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RAMPS The parts of a camshaft lobe that actually initiate the lifting and descending movement of the lifter are called
“ramps”. Ramps include the lash ramp, the opening ramp, and the closing ramp. Camshaft lobe ramps are ground to
have different rates of lifter movement in terms of velocity and degrees of duration, as measured in degrees of crankshaft
rotation.

The “lash ramp” of a camshaft lobe is a mid-point location between
the opening ramp and closing ramp.
The “opening ramp” of a camshaft lobe is the point where the
lifter just begins to lift until the point that it reaches the nose of the
lobe.

The “closing ramp” is the point of the camshaft lobe from the nose
back down to the lash ramp

NOSE The “nose” of a camshaft lobe is the top or the highest maximum
lift point for the valve. It is where valves are kept open for
as long as possible before making the transition to the closing
ramp.

BASE CIRCLE The “base circle”, also known as the “heel”, is the
lowest point of the camshaft lobe and is the place where the valve
is in the closed position. The “base circle” is the point where all
valve lash settings are made.

SYMMETRICAL is a term that refers to the “profiles” of the opening
and closing ramps of a camshaft lobe. All “early technology”
camshafts were ground on a symmetrical design, meaning both
sides are exactly the same. That is to say the profile of the closing
ramp is a “mirror image” of the opening ramp.

ASYMMETRICAL refers to a camshaft lobe profile where the opening
and closing ramps are not exactly the same. The reason some
camshafts are this way is to try to achieve an opening ramp profile
that has a high velocity and a closing ramp profile that has a
slower velocity. In this way the valve can be set down more “gently”
than the rate at which it was first opened.

A DUAL PATTERN camshaft has an intake lobe profile design that
differs from that of the exhaust lobe profile design. For example,
camshaft “A” has intake lobes of 260º duration while the exhaust
lobes are 270ºduration. Camshaft “B”, has intake and exhaust
lobes that are both at 260º. Camshaft “A” is referred to as a dual
pattern, while camshaft “B” is referred to as a single pattern.

With the advent of emissions laws and the widespread use of computer
systems, more modern single and dual profile pattern
designs have been developed. A dual pattern camshaft is ground
to “bias” the duration of either the intake or exhaust lobe. For
example, if an engine is restricted on the exhaust side, compared
to the intake side, the camshaft designer would try to compensate
by grinding in more lift and/or duration on the exhaust lobe.







PISTON POSITION
The following table defines the abbreviations
the bottom or top of its stroke:

TDC  Top dead center
BDC  Bottom dead center
ATDC After top dead center
BTDC Before top dead center
ABDC After bottom dead center
BBDC Before bottom dead center

LIFT
Lift refers to maximum valve lift. This is how much the valve
is “lifted” off its seat at the cam lobe’s highest point.

How is it measured?
Valve Lift is the amount (usually in inches) that the valve is
lifted off of its seat. It is usually measured with a dial indicator
at the tip of the valve. Lobe Lift is the amount (usually in
inches) that the cam lobe increases in radius above the cam
base circle.

Tip: To quickly find maximum lobe lift, measure the base circle
of the cam and subtract it from the thickness across the cam
lobe’s highest point (see the diagram below).

Tip: Maximum valve lift can be calculated by multiplying the
maximum lobe lift times the rocker ratio. For example, a
0.310” lobe lift cam yields 0.496” of valve lift when using a 1.6
ratio rocker arm.

Formula: valve lift = lobe lift x rocker ratio

What does it do?

The intake and exhaust valves need to open to let air/fuel in and exhaust out of the cylinders. Generally,
opening the valves quicker and further will increase engine output. Increasing valve lift, without increasing
duration, can yield more power without much change to the nature of the power curve. However, an
increase in valve lift almost always is accompanied by an increase in duration. This is because ramps are
limited in their shape which is directly related to the type of lifters being used, such as flat or roller.

DURATION

Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the
cam lobe.

How is it measured?

Advertised duration is the angle in crankshaft degrees that the cam follower is lifted more than a predetermined
amount (the SAE standard is 0.006”) off of its seat. Duration @.050” is a measurement of the
movement the cam follower, in crankshaft degrees, from the point where it’s first lifted .050” off the base
circle on the opening ramp side of the camshaft lobe, to the point where it ends up being .050” from the
base circle on the closing ramp side of the camshaft lobe. This is the industry standard, and is a good value
to use to compare cams from different manufacturers. Both are usually measured with a dial indicator and a
degree wheel.

What does it do?

Increasing duration keeps the valve open longer, and can increase high-rpm power. Doing so increases the
RPM range that the engine produces power. Increasing duration without a change in lobe separation angle
will result in increased valve overlap.

UNDERSTANDING CAMSHAFT SPECIFICATIONS

LOBE SEPARATION
Lobe separation is the angle in camshaft
degrees between the maximum lift
points of the intake and exhaust valves.
It is the result of the placement of the
intake and exhaust lobes on the camshaft.

How is it measured?
Lobe separation can be measured using a dial
indicator and a degree wheel, but is usually
calculated by dividing the sum of the intake
centerline and the exhaust centerline by two.

What does it do?
Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, idle vacuum,
etc.

OVERLAP
Overlap is the angle in crankshaft degrees that both the intake and exhaust valves are open. This occurs
at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift duration and/or
decreasing lobe separation increases overlap.

How is it measured?
Overlap can be calculated by adding the exhaust closing and the intake opening points. For example, a
cam with an exhaust closing at 4º ATDC and an intake opening of 8º BTDC has 12º of overlap.

But keep in mind that since these timing figures are at 0.050” of valve lift, this therefore is overlap at
0.050.” A better way to think about overlap is the area that both lift curves overlap, rather than just the
crankshaft angle that both valves are open. Therefore, one can see that decreasing the lobe separation
only a few degrees can have a huge effect on overlap area.

What does it do?
At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the
fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the
effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality.

CENTERLINES
The intake centerline is the point of highest lift on the intake lobe. It is expressed in crankshaft degrees
after top dead center (ATDC). Likewise the exhaust centerline is the point of highest lift on the exhaust
lobe. . It is expressed in crankshaft degrees before top dead center (BTDC). The cam centerline is the point
halfway between the intake and exhaust centerlines.



ADVANCE/RETARD
Advancing or retarding the camshaft moves the engine’s torque band around the RPM scale by moving the valve
events further ahead or behind the movement of the piston. Typically, a racer will experiment with advancing or
retarding a cam from “straight up” and see what works best for their application. Lunati camshafts are ground to
provide maximum performance and are designed to be installed to the specifications listed on the cam card.

How is it measured?
A cam with a 107º intake lobe centerline will actually
be centered at 103º ATDC when installed 4º
advanced.

Some camshafts have a certain amount of
advance “ground in. “Ground-in advance” can also
be found by subtracting the intake lobe centerline
from the lobe separation.

What does it do?
Advance improves low-end power and response. For a
general summary of the affects of camshaft timing,
refer to the following table:

Advance
begins intake event sooner
opens intake valve sooner
builds more low-end torque
decreases piston-to-intake-valve clearance
increases piston-to-exhaust-valve clearance

Retard
delays intake event
opens intake valve later
builds more high-end power
increases piston-to-intake-valve clearance
decreases piston-to-exhaust-valve clearance



UNDERSTANDING VALVE TRAIN COMPONENTS

LIFTER

The cam lifter (also called a “follower” or “tappet”) is the component that makes direct contact with the
cam lobes and “follows” the profile of the cam. There are generally four types of lifters:

Hydraulic Flat Tappet

The hydraulic flat tappet is self-adjusting, due to the valve controlled plunger within the tappet body. It
operates to pre-load the push-rod by using the oil system pressure to maintain this pre-load in the closed
valve position. Hydraulic tappets are quieter than mechanical tappet lifters since there is no lash or freeplay.
However, it is generally agreed that they fall short of offering optimum performance above 6,000 -
6,500 RPM. Many cheaper designs fall even shorter than this. This poor performance at high RPM is due
mainly to the inability of the lifter to “bleed down” the excessive oil pressure , and thus does not allow the
valves to seat.

Mechanical Flat Tappet

The mechanical (solid) tappet is essentially a solid “link” between the cam lobe, and the push-rod. In most
cases it is a simple heat-treated cylinder with a radiused contact face. It allows more RPM potential than
that of the hydraulic tappet since there are no worries about the inability of the lifter to “bleed down.”
Solid lifters do, however require lash or clearance to allow for part expansion as the engine heats up.

Mechanical Roller Tappet

The mechanical (solid) roller tappet allows for the most aggressive lobe designs. Roller tappets allow faster,
“steeper” opening and closing ramps. This allows the cam to produce more lift for a given duration. They
are not limited to a particular lifter diameter to obtain higher cam lifts. They also contain a roller that
reduces friction between cam and followers. Roller cams require the use of higher valve spring forces
making high engine speeds (over 10,000 RPM’s) possible.

Hydraulic Roller Tappet

The hydraulic roller tappet camshaft can provide the best of both worlds. Diesel engines and some motor
cycle engines have used this design for many years. They provide most of the virtues of a solid mechanical
roller tappet while providing the benefits of quiet operation and ease of valve lash setting.
This type of design still has the limitations of an oil bleed-off control type follower. If your application
requires high RPM potential you should use a solid roller tappet design.

Roller or Falt Tappet?

Manufacturers and racers have used flat tappet camshaft systems over the years with great success. However,
manufacturers and racers favor roller tappet cams (when rules permit their use) because roller cam designs have
distinct advantages over flat tappet designs:

Friction
Sliding frictional forces are higher than rolling frictional forces. Therefore, a roller cam takes less horsepower to
turn and generally does not wear out as quickly. An added benefit is that roller tappets do not require replacement
when changing cams. And, if “pop-up” solid roller tappets are used (such as P/N 72840), the camshaft
can be swapped without removing the intake manifold.

Profile
If a cam profile has more “area under
the curve,” it has the potential to make
more power. Roller profiles can be more
“aggressive” and accelerate the tappet
more than a flat tappet profile.

Flat tappet profiles can only be shaped
up to the point where the tappet “digs
into” the profile. Roller tappet profiles
are not limited by this condition-so
much that even “inverted radius” profiles
are possible.

This benefits engine performance in two
ways: more tappet lift can be achieved
without the added duration that would
normally be required to “ramp up” a flat
tappet to the added lift-making the lift
curve more “pointy”; the lift curve can
be made “broader” without increasing
lift. Of course, both of these benefits can
be combined to create a profile that can
easily outperform flat tappet cams.

Cost
Unfortunately, roller camshaft systems
cost more than a flat tappet cam and
lifters. Much of the added cost is due to
the lifters. However, roller tappets can be
re-used, where as flat tappets cannot not
be re-used. If you tear down your engines
frequently, the rollers can be used over
and over again provided they are not
damaged or show signs of wear.

Thats all for now 

Like I said, there is a lot to be learned there when it comes to engine compnents, theory, and maximizing setups.  Don't listen to anything they say concerning Speed Density though.  For that http://www.50tech.com is the place to be.  At one point there was a guy over there running 36 pound injectors with a STOCK A9P computer.

AHEM... The A9P EEC is Mass Air

A poor idle and 3 mpg ain't my idea of good all round vehicle

the problem is that you will force the system to run into what's called, an "Adaptive Strategy  " condition. When you check SD/MA EEC-IV systems ECM pinout at the ECM ('86-'93), HO and non-HO, with the exception of the '91-'93 T-Bird MA system (similar to '94-'95 Mustang systems).....all have the same arrangement.....check it here.

If you change the injector pins, the system will adjust fuel trim on a bank 1 injector, based on the B1 O2 readings, for an injector that is now connected in bank 2, and vice versa........for example, using their layout you have a 154.... firing order

1 - 5 - 4 - 2 - 6 - 3 - 7 - 8  which divided by bank (B1 = cyl 1-4 and B2 = cyl. 5-8) would be.....

B1-B2-B1-B1-B2-B1-B2-B2......now you switch the injector wiring .....5-to-3, 4-to-7, 3-to-5 and 7-to-4......to ensure the injectors firing order......

1 - 3 - 7 - 2 - 6 - 5 - 4 - 8 ......which should be.....

B1-B1-B2-B1-B2-B2-B1-B2.....when you lay it out by bank, but it's not.... what happens to the "logic".....

EXAMPLE: B1 O2 reads RICH condition and adjusts (shortens) fuel trim pulse for B1 injectors (1-4)

1. System shortens B1 fuel trim, but since #3 and #4 are now in B2 (5 and 7).....such a change will not be enough since the O2 in B1 will read half of the fuel trim effect (2 injectors), so the system continues to shorten fuel trim even further.....looking for a change in B1 AF readings....but wait, there's more......The fuel pulse tpuppies for B1 will affect B2 O2 readings (#3 and #4 are in B2)....causing B2 readings to be LEAN...

2. The system then determines it needs to lengthen B2 fuel pulse due to #1 above, and it does for the 5-8 injectors, but since #5 and #7 are now in B1, the adjustment for B2 affects B1 O2 readings....causing B1 to continue to read RICH. And since B2 O2 readings have not changed that much, the system continues to lengthen B2 fuel trim pulse.........

For crying out loud, the system is going crazy..... ...(I know I am explaining this.....)...and will eventually cause a ....condition from the ECM.

It's like having a normal EEC-IV system, but installing the LH O2 sensor to the RH connector and vice versa.....the system will adjust injectors 1-4 based on the AF readings from injectors 5-8......and ....I've seen a few of those cases as well......