Special Firing-Order Camshafts

EP 10-2009 51-68_Layout 1 10/8/09 1:52 PM Page 52
TECHSIDE
BY DAVE HAGEN, MIKE CARUSO AND STEVE FOX
Special
Firing-Order
Camshafts
Advanced engine performance tuning
via camshaft design
In certain racing applications, a special
firing order camshaft (SFO) can be used
as a tuning aid, allowing the competition
engine builder to further address
combustion heat and crankshaft
disturbance (harmonic) issues. In essence,
the goal in changing firing order is to
create a smoother running engine and
more even fuel distribution, with
enhanced crankshaft and main bearing
durability. In the process, horsepower
gains may be achieved as well (no
guarantees here, but in most cases, a
slight power increase does result).
Experimenting with special firing
orders (based on camshaft design) isn’t
limited to the advanced race engine
builder. GM adopted a special firing order
in their LS engine series (Gen 3 & 4),
which feature a 4/7 and 2/3 swap for the
same reasons…to smooth out the
harmonics in the pursuit of greater engine
durability and to potentially generate
more power.
The primary reason to address (and
alter) cylinder firing order is to achieve a
smoother-running engine (resulting in a
smoother, more lineal acceleration ramp),
with less harmonic effect and deflection
on the crankshaft and the main bearings.
Which engines can benefit from this? In
theory, virtually all. Typically, the engines
that can realize the greatest benefit
include those powerplants that are
intended to run at or near peak RPM
levels for long periods of time, such as
oval track, road race and marine engine
applications, as well as engines that are
called upon to produce maximum power
in a very short period of time (drag race).
In a V8 configuration, a 4/7 swap
52 OCT-DEC 2009 engine professional
theoretically reduces crankshaft torsional
vibration for smoother dampening and
(potentially) more power.
By swapping firing order positions,
one of the primary goals is to reduce
crankshaft harmonic effects caused by
two adjacent cylinders firing in succession
(let’s call these “companion” cylinders).
By strategically relocating these
companions, it’s possible for the engine to
idle and run smoother, and to reduce
isolated hot spots (cylinder-to-adjacentcylinder walls), and to even-out fuel
distribution, primarily in applications that
feature a single plane intake manifold,
and even more noticeably in tunnel-ram
intake manifold applications.
The “traditional” firing order for
Chevy small and bigblocks in automotive
applications has commonly been 1-8-4-36-5-7-2. Each cylinder has a
“companion” in the firing order. This
companion cylinder will reach TDC at the
same time as its counterpart, one on the
power stroke and one on the exhaust
stroke. These cylinders (paired as 1 & 6,
2 & 3, 4 & 7 and 5 & 8) can be
interchanged in the firing order without
altering the crankshaft. While some
builders report seeing no power
improvement, other builders claim to
have achieved power gains by switching
cylinders 4 & 7 (to create a new firing
order of 1-8-7-3-6-5-4-2). This can
enhance fuel distribution, especially in
open plenum type intake manifolds, and
reportedly can result in an added 5 to 10
horsepower.
According to engine builders at ReherMorrison, Pro Stock drag engines
typically take advantage of a 4/7 swap. By
The cam on the left is a standard firing
order bigblock Chevy. The cam on the
right is a 4/7 swap cam. Notice that
the second and fourth lobes from the
rear on the 4/7 are opposed vs. the
standard cam. This is an easy way to
identify a 4/7 swap cam.
(Photo courtesy Comp Cams)
EP 10-2009 51-68_Layout 1 10/8/09 1:53 PM Page 53
Shown here are three Erson Big Block
Chevy cams (from left to right): a standard
firing order, a 4/7 swap and an LS firing
order cam. (Photo by Mike Mavrigian)
engine professional OCT-DEC 2009 53
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TECHSIDE
BY DAVE HAGEN, MIKE CARUSO AND STEVE FOX
Note that both the 4/7 swap cam
(center) and the LS cam (right) feature
the second and fourth lobes from the
front in an opposed position as
compared to the stock firing order cam.
(Photo by Mike Mavrigian)
swapping #4 and #7 cylinders in the firing
order, this eliminates the fuel distribution
and heat problems caused by cylinders #5
and #7 firing in succession. With the
revised firing order, the two end cylinders
don’t have to fight for fuel from the
manifold plenum. The result, in many
cases, is a measurable power increase
(typically 8-10 HP, according to R-M)
and a smoother, cooler running engine.
However, achieving this special firing
order requires a specially-designed
camshaft (not achieved by simply
switching plug wires). The camshaft lobes
must be repositioned to accomplish this
power stroke/exhaust switch. Years ago,
this required making a special firing order
camshaft from scratch, which was timeconsuming (and naturally more
expensive).
By taking advantage of today’s CAD
programs and CNC machining, however,
special cams can be designed and
fabricated in much shorter timeframes
(also helping to reduce cost).
Note: If a special-firing-order camshaft
is installed in a customer’s engine, the
customer must be alerted to this, to avoid
any confusion during spark plug wire
routing during future service. It’s a good
idea to provide the customer with a decal
that displays the correct firing order,
which can be installed on the race vehicle
(underside of the hood, in the engine bay,
etc.).
CAMSHAFT MANUFACTURER
COMMENTS
We spoke with a few cam makers to
obtain their views on this subject. Steve
Tanzi at Erson Cams noted that a firing
order change accomplishes that task of
alleviating the problem of cylinders 5 and
54 OCT-DEC 2009 engine professional
7 firing next to each other (in a Chevy
V8). However, Steve noted that this
“moves the problem” to the cylinders 2
and 4 area (no matter what the firing
order, you’ll always have a pair firing in
succession, either in adjacent cylinders or
cylinders that share the same rod pin).
However, the front of the block will
generally cool more efficiently, so the
“problem” isn’t much of an issue.
Over the years, GM performed quite a
bit of research in this area, beginning
back in the days of the early Oldsmobile
and Cadillac engines, and most recently
the LS engine family. All along, the goal
was the same…to smooth out engine
pulsations and to create a smoother
accelerating engine. Smoothness of
operation was always the target. If
additional power resulted in the process,
so much the better.
Tanzi also noted that “to yield the
greatest gains requires header design
work…matching primary tubes with
regard to the intake manifold and cylinder
head ports is also necessary. This usually
relates more directly to applications that
use a single plane manifold, and tunnel
ram manifolds in particular. In terms of
fuel distribution, we see greater benefits
with single plane manifolds as compared
to dual plane manifolds, since dual plane
manifolds are less prone to reversion and
negative pulsation.
In Top Fuel engines, as an example,
engine builders have set blowers further
rearward on the engine as a way to
address fuel distribution. In addition,
these guys are experimenting with both
4/7 firing order swaps, and the LS 4/7 and
2/3 swaps.
The issue of firing order is a much
more complicated issue than it appears on
the surface.”
“The greatest benefits,” said Tanzi,
“are seen in oval track and road racing,
because those engines run for longer
periods of time. In a quarter mile
situation, you have only a few seconds to
determine any gains. But, when a builder
is trying to find any repeatable gains (even
1 or 2 HP), it’s worth experimenting with
firing order changes. It’s common practice
for many Top Fuel, Pro Stock and Comp
Eliminator builders to take advantage of
firing order modifications. Keep in mind
though, that depending on the sanctioning
body rules, firing order deviations may
not be allowed, such as in IMCA
Modifieds.”
“Generally speaking,” Tanzi
continued, smoothing out the engine (by
virtue of a firing order change) serves to
diminish harmonics experienced by the
crankshaft, which has a direct impact on
bearing life. When you have a lean (hot)
cylinder, detonation shocks are
transmitted to the crank and main
bearings.
With a fuel injection setup, a lean
cylinder can be richened (via the engine
controller) to eliminate detonation, so
firing order changes may not be as
beneficial in an injected engine, since fuel
is delivered on an individual-cylinder
basis. However, the LS firing order takes
advantage of a 4/7 and 2/3 swap as an
additional tuning aid, to produce an even
smoother acceleration profile and to
benefit crank and bearing life.
Special firing order camshafts have
become so popular that today, what was
once considered a special grind has
become the norm, and what was once
“normal” is now considered special.”
Crane Cams’ Chase Knight notes that
Crane offered SFO cams at no extra
EP 10-2009 51-68_Layout 1 10/8/09 1:53 PM Page 55
This view of the rear of the cams shows the
same lobe orientation of the rear lobes on
the stock cam (left) and the 4/7 cam
(center), but the second and fourth lobes
from the rear of the LS cam (right) are
opposed as compared to the stock and
4/7 cams. These tips help to easily identify a
4/7 swap and an LS firing order camshaft.
(Photo by Mike Mavrigian)
charge. Order time for a custom SFO was
about four days.
Applications included smallblock and
bigblock Chevy, 429-460 Ford, Chrysler
LA smallblock, Chrysler B blocks and
Chrysler 426 Hemi.
Chase noted that “Regardless of what
approach you take, you’ll always have
two cylinders firing next to each other (or
two opposing cylinders that share he same
rod pin). But, by swapping certain
cylinder firing orders, you can more
evenly distribute combustion pressures
and resulting crankshaft loads to either
generate more power, or to extend
crankshaft, main bearing and crankshaft
seal life, or both power and durability.
There are so many variables, depending
on factors such as intake manifold design,
engine speed, type of use, etc., that the
benefits are sometimes difficult to
quantify. There are cases where no power
improvement is evident on the dyno, yet
on-track power is improved.”
The following are comments provided
by Billy Godbold of Comp Cams. This is
very insightful info, so I urge you to read
this. We’ve provided this information in a
question & answer format.
1. A typical camshaft firing order swap of 4/7
seems to be fairly common today. Why is this
firing order beneficial?
There are three basic issues that engine
builders or developers try to address with
firing order as follows:
A) Hot Spots in the Head and Block –
With a common pin V8 crankshaft, it is
impossible to eliminate having adjacent
cylinders fire subsequent to one another
in the sequence. While this is unavoidable
on a four throw crank, you do have some
choice as to which pair(s) fire together.
The 4&7 firing order moves that hot spot
from the 5&7 cylinders up to the 4&2
cylinders. Clearly, the front pair is easier
to keep cool with a front mounted water
pump than the back pair.
B) Main Bearing Issues – Most engine
builders see better bearing life and less
indications of scuffing when going to the
4&7 swap. The LS firing order (the 4&7
swap plus an additional 2&3 swap) may
be even better for bearing life. Again,
firing pairs is what we are trying to
change. Here I think the focus is on pairs
that fire on the same pin, thereby focusing
the force on the adjacent crank main
bearings. Moving this to the back of the
engine seems to be a good idea because,
even with a crank dampener, the drive
train is much better at dampening these
forces than a small mass on the end of the
crank. When we consider the power that
can be gained with lighter weight, lower
viscosity oils, bearing life becomes not
only a durability, but also a power
concern.
C) Fuel Distribution – Changing the
firing order is one of the best ways to
change the cylinder to cylinder fuel and
air distribution in the engine. Just like
throws on the crank and cylinders next to
each other in the block or head, we have
to deal with ports next to each other and
across from each other asking the
manifold for air right after one another.
This creates a very dynamic system in the
manifold plenum where pressure waves of
air (and also fuel in a wet manifold) are
moving from front to back and side to
side. Changing the firing order definitely
changes how the ports interact.
Depending on the configuration, this can
be the main plus or minus for an engine
builder when they consider changing
firing order.
2. In what type of motorsports application is a
firing order swap most helpful? (drag racing,
oval track, road race, etc.)
We have certainly seen the types of
benefits engine builders look for with
firing order swaps being beneficial across
the board. You see them more in drag
racing and road racing than in oval track,
but that is likely a function of the
sanctioning body rules. Certainly, OEM’s
competing in NASCAR try various firing
orders before submitting a new engine to
NASCAR because they know it will be
tied down if it is accepted.
3. It’s commonly said that a firing order swap
(4/7 or the LS swap of 4/7 and 2/3) results in
reduced crankshaft and main bearing
deflection. Is this true?
See part B of #1 above, but it simply has
to do with neighboring cylinders firing
subsequent and the subsequent force
pulses due to the firing sequence.
4. As far as we are aware, SFO cams for small
and bigblock Chevy include the 4/7 swap and
the LS firing order. Are there any different
firing order swaps that are applicable to
other make of engines?
On any even fire, common pin, 90 degree
V8 application, a cam can be made to
swap any of the cylinders that are four
apart in the firing order. What may be the
third most common order is called a
“Bank-Bank” where you fire all the
cylinders on one side and then the other.
Simply swapping 2&3 (w/o 4&7) will
give 1-8-4-2-6-5-7-3 with the each bank’s
cylinders firing all four before jumping to
the other side. Some engine builders
believe this helps traction limited and/or
restricted applications. It may be that a
particularly clever NASCAR engine
builder used something like this at
engine professional OCT-DEC 2009 55
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TECHSIDE
BY DAVE HAGEN, MIKE CARUSO AND STEVE FOX
Daytona one year and this led to
NASCAR not allowing ANY firing order
changes…
5. Are there any concerns or issues with
regard to valve operation with the use of a
special firing order camshaft?
We have not measured a change in valve
duration that we can trace to a firing
order change.
6. How does an SFO cam benefit engine
horsepower and/or torque?
The power and torque changes vary
depending on the intake manifold, fuel
delivery exhaust system along with a host
of other considerations. Improvements of
1-3% are actually quite common (much
to my personal surprise). If you see
changes greater than 3%, I would
imagine you have either created or
eliminated a major distribution problem
that could have been addressed in another
way (likely in the manifold).
56 OCT-DEC 2009 engine professional
7. Is it correct to assume that all SFO cams
require the use of steel billet stock?
Actually COMP Cams does have cast iron
flat tappet cores to make flat tappet 4&7
swap camshafts for Small Block and Big
Block Chevys. Also, most cam companies
have two firing orders available for small
block Fords due to the factory 302 versus
the later 351W (5.0 HO) firing order.
That 351 firing order is basically Ford’s
version of the Caddy/LS1 4&7 & 2&3
GM firing order. There are also billet steel
cores on the shelf for the common two
Chevy and Ford firing orders readily
available from COMP Cams. Most of the
other firing orders require a very
expensive custom core.■
FIRING ORDER EXAMPLES
SMALL BLOCK / BIG BLOCK CHEVY
STANDARD FIRING ORDER...1-8-4-3-6-5-7-2
4/7 SWAP FIRING ORDER.....1-8-7-3-6-5-4-2
LS FIRING ORDER (OE GM)...1-8-7-2-6-5-4-3
The AERA tech team, from left to right: Steve Fox has
over 16 years experience in the engine building
industry with eight of those years spent working in the
machine shop. Steve is an ASE-certified Master
Machinist, as well as a longtime member of the drag
racing circuit. Dave Hagen, our Senior Technician, has
over 32 years of experience in our industry. An ASEcertified Master Machinist, Dave specialized in cylinder
head work and complete engine assembly for the first
17 years of his career. Mike Caruso brings over 35
years of rebuilding and high-performance experience
to AERA. An ASE-certified Master Machinist, Mike
came to us from FEL-PRO’s high-performance R&D
and tech line, where he worked for 11 years.