ESE's works engine tuner

[peewee]

and where do you find a 200mm conrod

[Martin1981]

custom made

www.crankworks.com

indeed, the stock rod is about 140mm. so when i am right with the insanely small crankcase it must be about 200mm. lets wait for wob`s opinion.

but there must be something wrong with the 500 ccm mx engines. they only make 50-60 hp stock. thats what wobblys and jan thiels 125ccm engines make...!
i often saw kx 500 cylinders with black transferducts and even inlets. and that was not black color. it was carbon residues caused by endgas that entered. nothing to do with the small crankcase but another hint that there is something wrong with the big single mx engines and plenty of room for improvement. And a 39mm carb maybe good for a 125ccm engine. but not for 500ccm.

[speedpro]

Ever ridden one?

[senso]

I know that setting the mechanical valve actuator is an art in itself, but the only thing that can be easily adjusted is the spring, there are no end-stops to adjust the allowed travel, but the valves hitting the cylinder seems like a design flaw, I have seen lots of gas gas ec 125 cylinders with broken exhaust bridges, so its not an isolated case, I have though about buying a good RC servo and make a simple linkage setup, but with the exhaust pipe passing a couple millimeters away from the valve cover its impossible to do it neatly or without recurring to a sort of YPVS approach with cables and maybe put the servo inside the air-box the only place in the bike that has a bit of free space, the fuel tank is molded in a way that only a small plug wrench can be used to turn the plug 1/8 rev each time, its molded around the carb so no easy way to even change the needle position, any work needed in the bike always ends with the side covers off, seat off, fuel tank off, just to get to the engine, oh well, lets see how it will perform with locked valves and a slightly shorter exhaust with Wobbly magic numbers.

Big cc's two strokes are "strange", I have rode a KTM 380 with a toroidal head and stock carb bored to 41mm, the torque is just crazy, but the engine is very linear, its just a beast from idling up to over-rev(it goes a wee over 11k rpm with 72 our 74mm stroke, crazy).

[jasonu]

custom made

www.crankworks.com

indeed, the stock rod is about 140mm. so when i am right with the insanely small crankcase it must be about 200mm. lets wait for wob`s opinion.

but there must be something wrong with the 500 ccm mx engines. they only make 50-60 hp stock. thats what wobblys and jan thiels 125ccm engines make...!
i often saw kx 500 cylinders with black transferducts and even inlets. and that was not black color. it was carbon residues caused by endgas that entered. nothing to do with the small crankcase but another hint that there is something wrong with the big single mx engines and plenty of room for improvement. And a 39mm carb maybe good for a 125ccm engine. but not for 500ccm.

Have you ever ridden a big bore 2 stroke single? They might peak at 60hp but they make 40hp pretty much from idle when a 125 might be making 5hp. Big difference.

[F5 Dave]

And on the dirt most of us would spend much of the time well off peak pipe efficiency, I know I do on my little 300.

[wobbly]

Using the bridge in the cylinder as an end stop for the PV travel is about as dumb as it gets, surely there is a limit in the actuator
stroke length and the pushrod ( or whatever ) drive up to the valve mechanism can be adjusted so the valve wont hit the bridge ?????

Re the case volume in the big 500 motors, I have never seriously worked on one, as those who ride them are basically shit scared of them the whole time.
So I suppose it makes no odds to the factory what they do - the things have too much unusable power as it is.
But I cant see any reason why they would not respond in the same way as the smaller engines do - but of course the rev ceiling so so much lower so
this must factor into what happens with the interaction of the reed, the case, and the transfers.

The crossover tube on the twins is there to help augment the intake flow when there are small reeds and small carbs.
As each cylinder draws on its intake some flow is available from the other side ,down the crossover tube.
When you hotrod the things with big reeds and carbs, then the tube becomes redundant.
But what does work is individual " boost bottles ", with short 16mm hoses onto the reed manifold with a volume no less than around 1.5 X the cylinder from memory.
Individual bottles work alot better than a single volume connected to both.

[husaberg]

I still have a CR500, I have had others previously. The power output is what Rolls Royce describes as adequate.
The biggest issue (other than the speed they exhaust us lesser mortals. ) I can see (that aside) with seriously tuning one would have to be carb size. as carbs generally don't come bigger than 40mm which is only 125gp bike size.
In general handling, They turn far slower than Cr250's (Larger gyro forces)and only have a few extra hp.
They have (as have been mentioned) serious power off idle, yet conversly actually have a narrower operational speed range than most other two stokes on account of their lower redline.
They also have no counter balancer.
A modern kTM300 would piss all over one in real workld power and ridability, and still leave the rider in a fit state to still turn fast laps, lap after lap.
The CR500 engine shares a lot in common with the early cr250's basic design. Which likely accounts for the small crankcase.
later fitting in a decent pipe would be a bit hard but not impossible

here is the lectron carb
Golly 53mm big boy
http://www.lectronfuelsystems.com/ca...arburetor.html

[Frits Overmars]

Ever ridden one?

That's what it's all about. A 500 cc MX two-stroke may have hardly more power than a good 125 cc roadracer, but using that power off-road will demolish its rider in no-time. Like Wob says, the last thing you want to do is give it more power.
My friend Jan Schäffer of Langtuning is not only a gifted tuner but also a gifted rider, on both asphalt and dirt. He rides a 250 cc KTM and a 250 cc Yamaha, and he tried new pipes to make them more rideable. He went looking for laptimes instead of horsepower and he came up with a solution that makes you think.
Looking at the power graph (red=stock, blue=new) you'd say he castrated the bikes. But the resultant power delivery leaves his opponents standing.


I think the ultimate goal should be to achieve the improved throttle resonse and linear power delivery without taking away the power peaks of those bikes. So the power will be there when you want it, but only when you want it.
Two-strokes have a mind of their own and domesticating them requires some out-of-the-box thinking. A solution might be throttling the exhaust.
Richard Maas, the guy who built the trombone pipe that I showed here some time ago, found out that a simple exhaust throttle slide, not at the cylinder but further downstream in the header, gives a beautiful linear power delivery (half open = half the power) without causing any overheating problems.
I think we'll try it for the Zabel next. That is an MX engine too, but it's not a 250... http://www.zabel-racing.de/zabel-motor-2010-2011

[adegnes]

That's what it's all about. A 500 cc MX two-stroke may have hardly more power than a good 125 cc roadracer, but using that power off-road will demolish its rider in no-time. Like Wob says, the last thing you want to do is give it more power.
My friend Jan Schäffer of Langtuning is not only a gifted tuner but also a gifted rider, on both asphalt and dirt. He rides a 250 cc KTM and a 250 cc Yamaha, and he tried new pipes to make them more rideable. He went looking for laptimes instead of horsepower and he came up with a solution that makes you think.
Looking at the power graph (red=stock, blue=new) you'd say he castrated the bikes. But the resultant power delivery leaves his opponents standing.



I think the ultimate goal should be to achieve the improved throttle resonse and linear power delivery without taking away the power peaks of those bikes. So the power will be there when you want it, but only when you want it.
Two-strokes have a mind of their own and domesticating them requires some out-of-the-box thinking. A solution might be throttling the exhaust.
Richard Maas, the guy who built the trombone pipe that I showed here some time ago, found out that a simple exhaust throttle slide, not at the cylinder but further downstream in the header, gives a beautiful linear power delivery (half open = half the power) without causing any overheating problems.
I think we'll try it for the Zabel next. That is an MX engine too, but it's not a 250... http://www.zabel-racing.de/zabel-motor-2010-2011

Wow! That pipe doesn't really need to perform, it wins on looks alone!
And that Zabel is just insane!

[Martin1981]

Ever ridden one?

Hi speedy,

i said i own a kx 500. so yes, i guess i have ridden it a few times already.

of course i am also scared by the power of the engine. but i like it in spite of that (or because).
i was just curious about that big singles and their small crankcases and wanted to know what the experts think of it.

the zabel has 700ccm. even more a monster. but the borexstroke ratio is not so good maybe. i like the 86x86 ratio of the kx.

[Flettner]

Hi speedy,

i said i own a kx 500. so yes, i guess i have ridden it a few times already.

of course i am also scared by the power of the engine. but i like it in spite of that (or because).
i was just curious about that big singles and their small crankcases and wanted to know what the experts think of it.

the zabel has 700ccm. even more a monster. but the borexstroke ratio is not so good maybe. i like the 86x86 ratio of the kx.

A KX 500 would be a good candidate for EFI, perhaps make it a little less monster.

[Frits Overmars]

Wow! That pipe doesn't really need to perform, it wins on looks alone!

I think so too. Using titanium wouldn't have been necessary but the guy who builds these pipes, does it just for fun. He is an engineer at BMW Sport and he likes to get away from the four-strokes from time to time. With a day job like that he doesn't need to take any orders; he puts a 'MAX' sticker on his pipes but other than that he prefers to remain anonymous.

And that Zabel is just insane!

You can say that. The first time I laid eyes on it, we had it on the dyno at the Technische Hochschule in Zwickau (were the Trabants were built).
The owner brought the bike (a world championship MX-sidecar) and a right boot; starting the monster was as challenging as riding it.

[Frits Overmars]

A KX 500 would be a good candidate for EFI, perhaps make it a little less monster.

The Zabel dearly needs injection. Momentarily it is being fed by a 50 mm Bing carburettor. Not because it's such a fine instrument, but simply because it's the biggest carb available. Starting is a nightmare; so is riding because it won't run decently below half-throttle. And half-throttle is about 60 HP.

[Tim Ey]

A friend of a friend has a Zabel too.


This is a power curve of a Zabel Engine. I do not know which type of engine it is exactly.
The lower curve is "as it is", the upper curve is with NOS injection.
I think a good point to prove Frits argument about the bigger carb in need :-D

So the question would be - why in the world would someone put nitrous oxide in such a monster?!
Because the shovel tire needs such an amount of power to crawl up the mountain