Harley-Davidson's Twin Cam 88 motor – the Motor Company's most recent technological 'Great Leap Forward' - has been gracing their showrooms for a couple of years now, and although it's generally been received as a genuinely more advanced development from the Evolution engine, opinion and experience still seem somewhat divided. For what it's worth, I was well and truly converted to the Twin Cam cause during the 3500-mile trip to and from Faro 2000 (thanks again to Jerry and H-D there), despite the fact that the Twin Cam was destined to jump into the ring with one metaphorical arm tied behind its back, thanks to the motor-stifling American emission legislation that the company is obliged to observe.

Yes, I loved that Twin Cam last year, but I always felt that, just when it really seemed as though it wanted to break loose and surprise a few Jap-mounted people, it simply ran out of breath. The cold facts are that, in standard form, the 88 Big Twin yields only a little more useable power than its Evolution predecessor - 56hp at the rear wheel isn't, by any stretch of the imagination, an overwhelming output for a motorcycle weighing six or seven hundred pounds, especially when common sense (not to mention your instincts) tells you that there should be much more than that on tap from an engine like this.

So when Boz, of , yes, BOZ Engineering, called one day to say that he was confident he'd now perfected a formula for upping that meagre 56hp to 100 in a useable, practical package, we wanted to know how he'd done it (more accurately, we wanted a go on one, but more of that later…). Now, for those of you at the back who haven't been paying attention, over the last decade or so, Boz has gained himself a reputation for building Harley engines that's now second to none, so it's not surprising that the moment the Twin Cam engine was unveiled, he began gearing up to work on them too. He had his name down for one of the first '99 model year Twin Cams available, with the express intent of taking the stock bike and extracting from the engine the kind of power that the Harley production line will never be able, or allowed to produce … making a Harley more Harley, if you like. This is Boz's fourth 88 thus far, and of the component combinations he's been experimenting with, the one we've documented is very well suited to the FXSDT - the T-Sport to you and me. The T-Sport comes replete with an uncharacteristically (for H-D) fully functioning suspension system and satisfactory brake set-up, which it'll certainly need if it's to handle the hundred horses on offer here. We'll be checking up on how the pumped-up Twin Cam handles in the roadtest section, but for now, let's have a look at exactly how the transformation takes place.

Firstly, we remove everything that's in the way; tank, seat, exhaust, footrests, brake pedal, cylinder head steady, carburettor and air cleaner. This is relatively easy on the Dyna, but is obviously more time consuming on a Glide, with all its extra bodywork. The top end is removed completely - rocker covers, rocker assemblies, heads, cylinders and pistons. There are three significant points to note in this picture that differ from the Twin Cam's Evolution predecessor. One, the notches in the flywheel which trigger a crankshaft position sensor as part of the ignition system; two, the counterbored crankcase mouths which accommodate O-rings to seal the cylinder bases rather than gaskets; and three, the tappets run directly in the crankcases a la five-speed Sportster. The cam cover removed. Unlike the Evo, the cover isn't structural, ie all it does is contain the oil. The two cams are held in a support plate, which is accessed first by removing the primary cam chain and sprockets. This requires a sprocket locking tool and an unlocking tool for the heavily sprung tensioner. Cam support plate is now clearly visible. With the plate and cams removed as an assembly, notice the oil pump. Earlier Big Twins had a gear pump located externally on the rear of the crankcase. The Twin Cam's pump is a 'gerotor' type that's concentric with the crankshaft. The two cams, their bearings and the secondary cam chain are pressed out of the support plate together using another service tool and a press. New bearings are pressed into the support plate using service tools and a press. The new Head Quarters cams and secondary cam chain are pressed into the support plate bearings. By this stage you'll have realised that one or two special tools are required for a job like this … … and here they all are. Harley won't sell them, but Jims Machine do (I'll warn you, they're not cheap!). Re-assembly is the reverse of assembly, as they say, with special attention being paid to torque settings, sequences, etc. Cylinders are bored out 1/8" to increase capacity from 1450cc to 1550cc. Cylinders are finished honed on automatic honing machine to give the correct finish conducive to oil consumption, ring life and compression sealing. Before and after. Pistons and cylinders installed. These are H-D high compression cast pistons and give 10.5:1 with the head configuration we are using. Flat top pistons can also be used with different cams, but give less power. Heads and rocker assemblies are installed. Head Quarters adjustable pushrods are used. The Twin Cam motor uses the same rocker arms and shafts as the Evolution, but they are supported on pedestals that bolt directly to the heads. The rocker covers, like the cam cover, are only there to keep the oil in!

It's an accepted principle that, when tuning any internal combustion engine – be it a Honda 125 or a Harley 1550 – altering one component will inevitably affect another, and at this level of anticipated performance increase (approaching 90%!), the correct combination of parts is even more vital if the full potential of these engine modifications is to be realised. So Boz will therefore duly be dealing with the other key factors in the equation – the carburettor, the ignition system and the exhaust pipes. Then it'll be a case of checking out what proof there really is in the pudding with a few runs on the dyno … but that is all happening in the roadtest section (accessed by clicking here ... service or what?), as Boz has foolishly agreed to allow Misterdavemanning and meself to corroborate the claims we've made here on his behalf and take to the M20 aboard the very hundred brake Twin Cam 88 you see here. That's either the action of a misguided madman or he's very, very confident about what he does for a living …

This feature first appeared in Back Street Heroes 201