My wife Jane bought a 2012 Dyna Switchback after 22 years of FXR ownership, and this new bike has become another test bed machine for Heavy Duty magazine (www.heavyduty.com.au). In terms of performance, we began by switching out the stock cams for a set of S&S 585 units, fitted an S&S air cleaner and a Harley-Davidson Nightstick muffler. The bike was then fully dyno tuned at Neville Lush Racing using SE software and achieved a respectable 90.15 hp.
The next step to boost its power was to consider a better performing exhaust for which we turned to D&D for one of their Fat Cat 2-into-1 full systems. Now after bolting it on we did a dyno test run to see what difference it immediately made prior to doing any tuning.
Well the horsepower jumped to 99.19, a difference of 9 horsepower. Plus you can see that where the old system became restrictive from about 4500 revs and on, causing a levelling out of the power curve, the pipe change allowed it to keep climbing. Very impressive to say the least.
However, making any major changes such as fitting a performance exhaust such as the Fat Cat is going to affect the mixture set up with the old tune and as you can see from the bottom part of the graph, it became dangerously lean in places. The old mixture is shown in blue and the mixture after changing the exhaust system is shown in the red and this strongly makes the case why you need to dyno tune your bike after making performance modifications.
Now I have been very happy with the performance and functions of the Dynojet Power Vision flash tuning device that I fitted to my 2012 Road Glide with S&S 106ci kit and decided to purchase one to tune Jane’s bike. There are many advantages of these neat units but one that had particular appeal to me was the ability to store different tunes and select them with the press of a button.
So with the bike up on the Neville Lush Racing Dynojet dynamometer, Neville plugged in Jane’s Power Vision and began tuning, with the result you see in the graph, a whopping 104.07 ponies and a fat 112.09 lbs/ft of torque.
Why such a difference? Well take a look at the difference between the stock header pipes in pic 1 below.
The stock headers merge into the section of pipe where the catalytic converter is located and after the gases battle their way through that, they emerge into a single pipe of a fairly restricted diameter.
Now contrast that with the way the gases can flow smoothly through the D&D header pipes in pic 2 below.
Also, compare the two mufflers as shown in pics 3&4 with the D&D on the left and the Nightstick on the right.
If we go right back to basics, an internal combustion engine is simply an air pump, so the more efficiently the air flows through it, the more power that can be generated. D&D Exhaust have done another superb job in designing and manufacturing this sweet system and I can highly recommend their products.
I rode the bike back home, a distance of some 50 miles with 40 of those out in the countryside so I was able to twist the wick pretty vigorously and boy, did that put a smile on my face. Dyno graphs provide good technical information about the performance of an engine but how it feels on the road cannot always be conveyed with total accuracy. On the way home the Switchback felt like a totally different bike, with much more pep and was way more fun to ride. And Jane? Well she hasn’t stopped smiling since she first threw a leg over it with this system.
Fact Sheet
D&D Harley-Davidson Dyna Switchback Fat Cat 2:1 Full system.
Year: 2012-2013
Product Number: 583-31 Black/583-32 Chrome
The 2:1 Fat Cat is a stepped header system and at the head is 1 5/8 inch to 1 3/4 inch to 1 7/8 inch at the collector and 2 1/2 inch where the muffler goes to the header. All full systems are equipped with heat shields, bolt kit, brackets, exhaust gaskets and baffles.
Each exhaust system is designed and dyno tested in the D&D facility and all D&D testing is done with Harley-Davidson’s SE Tuner.
Every D&D pipe is designed to increase low-end torque, horsepower and performance. Increases are about 8 to 10 percent with the appropriate tune in the bike.
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