When you’re working on a classic Porsche, there’s a good chance the original exhaust has seen better days. And if you’ve spent any time in the Porsche scene, the name SSI has probably come up more than once. Known for their tough stainless steel heat exchangers and exhaust parts, SSI has been a go-to option for decades — not just for durability, but for that clean fit and feel that keeps these cars driving like they should.

At Design911, we’ve seen firsthand how well SSI parts hold up. From full restoration projects to weekend upgrades, they’ve become a solid choice for air-cooled Porsche owners. But where did SSI come from, and why are their exhausts still talked about today?

Back to the Beginning: How SSI Started

SSI (short for Stainless Systems Inc.) started back in the 1970s in California, at a time when early 911s and 914s were becoming popular among drivers and tuners. The original heat exchangers on these cars were made from mild steel, and while they did the job, they weren’t known for lasting long — especially in damp or salty conditions.

John Daniels, a Porsche owner and fabricator, began building his own stainless steel versions. He wasn’t chasing trends — he just wanted parts that didn’t rust and could stand up to real driving. His work quickly caught on with other enthusiasts, especially as people realised they could improve performance without butchering the car’s originality.

For years, these parts were handmade in small numbers, often sold through word of mouth or to specialists in the know. But the quality spoke for itself.

In 2012, Danish company JP Group took over the brand and moved production to Viborg. Rather than changing things, they kept the focus on proper materials and tight tolerances — just on a slightly larger scale. It’s still very much a product made for people who understand how these cars work.

What Makes SSI Exhausts Worth Considering

There are plenty of aftermarket exhaust brands out there. Some focus on sound, others on maximum performance. SSI, on the other hand, has always aimed to hit a balance — improving flow and lifespan while sticking to the original feel of the car.

Here’s why they’ve stayed relevant:

• They last – Made from T-304 stainless steel, SSI systems don’t rust like the factory ones often did.

• They fit properly – These are bolt-on parts, designed to work with the stock layout and mounting points.

• They improve response – Better flow means better throttle feel and a stronger pull through the rev range.

• They sound right – Not too loud, not too quiet. Just a cleaner, deeper tone that feels period-correct.

You won’t get over-the-top noise or modern styling here — that’s not what SSI is about. These are for people who want their classic Porsche to run better, without losing what makes it special.

A Few Picks from the Design911 Range

If you’re thinking about going the SSI route, here are a few of the options we stock that stand out:

• Sport Exhaust Conversion Kit – Porsche 911 3.2 Carrera
  A solid option if you want to ditch the restrictive catalytic setup. It’s a noticeable upgrade in both flow and feel.

• 41mm Stainless Heat Exchanger Set
  Larger tubing for better flow — ideal if you’ve got a higher-powered engine or just want a little more out of your setup.

• Muffler / Rear Box – 911 CS (1983–89)
  Keeps the look and mountings close to original, but swaps in stainless steel and a deeper sound.

• Exhaust Conversion Set – 911 2.7–3.0L (1974–83)
  Covers one of the most popular eras for air-cooled builds. It’s a straightforward, effective upgrade.

• Heat Exchanger Set – Porsche 914/4 (1972–75)
  Options for the 914 are much harder to find, and this one’s built with the same care and finish as the 911 parts.

Still Built for Real Drivers

Plenty of Porsche parts look good in a catalogue but fall short on the road. That’s not the case with SSI Exhausts. The build quality, the ease of fitting, the way they behave at high RPM — they’re clearly built by people who know how these engines breathe.

If you’re used to driving your car regularly, doing road trips, or even the odd track day, these systems will hold up. They’re not just about ticking a box for stainless steel — they make your Porsche more enjoyable to drive without creating new problems.

Design911 x SSI

We work closely with SSI to ensure our customers have access to the right systems for their build. Whether you’re doing a full nut-and-bolt restoration or simply swapping out a tired rear box, we’ve got you covered.

Need help deciding what fits your car? Our team can guide you through the range and help make sure you get the right parts for your model year and engine.

Take a look at the full selection here:
Explore SSI Exhausts at Design911

Final Thoughts

When it comes to upgrading an air-cooled Porsche, some things are worth doing properly. SSI Exhausts have been around long enough to prove they work — and they look the part too. Whether you’re aiming for period correctness, reliability, or a bit more character from your engine, it’s hard to go wrong with SSI.

At Design911, we’re proud to offer their range and help keep these cars running as they should. Take a look at what’s available and get in touch if you have any questions.