Camshaft design

[hoffman900]

Another thread:
Solid Cam with "Forgiving" Lash Ramp Design
https://www.speed-talk.com/forum/viewtopic.p ... 0&start=60

[GARY C]

When choosing a cam for a given application how do you determine an asymmetrical vs symmetrical or inverse radius vs stnd radius lobe?

What is the power difference between the 2?

[hoffman900]

When choosing a cam for a given application how do you determine an asymmetrical vs symmetrical or inverse radius vs stnd radius lobe?

What is the power difference between the 2?

The answer is going to be by the valve lift curve and working back through the valvetrain geometry. A sliding follower type camshaft really makes this apparent.

Really great podcast interview with Billy Godbold: https://www.youtube.com/watch?v=whmOxK4XDYQ Covers a lot of what we have talked about here (LSA, Lift, Duration, Spintron, Jerk, Acceleration, etc.)

I wonder who he is talking about when he refers to the "one of the old cam designers, I use to call him the John Daily of cam designer, grip it, rip it, and try to put a tail on it to close"? Harold?

Cool discussion at 52:00 about Harvey Crane and negative jerk.

[GARY C]

When choosing a cam for a given application how do you determine an asymmetrical vs symmetrical or inverse radius vs stnd radius lobe?

What is the power difference between the 2?

The answer is going to be by the valve lift curve and working back through the valvetrain geometry. A sliding follower type camshaft really makes this apparent.

Really great podcast interview with Billy Godbold: https://www.youtube.com/watch?v=whmOxK4XDYQ Covers a lot of what we have talked about here (LSA, Lift, Duration, Spintron, Jerk, Acceleration, etc.)

I wonder who he is talking about when he refers to the "one of the old cam designers, I use to call him the John Daily of cam designer, grip it, rip it, and try to put a tail on it to close"? Harold?

Cool discussion at 52:00 about Harvey Crane and negative jerk.

Good Podcast.

[CGT]

I wonder who he is talking about when he refers to the "one of the old cam designers, I use to call him the John Daily of cam designer, grip it, rip it, and try to put a tail on it to close"? Harold?

That's how I took it. I thought Brookshire when I heard that. Cool video, thanks for the link. A smart, humble guy there that has been involved with a ton of stuff...wow. Definitely stands apart from the typical camshaft chest-beaters.

[user-29956]

I wonder who he is talking about when he refers to the "one of the old cam designers, I use to call him the John Daily of cam designer, grip it, rip it, and try to put a tail on it to close"? Harold?

That's how I took it. I thought Brookshire when I heard that. Cool video, thanks for the link. A smart, humble guy there that has been involved with a ton of stuff...wow. Definitely stands apart from the typical camshaft chest-beaters.

There is definitely no shortage of those!!!!!!! Good ole Billy....always has a knack for perspective..............

[CGT]

There is definitely no shortage of those!!!!!!!

Chest-beaters? Are you included in this group?

[GARY C]

I wonder who he is talking about when he refers to the "one of the old cam designers, I use to call him the John Daily of cam designer, grip it, rip it, and try to put a tail on it to close"? Harold?

That's how I took it. I thought Brookshire when I heard that. Cool video, thanks for the link. A smart, humble guy there that has been involved with a ton of stuff...wow. Definitely stands apart from the typical camshaft chest-beaters.

He is the same on phone and email, he told me that they have dyno challenges among them selves and he only wins when he cheats with a new lobe that he hasn't given to the guys yet.

[hoffman900]

Billy’s AETC presentation from this past December: http://www.aetconline.com/wp-content/ed ... odbold.pdf

Page 26 of two example cams is the most interesting to me.

That's how I took it. I thought Brookshire when I heard that.

It just sounded like Harold's design style. By all means, he was very successful at it, I just think he was so in-tune with his way of designing cams, and he did it for a long time without visual aids, that only he could have really pulled it off. I believe Mike Jones said, paraphrasing, that Harold was as much of a mathematician as he was a cam designer. From what I've learned, I tend to agree.

The photos I've seen from Billy at his desk appear to have the Blair 4stHEAD open on his computer. One of the big selling points with this program is the ability to click and drag the acceleration curve around, it will then integrate back to velocity and lift, and differentiate to jerk. This gives you A LOT more control over the velocity and jerk curves than trying to adjust from the lift curve itself.

[hoffman900]

And one of my favorite tech writers, Kevin Cameron.

https://www.cycleworld.com/valve-float- ... ead-center

In a normally functioning conventional valve train, a cam rotating at one-half of crankshaft speed pushes the valve open, and a spring or springs on the valve compel the valve train to follow the cam’s closing side, returning the valve to its seat. Valves are not snapped shut by the spring after being opened by the cam – the closing impact would quickly damage the seal between valve and seat, and would shortly break the valve. The spring, holding the valve train in firm contact with the closing side of the cam lobe, first accelerates the valve toward its seat, then in the last ~ 25% of travel the cam decelerates the valve to a survivable seating velocity of a couple of feet per second.

If an engine revs high enough, the stiffness of its valve springs may no longer be enough to keep the valve train in contact with the cam lobe. This is called valve float because the valve train “floats up” off the cam contour because the spring force is at high speed too weak to overcome valve train inertia. It is typical for this to occur shortly after the cam lobe has finished accelerating the valve upward, and transfers valve control to the spring.

Valve float has traditionally been regarded as undesirable because it can be destructive, resulting in violent contact between the piston, nearing the top of its exhaust stroke, and the exhaust valve, which is in the process of closing. The usual outcome – the head of the exhaust valve breaking off its stem and then being hammered into the piston crown – was given the name “penny-in-the-slot” by Harold Willis, Velocette’s phrase-loving rider-engineer of the 1930s. A romantic view of valve float was that of motorcyclist-turned-auto-racer Tazio Nuvolari, who once said, “For me, there is only one speed – that at which the valves bounce hard off the pistons!”

Yet it turns out that valve float is not always harmful. When British manufacturers who competed in the Isle of Man TT races were switching from pushrod OHV valve operation to overhead cam (OHC) in the mid-1920s, they had the experience of finding that their new OHC prototypes performed significantly less well than the OHVs they were designed to replace. How could this be?

These makers had naturally given their new OHC prototypes the same cam profiles proven in their OHV engines. Without the extra weight of pushrods and rocker-arms, valves in the OHC engine followed the cam profile exactly. They did not float up off it at about half lift, then fly over the nose of the cam lobe to land somewhere on the closing flank – a process which usefully increased valve lift. That extra “float-induced” lift was improving engine breathing in the OHV engine, but that extra lift disappeared with the OHC engine’s superior valve control, reducing its performance.

When engineers at AJS (a large manufacturer 90 years ago) understood this and gave their OHC engine the extra lift its improved valve control could easily handle, its performance left the pushrod OHV engine behind. At Sunbeam, the OHC prototype was quietly put aside, the team reverted to pushrod, and nothing more was said about it.

Nobody in this world knows more about valve control than the technicians on NASCAR teams who are operating their Spintron valve motion analysis systems 8 – 12 hours of every working day. Such systems reveal every detail of valve motion, including the bow-stringing of pushrods, rocker flex, cyclic tilting of rocker stands, cam bending, and the number of times a valve bounces up off its seat at closing.

Fifty years ago, so-called “polydyne” cam profiles were hailed as a way to “anti-vibrate” a valve train to suppress unwanted oscillations (such as the above list). Skeptics pointed out that the tiny variations in cam profile height necessary to accomplish this were smaller than manufacturing error, and were thus impossible.

Be that as it may, you can bet that nearly every NASCAR Spintron operator has called the shop foreman to the screen, saying, “Look at this”. On the screen could be seen stable, non-destructive, large-scale valve float of the kind that accidentally boosted power in 1920s OHV bike engines.

“It’s been running like this for ten minutes, and nothing’s broken”, says the operator.

The next step was to try it in a full engine build. Extra valve lift – no matter how it occurs – has the potential to fill cylinders more completely, boosting power. Thus was born the short-lived fad (some say) for “loft” as a power-boosting concept in NASCAR.

When we suddenly find a need for something once considered harmful, we make up a trendy new name for it. Thus economic inflation was in 2009 re-named “quantitative easing”.

Similarly, when failure to follow the cam lobe broke parts, we called it “float”, but when it boosted power and broke nothing, we call it “loft”. The cam lobe is ‘lofting’ the valve train off the deceleration part of the opening flank, allowing it to sail over the nose of the cam with a useful amount of extra lift, then making a survivable landing somewhere on the closing flank.

TIOC May 2005
Eaten Alive by Parasitic Oscillations
by Kevin Cameron

As a new hi-fi amplifier is designed by an electronic engineer,
particular care must be taken to be sure that unforeseen combinations
of resistance, inductance, and capacitance do not permit so-called parasitic
oscillations; to build up, destroying the music.

Each property of electrical circuits has a mechanical analog, and one
mechanical system that is often rife with its own parasitic
oscillations is the valve train. Rocker arms bend, pushrods compress
and expand, camshafts deflect between their bearings, and valve stems
flop from side to side while valve heads deflect like trampolines or
floppy disks. All of this is invisible to us. Its symptoms are valve
seat recession and valve spring and valve breakage. In many cases,
after tests with a new cam that gives really good power, we have to
reluctantly back up to a previous, less powerful set-up because we
can't afford the DNFs and breakages that the hot set-up
produces. Valve train failures are hit-and-miss, trial-and-error, a
mystery. Lighter valve train parts and stronger springs sometimes just
seem to make everything worse. Is there any truth?

Back in the 1920s Percy Goodman decided it was time to put aside
clattering pushrods and adopt trendy OHC valve drive on the TT
Velocettes he manufactured. Soon he was driven crazy by erratic valve
motion and sensibly resorted to the use of a strobe light to reveal
what was happening. But naming the illness is not the same as a cure.

When I was recently at the NHRA drag nationals in Houston, I had the
opportunity of conversation with Byron Hines, whose purpose-designed
giant 160-cubic-inch V-twin engine has recently begun to win Pro Stock
races. I asked what had made the difference after some uncompetitive
seasons.
The Spintron, was his answer. It showed us that our valve
motion was nothing like what was in the cam profiles.

When I was recently at the NHRA drag nationals in Houston, I had the
opportunity of conversation with Byron Hines, whose purpose-designed
giant 160-cubic-inch V-twin engine has recently begun to win Pro Stock
races. I asked what had made the difference after some uncompetitive
seasons.
The Spintron, was his answer. It showed us that our valve
motion was nothing like what was in the cam profiles.

Spintron use a big electric motor to spin your engine while a variety
of instrumentation is used to measure the actual trajectories of the
parts you are interested in. This is different from using a
strobelight in that the information you get is detailed enough to
allow the flexing of each part to be isolated and understood.

Byron went on to say that valve train dynamics are particularly
difficult to control in big twins because of the large variations in
crank speed as each cylinder fires. The cam profiles were originally
developed to work at a particular maximum rpm, provided that the
camshafts turn smoothly. They do not turn smoothly because the crank
does not turn smoothly; it advances in a series of fairly violent
jerks. 80 percent of the recoverable energy in the hot combustion gas
does its work between 10-deg ATDC and 80 ATDC. Out of the 720 crank
degrees in the engine cycle, power is given during only 10%. This
means that the instantaneous speed of the cam can often be much higher
than its average speed. This also means that as a cylinder fires and
the crank accelerates suddenly, an open valve in the other cylinder
may be tossed right off its cam profile, or dropped prematurely onto
its seat.

This reveals why tuners of singles and twins found that their bikes
top-ended better and faster the heavier their cranks were made. A
younger generation of tuners has rejected this idea as turn-of-the-century
dirt-track nonsense, reasoning that physics requires lighter flywheels to
result in faster acceleration.
Vintage racer Todd Henning learned the heavy crank truth
in back-to-back testing of his highly tuned Honda twins, as did Rob
Muzzy in 1981-83 with 1025-cc Kawasaki in-line fours. The heavier the
crank, the smoother its rotation becomes, and the less power stroke
disturbance, or is transmitted to the cams. Where
does the lost power go when a light crank is used? Erratic valve
motion is one answer, and big valve bounce after closing is another.

Power pulsing is not the only disturbance to the valve train. Consider
a parallel twin, a flat twin, or an in-line four. In all of these, all
the pistons stop simultaneously. This means that as pistons decelerate
to a stop, the crank must accelerate rapidly because there is nowhere
else for the pistons' energy to go ; its conservation of
energy. Peak piston speed is about 1.5 times mean piston speed. This
means that all the kinetic energy in the pistons, moving at near 100
feet per second, is suddenly dumped into the crank. This is especially
bad for in-line fours, which have small-diameter cranks and little in
the way of flywheel mass. This sudden crank deceleration/acceleration
cycle is performed twice per revolution. No wonder new engine
development usually involves coping with cam drive breakage. No wonder
there are mystery failures of valve train parts.

Allan Lockheed is the man behind the engine design software Engine
Expert, and he talks to engine people all over the world. He has
tales of engines whose valves were stable with a chain or belt cam
drive, but which mysteriously began to break valve springs as soon as
a much more rigid gear drive was put in its place. The slight
flexibility of chain or belt took the sharp edge off the sudden crank
speed variations, preventing high frequency motions from reaching the
valve train. This may be why Yamaha retain a chain cam drive in their
M1 in-line four MotoGP race engine. The oil film between each of the
cam chain's pins, bushings, and rollers can be thought of as a kind
of viscous damper. Such fluid film damping is one of the motivations
inclining the designers of rocket engine turbopumps to give up rolling
element shaft bearings in favor of plain journal bearings. A gear cam
drive has fewer than 10 oil films between the crank and cam, but a
chain has a great many more.

Phil Irving, designer of Vincent motorcycles, suggested construction
of parallel twins with crankpins not at the traditional 360 degrees,
but separated by 76 degrees. With usual rod ratios, the piston reaches
maximum velocity at about 76-deg ATDC. At this point, the crank arm is
at right angles to the con-rod; the condition for maximum piston
velocity. This crankpin angle would therefore cause one piston to be
stopped when the other was at maximum speed. The result would be that
the two pistons would exchange their kinetic energy only with each
other, and not with the crankshaft, eliminating one important source
of cam drive disturbance.

Wide-angle Vee engines are better in this respect than parallel twins
but even they have their problems. The classic Cosworth DFV V8 GP car
engine of 1967 was estimated during design to have no more than a 35
pounds-foot torque peak in its cam drive, but actual testing revealed
peaks ten times greater; leading to drive failure. As the engine
was already near production when this was discovered, designer Keith
Duckworth had to scurry around and design a compact spring drive
(analogous to what is found in clutch cush hubs) that could be
incorporated into one of the gears in the drive.

Another approach is that seen on certain WW II German V-12 aircraft
engines, and on late race versions of Honda's RC30. In these and
other cases, small flywheels have been attached to the cams
themselves.

It is interesting to note that both Velocette and Ducati have found
that changing the stiffness of cam drive towershafts can be used as a
tuning measure to adapt an engine to a given race track a stiff
towershaft on short courses, and a more limber one for longer
tracks. The parts seem stiff and strong only in our imaginations and
in our not-very-stiff protein hands. In fact, at speed, everything in
engines is flexible because the amounts of energy moving from part to
part can be so large.

Byron Hines noted that as useful as Spintron's instrumentation is,
even more so is the experience and advice of Spintron personnel. One
of the first things they suggested was that he replace his aluminum
rocker arms with steel, for accurate motion depends more on stiffness
than on weight. He also said that full benefit from Spintron requires
making several laps through their process. A first lap involves re-configuring
the cam profiles and valve train to settle the motion and eliminate float
and excessive bounce. A second lap becomes necessary when it is realized
that after lap one, the engine's power curve has sagged in some places.
This is because before, cam timing and lift had been unwittingly chosen to
at least partly compensate for the uncontrolled valve motion. Once the valve
motion is settled, timing and lift are wrong. Now lap two consists of finding
new optimum cam timings and profiles to again maximize power. That, in turn,
brings to view new dynamic problems to be solved in lap three, and so on.
The people with the greatest sophistication in all this are, naturally, NASCAR engine
builders.

As an extreme example of what can happen, airflow
pioneer Jerry Branch was once called upon to dyno a special V-twin
that was conceptually a slice off a small-block Chevy, crank and all.
Being intended as a motorcycle engine, it had no flywheel other than
its little piece of V8 crankshaft. Branch said that although the engine
had plenty of displacement and hot tuning parts that suggested an
easy 100-hp, it never made over 35 horsepower. Each time it fired,
with almost no flywheel mass to smooth the pulse, it launched its
valves into orbit.

Another aspect of unplanned valve motion is the vibratory modes of
valves themselves. Particularly with rocker-arms (which exert some
side-thrust), a valve can be excited laterally as it lifts, the head
of the valve whipping from side-to-side on the stem; the stem
possibly made more flexible by undercutting to squeeze out that last
CFM of airflow. When this flopping valve approaches the seat, one edge
can hit first, causing a motion not unlike the final stages of a spun
coin's motion. Or, approaching its seat squarely, the rim of the
valve stops but the stem and center of the valve head keep right on
going; the trampoline mode of valve flex. When the motion
at the center finally stops, the valve head is quite deformed and it
now snaps back, tossing itself back up off the seat in a cycle that
can make several hops; with considerable lift being reached in the
process. This is a cautionary tale for those who wish to carve away
valve head mass in search of ultimate lightness. Or for those who wish
to replace existing valve shapes with something quite different. Think
about it if things don't go right. You may have made transformed
those elegant chunks of metal from valves into springs.

Spintron is not cheap but all of us can afford imagination. If you
have valve or spring problems, think about what has worked in your
experience with your particular engine, and what has not. Careful
mental sorting here can reveal a lot. Besides, what else is a body to
think about while waiting for a dental appointment? Sit with the
engine and rotate it through its cycle, thinking about what is
happening at each point. Over time you can develop a mental picture of
what may be happening and what might correct the problems. There is
more to valve trains than light parts and heavy springs."

[Stan Weiss]

Billy’s AETC presentation from this past December: http://www.aetconline.com/wp-content/ed ... odbold.pdf

Page 26 of two example cams is the most interesting to me.

That's how I took it. I thought Brookshire when I heard that.

It just sounded like Harold's design style. By all means, he was very successful at it, I just think he was so in-tune with his way of designing cams, and he did it for a long time without visual aids, that only he could have really pulled it off. I believe Mike Jones said, paraphrasing, that Harold was as much of a mathematician as he was a cam designer. From what I've learned, I tend to agree.

The photos I've seen from Billy at his desk appear to have the Blair 4stHEAD open on his computer. One of the big selling points with this program is the ability to click and drag the acceleration curve around, it will then integrate back to velocity and lift, and differentiate to jerk. This gives you A LOT more control over the velocity and jerk curves than trying to adjust from the lift curve itself.

Bob,
Page 14
• The shape of the overlap can be more important than the duration or area
• By tailoring the exhaust closing ramp and the intake opening ramp we can optimize this shape

Page 23
• On the exhaust, delaying the opening without reducing BDC lift can be significantly beneficial for a longer power stroke without the pumping losses typically associated with a shorter exh duration:

So how would these points influence your lobe designs?

Stan

[SchmidtMotorWorks]

Page 23
• On the exhaust, delaying the opening without reducing BDC lift can be significantly beneficial for a longer power stroke without the pumping losses typically associated with a shorter exh duration:

So how would these points influence your lobe designs?

Stan

The first one is incomplete.

With regard to page 23; delaying the start of a motion the with the requirement to reach the same lift requires higher rates of acceleration and the surrounding derivatives.
You can simply try that and see what you get.
If you get trouble,,,,the recipe of those derivatives can be optimized with analysis that is comprehensive of the system as a whole.

[hoffman900]

Billy’s AETC presentation from this past December: http://www.aetconline.com/wp-content/ed ... odbold.pdf

Page 26 of two example cams is the most interesting to me.

That's how I took it. I thought Brookshire when I heard that.

It just sounded like Harold's design style. By all means, he was very successful at it, I just think he was so in-tune with his way of designing cams, and he did it for a long time without visual aids, that only he could have really pulled it off. I believe Mike Jones said, paraphrasing, that Harold was as much of a mathematician as he was a cam designer. From what I've learned, I tend to agree.

The photos I've seen from Billy at his desk appear to have the Blair 4stHEAD open on his computer. One of the big selling points with this program is the ability to click and drag the acceleration curve around, it will then integrate back to velocity and lift, and differentiate to jerk. This gives you A LOT more control over the velocity and jerk curves than trying to adjust from the lift curve itself.

Bob,
Page 14
• The shape of the overlap can be more important than the duration or area
• By tailoring the exhaust closing ramp and the intake opening ramp we can optimize this shape

Page 23
• On the exhaust, delaying the opening without reducing BDC lift can be significantly beneficial for a longer power stroke without the pumping losses typically associated with a shorter exh duration:

So how would these points influence your lobe designs?

Stan

Sounds like all the more reason to have an asymmetrical lobe with a more aggressive opening (which works to a point as Jon pointed out). Rocker ratio would probably be your friend here. I agree with Jon about the first part.

Check out the asymmetrical NASCAR flat tappet on page 26 (Billy confirmed that’s what that was). An aggressive, delayed opening and softer closing was Harold’s style. As Mike J. has pointed out, Harold had asymmetrical ramps, and as someone else has pointed out, Harold’s designs were symmetrical by .200” lift. Mike has also pointed out this is how Comp designs theirs as well.

The hydraulic on the same page looks like what Harold has posted and others have described of his designs this is also what Harvey Crane was doing with the no pulse opening / reversal closing. Billy said he prefers the near constant jerk closing than a full reversal back to zero (which would cause more jerk), and near constant / constant jerk has been used by Comp for a while now on a bunch of their designs. Harvey had an example on his site of a constant jerk closing as well. Harold did share he was using a lot of constant snap designs while at Arrington. I would love to see those curves profiled as I haven’t seen a constant snap curve.

I have only seen a couple Comp designs profiled (and none of Harold’s other than what he shared), so I can’t speak to this first hand. At this point, if I had a Cam Analyzer, I wouldn’t be getting much else done and would be profiling as many cams as I could get my hands on. The acceleration curves are the most interesting / revealing part about this and it’s interesting to see how all the designers approach their design.

In 1977, I joined the guys at Competition Cams as their original cam designer. I brought the concept of the unsymmetrical cam with me, and started developing it.
To fill in a hole in their inherited hydraulic cam line, I designed a cam we called the 268 High Energy, using the same technigues I was using on my roller cams, including unsymmetricalness.
It worked. Boy, did it work.
In 1980, I left Competition Cams and started UltraDyne.
I had a concept of using a blend of Constant Acceleration, Constant Jerk, and polynomial curves into what I called a "Multi-Segmented Polynomial" equation, or 'MSP'. Constant Acceleration and Constant Jerk curves are forms of simplified polynomials, so polynomial describes them all. The cams were unsymmetrical, with different opening and closing sides.
You guys all know the rest from there.

[hoffman900]

Billy’s AETC presentation from this past December: http://www.aetconline.com/wp-content/ed ... odbold.pdf

Page 26 of two example cams is the most interesting to me.

That's how I took it. I thought Brookshire when I heard that.

It just sounded like Harold's design style. By all means, he was very successful at it, I just think he was so in-tune with his way of designing cams, and he did it for a long time without visual aids, that only he could have really pulled it off. I believe Mike Jones said, paraphrasing, that Harold was as much of a mathematician as he was a cam designer. From what I've learned, I tend to agree.

The photos I've seen from Billy at his desk appear to have the Blair 4stHEAD open on his computer. One of the big selling points with this program is the ability to click and drag the acceleration curve around, it will then integrate back to velocity and lift, and differentiate to jerk. This gives you A LOT more control over the velocity and jerk curves than trying to adjust from the lift curve itself.

Bob,
Page 14
• The shape of the overlap can be more important than the duration or area
• By tailoring the exhaust closing ramp and the intake opening ramp we can optimize this shape

Page 23
• On the exhaust, delaying the opening without reducing BDC lift can be significantly beneficial for a longer power stroke without the pumping losses typically associated with a shorter exh duration:

So how would these points influence your lobe designs?

Stan

From the thread, Valve Timing Events??: http://www.speedtalk.com/forum/viewtopic.php?p=73892

It depends on what you mean as "the best attributes for driving".
If we look at factory cars, that are made to have the "best attributes for driving", we see that they generally have wide, or very wide, lobe seperation angles, for good idle and vacuum, and a flat torque curve.
No matter what the duration or LSA, I rank the importance of valve timing in the following order:
1ST(& 2ND!)---Exhaust opening(which occurs first) and Intake opening.
3rd---Intake closing.
4th---Exhaust closing.

The exhaust opening point will govern how the intake fills, no matter where the intake opening occurs. It does this by cleaning out the cylinder of burned exhaust gasses, which determines the volume and pressure of whatever residual exhaust gasses are in the cylinder when the intake valve opens.
The amount of exhaust gasses in the cylinder at intake valve opening cause reversion---less exhaust gasses, less reversion, more exhaust gasses, more reversion.
The amount of reversion determines cylinder filling on the intake stroke, less reversion, earlier port flow, more reversion, longer port recovery time.
It goes on from there, but I have posted this a number of times, and I do not want to let the cat out of the bag too many times........

UDHarold

Digger,

The valve events needed for an engine with a 500 to 4500 power band are completely different in what they affect compared to an engine with a power band from 4500 to 9000, and to all variations in between.
Exhaust events are compromised by the need to extract all the torque possible before opening the exhaust valve, and the need to extract all the burned exhaust gases possible before the intake valve opens. After TDC the exhaust valve closing, if longer than needed for low-speed dynamic control, allows excess exhaust reversion to enter the intake from exhaust gas pulsations. This is why I claim the exhaust valve closing is the least important of the four events; It only affects low-speed power. at higher speeds the other events are much more important.
The exhaust cam gets in a race all its' own, a race between how much torque can be made by delaying exhaust valve opening, and how much exhaust can get out before the intake valve opens. How much exhaust gas is out of the cylinder affects how much intake charge can get in.
Peak Horsepower occurs when the exhaust can no longer effectively clean out the cylinder, and leaves residual gases in the cylinder, hindering intake filling.
Intake opening before TDC is to minimize exhaust gas reversion into the intake port, which aids in cleaning out the port entrance after the piston starts down ATDC. The sooner the intake can start flow into the cylinder, the higher the intake port velocity can be, the more inertia ram you can develop in the intake port, and the longer you can fill the cylinder ABDC.
As long as intake charge is still entering the cylinder, it doesn't matter too much when you shut the intake valve. I have had this proved to me for 30 years, with unsymmetrical cams still providing good bottom-end torque, even with delayed intake closings.
I'll talk more later, now it's Honey-Dew.....

UDHarold

Mark,

Look at any dyno engive curve; whether stock, hot street, street-n-strip, bracket, full-race, oval track, it makes no difference. They all show a peak torque point, then decreasing torque and increasing horsepower, then peak horsepower and a tumbling torque curve.
There are all sorts of theories to explain what is happening; Here is mine.
Peak torque is where peak cylinder pressure occurs, and after this point, torque starts decreasing, yet the horsepower curve is still going up. This is because horsepower is a measurement of torque and rpm, divided by a conversion factor ---5252---.
As long as the torque curve is dropping at a slow rate, the math of the equation keeps the horsepower number going up. But at some RPM point, the torque curve starts dropping more rapidly, and the equation shows this point as peak horsepower.
What happened at that RPM and afterwards, that made the torque curve drop? The torque is just a product of how much charge you got into the cylinder, etc.
You had to get less air/fuel charge in the cylinder.
I maintain that at the point of peak power, the exhaust cam became unable to get as much burned exhaust gases out of the cylinder as before, and some gases were left in when the intake valve opens, in excess of the normal left there. The cylinder had some residual exhaust gases in it, and could not accept the normal amount of clean air/gas mixture. Not as much got in, the engine produced less torque than normal, and the horsepower curve tipped over.
The next cycle, more residual exhaust gases were left in, and less clean air and gas got in.
The next cycle, it got worse, and the horsepower and torque curves are both dropping rapidly.
Wider LSAs and bigger exhaust cams promote better top-end torque and horsepower curves, a la ProStock cams.
At least, this has been my theory for about 30 years.......

UDHarold

Procision Auto,

For about 31 years I have had engine builders who have tried the same dual-pattern cam, on 2 different LSAs, and installed on the identical ICL. The intake timing events were identical, only the exhaust timing events changed.
The wider LSA, with an earlier opening and earlier closing, always made less bottom-end, and more top-end. The cam blew the bottom-end torque out the exhaust, and cleaned the cylinder out better on top-end. It would have a wider power band.
The tighter LSA, with a later opening and a later closing, made more bottom-end/mid-range torque, and dropped the power curve faster after peak horsepower. When it came into power, the torque curve would rise faster, and then drop faster after peak power.
It is my understanding that this is common to all cams.
One caveat: At very low-speeds, between idle and the main torque curve, wider LSA cams make a little better power that tight LSA cams. I believe this is caused by the amount of exhaust overlap ATDC. The wider LSA cams have less, the tighter LSA cams have more. Because of the time in milliseconds involved, the more time the exhaust valve is open ATDC, the more time there is for exhaust pulses to mess up engine airflow.
This is why cams with wide LSAs idle as good as they do.

UDAHarold

No matter what the duration or LSA, I rank the importance of valve timing in the following order:
1ST(& 2ND!)---Exhaust opening(which occurs first) and Intake opening.
3rd---Intake closing.
4th---Exhaust closing.

UDHarold

I would have to agree with that order based on our data, at least for performance applications (we don't have too much data on lesser applications). Of course the intake and exhaust designs can always be changed to make bad things look better, but only to a point.

Clint Gray
TFX Engine Technology Inc.
www.tfxengine.com

[Stan Weiss]

Bob,
Page 14
• The shape of the overlap can be more important than the duration or area
• By tailoring the exhaust closing ramp and the intake opening ramp we can optimize this shape

Page 23
• On the exhaust, delaying the opening without reducing BDC lift can be significantly beneficial for a longer power stroke without the pumping losses typically associated with a shorter exh duration:

So how would these points influence your lobe designs?

Stan

From the thread, Valve Timing Events??: http://www.speedtalk.com/forum/viewtopic.php?p=73892

Procision Auto,

For about 31 years I have had engine builders who have tried the same dual-pattern cam, on 2 different LSAs, and installed on the identical ICL. The intake timing events were identical, only the exhaust timing events changed.
The wider LSA, with an earlier opening and earlier closing, always made less bottom-end, and more top-end. The cam blew the bottom-end torque out the exhaust, and cleaned the cylinder out better on top-end. It would have a wider power band.
The tighter LSA, with a later opening and a later closing, made more bottom-end/mid-range torque, and dropped the power curve faster after peak horsepower. When it came into power, the torque curve would rise faster, and then drop faster after peak power.
It is my understanding that this is common to all cams.
One caveat: At very low-speeds, between idle and the main torque curve, wider LSA cams make a little better power that tight LSA cams. I believe this is caused by the amount of exhaust overlap ATDC. The wider LSA cams have less, the tighter LSA cams have more. Because of the time in milliseconds involved, the more time the exhaust valve is open ATDC, the more time there is for exhaust pulses to mess up engine airflow.
This is why cams with wide LSAs idle as good as they do.

UDAHarold

No matter what the duration or LSA, I rank the importance of valve timing in the following order:
1ST(& 2ND!)---Exhaust opening(which occurs first) and Intake opening.
3rd---Intake closing.
4th---Exhaust closing.

UDHarold

I would have to agree with that order based on our data, at least for performance applications (we don't have too much data on lesser applications). Of course the intake and exhaust designs can always be changed to make bad things look better, but only to a point.

Clint Gray
TFX Engine Technology Inc.
www.tfxengine.com

Bob,
This may play into page 14.

Stan