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Home > 911 Catalog911 (1965-73) >  Early Porsche 911 Enhancements > SSI Stainless Steel Heat Exchangers

SSI Stainless Steel Heat Exchangers

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  For years, SSI has set the standard for Porsche stainless exhaust heat exchangers. Each unit is a literal work of art, with craftsmanship that rivals the finest German artisans. It's a shame these beauties are hidden underneath the car when it's on the road. Rust-proof and durable, they will last the life of your car and are basically indestructible! They are manufactured out of 100% stainless steel so they won't rust. On older systems, rust can eat through the metal pipes, and leak carbon monoxide into the heater system - something that you want to avoid. Rust also eats away at the thin metal that surrounds the exhaust pipes. This results in lost heat that would normally be funneled to the cockpit.

In addition, replacing your 1975 and later exhaust system with these stainless steel beauties is often good for about 15 more horsepower. Why is this? The SSI heat exchangers are based on the 1974 and earlier 911 exhaust design that was highly optimized for the Porsche 911 engine. 1975 brought about changes in the exhaust that severely limited the flow capacities of the engine, in order to make the engines pass stricter smog standards. The SSI 1974-style heat exchangers are a bolt-on replacement for all thermal reactor cars (1975-77). Using the SSI heat exchangers will make these engines run cooler, make 16 more horsepower (10%), and 28 ft-lb more torque at 3,000 RPM (26% improvement). In addition, the reduced heat from the SSIs will help the engines last much longer. 911SC engines can expect to see an addition of 30 ft-lb of additional torque at 3,000 RPM (increase of 24%). Before replacing your 1975 and later exhaust, check with local authorities to make sure that the swap is permitted under local smog laws.

Why are SSIs so legendary in the Porsche marketplace? Let's talk first about technical details. The most important decision a manufacturer of heat exchangers can make is what materials to use in the tube work and the ducting. The ducting must fail first, otherwise carbon monoxide has the potential to leak from the tubes inside the ductwork resulting in a dangerous situation. To this end, SSI uses only time-tested stainless steel #304 (18% Cr, 8%+ NI) for both tubes and ducting. Why? The 304 steel tubing is highly resistant to the H2SO4 (sulfuric acid) that is present in exhaust gas condensate. It has a corrosion rate of approximately 1mil/year in 5% H2SO4 at 190F. Road salts eat away at 304 stainless steel about twice as fast as exhaust condensate. Lower-quality 400-series stainless steel (chrome only and magnetic) is eaten away by sulfuric condensate about 5 or 6 times faster than the rate of 304 stainless steel. SSI only uses .065" 304 stainless steel for tubes and .028" for ducting. Other competitors use inferior quality 409 for tubes and 304 for the ducting only, as only the 304 has the elastic properties necessary for forming the ductwork. On the flow side of equation, the primary and secondary tubes on Porsche normally aspirated race exhaust systems are 62-69% of the primaries (which are sized first to determine at what RPM the engineer wants the peak torque to occur within realm of practicality). SSI heat exchangers incorporate these ratios into their 1.5" pipe diameter heat exchangers, echoing the experience that the factory learned from racing.

So, which set do you need for your car? SSI has many different styles, with each one designed specifically to suit your application. The 1976 cars had a mid-year switch in configuration to the later-style gasket with the ring inside. If you use these gaskets on your 1976 car (check first), order the later style heat exchangers. All USA, Canada, and Japanese 911SCs from 1980-83 have 21mm flanges with appropriately sized exhaust studs. They require SSI models 91-915SSI. SSI heat exchangers are also available for 3.6 engine conversions! Be sure to order the style of heat exchanger that matches your engine, not your chassis, if you happen to have upgraded your engine in your car.

Oil Line Update: It is important to note that all cars with cross-over exhaust systems (all 1978-89 911SC and Carrera) require the replacement of two oil lines with two older-style ones when installing the SSI heat exchangers (or any 1974 and earlier exhaust). These lines are part numbers 911-107-729-10-M127 (cars with a front-mounted cooler) and 911-107-728-00-M20 (no front-mounted cooler) and 911-107-739-10-M127 and are available for purchase below.

Note that SSIs are no longer available with the optional O2-sensor plug.

SSI Heat Exchanger Set (pair), thin flanges, 911 (1975-76 49-State USA), 911SC (1978-83 ROW), 911SC (1978-79 USA)



SSI Heat Exchanger Set (pair), thick flange with outside taper, 911 (Late 1976-77 Thermal Reactor Cars), 911SC (1980-83 USA)

No Longer Available


SSI Heat Exchanger Set (pair) Thick Flange 820" (21.5mm) Inside Taper 38mm O.D., 911 Carrera 3.2 Ltr. (1984-89)



SSI Heat Exchanger Set (pair) Note that SSIs are no longer available with the optional O2-sensor plug, but can be fitted by a muffler shop. Thick flush flange, requires modifications to fit, 911 with 3.6L Transplant Motor



Oil Line Hose, From Solid Line to Tank, For Cars Without Front Oil Cooler Brand: German



Oil Line Hose - From Solid Line to Thermostat, For Cars With Front Oil Cooler Brand: German



Engine Block Oil Pressure Line (metal) Cross Over Pipe Brand: Cohline



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Page last updated: Sun 3/18/2018 12:08:59 AM