Horse Power Improvement

The Harrier has a substantial 60 per cent horse power improvement over stock, with 83 Dynojet bhp produced at the rear wheel at 7200rpm. The original 790cc base-model Bonneville produced a claimed 61 bhp (crank - so around 53 at the wheel). Hyde has bored the dohc engine out to 902cc (92 x 68mm) via 6mm-over Wiseco pistons delivering 10.5:1 compression and beautifully made, freer-flowing and decidedly rortier-sounding twin-silencer stain less steel exhaust which, while carrying Harris labels, was in fact manufactured by Richard Bushell's Urbane Exhausts and incorporates his patented Intech valve, which regulates the combustion of a four-stroke engine and decreases exhaust emissions. This is the main reason the Harrier sailed through the strict Euro 3 compliance tests while still sounding just as fruity as you'd expect a 360-degree cafe racer to sound ... and then some.

The tuned engine's 14 per cent capacity hike is alone a worthwhile performance upgrade on the Harrier, even without the optimised carburation of two 35mm Keihin CR smoothbores, matched to a ported and gas flowed head carrying 2mm larger Italian-made stainless steel valves fitted with stronger UK-sourced springs, and operated via special Hyde Performance cams increasing lift and duration.

Transmission is stock Bonnie five-speed with an oil bath clutch incorporating heavier springs and smaller alloy Surflex plates. "We've done many big bore conversions, and with the extra power and especially torque from the Harrier, we knew we'd be marginal on the clutch otherwise," says Norman. "The other issue is the crankcase breather - it has an incredibly small internal breathing system and the first time I rode it with the tuned Harrier motor, it chucked oil out everywhere.

We've tripled the diameter of the breather to 25mm and used the primary case as a plenum chamber, same as we did with the Daytona breather on the Meriden racers and the ISDT dirt bikes, which was Doug Hele's idea that eventually reached production. It cut down oil leaks and increased performance via reduced crankcase pressure. So, on the Harrier we scrapped Triumph's internal breather, vented the crankcase into the primary casing, then attached the biggest braided metal hose we could find from the primary cover to the catch tank above the gearbox, from which any oil runs back to the crankcase. An intelligent idea born of experience.

The resulting engine, this kind of dirt bike parts, isn't just a whole lot faster, but thanks to a massive torque increase also has a noticeable improvement in acceleration, even with a higher 19T (stock 17) gearbox sprocket fitted, which delivers an effective 6 T longer gearing on the back wheel, and prevents premature peaking en route to a claimed top speed in excess of 145mph.More info here
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