Driving report Turbo Harley
Today a king
A Harley with well over 100 hp – that’s the icing on the cake.
Let’s take a Road King. It weighs a good six and a half quintals, has the aerodynamics of a gothic cathedral and does not even generate 60 hp in the standard trim. No wonder that the machine – true to its generic name Electra-Glide – allows you to glide lordly, but when it comes to driving dynamics, it doesn’t knock anyone off their chair – pardon: throne.
The desire for more energetic propulsion, which makes overtaking maneuvers more calculable and appropriate marching speeds realizable, usually leads to illegality: an old tuner custom with more displacement, sharper camshafts, larger carburettors and more throughput-friendly exhaust systems, doped 1340 Evo engine may certainly lead to amazing bursts of performance , but not be able to comply with relevant noise and emissions regulations.
But it does not have to be like this. How about a Harley – let’s stay with the Road King – that delivers around 130 hp to the rear wheel without a ruckus, without profound changes to the engine innards, that purrs at quarter throttle at 180 km / h on the highway and at this speed has ample overtaking reserves? Doesn`t exist? Yes, there is.
A turbocharger from the American company Aerocharger accomplishes the feat of doubling the power, which breathes new life into the Evo engine with 0.8 bar boost pressure.
The mechanical structure of the turbo kit is simple and clear. The loader, which is located on the front left of the engine in the direction of travel, receives the driving force of the exhaust gases via a two-in-one manifold that winds around the base of the front cylinder. Filtered and compressed fresh air flows through a charge air cooler placed in front of the frame beams to a chamber mounted on the carburetor instead of the original air filter.
The Aerocharger itself has two interesting design features. It is self-lubricating, so it does not depend on the drip of the engine oil circuit: The ball-bearing shaft that carries the tubine and compressor wheels is supplied by an oil supply stored in the charger housing, which is sufficient for 700 operating hours at maximum charge pressure. And it works without an overpressure valve: once the specified “boost” has been reached, it regulates itself automatically. This is done via movable vanes arranged radially in the turbine housing, which influence the flow of exhaust gases relative to the turbine wheel.
In good kit fashion, the turbo conversion requires only minor changes to the engine: a camshaft for more valve lift, more resistant cylinder head gaskets, a different ignition – that’s all.
And how does such an inflated Harley drive? Initially quite unspectacular. The aforementioned Road King, test vehicle from the Swiss Aerocharger importer, allows discreet start-up and low-speed chugging along as with a series engine. With the carburetor slide open and at speeds of around 2500 rpm, the aha experience: the boost pressure indicator jumps to storm, and the Road King develops – with a blink of an eye – completely unbelievable haste. But without brutality or insidiousness: the thrust is powerful and determined, but starts soft and easily controllable.
D.he sounds almost too good to be affordable, let alone legal. Well, turbo fun doesn’t come cheap, the kit costs just under 11,000 marks including engine adaptation and assembly. But the best part: The conversion has already cleared the approval hurdles in terms of exhaust emissions, and the noise problem was solved with the help of the exhaust specialist Remus. The company Red Neck Cycles (73650 Winterbach, Fabrikstrasse 20, telephone 07181/46248) dared to take the costly and time-consuming walk through the thicket of StVZO regulations. Rotnacken-Boss Zange is confident that the TÜV procedure, which only depends on the driving tests that are still outstanding (yes, the winter temperatures), will be completed shortly. The fact that the approved Aerocharger power pack “only”, as measured by MOTORRAD, will have 112 hp is to be tolerated in view of the torque offered: 167 Nm at 4000 rpm – royal.
Technology: engine charging options
An engine supercharging has the fundamental advantage that an already pre-compressed fuel / air mixture is pressed into the intake ducts. This means that significantly more flammable gas enters the cylinder than with a naturally aspirated engine; more heat is released during combustion, which the engine converts into more power. The usual boost pressure is between 0.4 and 0.5 bar. As a rule, the ignition and compression must be reduced a little to prevent thermal or mechanical overloading of the engine and knocking combustion. The significantly higher liter output that can be achieved by engine charging compensates for the additional weight for the charger and intercooler by far. The era of turbocharging in motorcycle construction was in the mid-1980s. At that time, all four Japanese manufacturers launched turbo motorcycles one after the other. Honda started with the CX 500 T. This was followed by the Yamaha XJ 650 T and the Suzuki XN 85, most recently the Z 750 Turbo from Kawasaki. Compared to the respective basic version with a naturally aspirated engine, their peak performance was up to 64 percent higher (with the Honda). However, when accelerating from lower engine speeds, the power gained started only with a certain delay, but then all the more brutally. This so-called turbo lag occurs because the turbine, which shovels the charge air into the cylinder, first has to be brought up to speed by the exhaust gas back pressure that builds up slowly. The turbo lag was also the reason why these motorcycles ultimately disappeared again. In contrast to the turbocharger, a compressor is driven directly by the crankshaft, for example by a toothed belt, and therefore reacts spontaneously to any change in speed. The best-known such mechanically driven superchargers are the Roots compressor (also known as Roots compressor) and the vane compressor (also known as star piston charger). When compressor motors were banned from racing after the Second World War because the chassis of the time couldn’t cope with the enormous power, their further development unfortunately fell asleep. Since then, motorcycle manufacturers have been haggling over every horsepower with as many valves as possible and as thick intake pipes as possible, while a compressor can get a good 30 percent more power over the entire speed range. Only the enormous noise generated by the mechanical superchargers still needs to be brought under control for series production. The Comprex pressure wave supercharger offers a third option for engine charging. Like the turbocharger, it uses the energy of the exhaust gases, but not to drive a paddle wheel, but to compress the charge air with the pressure waves in the exhaust gas. The whole thing happens in a belt-driven cell wheel. Adjacent cells in it are flowed through by exhaust gas on one side and fresh air drawn in on the other. The Comprex charger has a similar short response time as a mechanical charger, but the charge air heats up enormously on the cell walls, so that huge charge air coolers are necessary. rb
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