Upgrades for the Mini Cooper MPI/TBI models
This is the 3rd installment in a series of articles that are intended to provide some insight and direction to new owners of the late model range of Classic Mini Cooper. (Part One and Two can be found here.) The term MPI and/or TBI is often used to identify the range of cars produced by the Rover factory in 1996 and continued unto the end of the production of the Mini Cooper. The best way to identify one of these models is that all production (except those produced for Japan) had front mounted radiators and no distributor. The radiator was moved to the front to comply with drive-by noise regulation then in effect and the distributor was gone as it became a fully electronic crank fired ignition system. The MPI/TBI designation was coined to differentiate it from its predecessors know as SPI. The SPI stands for Single Point Injected while the TBI indicates Twin Point Injected. The MPI phrase is used similar to how a 1275cc engine is often referred to as a ‘1300’. When a marketing department ‘rounds-up’ a number or phrase it is simply look better and it has a tendency to keep everyone guessing.
The Twin Point Fuel Injected Mini Cooper was the last model ever in a 40+ year evolution of the marque. It incorporated every refinement thought practical for the time and marketplace. It was a car produced by a company that was simply trying to survive and incorporated many compromises both in technology and performance. It was a car produced in an effort to satisfy the largest potential population of customers. Competitive automotive technology and resulting performance had long passed it by and thus it’s place in the marketplace was relegated to that of ‘nice little car for everyday use’! It no longer was sought after by the young driving enthusiasts or the guy looking to by a ‘Hotrod’.
The complete suspension and under-carriage of the TBI Mini is shared with all of it’s resent predecessors and thus all the normal tuning upgrades for early cars can and should be used. The very tall final drive ratio was instituted in an attempt to improve fuel economy at the sacrifice of acceleration and thus is an area for potential upgrade.
The same technology that makes the TBI Mini Cooper more user friendly for a daily driver also is the single biggest problem is trying to apply any conventional performance upgrades to the engine. The ECU used is very unique in design and has been put in total control of many functions of the cars operation. In contrast to the earlier SPI models where the ECU could simply be bypassed, it is simply not practical in the TBI Mini Cooper. This fact alone prevents us from mounting any real efforts to achieve any kind of serious horsepower gains from upgrading. The modern aftermarket tuning trick of ‘chipping’ a modern ECU based car has not been successful. Not that people have not tried, many of the best in the UK industry have tried, to date no one has succeeded. Not only is the encoding used within the ECU very difficult, it is also very unique and thus not even understood by most tuners. There are NO either chip sets or piggy-back or anything reputable that can be applied to the ECU- we are stuck with what the factory intended. It should also be noted that diagnoses of this system is also very difficult. The factory computer system appears to be the only method available to trouble shoot or identify a problem. The best options are expensive and will not produce striking results but include many of the common tricks. You can find cylinders heads and camshafts both that claim to upgrade performance. But any real gains are totally controlled by the ECU that limits fuel delivery and ignition timing to maximize economy and engine life. These will never be consistent with high performance. So if you are willing to spend serious money for a little increase there are a few products available. The one upgrade that appears to be a very cost effective one is to exchange the throttle body. The stock throttle body has a bore size of 48mm and is made of some sort of high tech plastic. The upgrade path provides 2 options. A simply direct swap to the metal version now available will yield gains in simply allowing the system to regain it’s performance as new. The original plastic version is prone to heat distortion and cracking. The second option is to upgrade to a big bore throttle body. The 52mm version has been used successfully even with the ECU limitation to yield an almost 10% performance increase.
I would suggest that the minimum that should be done is to upgrade both the air filter system and the exhaust system. It will enhance the driving pleasure if nothing more than making it sound better.
Sorry to say that there is not much more encouraging to say about the TBI models but satisfaction can be had in that they are from the factory a great daily driver that can be depended upon to start and dive for a long time to come. The end of the range of models that will never be equaled in the automotive industry is still a great car and testament to its great history.
Mini Cooper Specials