The
RX-7
Performance Handbook
Mystery Chapters
All material on this page is copyright 2000-2006 Mike Ancas, Dale Black and Dennis Witt
ORIGINAL INTRODUCTION
As we travel through this new millennium, many people are
searching for renewed meaning in their lives, and coming up
empty. Science fiction writers depicted us living on the moon and
exploring distant galaxies by the year 2000, but in reality, a
large portion of our population still can’t figure out how
to set the clock on their VCRs. But there is a lot we can be
proud of. Even though we are not yet breaking bread with our
Vulcan neighbors, from a scientific viewpoint our race has done
rather well.
Many of the advances we take for granted today can be traced back
to the engineers from the 1960’s. Their task was figuring
out a way to blast our astronauts into space, and then bring them
safely back to earth. As a result of this endeavor, current
technology has progressed to the point where computer science is
developing at the speed of light; the internet is changing the
way many of us work and play, and physicists are struggling with
mind-boggling issues such as the infinitely expanding universe.
So, what does all of this have to do with cars? Except for the
fact that the internal combustion engine is still around,
automobile technology has also evolved in terms of design,
mechanics, and electronics. When the hop-up movement first took
hold in the 1950’s, cars were relatively simple creatures.
The introduction of affordable aftermarket parts made it possible
for the average guy to improve the performance of his American
made muscle car, and “working on the car” became a
popular pastime.
In the 1960’s, Detroit began to take notice of the
public’s increasing desire for performance and offered
factory hopped-up versions of the more popular models: Corvette
Sting Rays, Shelby Cobra Mustangs, Chevy Z28 Camaros, Plymouth
Roadrunners, etc. Those who had a “need for speed”
began flocking to the local drag strips for bragging rights as to
which of the “Big Three” built the better car.
The early 1970’s was a crucial time for the development of
the rotary engine. Deemed the “engine of the future”,
most auto companies (especially GM) had already lost millions of
dollars in licensing fees trying to develop the engine for
commercial use. Speculation on the rotary engine nearly put GM
into a financial crisis before they finally abandoned the idea.
But then 2 things happened that would change history. Not a
natural disaster, such as a hurricane, flood, or earthquake which
are usually attributed to such moments. But 2 man made artificial
events, the first of which was the OPEC oil embargo and resulting
energy crisis of 1973. This nearly killed Toyo Kogyo’s new
importing company, Mazda, who set up shop in Seattle Washington.
The rotary engine got poor gas mileage. Other Japanese auto
companies were in the right place at the right time to capitalize
on this crisis. Honda began importing it’s first car, the
600 coupe, into the US one your prior to this oil embargo. The us
embraced Also VW Beetle. But then, another artificial event
happened. The newly formed US EPA announced emission standards
that would take effect in 1975. Panic was widespread in the auto
industry since there would be no way piston engines at the time
would be able to meet those standards. Rotary engines, due to
their low emission of nitrogen oxide, were again looked to save
the auto industry. And this time, the new company out of Seattle
was in the right place at the right time. It seem funny to look
back then and see how the piston engine was viewed as polluting,
and the rotary as clean. With the development of the low emission
piston engines in the 1990’s, the tables have turned. The
economy had also shifted, and many families found it increasingly
difficult to make ends meet. As we became more environmentally
and economically conscious, the cars we designed reflected this
shift in priorities. Emission controls choked the horsepower from
even the high performance models. The outlandish was gradually
replaced by the practical, speed and excitement gave way to
sensibility and efficiency.
The 1980s, however, saw a different kind of movement take place.
Companies like IBM and Macintosh were making computer technology
available to the general public. As the demand for more efficient
computers grew, technology began to advance exponentially. The
auto industry had already been using computers and robotics for
some time, and took advantage of these new technological
breakthroughs to help design cars more quickly, and bring them to
production in a more timely manner.
The motto of the 1990’s could easily have been: “Better
and Faster“. Our lives consisted of cellular phones, FAX
machines, Fed-Ex, e-mail, gigabites, and nanoseconds. We had put
increasing emphasis on the value of our time and the efficiency
of our machines. The result was an overall attitude of
impatience. Some people even experienced anxiety waiting for the
light to come on after they had thrown the switch.
This lack of tolerance for inefficiency, however, wasn’t all
bad. Japanese auto companies had long adopted a doctrine of
open-minded productivity, and were in position to embrace this
“better and faster” philosophy. This was demonstrated
in the progression of technology that took place over the past 20
years with the RX-7, one of the most significant sports car to
emerge from Japan (or any other country) in the 20th Century.
The import performance movement may have started in 1970 when
Datsun introduced the 240Z. Until then there had not been an
affordable and reliable high performance automobile available to
the U.S. consumer. With the success of the Z-cars, Japanese auto
manufacturers began to realize that the American market was
willing to expand the definition of “sports car” to
include a vehicle powered by something other than a V-8 engine.
But the unsuspecting enthusiast could never have expected what
would follow.
Mazda had been laying the ground work for what was to come when
the Wankel Rotary Combustion Engine appeared in the popular R-100
and RX-2. With the US barely noticing the advancement of this
revolutionary powerplant, it must have been a shock when the RX-7
was first imported into the U.S. as a 1979 model. Sure, it looked
like a sports car, but what was up with that engine? It was
barely larger than a differential. So right from the start, the
first generation RX-7’s mission was to gain the respect of
skeptical U.S. sports car enthusiasts.
As time when on, Mazda continued to make slight improvements in
the body style, frame and engine. But when the 6 port 13B was
finally fitted into the 1984 GLE, the RX-7 hop-up movement really
took off. Car enthusiasts began transplanting this new powerplant
into the earlier cars that were somewhat horsepower challenged.
At the same time, Mazda tuning innovators such as Dave Lemon
(Mazdatrix) and Jim Mederer (Racing Beat) began finding ways to
make RX-7’s go faster and handle better.
The import performance movement, which really began to gain
momentum in the mid 1980’s, reached new heights in the late
1990’s. This was probably due to a readily accessible supply
of aftermarket performance parts, the growth of motorsports in
general, plus a wealth of information and support that became
available on the internet. With names like Peter Farrell, Cameron
Worth and Sylvan Trembly continually inventing ways to make more
and more reliable horsepower from the 2 and 3-rotor Wankel, it
didn’t take long before the 3G RX-7 began to establish
itself as a true supercar. Now, with hundreds of RX-7 clubs in
the U.S. and throughout the world, the RX-7’s popularity has
reached new heights despite the fact that the car was no longer
imported into the U.S. after 1998. It remains as one of the most
beloved and enduring sports cars in history.
Form versus function
In the beginning, when it came to hopping up an RX-7,
traditionally the first thing the car owner needed to resolve was
this dichotomy. In the past, form was often diametrically opposed
to function, and the car owner had to choose one over the other
based on the intended use of the vehicle. Would the goal be good
looks, or would it be performance? As the import movement of the
1990’s grew, it created competition among aftermarket parts
manufacturers so that car owners were given more choices when it
comes to selecting affordable performance parts that possess both
function as well as form.
But the “form versus function” conflict exists on yet
another level which can be exemplified when considering what kind
of wheels and tires to buy for your RX-7. 19” wheels are not
intended for racing, but 14” rims are no longer cool. They
don’t fill up the fender wells, unless you lower the car to
the point where you can’t drive it anywhere without ripping
the exhaust system off. But as you increase rim diameter and
decrease tire section height, you reduce the size of the air
chamber, which decreases load capacity often resulting in
diminished handling. So how do you choose?
First decide whether your goal is “form” or
“function”. If you can’t make up your mind, buy
two sets of rims, one for racing and one for show. But
unfortunately the form versus function debate will persist even
after you resolve the wheel and tire dilemma. The sad fact is
that race cars don’t make good street cars. They are too
stiff, don’t always idle well, get poor gas mileage, and
have few creature comforts. On the other hand, great street cars
don’t usually make good race cars. They are too heavy, have
softer suspensions and stereo systems.
This leads us to the primary lesson of performance tuning: All
performance improvements come at a price, and that price is the
loss (on some level) of streetability. Everything that makes your
car go faster and handle better forces you to make some sort of
compromise. You may have to give up a comfortable ride in order
to experience stiff and precise handling. You may have to give up
a quiet ride in order to experience an increase in horsepower.
Sometimes even with the best intentions, many of us go too far
trying to build a faster street car, and end up turning our daily
drivers into a race-only vehicles. It must be a male hormone
thing. But by exercising some margin of restraint, an RX-7 can be
built to serve both purposes well. Learning from our mistakes and
successes recounted in this book, you should be able to build
awesome street car, capable of blowing the doors off of most
other cars on the road.
But to return to the fundamental dilemma, before undertaking any
type of performance improvement project, a car owner really needs
to make a decision as to whether or not the priority will be
based on form or function. Once a decision is made, this book
will provide some guidance to help you realize your goals. Most
chapters cover form as well as function. Street racers will be
able to take advantage of the latest good looking “go
fast” and handling modifications, while pure racers will be
able to access practical information to help their cars become
more competitive.
This book assumes that anyone planning performance improvements
to their car already has a workshop manual. This book is in no
way intended to replace or supersede and information in an RX-7
workshop or owners manual. For that reason, it is devoid of the
boring charts and schematics that often fill the pages of typical
aftermarket performance handbooks. Exploded views of your
car’s suspension or engine are already in a typical workshop
manual.
Don’t look for discussions about highly technical
information, or in-depth demonstrations of any internal engine
modification procedures. Attempting to do a bridge port on a
rotary engine by your self is a waste of both your time and
money. You could easily end up ruining an expensive engine. This
type of work should be left to the experts, and there are many
competent RX-7 specialists out there. In any event, 99.9% of the
people who buy this book don’t have the equipment to do this
type of job properly, and if you are the 0.1% of those who do,
then you don’t really need it.
You will find that this book concentrates more on what average
weekend mechanic can do to improve the performance of their car.
Countless aftermarket parts are discussed, and many
do-it-yourself projects are reviewed. The first step in any
project, however, is setting priorities, such as “form”
versus “function”. Chapter 1 will help you make some
preliminary decisions and get you started on your way to a great
experience in the realm of Mazda performance. The rest of the
book won’t help anyone with their journey to achieve meaning
in the new millennium, but it could be a fun diversion along the
way.
Engine Management for the Third Generation RX-7
by Dale Black
 |
| Racing Beat's second generation RX-7 set a record at Bonneville |
When you consider that the effects of most upgrades are greater
on the rotaries than on comparable-sized piston engines, then you
can understand that engine management becomes more important. For
example, throwing on an open intake and free-flowing exhaust
might get you a few ponies on a 4-cylinder Honda, but it can get
you twice as much on a 12A or four times more on a turbocharged
13B! So when exactly does engine management become critical? The
closer you get to a rotary’s power threshold, as with forced
induction, the more fragile they become. You might say that if
you are pushing the stock fuel delivery system (including the
stock preprogrammed fuel maps) to its limit, then it’s time
to consider an ECU modification. As with most fuel injected
rotaries, changing the ECU programming it about the only way to
make fuel related power adjustments, short of using added
injectors and separate controllers.
Before getting too involved, let’s go over fuel delivery, as
it is crucial to understand it’s relation to optimum power
from a programming standpoint. Many owners of fuel injected cars
think the way to increase power is to get more fuel in the
air/fuel mixture by either raising the fuel pressure, installing
larger injectors, or by installing additional injectors. This is
misleading since more fuel is not necessarily the goal. However,
getting the right amount of fuel for the volume of air being
brought in is the key. An air/fuel ratio gauge is a useful tool
for tuning if you don’t have access to diagnostics
equipment.
Fuel mixture control is separated into two modes: closed-loop and
open-loop. During closed-loop engine operation (idle and low load
– 2000 RPM and below), the ECU uses the oxygen sensor to
trim the air/fuel ration to the chemically ideal value of 14.7:1)
for best emissions performance, thus, any adjustments you make
within this range get cancelled out by the stock ECU. Open-loop
fuel adjustments are not cancelled out, and generally considered
to affect medium to high load, which is considered 4000 RPM and
above and of course, wide-open throttle (WOT). Since emission at
these loads and speeds are essentially unregulated, engineers
generally choose a very rich fuel curve to protect the engine
against knock and thermal stress and to ensure that fuel pump and
injector wear will not result in dangerously lean conditions over
the life of the engine. In doing so, they compromise peak power
and harm fuel efficiency. Stock vehicles generally respond to
fuel subtractions in these open-loop ranges. For modified
engines, the guidelines above also apply, however heavily
modified engine may need fuel addition in the upper RPM range.
Timing becomes a critical variable in power tuning and a device
which can measure injector “duty” cycle is helpful as
well (for example, if you find the stock injectors frequently hit
95% or above, then larger or additional injectors are probably
needed.) Again, more on that later.
Fuel-injected rotaries can be a real brain teaser to set up just
right. Regarding the old adage, “three strikes and
your’e out”, you might say that in tuning a rotary
engine, it is very possible to be out after only one
“strike”, meaning a detonation causing knock. That is
why it is always best to start with either the stock programming
or an extra rich-air’fuel mixture as a baseline to start.
But regardless of how you go about tuning, you should be able to
add and subtract fuel.
Aside from the aforementioned additional injectors/controllers,
which will be discussed later, there are basically three ways to
retune a third generation Mazda RX-7’s engine for optimal
performance. The first is by using a reprogrammed stock ECU.
Here, the main chip is swapped out with one that has been
specifically programmed for you modifications. There are a number
of performance companies with the right amount of know how to do
this, often without even having the car on site. Among those are
Pettit Racing, Mostly Mazda, XS Engineering,, and Rotary
Performance of Texas. One downside to this type of engine
management is that there programming is not changeable without
removing the ECU and sending it out along with a list of
modification changes.
The second way to go about tuning an engine by reprogramming is
by using what’s called a “piggy back” system,
which basically means that there is an external computer that
plugs inline of the stock ECU. Here, it is possible to
incorporate various program settings for different venues of
performance. Plus, it becomes possible to change the programming
with changes made to your car. Two good piggy-back systems
currently available for the third gen are the Peter Farrell
Supercars’ Programmable Management Computer (PFS PMC for
short) and the Wolf 3d System. The PFS PMC is the same as EFI
System’s PMS (Programmable Management System), but cannot be
obtained directly.
Finally, if you’ve made modifications beyond that of popular
bolt-ons, such as porting of the internal engine, throttle body,
intake, and/or turbo manifold, then you should consider a
complete ECU replacement. Often referred to as a
“standalone” because it’s sole purpose is to
control the engine’s functions and nothing else, it is a
popular option among racers, especially those competing
professionally and whose cars are not driven on the street. As
you might guess, this is an extreme performance method of
optimizing power and is not only highly illegal, but extremely
difficult to program for street use anyway. It is not recommended
you pursue this avenue unless your sole intention to trailer your
car to competition events. I say this, not in fair warning by any
means, but because it does not provide any compromise between
high performance and street-ability. Examples of such systems are
the Electromotive Tech II, Motec, DFI and the Haltech.
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