Cycle News - Archive Issues - 1980's

• Bike Honda VF 750 Superbike Ducati 950 Ducati 750 Pantah H-D XR1oo0R MV Agusta 500 (19761 , ... 40mm stroke as Honda had claimed. The piston is 134.3rnm on its long axis and is 41 mm "wide" and to get a 500cc four displacing 124.75cc per cylinder we need a 24mm stroke. We also observed that the valve angle is 45-degrees and not the 60 to 65-degrees that Honda once claimed. The valve sizes appear to be 18mm for the inlets and 16mm for the exhausts. Suddenly, we are off and running again. Rumors have it that Honda will never say die and that they are determined to win a race, a GP, with the NR. Once again, the "usually reliable sources" of the old days are Doating in and outof focus. The first to talk to me about "oval pistons" and eight-valve combustion chambers called to say that the NR is running hard on the Honda test beds and that the horsepower figure currently being achieved is a competi tive 130 at just over 20,000 rpm. But no one knows the stroke. My source says there has never been an NR running less than a 36mm stroke, but that strokes as Ion as 43mm have been Honda Honda Honda Honda tried. Lineal average piston speed (stroke X 2 X rpm -;- 60 gives meters per second to be converted, if you like, to feet per minute) doesn'ttelJ the whole story and it is obvious that Honda is clever enough to go well beyond the old 4,000 feet per minute "redline" of the old days, but it seems highly unlikely that Honda's NR would be producing piston speeds well below those of current racing four-strokes. 1£ we accept the hypothesis of a 24mm stroke io accommodate our oblong piston then at Honda's 20,500 redline we are talking about a lazy motor with linear average piston speed of only 3,228 ft/min ... like a Guzzi LeMans road bike tooling along at a conservative 7,000 rpm. Here are the piston speeds achieved by some highly successful four-stroke racing motorcycles and along with them three theoretical Honda NR 500cc with varying strokes. Only one of them, the 24mm stroke hypothesis, could run with the piston shown on these pages. NR NR NR NR 500 500 500 500. Stroke Absolute (mml maximum rpm Average linear piston speed (ft/,minl 48.6 74.4 61.5 96.8 49 14,000 9,500 11.500 7.500 15.000 4465 4638 4642 4764 4823 247 367 20,500 20.500 20.500 18.5007 3228 4842 5380 4856 ~07 407 The current state of the art indicates a piston speed around 4,800 feet per minute, at least, if the Honda NR is seeking power at astronomical revs. So, it seems clear that Honda is running their oblong pistons up and down the bore at considerably more than a piddling 3,228 feet per minute. All sorts of theories crop up: Was Honda using, for example, a 24mm stroke and revving, to 30,000 rpm and keeping that secret even from the riders by using a tachometer that showed 10,000 rpm less? I can't buy that one for two reasons: because the engineers I know don't believe in a freakish 3.38: I bore/stroke ratio and becduse I can't believe Honda would ever risk giving false stroke information to FIM officials during noise checks at World Championship events. Honda smiles at all this, but as we all have learned that is not Japanese for yes or no or anything other than Oriental amusement. Yet it appears certain that Honda wants us to start talking about the NR again and that they have leaked a piston that may be a mock-up or may be from a 750 or 850cc experimental version of the NR for the sole purpose of restoring our faith. The most cynical, old, sleazy geezer I know in this business-a Limey who hangs out in Tokyo, will tell you- if you buy him enough drinks that there never was an NR V-4. He says Honda raced with a V-8 and ordered their riders never to finish in the points so as to avoid having to open the cases and lift the heads if there was a protest. He says that Honda ran a V-8 while trying to talk, bribe and pressure the FIM into dropping their four cylinder limits in the 500cc class. But you and I and Virginia really believe there is a Honda. V-4 with four oblong pistons, 32 valves and two rods per piston, don't we? Honda has not given up on the NR. The NR fourstroke will endure and prevail! Someday, when the "Never Ready" is ready. Just cut out this picture ofthe genuine NR piston and hang it over your bed and ... believel •

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