Horex Motorcycle Patent Reveals W8 Configuration
According to the company, the engine is slightly wider than a conventional inline-four but also slightly shorter. As a fresh reminder, the Horex VR6 is powered by a 1200cc supercharged 15-degree V6 outputting 197 horsepower at 8,500 rpm and 150 Nm of torque (110 lb.ft.), which is connected to the rear wheel via a six-speed cog swapper and belt drive.
Illustrations revealed by the aforementioned source give as a hint on how a W8 engine could be mounted longitudinally on a motorcycle with the cylinders pointing outward. The adjacent images show a 1500cc W8 with a 60.6mm bore and 65mm stroke. The engine is comprised of two 15-degree V-inline banks joined in at a 72 degree angle.
However, as the VR6 Roadster won’t enter production until later this year, in very small numbers and priced at some EUR20,000 (US$27,070 at the current exchange rate), we could wait a while longer for the Horex W8.
Horex has also performed dyno tests of their VR6 engine, an engine that will be offered in two guises, one naturally aspirated and the other supercharged, which you can watch by accessing this link.
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Although clearly not a direct competitor to the BMW K1600 market, the Horex VR6 is an interesting development in six cylinder development for motorcycles.
At 15 degrees the V6 engine is very compact and seems to fit a motorcycle well. The bike?s proportions seem nicely arranged if you favour a more classic naked styling.
At 1218 cc it has just a little more total piston area than the BMW K1600.
Bore of the Horex is 68mm while the K1600 comes in at 67.5 mm.
The stroke of the Horex is much less at 55 mm compared to the K1600?s 71 mm.
The use of a belt driven supercharger will improve torque in both the lower and upper RPM ranges. The variable ratio belt driven supercharge should go a long way to improve low engine speed grunt to compensate for the shorter 55 mm stroke.
Several motorcycle manufacturers in the past have tried turbo chargers but it didn't catch on. The extra complexity, weight, turbo lag and poor boost at low engine RPM was unacceptable to many riders.
This new system addresses many of these issues. There is still a small weight gain which may not be acceptable to the pure sport bike rider who spends more time in the upper half of the RPM range but for the power cruiser and roadster group where the accent is on excellent torque at both low and high RPM this will be appealing.
They are claiming a crank BHP of 197 at 8500 RPM. The piston speed at 8500 RPM works out to a low 3067.6 feet per minute. It would be interesting to know why they limited the RPM to just 8500. A more typical modern motorcycle engine speed with a 55 mm stroke at 3900 feet per minute comes out to 10,800 RPM. Maybe with the supercharger Horex concluded high RPM was not necessary to achieve their target HP.
At 530 lbs (probably a dry weight) it is no light weight but compared to the Vmax at 700 lbs wet it?s significantly better. At least it has a little bigger gas tank, an extra 6th gear and about 6 inches shorter.
While the Horex V6 engine is an interesting concept I believe the variable traction transmission used in the belt driven turbo charger could have an even greater impact in the future.
Especially if the technology is also used to replace the standard gear box.
The variable traction transmission was developed by Torotrak.
It was originally designed to be used as transmissions in all kinds of vehicles from riding lawn mowers to heavy trucks and buses. Even heavy off road vehicles.
The mechanical efficiency is a high 95%. I believe this is better than typical automotive automatic transmissions and equal to or better than standard transmissions.
In the continuously variable transmission style there still is a clutch. In the infinitely variable transmission type no clutch is required and there is a neutral and even reverse.
There are no belts, chains or gears. The torque is transmitted through a very thin (measured in microns) layer of oil between the very finely finished rotating discs. The driven and driving components actually never touch.
With many bikes already using drive by wire throttle controls it doesn't take a lot to see the advantages of an engine with a mechanically driven variable turbo charger using a Torotrak variable transmission and a Torotrak to replace the gear box. In a sense the throttle would not directly control engine RPM. It would control the amount of torque applied to the rear wheel.
One other feature of the traction drive transmission is that it has both under drive and over drive ratios.
The on board computer would decide the ideal engine RPM, turbo boost and gear ratio to achieve the desired torque at the rear wheel based on the throttle position and rate of change of the throttle position.
This way we can have our cake and eat it too.
Really good fuel economy when cruising with low engine RPM and minimum turbo boost but still have lots of torque available when we turn the throttle.
One of the advantages of a mechanically driven turbo-charger over a positive displacement supercharger is that if the turbo stops working for some reason the engine can still function. Air can still enter the engine by bypassing the turbo. Maximum performance will of course be affected but at least you can "limp home".
Other advantages are that the mechanically driven turbo-charger is no longer exposed to the exhaust?s high temperatures. Special, complicated, space robbing exhaust plumbing would not be required.
In regards to a Torotrak replacing the gear box I suspect many would miss the clutch and shifting gears though. One advantage of a standard transmission and throttle control is that the ride can react to changing conditions before the condition arrives.
One possible solution would be to offer the rider an optional simulated stepped gear ratio control of the transmission.
Something like on the Honda VFR 1200.
Total piston area of the Horex VR6 with a 68 mm bore is 33.75 square inches.
Total piston area of the W8 with a 60.6 mm bore is 35.75 square inches.
The maximum total piston area of any motorcycle in mass production at 40 square inches are the Honda 1800 Goldwing and Vmax 1700.
The Triumph Rocket III has 37.5 square inches of total piston area.
A typical maximum RWHP of a modern naturally aspirated non-racing motorcycle engines at a piston speed of 3800 feet per minute is about 4.25 RWHP per square inch of total piston area.
This would suggest the RWHP difference between the VR6 without a turbo-charger and W8 would be about 9 RWHP at a 3800 feet per minute piston speed.
VR6 naturally aspirated = 143 RWHP at 10500 RPM (3800 feet per minute piston speed)
VR6 turbo-charged = 177 RWHP at 8500 RPM (3068 feet per minute piston speed)
W8 naturally aspirated = 152 RWHP at 8900 RPM (3800 feet per minute piston speed)
The proposed W8 does not mention if a mechanically driven turbo-charger is to be also used.
If the turbo charger is not included in the W8 design it would suggest the VR6 with the turbo-charger would actually develop more RWHP than the W8 and at least match the torque characteristics at lower engine speeds.
If you also factor in the extra weight of the W8 it appears the VR6 engine would be a better choice.
For these reasons I do not expect the W8 will be developed by Horex at this time or in the near future.
The present low piston speed of the Horex VR6 at 3068 feet per minute at maximum HP would suggest there is potential for significant increases in HP by increasing the maximum RPM to a typical piston speed of 3800 feet per minute (10500 RPM).
Torque output is largely dependent on the level of turbo boost. Boost level to a great extent depends on the computer's program.
Aftermarket tuners are going to have a hayday re-programing the computer.
If the engine can handle the encreased loads, outputs over 210 RWHP may be possible at 10500 RPM.