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993 MODIFICATIONS 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.