Custom Motorcycle Exhausts – Built in House at Purpose Built Moto

With everything we do, Purpose Built Moto is consistently aiming to improve. A natural step in our custom motorcycle fabrication, was to get our hands into building exhausts. In the past we have outsourced these things, but with our provider looking to retire soon, we needed to step it up a gear and push ourselves forward into fabrication our own motorcycle exhausts.

Over the last few years we’ve been improving the fabrication of motorcycle exhausts in our Gold Coast workshop. Always learning and looking for those improvements in our work that can only be gained from experience. 

In this blog I’ll share with you what we’ve learned about building our exhausts to achieve the quality, sound and look that our clients demand. Off the shelf products are plentiful these days, but that definitely doesn’t deter the customers with higher expectations walking through our door to make sure we can build them something totally unique for their custom bike.

This information will guide you in choosing which direction to take with your exhaust before getting in touch with us to make it happen.

Email us to have a chat about building your custom motorcycle exhaust

tom@purposebuiltmoto.com

The sound of your custom motorcycle exhaust

This is what everyone wants to achieve, that perfect sounding motorcycle exhaust. Of course, its subjective according to the rider. Some want it ear piercingly loud, others want a smoother more subtle note.

With the various engine types, some are easier to work with than others. Below I’ll break down my personal experience with exhaust sound on some of the popular engine types.

Single Cylinder motorcycle exhaust sound:

Bikes like the Yamaha SR400 or 500, Husqvarna Vitpilen 401, Suzuki GN250, DRZ400. All insanely popular custom donor bikes. The challenge with these bikes (especially the lower revving Air cooled models) is smoothing out the thump of that big single piston.

For these models the suggestion is a larger header pipe, fabricated as long as practical and fitted with a good quality muffler. The muffler is critical here, with a good quality dual muffler packing to ensure enough sound deadening is achieved with your custom exhaust.

Shorter headers with older mechanical baffle mufflers will leave you with 2 problems: a bike that sounds like an old petrol generator, and the constant threat of the boys in blue giving you trouble for a bike that’s overly loud.

The Husky 401 build has lead us to build and experiment on a number of different exhaust designs. All achieving different style and sound results.

 

Parallel Twin Cylinder Motorcycle Exhaust sound:

These are my favourite exhausts to build and the engine type I’m most familiar with. You have 2 options with engines like the Triumph Bonneville, Triumph Thruxton, Yamaha XS650, Kawasaki W800 and W650, Royal Enfield GT650 and the less popular Suzuki GR650. Fabricate a nice 2-1 exhaust that will generally deliver better performance and a smoother less intrusive exhaust note. Or go with a far lumpier sound and keep each cylinders exhaust separate in a 2-2 set up. Personally I always opt for the 2-1 set up. I don’t like my motorcycles too loud, and if you can achieve better performance while doing that you’re onto a winner.

Sound also has a lot to do with firing pattern of your particular motor.

Shown in the pictures through this section are a number of options using hand build mufflers and our popular stainless steel Torpedo Shorty Muffler. The loudest being Allan’s Triumph Bonneville where we hand built a 2 into 2 exhaust on one side of the motor. Although these look like straight drag pipes the exhaust has inbuilt hidden mufflers to take the rasp out of the exhaust. She’s definitely loud, but we’ve removed the high pitched crack that comes with straight pipes.

One of the ideas we’ve been experimenting with when we can is a high flow X-pipe, that retains the symmetrical look of a 2 into 2 pipe but gives the performance advantage of the 2 into 1. More on this when we release our latest XS650 build.

 

V-twin exhaust sound

In this category I’ll also include the higher revving cousins of the v-twin the V4 motors. On the Harley Sportster and Indian Scout Bobber exhausts I’ve built its always been 2-1. I just love the smoother sound that you don’t often hear out of these bikes. My personal Harley Sportster Scrambler Project was a tough one simply because of the tight space we had to fabricate the header, collector and high sided muffler. In the end though we were left with a great sounding exhaust that was quieter than most aftermarket solutions off the shelf, and it look way better (I think).

Leaving a 2-2 exhaust set up on a v-twin will give you the thumping sound you’re used to out of these cruiser style bikes. A lot of people go this route even on the smaller metric bobbers, and end up with a hollow exhaust sound. This is because you’re putting the same exhaust on a 1200CC motor as you’re building on a 650cc Jap cruiser. It just doesn’t work.

If you’re building a 2-2 exhaust on a smaller capacity bobber, building in some internal baffling will give you a far better sound over a straight pipe or oversized muffler.

On the V4 front, the only experience we’ve had here was on our 2020 build of the 1994 Honda VFR750. One of the best sounding exhausts to come out of the shop. Simply pairing a twin torpedo muffler set up with a performance 4-1 header system delivered an amazing note, and great performance. You can check out the sound clip in out Youtube Build video.

 

4 Cylinder motorcycles

My first road bike love. Getting a 2007 GSXR600R at the tender age of 19, the undeniable symphony of a 4 cylinder motorcycle revving its fucking head off spurred my love for street bikes. One of my personal bikes is a Suzuki GS550, and the vintage 4 cylinder Hondas we have through the shop are always a delight to listen too.

By far the most popular exhaust set up for performance and sound is the 4 into 1 header. You cannot beat it! We’ve paired numerous 4-1 header set ups with our torpedo mufflers and the results are just shy of magic. 4 into 2 set up are a close second but will often have a share pipe between the 2 collectors.

If you’re going the route of a 4 into 1 set up just be aware of the fabrication time and cost (pretty high here). You’re working with 4 cylinders, and each needs to be built to exact length and run into a collector precisely for good fit.

 

Exhaust Materials and Fabrication

We have serviced a large variation of customer needs for building exhausts and are always up for a challenge. When building an exhaust for any bike, we prefer to work with 316 stainless steel for the headers, welded using a back purge set up to ensure the strongest weld possible.

Using stainless steel opens up your options in terms of finish as well. The custom exhaust can be finished in high temp cerakote of almost any colour (usually black), left raw with the welding heat signature, brush finished with the welds left on or brush finish with the welds removed. I’ve even heat treated colour into the exhaust before for a really special finish.

When it comes to muffler we’re always open to testing new ideas. We’ve built everything from hidden internal baffles to keep the straight pipe look, retro fitting aftermarket Motorcross pipes from FMF, hand building our own mufflers from raw materials or simply fitting up our off the shelf Torpedo mufflers.

At the end of the day, its our job at Purpose Built Moto to make sure you get something unique, and fitting to your needs. So whatever you have in mind its always great to throw ideas around with our clients to make sure we land on something great.

Email us to have a chat about building your custom motorcycle exhaust

tom@purposebuiltmoto.com

 

Check our Torpedo Muffler in our online shop