Custom Royal Enfield Interceptor 650 dyno test

If you’re craving more power from the 650cc parallel twin of your Royal Enfield Interceptor or Continental GT then you’re in luck: the easiest, obvious mods are immediately noticeable, hugely beneficial, and they won’t break the bank.

We came across a privately owned Interceptor 650 adorning an array of Royal Enfield styling accessories, headlined by a full S&S exhaust system for a bigger bark.

With the owner’s blessing, we took the bike for a spirited ride and, by the seat of the pants, felt a performance gain of around 10 per cent over the standard bike thanks to the better-breathing pipes and a DNA performance air filter.

Apart from sounding the business, the more athletic Interceptor has a greater sense of urgency than the regular bike, with vastly improved mid-speed acceleration to overtake traffic, pull away from the lights and punch out of apexes. Comparatively speaking, it rips.

So, with curiosity getting the better of us, we sourced a standard Interceptor 650 to compare the pair on a dyno and confirm our seat-of-the-pants feeling.

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Power talk

Powering the Interceptor and its mechanically identical, café racer-inspired Continental GT sibling is an air/oil-cooled 648cc parallel twin with a single-overhead cam, four valves per cylinder, a 270-degree crank and balancer shaft.

Compression is a relaxed 9.5:1, so claimed outputs of 47hp (35kW) at 7250rpm and 52Nm at 5250rpm (these figures were provided at the world launch and may differ from final local specification) aren’t mind-blowing in outright performance terms, but they were never meant to be. We’re talking about a relaxed, retro-inspired riding experience where it’s all about smiles per mile.

The first test was to confirm Royal Enfield’s claims and measure the standard Interceptor’s outputs.

For reference, a manufacturer’s power and torque outputs are typically measured from the engine’s crankshaft, which gives higher figures thus bigger bragging rights for greater showroom appeal.

Dynos (which are essentially big treadmills for bikes or cars) measure outputs produced at the wheel, the results of which are typically lower due to drivetrain loss (in a motorcycle’s case its chain, belt or shaft drive). In short, they’re real-world numbers. All dynos are slightly different too. Our tests were conducted at Dynobike, in Melbourne’s south-east suburb of Moorabbin, which uses a Dynojet dyno (pretty much the industry standard).

The results are in

So, without further ado, the standard bike produced 43hp at 7000rpm and 51.5Nm at 4900rpm – incredibly close to the factory claim, so what you see is in fact what you get.

More importantly, however, the torque curve is flat and surprisingly fat, with 80 per cent on tap by just 2500rpm. That, combined with a deceiving dry weight (198kg and 202kg for Continental GT and Interceptor respectively), allows either bike to strike a balance between agility and user-friendliness as well as good acceleration and usable, everyday performance.

Now for the better-breathing bike. The custom Interceptor with the full S&S exhaust and DNA air filter produced 43hp at 7000rpm and 55Nm at 5000rpm. Yes, that’s pretty much the same, but that’s also where the similarities end. Take a good look at the dyno graphs for the real story.

As you can see, the custom bike (as represented by the blue line) starts to pull away in the horsepower race from 3000rpm to around 6500rpm with the biggest gains taking effect between 3500 and 5500rpm.

Better yet, however, is the resultant torque increase. From around 2500rpm, the custom bike walks away from the standard with a fat wedge of Sir Isaac Newton’s finest between 3000 and 5000rpm – exactly where you want it in the real world. This is the big 'torquing' point and what you’re immediately feeling day in day out.

Living in the real world

‘Dyno Dave’ Edgecombe of Dynobike typically works on performance-oriented machinery, but the experienced, former Team Honda race mechanic is impressed nonetheless and reiterates that peak figures rarely tell the full story.

“People always bang on about peak figures. ‘How much has it got, mate?’ ‘Mine’s got 50hp.’ ‘Is that all? Mine’s got 65!’ Yeah, but where in the rev range? In the mid-range or at redline? That’s the difference,” Edgecombe says.

“From 3500rpm, there’s a big, fat, juicy torque curve, to 5000rpm. That’s what you want. Even if we got another 10hp at 7000rpm, you wouldn’t notice it on the road. It’s that bottom bit – the real-world stuff – that you notice when you’re pulling off from the lights.

“It would absolutely smoke the standard bike in a straight line!”

Indeed it does. So, what would be the next step to greater performance?

The next step

“I’d like to see it holding torque for longer instead of dropping off after 5000rpm. You could achieve that with a tune,” Edgecombe says.

Furthermore, the choice of go-fast parts is rapidly expanding with several reputable makers already offering a range of performance upgrades for the popular Royal Enfield models.

In the case of S&S Cycle, a 62-year-old American motorcycle engine and parts company synonymous with Harley-Davidson performance upgrades, that includes big-bore piston kits in 750 and 865cc guises ($888 and $1215 respectively); a high-performance camshaft kit ($355); an upgraded clutch kit ($755) and a DNA air filter ($125). All quoted prices exclude labour. Dynobike sells and installs the lot.

As for the S&S exhaust, the custom bike has a full system, which the owner personally sourced from the US for around $A1800. At the time of writing, however, S&S only imports a slip-on muffler set ($895), which admittedly won’t provide quite the same performance gains as the full system.

Other than sourcing one from overseas, a better – and possibly cheap – solution would be to reach out to an Australian exhaust fabricator such as Megacycle Exhausts in Melbourne, for example.

So there you have it. Turns out the performance gains weren’t just a placebo effect from false audible stimulation of a snarlier exhaust. We’ve confirmed it’s got the go to match the show. You’re welcome.

Many thanks to Dynobike for testing the bikes at short notice. Check out Dynobike’s range of S&S upgrades for the Royal Enfield 650 twins HERE.