If it aint broke dont fix it, should be changed abit.
If it aint broke, MODIFY it!!!!

 

Hemi heads do have a more natural flow but they don't have a cleaner burn. Domed pistons don't make a good combustion chamber (the flame travel isn't as nice) and add that hemi heads don't have a proper quench area makes them highly octane dependent. The only way to make a hemi burn clean is to have two spark plugs per cylinder. Dodge quit making the hemi due to it couldn't meet the emission requirements of 1972. Hemi heads also cost more to make and weight more than other head designs. The hemi is a good race engine but it's not a street engine. The 426 hemi is only used in fuel dragsters now and shares nothing with it's street counterpart.

 

Camshaft Basics courtesy of Woody from SBFTECH:

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.

 

this is an excellent thread!! Hey Fom... if you're around, how about making this one a sticky to stay at the top of the list??

 

Now that the camshaft basics are covered we can go back to the Q&A:

"At what point should I choose my camshaft?"

The camshaft SHOULD ONLY be picked once the rest of the engine components have been chosen. The camshaft is the brain of the whole engine. Designing an engine around a camshaft or choosing one by a certain characteristic is downright stupid. Choosing the right camshaft can make an average engine into a performer. Never CHEAP OUT on a camshaft or you will regret it.

"Should I use an off the shelf camshaft or get a custom?"

First off you have to decide on how much you want your engine to perform. OTS camshafts are generic grinds and suit very few engines well. That being said there are many good OTS camshafts but there are even more bad/outdated ones. Ever since fuel injected engines came out, camshaft design has made leaps and bounds. Custom camshafts are ground with specifications down to two decimal places! Ever engine built is different and each owner has different needs. The only way to have a camshaft to make each of the engines components work together is harmony and meet the owners expectations is to go custom. Custom camshafts aren't only for all out race engines. Most custom camshafts are priced within $50-100 of their OTS counterparts.

 

Someone!!!! please get me a hammer.

 

Definatly awesome info.

I second that there should be a tech sticky. It wouldnt have to be just what Nathan wrote here, but different stuff that local guys know about. I know Ryan would probably add some flathead stuff, same with chris.

 

I think we'll just keep our 2 cents to ourselves keep the peace and make Fom's job easier anyone want Flathead, general mechanical info. from us just use MSN.

 

Whatever ya prefer Was just a thought!

 

I`d like to stickie this info but too many stickies in chapters are frowned upon and we have three already.
When I get more time I`ll inquire into making this a stickie, this is awesome info.

 

Thats too bad, this kinda info makes for some good reading.

 

guess there's always the personalized Favorites list in your browser...

 

Or the search function haha

 

I never figured out that search function, how that work?

 

I`m not sure if the FTE search function is back up yet, it maybe.
I haven`t had time to try it out lately.