Powerflow Exhaust System

K

ermit’s Janspeed back box looked good and sounded the part, too, but I knew that it would eventually rust away. It was always our plan to have his exhaust replaced with a stainless steel catalytic converter back system, however we had some problems with the fitting of the Janspeed so we accelerated our plans for the new exhaust, to be fitted by Rebel PowerPipes of Scunthorpe.

Powerflow custom systems offer the benefit of a lifetime warranty and the ability to tune both the type of noise and the volume of the exhaust note to suit your own personal preferences.

In the end, we went for a moderately loud system. We wanted something with a nice burble, but that would be reasonably loud at a typical motorway cruise rather than bellow away. When new, the system does bellow at a genuine 70 mph, but it will mellow out in due course.

As for the exit, well I really wanted a twin exit, a little bit like certain BMWs, and this is what we went for in the end.

Changes to Kermit’s Performance?

Many people buy an aftermarket stainless steel exhaust system for two reasons. The first is to make a nicer sound and the second is to improve engine performance.

Unfortunately, the common belief that replacing the mid pipe and back box of the exhaust can provide a meaningful performance boost for all cars is a myth perpetuated by many “fast car” magazines, ill informed websites and I daresay, the manufacturers of the exhausts. Some cars show some small improvement, some don’t. Although there are some cars that come with a restrictive exhaust system, the majority don’t show a material increase in engine output unless you replace the manifold and catalytic converter. By “material” I mean “enough of an increase to be able to out-accelerate the model but with a standard exhaust.”

Kermit’s PowerFlow system has a slightly larger bore from the mid pipe backwards. In theory, this helps efficiency at mid range and higher engine speeds with little detectable reduction in low down torque. Because the pipe is slightly larger, the exhaust gasses flow slightly slower so there is more potential for noise.

We did notice some improvement in engine response from around 2,000 rpm upwards but it’s not a measurable improvement in performance. I can’t write that the exhaust lopped a second off his fifty to seventy time in top gear for example.

But it has helped motorway fuel consumption: after the operation his long run, motorway fuel consumption showed a slight reduction of around five percent. I cannot prove this via statistics because I don’t quite have enough data; we’ve changed too much since putting the PowerFlow on the Ka.

The main exception to the above is cars designed prior to the 1980s, which often had restrictive exhaust systems, and many turbocharged cars. Turbocharged cars are often set up with “driveability” as the priority rather than peak engine output and increasing the exhaust bore can result in more performance. But this isn’t really relevant to most Kas.