Introduction to 951 Performance Modifications
First off, let me start by saying that I am not
an authority on 944 Turbo performance modifications but I thought that a
general introduction would be helpful to those new to the 951. I
have been adding "mods" to my car now for a few years and I have
had a lot of fun doing it. I must say most of what I learned about
951 modifications has been learned from a 944 Turbo Forum that is a
pretty special place in the 944 community. If you are serious about
upgrading (or even maintaining) your 944 Turbo, the
Rennlist Forum is an incredible place to learn.
I believe you need to ask yourself a few
questions before you start down the risky but rewarding path of modding
a 944 Turbo. What are your goals for the car? Is the car a
daily driver? Who will install the mods on the car? How much money
can you afford to spend? In my opinion modding a 951 will seriously
effect its reliability. My experience says the more power the less
reliable the car will be. Certainly a sound approach will help but
it will never be as reliable as a unmolested car. Unless you are a
very capable mechanic (and a fast wrencher with lots of spare parts) i
would not recommend modding a 951 if it your ONLY car. Installing
performance components requires skill and knowledge. Are you
capable of doing the work your self? If not, then expect LARGE
shop bills. Porsche mechanics are not cheap and generally shop
rates run $80-$100 per hour. I have seen single shop bills on
these cars that exceed the value of the entire car. The point here
is understand what you have and what your goals are.
So you want to "mod" your 951.
Laying a solid foundation for modifications is an absolute must for
reliable performance and even more important; your safety.
1) Make sure the service of the timing and
balance shaft belts and rollers is up to date. These belts are
critical and they are a common failure point, and improper maintenance
has led to the death of many a 944 engine. Maintenance info can be found
at Clarks Garage, see
2) Fix all leaks (or at least the major
ones). These cars leak everywhere and it takes some effort to
track them down and stop them. These leaks can do a lot of damage,
especially to rubber suspension components. They also can lead to
an engine fire.
3) Check for vacuum/boost leaks. These
cars are 25 years old and rubber components break down and crack.
This is a good time to replace the vacuum lines. Vacuum kits such
this are cheap and worth every penny. You can check your system
for leaks using a technique such as can be found
4) Make sure your brakes are up to snuff.
When is the last time the brake fluid was flushed? What do the
pads look like? Check the calipers for damage and leaks.
5) Perform a careful inspection of the
suspension components. When I bought my car I noticed it had a
strange shudder on quick braking at high speed. Turned out that I
had a VERY bad ball joint. It literally had 1/8" play and I was
fortunate nothing really bad happened. If you are serious about
your car, the suspension will eventually need to be addressed.
What I am saying is address it up front. It will make the power
you add more fun and safe.
6) Install a boost gauge and a wideband
Air/Fuel Gauge. Over boost and improper air/fuel ratio (especially
lean) can result in rapid engine failure. These motors have
incredible power potential but they are fragile is some respects and you
must understand what is going on. If you are going to make
significant modification I would recommend a data logger so you can
carefully analyze what is taking place with respect to the engines vital
signs (boost, air/fuel ratio, RPM, TPS). Data loggers such as
this are worth every penny and a lot cheaper than a new motor.
7) Install a knock counter, especially if
you are going to be running more than 15 psi of boost. Chris White
at 944 Enhancements posted a great tech article about knock (detonation)
see here. A common formula for catastrophic engine failure is
to run lean at high boost resulting in destructive knock. With the
951 it is very easy to install an impulse counter such as found
here and install it as shown
here. This technique utilizes the the stock knock unit needed by the
KLR. You can also install a backlight and reset as shown
Performance Chips - The Motronics Computer (also called the Digital Motor Electronics or DME)
contains a removable chip that contain digital maps that control
ignition timing and fuel delivery. The DME takes input data from
numerous engine sensors such as temperature, altitude, crank angle,
throttle position, exhaust gas oxygen content, and air flow. The
stock chip is programmed from the factory with certain characteristics
(many conservative) so that the engine will perform well under a host of
conditions. The stock chip can be replaced with an aftermarket
performance chip that alters the digital maps to improve performance.
In addition to altering fuel and timing, the chip can be used to raise
the rpm limit (rev limiter) a the over boost protection limit.
Boost Controller - Either a Manual
(MBC) or Electronic (EBC) Boost Controller can be installed in place of
the Cycling Valve which is essentially the factory boost controller.
The Boost Controller can then be used to control the opening pressure of
the wastegate and thus control peak boost. An MBC is is cheap
(under $100) and pretty easy to install. An EBC is quite a bit
more expensive and difficult to install but is more accurate and
repeatable. A pretty common mod is to install a MBC and increase peak
boost to 15 psi rather than the approximate12 psi peak boost allowed by
the Cycling Valve. Keep in mind that if you install a boost
controller without chips and you exceed about 12 psi you will hit the
overboost limit coded into the stock chips and fuel will be abruptly cut
to the injectors.
Wastegate - The wastegate controls
the turbocharger speed and limits boost pressure by allowing some
exhaust to bypass the turbine. The 951 external wastegate is
controlled by boost pressure, a spring, and a vacuum line from the
cycling valve (or boost controller). The spring in the stock wastegate
can weaken over time and allows leakage that prevents maximum boost.
The stock wastegate can be shimmed which essentially stiffens the spring
or it can be replaced with an aftermarket wastgate such as a Tial or
Porsche® and the Porsche Crest® are Registered Trademarks of Dr. Ing. h.c.
F. Porsche AG
All other trademarks used within this site are property of their