An exhaustive process
I’VE LEARNT A LOT. First, that I’m enjoying the 944 a whole lot more simply because it sounds better. But I’ve learnt a few engineering terms, too. Such as ‘mandrel bending’ and ‘purge welding’. No, not things that go on around a maypole or in the vicinity of Morris dancers; instead, the work of artisan craftsmen who take the art of building a new exhaust system very seriously indeed. Art? Oh yes. Just take a look at it!
I’d first noticed a bit of fluffing from the 944’s exhaust when I was driving back from the NEC Classic Car Show in Birmingham, a fair few years ago. Decided I’d live with it until it got a lot worse. Well, the 944 wasn’t failing its MoT on exhaust, emissions or noise, but I finally figured it could be a lot better. So I got in touch with Demand Engineering in Suffolk, (demandengineering.co.uk), and booked the car in. That meant a 4.30am alarm in mid-June (I love a dawn start at this time of year), ready for a 90-mile blast into the heart of East Anglia, via a few wellknown and twisty routes to hook up each side of the A14 trunk road.
First things first: the old exhaust had to come off. The downpipe was in extremely good condition, so no need to fabricate the complicated section that twists its way down from the manifold. A cut was made and the old system was hefted out. Incredibly, the guys at Demand think it was the original, so it’s done rather well.
Technician Jack Rogers reckoned the main section should be 2in bore, into a resonator 2in shorter than the original, then a short but more complicated section (to avoid the CV boots on the rear axle) of 13∕4in tubing into the back box (again, 2in shorter), exiting via an oval outlet not dissimilar to the original. As a straight-through system, it would sound a bit fruitier than what went before, and it might even release a couple more horses, too.
The resonator is made from a pre-formed cylindrical section of steel, and Jack used a former to make the back box the correct ovoid shape. He then stuffed each with a perforated steel inner pipe and glassfibre wadding, welded on the end plates, then gradually built up the sections of tubing, bending them (on the mandrel bender, which shapes the tubing around linked balls, so there are no kinks), and tacking them together in situ before welding the whole assembly on the workbench.
This is where the magic came in. Purge welding involves flooding the inner and outer surfaces of the steel with inert argon gas, making for a beautifully clean join with no build-up and thus guaranteeing no flow disruption – the enemy of power. And it looks fantastic: visible joins (though they can be polished out) but smooth to the touch. All using 1.2mm 321 wire and 304 stainless tube.
Jack fabricated some new brackets, offered the system back up to the existing hangers, and it’s a beautiful fit. Like I said, a work of art. It even weighs less, apparently by as much as 10kg.
Demand Engineering was set up nearly ten years ago by Dan Dew, a Land Rover restorer who failed to find the exhaust system he wanted and decided to create his own. The business grew from there, and it was no surprise to find the Porsche sharing a workshop with a Ford Escort Mk1 Mexico and a Honda Integra Type R.
Finally the lift came down and it
was time for the start-up. No big dramas, just a gentle burble, slightly more forceful than before. No, the big difference kicks in when you accelerate away, with a properly purposeful blare that changes in timbre as the revs rise, and an appetising side order of Alfa-esque crackle too. Yet back off and all is quiet: no drone at a cruise thanks to the shorter resonator and that section of smaller-gauge tubing. Art and science.
But is the Porsche now more powerful? Well, the throttle response is much, much cleaner and more immediate (thank reduced back-pressure for that), and it feels as though it revs harder – though it’s entirely possible that might be due to my new-found enthusiasm, now that there’s some extremely listenable exhaust music to accompany the rather more mechanical voicings from under the bonnet.