Upfixin Porsche, Volume 11

Porsche Panorama's 11-volume technical anthology can be purchased from the
PCA Executive Office at 703/451-9000 or at www.pca.org.

993 MODIFICATIONS

A Technical Question Answered

I'm going to put my 1995 993 down soon for installation of some track-related
goodies: clubsport engine and transmission mounts, steel synchros and sliders
and a short ring and pinion. The car is street licensed but is used
exclusively for track events. I have installed a Cup suspension and done the
other obvious things and I still have a few questions. My mechanic is trying
to talk me into a lightened clutch and flywheel. Will this be drivable on the
street? Will I need a new chip to handle the clutch deceleration problem? Will
I have the idle problems that I keep hearing about?

Does anyone make a good cheater cam-ahem, let me rephrase that-
good sport cam for the 993? I know that the factory once had a sport kit that
included a mild street cam, mechanical rockers, and a few other bits at an
absurd price. Given the fact that the car has to be emissions legal (although
not the tougher California standard), what are my options?

An outfit called Crane Electronics makes a little purple box that
allows you to reprogram your Motronics (no need for a chip) for the track-you
simply dial in the parameters, advance the spark five degrees, pump in some
103 octane fuel and off you go. When the event is over, you switch back to
your normal settings. Have you heard of this gizmo? Any chance that it works
as advertised?

Any other thoughts for making more power while keep the car
semi-streetable?

Bruce Anderson: I am confused by all the problems that people say they are
having with the lightweight flywheel and clutch; the 964 RS used a light
flywheel and clutch and seemed to work fine and last a long time. I have
noticed that this is not an option on the 993 RS model, but I don't know why.
For a track car it would seem to be essential to get rid of the dual mass boat
anchor which weighs in at almost 30 pounds and replace it with a conventional
flywheel that weighs half of that or less. A heavy flywheel may be good for
transmission rattles but it not a good thing for acceleration.

The original 1989 C4 had a conventional flywheel and they did not
have this dying problem that we are seeing now when we install a light
flywheel, so I don't really know what is causing the problem. I have heard all
sorts of excuses from the timing marks being in the wrong place to the chip
not being designed for the light flywheel, but I honestly don't know what the
problem is. I have driven 964s (911 Carrera 2s) with light flywheels which did
not have this problem.

Porsche does have a motor kit for the 993 that uses 102mm pistons
and cylinders and converts the engine to a 3.8 liter. The kit changes to heads
with larger valves, changes the cams, the rockers and the DME engine
management box. This is an expensive conversion, but 300 hp (actually 299 PS)
is claimed.

There is a 993 sport cam available but I have not talked to anyone
who has had one that thought they really did anything. Jerry Woods has some
cams that work great, but it is doubtful that they will pass the emissions
test (Jerry Woods Enterprises, 491 McGlincey Lane #1, Campbell, CA 95008,
408/369-9607).

I think that the box you are talking about is what was once called
the Interceptor. The Interceptor is a programmable engine control computer
system that a company called EFI Systems designed based on the data chip
decoding system they had designed for their dyno. What the Interceptor does is
just what the name implies; it reads the signals coming out of the OEM
computer, modifies the signals and sends them on to the engine. The
Interceptor is a computer processor that measures what is coming out of the
factory computer and outputs exactly the same picture plus or minus percentage
changes. The percentages are based on rpm, load and so forth. The interceptor
has a whole set of tables that overlay what the factory computer is doing. The
Ford Interceptor was the first one that EFI Systems designed because at the
time they had done so much work with the Ford system with their performance
chips that they felt they understood the Ford system and market best.

When EFI Systems finished their first Interceptor in 1989, Crane
Cams heard about it and wanted it. So EFI Systems signed a licensing agreement
with Crane. The Interceptor is transparent to the original computer and they
map around the emission cycle so they can get a full California Emissions
Executive Order and are emissions legal. They have passed all of the tests for
the Mustang so that they were legal in all 50 states and the EPA and were
offered for the entire Ford engine family. To pass these tests, they must be
able to go to the extremes of their adjustability range and prove that they
can be as clean as (within ten percent) the original factory program.

EFI built and tested a GM version over four years ago, but Crane
Cams were concerned about marketability and never put it on the market under
their name. EFI Systems has bought back the rights to manufacture and sell the
Interceptor built to work with Bosch Motronic engine management systems and
has continued to develop the concept. Because of their previous association
with Crane, however, they have renamed the device and now call it Programmable
Management System (PMS).

The PMS is a state-of-the-art engine control computer with a
detachable data transfer terminal. The PMS reads the stock fuel injection and
spark timing signals from the Bosch Motronic computer and changes them by an
amount that you specify, allowing different fuel and timing adjustments to be
made for idle, part throttle and wide-open throttle conditions. The PMS, in
effect, makes aftermarket performance chips obsolete. Chips are made for the
average car and the PMS allows you to adjust the fuel and timing for your
specific car. Fuel adjustments are made in two percent steps and timing
adjustments in one degree increments. Because of the large storage capacity of
the PMS you can save three completely different performance programs. Each of
these three programs can be instantly activated even while driving.

Through the data transfer terminal you can monitor the Motronic's
fuel and timing commands and sensor signals in real time, letting you know
exactly what your engine is doing. You can leave the data transfer terminal
connected all the time, or you may remove it after programming your PMS unit.

There are specialized functions which allow you to maximize the
performance of a turbocharger, a supercharger, or nitrous oxide. The PMS can
even control the boost on cars equipped with electronic boost control. As an
option they also offer their InterACQ PC software which will allow you to do
data logging and capture and log performance data. You can buy the PMS
directly from EFI Systems or from Supercharging of Knoxville..

Porsche has done a really good job themselves with the new 993.
Probably the best thing that you could do would be to sell your 1995 993 and
buy one of the 1996 or 1997 993s with the VarioRam induction system. The
specific output of the current 993 engine exceeds the specific power output of
the 1973 Carrera RS. I am not sure that there is anything that will be that
easy to do to the 993 to gain power. I'm sure that some improvements can be
made to the exhaust, but you need to approach this carefully. I don't think
that there is anything on the market yet that really works. A lot more
development work and testing needs to be done in this area.