rough low RPM running). Modern cam designs are pretty amazing; you can pretty much get any perf characteristics you want depending on how much you are willing to put into the valve train.

My new cams for my 2.0S are very, very special. They don't require titanium valves, but the accel/decel speeds of this cam are close. John Dougherty and I went back and forth a lot to come up with a solution that will pull like an 'E' down low, yet rev to peak HP at 7800 RPM. The design criteria was something between a Mod-S and a GE60; I think he nailed it.

They are getting installed in the next few months; I'll give you guys an update when I know the results. I'm expecting somewhere around 190HP.

[Fritz A. Ficke]

"Getting on cam" is slang for "in the power band"
There is alot of slang used in the automotive world.
"dog house", your pickup did not have a house built in for pets.
or "you better put some grease in your pumkin" really means "put gear oil in your diffrential" Or when a part is no longer in tolerance it is a colorful verb for intercourse or "out to lunch" of course the parts do not eat. So be careful in dealing with mech. and their use of langauge, "Blow me" does not mean an exchange of services for instance. I hope this helps

[Zeke]

To say that I have been getting a bit obsessive about cams and gears lately is an understatement. I'll merely say that I have a very good memory for reciting the brilliance of others.

Milt, I'd recommend a few other cams if you want 'E' torque and ideal HP numbers. The Mod-E, Mod-Solex and Mod-S cams come to mind. Faster lobe ramps means more air flow like a high overlap cam, but without the overlap (and subsequent rough low RPM running). Modern cam designs are pretty amazing; you can pretty much get any perf characteristics you want depending on how much you are willing to put into the valve train.

My new cams for my 2.0S are very, very special. They don't require titanium valves, but the accel/decel speeds of this cam are close. John Dougherty and I went back and forth a lot to come up with a solution that will pull like an 'E' down low, yet rev to peak HP at 7800 RPM. The design criteria was something between a Mod-S and a GE60; I think he nailed it.

They are getting installed in the next few months; I'll give you guys an update when I know the results. I'm expecting somewhere around 190HP.

That would be "Camgrinder?" I have spoken with that John and I think he will be doing my cams and rockers.

[kenikh]

That would be "Camgrinder?" I have spoken with that John and I think he will be doing my cams and rockers.

I was indeed speaking of the illustrious Camgrinder.