The shift-cam (?) technology that BMW is using on the R1250 emgones MIGHT provide the same, ample low rpm torque at lower RPMs the current 1833cc engine posseses and allow the engine to breathe more and rev higher than it currently does, garnering that extra 25 HP. The only problem for Corporate Honda is that shift-cam would be "NIH", Not Invented Here, and therefore unaceptable technology. Just thinking aloud.
Tim
Honda's used variable cam technology (called VVT, then later VVTi) for a few decades in their cars, and it does work - but it adds to cylinder head height, weight and cost. So a wider engine - unless they go away from the flat 6 and start moving to a V shape (a la Moto Guzzi) - that costs and weighs more.
One thing people should realize - a dyno does NOT measure HP! Seriously, it does not. It measures TORQUE. And then HP is derived from torque (HP = torque * RPM / 5252). So you cannot get more HP without gaining more torque - the two are mathematically linked, and HP is dependent upon torque (torque being what your dyno reads).
Now, you can design an engine to be very torquey at low or high RPM - but not both, unless you can do things like change the intake configuration (valving, runner lengths, cam durations - some of that addressed by the variable valve technology stuff). So you either go for good low end grunt, or great top-end breathing (the reason being rather complex, but having to do with timing air pulses to maximize incoming air and fuel into the piston, and the fact we have velocities and non-zero timing to live with in the real world).
SPORTS ANALOGY: who do you want on your front line in football - Anthony Munoz, or Usain Bolt? Now who do you want at running back - Munoz or Bolt? Big, low end grunt in Munoz, top-end HP is Bolt. There's a reason guys who move big loads (300+ pound linemen) are big and tend to be slower, as compared to guys who have to really move fast. Torque moves mountains - HP will keep them moving fast.
It's why most of your high torque motors (big diesels, big block gas engines) don't rev high - they don't make a lot of torque up high because they started life as engines designed to move heavy stuff and get that heavy stuff moving, so you need a lot of torque down at low RPM. Those same engines fall on their face and you gain nothing there. Now, I am sure some are thinking "it's because the drive train is too heavy, they can't turn the RPMs!" to which I answer "see a top fuel dragster". A 500 cubic inch V8 with a long stroke, turning over 9000 RPM and making over 11,000 HP. Not a lot of low end grunt (relative to their top end output). A dragster will never win in a tug-of-war with a mud-towing competition truck because the torque each makes down low is dramatically different.
Other side of the coin - big semis. The Paccar MX-13 (a massive 13 liter engine) produces just 455 HP - and 1700 lb-ft of torque at 900 RPM! Lots of gears in the transmission means you can stay in the peak torque range over more speeds (gearing is your friend), and once you're up to speed, you can move to higher RPMs to gain HP (peak around 1900 RPM) to keep the load moving. But you have massive torque/HP ratio for a reason - you have to move heavy things.
It's why you've heard the old saying "torque gets you accelerating; HP keeps you moving". It's why Teslas launch so hard - all that torque at 0 RPM. It's not their peak HP (which is anemic; 100 kW is just 134 HP - 746W per HP), it's the fact they have massive torque at 0 RPM!
So we're kind of stuck choosing "do we want < 3000 RPM torque, or > 3000 RPM torque" and going from there. IF you could vary your cam timing (a la VVT as Honda does it, or the BMW shift cam which came later), you can fudge between the two - give up little at the low end, gain some at the top end (it does vary valve timing and lift, but not intake runner length which is also important). The fact the Goldwing torque is ruler-flat (relatively speaking) from idle to 4800 RPM is astonishing, even muscle cars don't get close to that - this is a HEAVILY optimized to be flat, quite a bit better than the previous Goldwings even.
But think of the issues around the adaptation: you necessarily have more cylinder head height - and that means a wider bike. You have more cost/complexity. You have more weight. And of course, this is a touring bike. So, given the relationship between HP and torque, and the realities of the physical width limits you can do - what do you do?
Most touring people are NOT going to want to tool around at 4000+ RPM like sport bike guys! Sure, a sport bike makes stupid power per liter - but only once you're well into the "we're approaching redline" range of a Goldwing. You want to tour for 8 hours at 5000 RPM?
So, Honda did what I consider near-impossible: give you a torque curve that is flat from idle to damn near 5200 RPM (where HP and torque cross over), which means it will pull off the line like crazy and get you up to touring speeds (60-80) really exceptionally fast. And the curve is better than the previous generation Wings - measurably so (those who are hung up on peak HP/peak TQ? Go away, we don't live at a static RPM level, you're basically acting as the helmet-wearing child stepping off the short bus; curves below show why you're wrong).
And they did it, in a smaller engine, with less weight. AND increased efficiency so we get better combustion of every charge such that less fuel is needed to generate a given amount of torque. And they did not increase the cost by adding complexity.
Yes, VVT could work - but would you accept a more expensive, heavier, and wider (think another 2-3 inches overall) motor that does not behave any differently until you're over 4000 RPM, and doesn't really start to shine until you're well over 5000 RPM? Your acceleration up to that point - torque curve - will still be the same - all we'll do is keep increasing HP beyond 5252 RPM, maybe up to 7500 RPM, where it could peak at 130-140 HP. It's not going to help you jump off the line in the first place, and it's not going to help you until you're into 5+ gear and hot on the boil (above 90 MPH or so).
To me, I think Honda made the right choice. We're damn-near close to sport-tourer performance, with more luxury, comfort and technology than any other touring bike, and with fuel economy that anything close to (or exceeding in) performance simply cannot touch. I mean, I am getting the same mileage on my Wing as I do on my CTX700 - something with 36% of the displacement and 70% of the weight - which also just gets 50-55 MPG.
More HP? Great for bragging. But remember - lots of heavily modded HDs have high "peak" numbers - but how many really keep up or even pass you, at the stop-light drag strip? My neighbor with the CBR1000RR (we go riding a few times a month in the Santa Monica mountains) can easily dust me - once we're rolling. Off the line, up to about 40 MPH (across the intersection)? It's mirror-to-mirror. He has precious little torque down low - I have more torque at idle than he makes at peak! But once he's on boil, and has that gearing keeping his RPMs high - he has more and walks away. He's also doing 7000+ RPM, too - and no way I want to ride around like that all day!
So bottom line: you can rework it for VVT, to gain more top-end (high RPM) HP numbers. The cost will be: more cost, more engine width, more weight. And it will be minimal gains, unless you want to give up some bottom end torque, and will only come at RPMs above 5000. And it will cost you fuel efficiency too. And you are riding God's Own Tourer (even though it's doing a pretty good Sport Touring imitation).
I think Honda nailed it, and I think many who want more HP really want it for bragging rights.
Now, about the helmet-wearing, short-bus riding folks I spoke of earlier. Here are dyno tests of a 2009 Goldwing and and 2018 Goldwing. The new Wing produces a LOT more torque over the entire range, and more HP until you're over 4000 RPM. Yeah, more HP in the top 1/3rd of RPM where you rarely live - and less torque (and therefore less HP) in the entire bottom 3000 RPM (idle to 4000) where you almost always live. In real world - and at the strip where gearing and RPM changes are facts - the new Wing will be faster, and not just because it's lighter and has better aerodynamics. It has an engine that will simply provide more average power over the range as compared to the previous version. The lower weight, smaller size, and 20% better fuel economy of the new engine is all gravy (and again - a massive testament to the engineering prowess of Honda).
2009 Dyno test (
2009 Honda GL1800 Gold Wing Road Test | Rider Magazine | Rider Magazine)
2018 Dyno test (
2018 Honda Gold Wing Dyno.)
