Comparison test Big Twins

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Comparison test Big Twins

Breathing technique

The three Vau-Zwo engines under the microscope.

No more excuses. No more straight four-cylinder apples have to be compared to V-two-cylinder pears. No more chance of concealing weaknesses behind allegedly concept-related disadvantages. Now the rule is: Japanese engine construction meets Italian in direct comparison.
The starting point for the sporting competition are 90-degree V-engines, whose transverse crankshafts each set two pistons in rotation over a stroke of 66 millimeters. While the pistons in the Ducati and Suzuki are allowed to cover this distance in coated aluminum liners, Honda relies on proven, cheap gray cast iron and thus accepts the disadvantage of poor heat dissipation from the piston to the cylinder wall.
Perhaps that is also a reason why the Honda engineers expect their V2 to have lower piston speeds and allow the red speed range to start at 9500 rpm – their colleagues from Ducati and Suzuki set this mark 500 rpm later.
In order to make the combustion chamber as compact as possible, the intake and exhaust valves of the two Japanese are at an angle of only 28 and 29 degrees to each other. On the Ducati, the angle is 40 degrees – a disadvantage of the early birth, the construction of the 916 cylinder head is based on the earlier 888 engine.
But let’s get to the heart of the matter, the output. It depends crucially on how much fuel / air mixture the engine can inhale per unit of time and convert it into useful work. A high peak performance therefore requires the largest possible free valve cross-sections in order to allow the engine to breathe uninhibited and thus to ensure that the cylinders are optimally filled with fresh gas. At first glance everything speaks in favor of the Suzuki and its 124 hp, but taking into account the displacement of 80 cc in the 916 and the common denominator of specific power, the tide turns in favor of the Italian: with 126 hp per liter it is just ahead of the Suzuki. Advantage through Desmo?
MOTORRAD investigated the matter, reduced the valve timing of the three engines, and lo and behold: the valves of the Honda and Suzuki, operated by two overhead camshafts and bucket tappets, open and close even faster than those of the Ducati, like the steeper climb and the there is evidence of a steeper drop in their two valve lift curves. The theoretical advantage of the desmodromic system of realizing higher valve accelerations through the forced control is not used, at least in the Strada. All that remains is the advantage of lower friction losses in the valve train and the disadvantage of the seven millimeter thick valve stems in order not to risk torn off valves despite the groove for the closing mechanism.
With the exception of the longer open inlet valves on the Ducati (they only close 80 degrees before top dead center!), The opening and closing angles of the three engines are close together. When it comes to valve lifts, the Honda steps out of line: while the TL 1000 and 916 leave it at 9.6 / 9.5 millimeters on the inlet side and 8.7 / 8.6 millimeters on the outlet side, the VTR cams push the inlet and outlet Exhaust valves about ten millimeters into the combustion chamber. As a result, the Honda can almost catch up with the Suzuki with its 40 valve discs despite its 38 inlet valves in the free valve cross-section. According to the motto “What goes in has to go out again”, the Firestorm even sets the best mark for the free outlet cross-section.
According to the performance diagram, the bigger firestorm rages in the Suzuki combustion chamber from 6500 rpm. This is mainly due to the mighty intake manifold with a diameter of 52 millimeters, through which both of the cylinders can still draw a lot of air even at high speeds.
This leads us back to the question asked at the beginning: How is it that the Duc trumps the Suzuki in terms of liter output? The disposal of the used air via the exhaust system and the resulting noise play the decisive role here: In order to accept the 80 dB (A) required by the 916, an inspector has to turn a blind eye. The two Japanese are noticeably quieter, consequently more clogged and hindered in their breathing.
NSomething interesting on the side: During the measurements of the valve timing, MOTORRAD found that, in addition to two intake manifolds of different lengths, Honda also uses inlet and outlet cams with different steep slopes on the front and rear cylinders to suppress the constant-speed jolt. For the same purpose, the intake timing of the front cylinder was shifted to that of the rear cylinder by about three degrees of crank angle, while Suzuki combats the annoying phenomenon in two-cylinder engines with different injection maps for the two cylinders. rb

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