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.

Prerequisites:

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 here.

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 as this are cheap and worth every penny. You can check your system for leaks using a technique such as can be found here.

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 here.

Common Modifications

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 Lindsey unit.

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