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Old 10-31-2012, 12:30 PM   #102
geometrician
let's keep going...
 
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Joined: May 2008
Location: West-By-God Virginia
Oddometer: 1,024
Wicked An Even Longer One...

Quote:
Originally Posted by LukasM View Post
Many of the "old school" 950/990 owners are claiming that this would be a useless exercise as you would just give up a lot of horsepower for only a couple of lbs of weight loss.

I think with some modern and creative engineering a 80-90 HP 700-800cc twin with 360-380lbs (wet no fuel) is a realistic goal, and I'd buy one tomorrow.
so you think there is 120~140lbs to lose? The 2012 Dakar on the showroom weighed 499.7lbs naked- no crash bars, racks, luggage, no battery, <1/2 gallon fuel in it when we put it on state-certified digital scales made for weighing vehicles...

Quote:
Originally Posted by Navin View Post
Why bother making it a 700-800? The LC-8 engine as a 950 could be reduced by 20 lbs thru a SOHC conversion and better casting tech that KTM now uses. Add a 2-1 stock exhaust, a plastic subframe/fuel tank and keep it SKINNY!!!

No reason they couldn't build a 90 HP version that gets far better MPG, need to carry less fuel for the same range
SOHC makes engines taller. The heads on a 690 are so tall that in a V-twin arrangement it would make the engine splay out futher, affecting steering head & seat /fuel/etc location. It's already tight pulling the valve covers off a 690E, nevermind a 690SM/Duke. SOHC have more mechanical parts, wear points & tolerances that open up as they run... and they do- all the 690's I have done valve clearance checks on have wear on the cams & rocker arms, far worse than any of the DOHC LC8's.

Where do you come up with "20lbs" savings? Guesstimating? The difference in the amount of metal is negligible. Combustion chamber design (which is limited with SOHC as is spark plug location) & valve timing dictate fuel consumption so I don't know how/where/what "far better MPG" comes from with 20% less displacement and the same ratio of power to displacement...

Quote:
Originally Posted by gunnerbuck View Post
Aprilia brought out a very lightweight V-twin in the RX a few years back that was a bit of leading edge... The problem is the engine proved unreliable as they were sucking too much power out of it... Drop the power by 20% and it is likely the reliability of that platform would go up while still providing plenty of punch...
Agreed. The Aprilia makes it power through spinning the living shit out of the motor- Less RPMs = Less Power... see below

Quote:
Originally Posted by gunnerbuck View Post
KTM or somebody should get there act together and create a 700-750 cc light Adventure
Honda, BMW & Triumph have this market covered- weight notwithstanding. But you can bet they worked on the weight all the time- they DO pay attention to the internet discussions, interview people at rallies, etc to determine what people are wanting/complaining about...

Quote:
Originally Posted by cyborg View Post
Oil cooler would add price, complexity and weight, but always a great option to add longevity to an engine.
+1 (to me) weight worth having

Quote:
Originally Posted by LukasM View Post
The 690 has an internal oil sump and tons of ground clearance, since the V-configuration of the cylinders and the shorter stroke would make a twin less tall you could make the sump bigger without losing any clearance.

And while many people were complaining about the lack of frame tubing below the engine at first, I have not heard of a single broken case. Install a good skid plate that is supported by two beams off the main frame up front and by the frame in the rear and it will be fine.
The 690 has less ground clearance than the 9x0 Adv's and steering lock so narrow you think you're riding a Ducati sometimes

It also holds less than 2quarts of oil!

V-twins aren't THAT much shorter than singles and they dictate frame layout... one could try what Britten did with his V1000 by attaching the steering head directly to the engine.

I have friends/customers that have had problems with the skidplates being offered for the 690 which keeps some of them safe at home- not out riding...

Quote:
Originally Posted by crofrog View Post
If you want a really small light motor with great ground clearance where is the sump going to be? And how much oil is it going to hold? I'd rather not have a 1qt motor like an RFS for a adv bike... Nor would I want to worry about if the motor is running low on oil loosing oil pressure
+1. Also the less oil you have the harder you work it...

Quote:
Originally Posted by LukasM View Post
I would also prefer a semi-dry sump engine
what in the hell is a semi-dry sump? it either is or it isn't- and with any remote oil tank you'd still have the same amount of hoses, check valves, oil tank & location to deal with. So you lose the wet sump simplicity/ground clearance & gain weight...

Quote:
Originally Posted by Schannulleke View Post
Take the 690 as a starting point, give it a modern light 790cc V-twin engine with lets say 90hp. Improve/reinforce the 690 frame where needed (my guess is not much reinforcement will be needed). Single exhaust muffler. Subframe rear tank. Make more bike versions from this platform (however all R-verions):
- Enduro: small tank, minimalistic instruments
- Adventure: medium tank, improved instruments, improved passenger comfort, dual front brake discs
- Rally: large tank, improved instruments
- Supermoto: small tank, minimalistic instruments
- Touring: medium tank, improved instruments, improved passenger comfort, dual front brake discs
- Duke:...
- RC:...

Voila, KTM could build 7 motorcycles out of the engineering effort for 1 good lightweight modular platform
Single mufflers aren't going to meet sound/emissions requirements without catalysts at least, which we all hate and throw away due to heat/etc, which make real-world investment in the bike higher.

7 bikes still require 7 engineering efforts (plus they have to work together which adds complexity/cost)... and 7 sets of bodywork & supply problems... etc. I like the idea personally but being in the loop of mechanical engineers/cost analysts I know what they go through...

Quote:
Originally Posted by Bubba Bauer View Post
because it`s big as a barn u need 1 square mile of plastic to cover it with its own heavy bracketry
My fuel tanks bolt to the frame don't yours? The front aluminum bracket is helping holding the weight of the fuel tanks & supporting the entire bike in the event of a tip-over (they built the lower fuel tank guards knowing the impact energy was coming in that direction)

I can't believe 450 singles even made it in to this discussion- . (nevermind a DR) With oil changes & valve clearance checks measured in hours (um, starting at 1 hour!) and piston wear that is atrocious (Vertex data sheet says 18~35hrs depending on use) they don't even come close to our needs. Plus you have to spin the hell out of them to make power. In a rally/race situation these things get components thrown at them all the time and get serviced every night. That doesn't make an Adventure bike

-----

So the crux of the OP's post: producing 90hp out of a 700 (or even 800) means spinning it faster. Torque is the ability to do work, to twist a shaft. Horsepower is a theoretical function of time, torque & RPM's. This is why all torque/horsepower charts cross at 5,252rpm. See here. It's not just engine design- that's why HP increases MORE than torque when modifications are done- there's a limit to the torque you can make given crank weight, rod angle, etc.

Torque is what gets the vehicle moving- and is why Harley-Davidson bikes beat the Japanese four-cylinders at NHRA dragraces every weekend. Your average street HD will beat your sportbike across the intersection and into the next block before you catch him & zoom on to stratospheric top speed (and redline). Horsepower sounds great when you don't know Torque is what we're after. I'd rather have more torque than horsepower on an Adventure bike anyday

Example: early air-cooled Volkswagen's had a engine producing 33HP yet rated at 70 ft/lbs of torque. While a modern sportbike engine might be rated at 150+hp, it has relatively smaller torque numbers- that is because HP is a function of the crank speed. Think a GSXR engine is gonna power your car to the top of a mountain? It ain't- not without an automatic transmission or one hell of a clutch system!

In summary wanting a 700-750cc 90hp bike means you've essentially got the same situation KTM has created with the new "150hp" 1190 Adventure- a bike that require spinning the engine to make its power- which takes away from the Adventure bike utility we're after.

The Soap Box is now up for grabs again...
__________________
Britt
'06 KTM 950 Adv 'S'
'03 KTM 250 EXC
'87 KLR650 - <200K miles "Like the Energizer Bunny, just keeps going & going..."

geometrician screwed with this post 10-31-2012 at 12:35 PM
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