When people talk about exhausts, the increase in power/torque, sound and lower weight are usually the main reasons for an exhaust upgrade. The Stock exhaust is quite restrictive and very heavy on a stock motor and 3-4 hp can easily be achieved with most exhaust upgrades for the Bonneville engine.

Adding a Breathe Stage 1 kit or stage 2 pod filters releases more again but you are starting to stretch the requirements for more power and the design of that exhaust, as most main stream exhaust makers are about making money. They make the most money by catering for the stock model, not the Performance Upgraded engines.

This is where Harrison Performance comes in. Take your bike up to “Bonnie” Scotland and this Scotsman will complete a full R&D program on your bike to the specs you require. So this is what we did.

The Brief was simple, I want a 100 rear wheel Horse power Bonneville 904. I want to make an exhaust that will make maximum top end power for the racers and fast road users while also keeping the exhaust noise level to a sensible level. Enough so you can ride to work in the morning and not wake up the street.  It needs to be offered in Stainless steel and Titanium and I want it as light as possible.

Harrision Performance: “Challenge accepted”

The Bike: “Arturious” is the UTP Bonneville Carb test bike. He has our TTP 904S bigbore kit. Our Stage 4 Fire starter Ignition, FCR39 flat slide carbs, upgrasded and a Poly quad ported and flowed head.  We started with the best exhaust for Hp ever made off the shelf. We had 92rwhp and 65lbft torque.

We spent 9 hours on the “Grant Racing” dyno adjusting lengths, diameters, tapers and silencers.

The end result was mind blowing. 100rwhp 70,5lbft torque.

To compare this to other bikes, Manufacturers use Crank Hp.

This puts our bike at 112hp and 82lbft. It must be felt to be believed








I never thought we would achieve our goal, as it was kind of a dream rather than what was expected.

8rwhp and 5lbft increase over the best exhaust available off the shelf.

We are extremely please with this result and alot of hard work went into this from all sides.

Too add the this crazy result, the Titanium system looks to only way a couple Kg TOTAL!!!

Let that sink in for a moment. Race teams spend fortunes increasing power to weight ratio’s.

Not only have we created the most powerful 904cc specific exhaust ever made to order!!!

We will also have the lightest exhaust system ever created for the Bonneville, Thruxton, Scrambler bar none!!!!

Pricing and weights will be added to the website very soon.

If you want the best and the most powerful 904cc big bore exhaust.

We have it, made in Scotland. Made by hand, by Harrison Performance, check them out.


And its not over yet. Coming soon!!!!

UTP stage 1 heads

UTP 2-2 exhausts

UTP Upgraded Cams.

UTP inlet manifolds

Exciting times in the world of Triumph Aircooled twins!!!!



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