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Old 01-04-2010, 03:23 PM   #1
MitchMan OP
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Are there any two stroke bikes in the Dakar this year?

Surely something like a KTM 300 EXC would be pretty competitive, reliable and simple to fix if anything went wrong?

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Old 01-04-2010, 03:25 PM   #2
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As would be a Honda Cub50...
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Old 01-05-2010, 02:34 AM   #3
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Mixed fuel isnt available at the stops, so you would have to carry all your oil for the day and mix it as your filled up, not terribly practical.
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Old 01-05-2010, 02:40 AM   #4
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Quote:
Originally Posted by mutt2jeff
Mixed fuel isnt available at the stops, so you would have to carry all your oil for the day and mix it as your filled up, not terribly practical.
Good point, however at 1:60 mix ratio the amount of fuel for the day probably wouldn't be that huge? It certainly wouldn't weigh as much as the additional weight difference of the 4 Stroke Bike.

Is that the only reason then stopping the 2 Strokes from competing?

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Old 01-05-2010, 03:33 AM   #5
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the 690's can carry 34-36l when they need it.
wonder how much a 300exc would need to carry to go the same range??
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Old 01-05-2010, 05:48 AM   #6
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Quote:
Originally Posted by MitchMan
Surely something like a KTM 300 EXC would be pretty competitive, reliable and simple to fix if anything went wrong?
I think a 2 stroke is not desirable for 3 reasons:

1) Half the Dakar is paved or at least untimed and open and boring, usually. That's a lot of km both for wear and tear and also for discomfort.

2) Power and power delivery: The big 4 strokes have an edge both on power and how it is delivered for carving up two track, which is the order of the day.

3) Fuel Economy: my 300, ridden at a fast pace and on the mainjet, burns substantially more fuel than my 530 ridden alongside it. Both are jetted to the best of my ability...

Don't get me wrong, I love the 2 strokes, but I'd hate to sit on one a few hundred klicks of pavement a day, between the good bits no less...
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Old 04-20-2010, 05:30 AM   #7
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Quote:
Originally Posted by neduro
I think a 2 stroke is not desirable for 3 reasons:

1) Half the Dakar is paved or at least untimed and open and boring, usually. That's a lot of km both for wear and tear and also for discomfort.

2) Power and power delivery: The big 4 strokes have an edge both on power and how it is delivered for carving up two track, which is the order of the day.

3) Fuel Economy: my 300, ridden at a fast pace and on the mainjet, burns substantially more fuel than my 530 ridden alongside it. Both are jetted to the best of my ability...

Don't get me wrong, I love the 2 strokes, but I'd hate to sit on one a few hundred klicks of pavement a day, between the good bits no less...
Hey Neduro,

When you refer to the 4 stroke having an edge are you refering in general to the larger bikes, 650cc plus or the 450's or 530's. Now that there is the 450 limit in place for pro's in 2011 and the rest of us 2012 onward can we disregard your point 2 or do you think there is still too much of a gap.

If a 300 KTM is close enough to the 450's in terms of torque etc we would just be left with comfort and fuel range.

When you say that the 300 is way more thirsty than the 530, what sort of riding did that involve. Was it a thrash or were you short shifting and riding the torque.

Neduro's comments or others very welcome.
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Old 04-20-2010, 10:48 PM   #8
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300cc 2 stroke in a rally...

It has been done (with varying degrees of success) and in light of the 450cc fourstroke restriction rule (2011/12 onwards in Dakar*) it would seem (as you point out) that it could be an alternative.

Here is a 1990 perimeter framed KX 250 (rally modifications and a KDX 250 motor) as ridden in the 1990 Australian Safari by Allan Cunnynghame to a 5th place (all XR600's in front of him).

(sorry about the faded old print)


The minimum fuel distance of that event was 300km (50 km's MORE than todays Dakar spec.) While it is true that did not include the same (fuel consuming) soft sand dune running that Dakar typically includes... but the bike still required a capacity of around 35 liters to go the distance.

The little KX/KDX was in it's element in the tighter or more technical sections (especially when the fuel load got lower into the stages), compared to the larger capacity fourstroke bikes of the day. Talking to Allan about it afterwards, he said that the hardest part of riding the thing in a rally (as Neduro alluded to earlier) was in fact; the long monotonous transports... the vibrations of the little 2 smoker were "mindnumbing" apparently.

This was 20 years ago... with some modern rally technology (lower COG tanks, cush rear hub etc.) maybe a 300cc two stroke is not such a silly alternative agains a 450cc fourstroke at Dakar*??

*The up to 700cc single fourstrokes are still (at the moment) allowed to compete in the other FIM rally events.


So barrier911, why not throw a larger tank, some navigation gear and a cush drive rear hub on an EXC 300 and head of to the next NRE with Hogwild and the boys to do some "real world" field research... ie. run it in rally conditions against other 450 and 690 cc rallye bikes?
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Old 04-21-2010, 05:12 AM   #9
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Quote:
Originally Posted by troy safari carpente

So barrier911, why not throw a larger tank, some navigation gear and a cush drive rear hub on an EXC 300 and head of to the next NRE with Hogwild and the boys to do some "real world" field research... ie. run it in rally conditions against other 450 and 690 cc rallye bikes?
Thanks! Troy, like I need any more encouragement to plan on entering the 'Big' one, Dakar, I mean. Now I've got you egging me on to rise to a challenge. I beat myself up every day deciding on what rally to enter next and which year to go for the Dak.

You may have seen a number of 4 stroke bikes I've built in to 'rallye bikes' on JMo's thread but I've never even ridden a two stroke.

The KTM 300 as a bike for Dakar interests me for a number of reasons....
  • It's different and would raise some interest. (hopefully not for all the wrong reasons) (Eg having to change a piston and rings at each mid stage re-fuel! )
  • Stories of the top end lasting upto 300hrs without work.
  • Runs cooler.
  • Weight.
  • Far simpler and quicker maintenance.
  • Ability to carry a top end overhaul kit, piston etc and repair on the fly. How many guys have gone out of the event with a holed piston or dropped valve.
I am guessing that the stroke and bore could be increased to add torque without even getting close to the 450 cc limit.
Higher torque should decrease revs, wear, vibration and fuel consumption. Or am I dreaming!!!!

As another first I believe it could also be 'Christinified!' That is AWD like my 08 530...
  • I know I could suffer the vibes for a Dakar finish and maybe more flywheel weight would help. Mr Renazco would be getting a call.
  • I know the Christini kit on my 530 dramatically reduces the requirement to rev in the soft sand, keeping the front wheel light and requiring a ton less fuel in those conditions.
  • I know Safari make a 9 litre rear tank or even the Meca twin tanks would help with some creative thinking to reach about 30 litres as a total.
Now I still need to decide which rallye to enter next, which year to enter Dakar and Now which bike to build next, thanks Troy!

barrier screwed with this post 04-21-2010 at 05:36 AM
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Old 04-21-2010, 06:00 AM   #10
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You might want to call Dave Fretigne over at Yamaha before you go too far down the two wheel drive route for a rallye bike...?

I know it's a different system to the Öhlins concept that Yamaha employed on the WR 450 F, but asisdes from the increased weight and some dubious reliability apects from having the front drive as well, there were some mixed reviews on the "high speed" handling traits in a rally application. No doubt though, it would give you better traction, climbing (and interesting to hear your increased fuel economy theory) in the soft sand dunes.

Yeah, I'd rather work on a 2 stroke, than a multi-valved, chain and cam driven, titanium wonder fourstroke motor out in a bivouac situation too...
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Old 04-21-2010, 08:30 AM   #11
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Quote:
Originally Posted by barrier911
If a 300 KTM is close enough to the 450's in terms of torque etc we would just be left with comfort and fuel range.
Having just come back from a few weeks of beating my 300 and 530 around the desert, I have an even fresher perspective on this than usual.

First, engine performance. On paper, the 300 and 530 aren't that far apart in terms of peak horsepower, especially when you consider the lower weight of the 300 as compensating for the few HP it gives up. Torque is not even that far off.

But, in the real world, they are miles apart. The 300 makes something approaching peak torque for just a couple thousand RPM, and is relatively weak elsewhere (this weakness is what people call "tractable" and makes it a real weapon in technical situations, because you can short shift it and it doesn't light up everywhere). The 530 makes great torque over a much wider range of RPM (aside: it is also great in the technical situations because it delivers that torque so subtly if you have good throttle control. The 300 really doesn't, it's a bit of a light switch, and you need good clutch control and to be in the right gear to get the best from it).

I haven't looked at a Dyno on my bikes, so take this with a big grain of salt... and jetting, exhaust port setup, and pipe choices can make worlds of difference, but if I had to guess, I'd say the 300 makes peak HP at something like 8K RPM, but doesn't really start pulling HARD until 5-6k, and runs out of steam shortly after it maxed out. It has useable torque below that, great torque for trail situations, but if faced with a big heavy rally bike trying to get max accel out of a turn, it would be underwhelming outside that band.

Furthermore, it comes on pretty hard and abruptly, relative to a 4 stroke. So it's not as easy to pitch and drift and slide on fire roads- it certainly can be done, but nowhere near as easily as the 530.

The 530, on the other hand, is incredibly smooth in how it delivers torque, making it easy to ride hard, and delivers useful torque from probably (again, a guess) 3000-9000 RPM. That's a band 3x as wide as the 2 stroke, even if the number isn't that much higher, it's a hell of a lot easier to keep the thing roosting forward.

Then there are the comfort elements of vibration and so on. My 300 is pretty smooth relative to the other open class 2 strokes I've ridden, but you start hating life not very far into a fire-road section, unless you are caning the bejeebus out of it. Then you're afraid enough not to notice the vibration. :-) That's not how you race a Rally, though.

Finally, with regard to maintenance, the 300 will go a bazillion hours without batting an eyelash in the hands of mortal riders, because they are generally in that underwhelming part of the torque band where trailriding actually happens. Start spinning it for hours on end at the torque and HP peak, and that story will change in a hurry.
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Old 01-05-2010, 07:04 AM   #12
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Quote:
Originally Posted by MitchMan
Surely something like a KTM 300 EXC would be pretty competitive, reliable and simple to fix if anything went wrong?

MitchMan
This question was (kinda) raised last year too...

Gerard Barbazant made a career (several times IIRC) of trying to get a 125 EXC to the finish... and as Rallye pointed out below... he used up a lot of pistons, cylinders etc. in the process...

Another guy from France named - Luc Grajwoda (spelling not quite sure) - made a habit out of riding a monocoque framed KX 500 creation in the Dakar and various other rallies in the early to mid nineties...

The thing used to vibrate that much that it often split/fractured the welds on the chassis and aluminium fuel tanks/subframe construction... and his eyeballs were still going up and down a half hour after he climbed off the thing at the bivouac of a night...

So basically the answers to all your questions are summed up nicely in Ned's post above...

Quote:
Originally Posted by rallye
a french dude Gerard Barbazant tried for many years to finish the dakar on a ktm 125 exc with a 28 liter tank fitted to it , i don't think he ever finished one but went through many a piston tying.



This may be his taken in Barcelona at the start of the '05 Dakar, KTM125

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Old 01-05-2010, 08:01 AM   #13
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Honda had a go at a 2 stroke Dakar bike in the mid 90's too.

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Old 01-05-2010, 09:09 AM   #14
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Quote:
Originally Posted by rjf
Honda had a go at a 2 stroke Dakar bike in the mid 90's too.

With all the talk of developmental direct injection/FI two stroke motorcycle engines back in vogue of late... the EXP Honda idea might come out of retirement for the Dakar in the near future again...?
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Old 01-05-2010, 09:12 AM   #15
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Quote:
Originally Posted by rjf
Honda had a go at a 2 stroke Dakar bike in the mid 90's too.

Funny that Honda, killer of 2-strokes in any other form of racing, actually built that bike. Direct injection engine, I believe.
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