The purpose of this page is to explain what is fact and what is fiction about the advertised products in magazines and on the Internet. There is a lot of misinformation out there, in fact, there are engine update kits that can do great harm to a Twin Turbo engine. 

Because of all of this misinformation and snake oil being advertised, I intended to get real facts and document the changes along with installation pictures. Only advertisers that provide real value, and that will stand behind their products 100% will be listed on these pages.

After looking at many of the offerings from different vendors, here is a list of parts that several owners of 993 Twin Turbos have added with good results. All of the parts listed below are 'bolt-on', and do not require the engine to be dismantled. The goal was to increase the horsepower to around 480-520, but also to keep the engine free from detonation and not compromise reliability. Be very careful when selecting a shop to do the work, or buying 'kits'. There are a couple of well known businesses around that advertise in Pano and Excellence magazines who will sell you high performance 'kits' that will eventually harm or destroy your engine. They typically just raise the boost pressures to unsafe levels, raise the rev-limiter, crank-up the advance, and don't include or recommend the add-on front oil cooler. The net result is detonation using street gas. Buyer beware.

The Electronic Control Unit (ECU)
 
The ECU is responsible for the entire engine management. It measures, checks and controls all important functions of the engine by monitoring the current load condition, ambient temperature, oil temperature, intake air density etc.

Sensors throughout the engine very accurately measures pressure, temperature, revolutions, speed, and air mass (density) signals. With this information, the ECU processes the ignition, injection, boost, and lambda patterns that are programmed on to a chip (EEPROM) inside the ECU. Depending on the load conditions and other environmental parameters, the ECU will determine the ideal ignition timing, the necessary fuel amount in respect of the optimal injection timing, and the corresponding boost.

During the process of chip-tuning, the database is optimized and programmed onto the EPROM (Chip) inside the ECU. All relevant patterns for injection and ignition timing, boost control, load limitation and exhaust emissions are being monitored over the entire rpm range of the engine. These parameters are then changed within certain limits, depending on load and engine-rpm, to generate the maximum horsepower and torque output.

Porsche Twin Turbo engines can be programmed to yield an increase of horsepower and torque of 20% to 40%. Moderate tuning will not have any effect on the durability of the engine as well as drivability of the car, as long as correct maintenance is provided and the engine is operated in a responsible manner. It is also very important to have the vendor tune the ECU to the fuel you plan on using. States like California are selling gas with a maximum octane rating of 91. If the ECU is programmed to aggressively, the engine could develop detonation very easily. The knock sensors can retard the ignition only so far.
 
Tasks of the ECU
 
Retarding and advancing ignition timing
For an economic and efficient fuel combustion under all possible driving conditions, it is important to compute the correct ignition timing depending on engine-rpm, load, and other relevant parameters. 
 
Dwell Control
Depending on the engine-rpm, the time between ignition trigger signals varies. To ensure a constant ignition energy requires a certain "Primary Current" to flow through the windings of the ignition coil. To sufficiently build up a magnetic field inside the coil requires time. The time delay from switching to interrupting the primary circuit has great influence on the voltage induction into the secondary circuit of the ignition coil the higher the engine-rpm, the shorter the delay from switching to interrupting the primary circuit, the less energy is inducted into the secondary circuit. This may lead to engine misfire at high rpm.
 
Detonation Detection via Knock Sensors
On all modern automobile engines, the compression ratio is high in order to achieve higher torque output and better fuel economy. Due to the high compression ratios, the risk of detonation of the air-fuel mixture is greater, especially under high loads running at high rpm. Detonation causes severe engine damage. Whenever detonation is detected, the ECU will retard the ignition timing for the particular cylinder. Keep in mind that the ECU can retard the timing only so far. If a reprogrammed ECU has a too aggressive timing map for the gasoline used, detonation will still occur and cause damage if the detonation is severe.  
 
Fuel Injection
The signals from the air-mass (air-flow), rpm, load and correctional factors - such as ambient as well as coolant temperature etc., the ECU determines the needed fuel amount and injection timing. This increases fuel economy, reduces exhaust emissions, and is responsible for a higher specific engine output.
 
Lambda Control
The lambda sensor located in the exhaust system in front of the catalytic converter, and is constantly measures the remaining oxygen in the exhaust gases. This signal is used by the ECU under all driving conditions (except under 'Full Load') to adjust the air to fuel ratio to Lambda 1" (14,8 kg of air to 1kg of fuel). This ensures the highest degree of effectiveness of the catalytic converter, and at the same time lowest exhaust emissions. Under a full load condition, i.e. top end speed, the Lambda system is deactivated in order to gain higher engine output and prevent severe engine damage due to the fuel mixture being too lean.
 
Idle-speed Control
Varying engine temperatures and engine wear as well as operating conditions such as engagement of the air-conditioning compressor, will lead to a strongly fluctuating idle-speed. The engine rpm signal and current operating information, such as, idle contact, a/c engagement, are used by the ECU to calculate the appropriate idle speed. Parameters for hot and cold start, depending on temperature, are implemented i.e. High Idle during engine-warm-up.
 
Boost Control
On cars with turbocharged engines, the ECU calculates and adjusts the appropriate boost by monitoring the load and the pressure and the currently needed air charge volume.
 
EGR - Exhaust Gas Recirculation
In order to improve the "Exhaust Gas Quality" (reduction of NOx), exhaust gasses, by a certain volume, are inducted into the intake manifold under partial engine load.
 
RPM Limitation
One very important function of the ECU is rpm limitation. Due to enormous mass and centrifugal forces applied to all rotating and oscillating parts of the engine at high rpm, the maximum rpm limit of the engine must be determined and programmed on to the EEPROM. Excessively exceeding this max. value i.e. 6500rpm, will eventually result in severe engine damage. The rpm signal is constantly monitored and in case the programmed value of i.e. 6500 rpm is reached, the ECU will interrupt the fuel supply. 

The modifications listed below will work and are safe and reliable.

Modified ECUs
The ECU is the heart of the horsepower increase for the Twin Turbo. The original mapping for the 993 Twin Turbo is very conservative and yields a nominal 400HP. Porsche also developed three additional timing and fuel maps to increase the horsepower to approximately 430, 480, and 520. It is very important to get an ECU or Chip from a reputable vendor that has the proper mapping. A too-aggressive timing map, or raising the rev limiter could lead to engine failure. Combine that with gasoline that may vary in octane can produce catastrophic results if the ECU mapping isn't executed properly. With today's re-formulated gasoline, which is used in many areas of the country during the Winter, there is no guarantee that you will always receive 92 or higher octane from the pump. In California, octane ratings as low as 91 are common for 'premium' gasoline.

ECU Vendors

There are many vendors that can supply a modified ECU, or instead swap the chip in a stock ECU (1997 only). On an exchange basis, Mike Schatz, at Schatz Motorsports is a vendor that can supply an ECU unit manufactured by FVD. 

Another approach is to have your ECU modified by a tuner such as Steve Weiner at Rennsport Systems. Steve has the re-mapped chips available to modify a 1997 ECU. If you own a 1996 model, you will need to purchase a 1997 ECU for the modification since the 1996 ECU uses a set of chips that is no longer available. You can send Steve your stock or new 1997 ECU, and Steve will replace the chip with the power level you choose. 

Note: If you buy a new 1997 ECU to be programmed by Steve, be sure to first install it in the car and have a Porsche dealership program the Drive-Block codes into it. After the dealership programs the new ECU, send it to Steve to have the performance chip installed. If the Drive-Block codes aren't first programmed by the dealership, the car may not start after you receive the ECU back from Steve.

Oil Coolers

Sport Oil Cooler 
If you increase the horsepower of your Twin Turbo, the engine will generate additional heat. To help get rid of this heat, the Turbo "S" front oil cooler must be installed. This is a kit from Porsche that includes the sport oil cooler and the necessary hardware and additional hoses. Do not buy a 'turbo kit' from a vendor that does not include the additional front oil cooler. If they tell you an additional front oil cooler is not necessary....  RUN away from them and call a different vendor. Remember, even Porsche felt it was necessary to add the additional sport front oil cooler in the Turbo "S" model that produces 424 HP. The price for the Turbo "S" cooler varies between $1,100 to $1,200 depending upon the vendor. Normally it takes a mechanic 4-5 hours to install the additional cooler.

GT Oil Cooler - More Efficient            
Although the Sport Turbo "S" oil cooler does provide some additional oil cooling, a better choice is the GT oil cooler offered by Car Graphic USA. This larger oil cooler and the existing air conditioner condenser are attached together and mounted in the space the original condenser was located. All of the brackets are included, and no sheet metal modifications are necessary. If the Twin Turbo being modified will produce over 440HP, this larger GT oil cooler will greatly help by keeping the oil temperature down. The price of this larger oil cooler is around $2,500.00. Contact Hershel Zelcer at 732-826-4700

Intercoolers

FVD and Car Graphic Large Intercooler

FVD            Car Graphic       

FVD and Car Graphic offers a much larger Intercooler that does a better job reducing the charge-air temperature. This Intercooler is huge, but it does fit. Take a look at the pictures above. Click on them to get a larger view. You can order the FVD Intercooler through Schatz Motorsports, and the one developed by Car Graphic from Car Graphic USA

I know of a case where a owner of a highly modified Twin turbo was driving on a track during a very hot day. These modifications didn't include a front oil cooler or a larger intercooler. On this hot day, the modified car wasn't producing much more power than the stock Twin Turbos that were on the same track. Since the ambient temperature was high and the car was being pushed hard, the engine was producing excessive heat and the ECU was automatically retarding the advance and reducing the power levels. Had the owner added the front oil cooler and the Sport Intercooler (or bigger), his car would have been producing much more power. The owner spent a lot of money for these modifications, and was not very happy of the outcome. This same 993TT owner added the Car Graphic front oil cooler and the large FVD Intercooler. He recently went back out on the track, and the engine ran cool without loosing any power this time.

Turbos
GT2 / GT1 Turbos



The stock K-16 Turbos do a good job producing up to the 430-450 horsepower level. Above that, and at high RPMs, the stock turbochargers can overspeed and generate sharp pressure spikes in the intake tract due to compressor stall in the turbochargers from the overspeed condition. This will damage the engine just like detonation. Porsche developed two different high performance Turbos that offers higher, sustainable boost levels without damage. There are Street and Race versions of the GT2 and the GT1 Turbos. For the most part, all versions of the Larger K-24 GT2 Turbos will loose power on the bottom end and increase power above 3,500 RPM. However, a recent test of the modified K-16 GT1 Street Turbos increased the power on the bottom-end!!, and had a smooth and increased power delivery to redline. These special Turbos have the same size input impeller (this gives the fast spool-up), with a larger output impeller (provides more boost).

Kevin, at Ultimate Motorwerks designs and manufactures these modified turbos, along with many other types of turbos to fit the customer's application.

Misc. Items

Fuel Pressure Regulator
As horsepower increases beyond 430, it is recommended to change the stock fuel pressure regulator with either an adjustable one, or the 5-Bar pressure regulator. As boost and power levels increase for the modified engine, more fuel is needed.

Sport Catalytic Converters (Click on the Pics to get a larger image)  
As our 993TT's age, one of the things that happens is the stock catalytic converters become plugged-up drastically reducing airflow, and robbing power. It's not uncommon to see a 60% blockage. The Sport Catalytic Converters are designed to pass more air through them as compared to the OEM units. However, dollars can be better spent elsewhere unless the ECU is programmed for the Sport Cats. There are a few different types of Sport CATS available in the marketplace. Be sure to get the 100-Cell 130mm Sports CATS, not the smaller ones. A good source for these is Kevin at Ultimate MotorWerks. Kevin removes the OEM CATS and replaces them with the 130mm Sports CAT Inserts.

Catalytic Converter Replacement Pipes
Steve in Los Angeles installed a set of pipes that replaced the CATS. He has added the GT2 K-24 Turbos / ECU, and noticed the loss of power below 3,800 RPM. With the replacement of the CATS, Steve has noticed a dramatic power gain at 2,500 RPM and above. These bypass pipes can be bought from Hershel at Car Graphic USA. Just remember it is illegal to run without catalytic converters, although the difference is huge with running the bypass pipes. The big power gain has been confirmed by several people on the Rennlist message boards.

Aftermarket Mufflers
There are many different aftermarket mufflers available for the 993 Twin Turbo. Robin Sun modifies yours and they have a much more aggressive sound when the car is idling, and at low RPMs. Adding aftermarket mufflers doesn't increase the sound very much when you stand on it. This is because the Turbos mask the exhaust noise very well. I understand that if the CATs are replaced with bypass pipes, the exhaust sound will increase as well. Robin's mufflers do sound good at lower RPM levels. For price and availability, Robin can be contacted at p-car.com.

Pricing

Below is a list of prices that I received from Steve Weiner at Rennsport Systems, and Mike Schatz at Schatz Motorsports in 2000. These prices are ballpark and vary.

The following is needed for a 450-460HP update for the Street

The following is needed for a 470-500HP update for the Street / Track

Recommendations

Schatz Motorsports and Rennsport Systems sells the modified K-16 GT1 Hybrid Street Turbos that are ideal for the street and the Track. The input impeller is slightly smaller than the GT2 Turbos, and provides greater boost levels at all RPMs as compared to the stock Turbos. These street GT1 Turbos may be the answer to retaining a linear torque curve similar to the stock Turbos, and not inducing the turbo lag as the standard K-24 Turbos are exhibiting. The GT1 Turbos won't be quite as strong as the GT2's on the very top end, but they will be much smoother throughout the RPM range. If the car is to be used 95% for the street, the street GT1 Turbos are probably the way to go. If you decide to go with the GT1 or GT2 Turbos, be sure to match them with the FVD ECU, or have your '97 ECU reprogrammed by Rennsport Systems.

The 993 Twin Turbo can be easily modified to produce much higher horsepower than stock. However, these aren't a cheap modifications. Figure on paying $100 to $150 per HP to have the modifications done properly! There are other excellent shops around that can perform similar work.

WARNING!!!
Be VERY careful with vendor claims of 600+ HP. Sure, you can get this kind of power from a 993TT engine, but it's not going to last very long using street gas. 

The discussion above has been an accumulation of information from customers of Rennsport Systems in Portland Oregon, Schatz Motorsports and Andial of Southern California. These vendors know what they are doing when modifying a Twin Turbo. 

If you have any additional information you would like to add, feel free to email me.

RickNW@verizon.net

Last updated: August 20, 2006