WTF is this?

[TooFastTim]

It looks like it's an expansion chamber. Would one of our more clued-up engine experts explain why it's needed?

[alexbrown64]

Its just a resonance chamber.  The pipe is still a header, but with some holes drilled in it.  The 2 stroke part that you see is simply two pressed plates welded each side of the pipe where the holes are. A bit like a muffler.  It changes the tune of the bike, but someone else on here may know how it does that.

[80-85 husky]

they used to have that little coke can welded on the top, this is a new flasher look

[mick25]

Is it a new power bomb pipe . I have seen them done like this a few years back .

[GMC]

I had a theory many years back that some four strokes may benefit from an expansion chamber.

A chamber on a 2 stroke ‘basically’ controls the flow of new fuel into the engine while all the ports are open.
I figured that a four stroke that has a valve overlap may benefit from a small chamber that may help control new fuel into the engine while all the valves are open.
Never got a chance to try anything so it was just one of many untried theories that bounce around inside my head.
Maybe KTM came up with the same idea?










Or maybe it’s just a gimmick

[mainline]

I had a theory many years back that some four strokes may benefit from an expansion chamber.
Never got a chance to try anything so it was just one of many untried theories that bounce around inside my head.
Maybe KTM came up with the same idea?

You should start wearing an alfoil hat to thwart any future industrial espionage. 

[Noel]

may be similiar to this


http://www.fmfracing.com/Products/MX/44
http://www.motosport.com/gytr-fmf-powerbomb-head-pipe

Quote
""""The principal is this: What makes a 4-stroke exhaust "tuned" is the timing of pressure waves within the system, and having them synchronize with a certain range of engine speeds. The timing is controlled by varying the diameter and length (mostly the length, as the usable diameter is limited). The range tends to be narrowly focused, and you normally have to choose top end over low end, or vice-versa. The chamber in the 'Bombs has a damping effect on the pressure waves within the exhaust, and the result is that the engine "sees" the header as not having a fixed length. This in turn has the effect of widening and flattening the power curve, sometimes quite remarkably. Most such FMF exhausts will seldom produce as much peak power as other pipes, but quite often produce a wider power curve than most others. """




Or it could be a gimmick

[Tim754]

 The prayer of the salesperson:

 If ya cant dazzle um with brilliance ,   Baffle um with bullshit.

[Lozza]

The prayer of the salesperson:

 If ya cant dazzle um with brilliance ,   Baffle um with bullshit.

  Seems FMF just copied someone else and marketing had to invent some schtick to go with it. 

[TooFastTim]

One of the few attractions for me of modern 4T off road bikes is that the exhaust is out of the way and not exposed to rocks, stumps etc. If things carry on like this even that (slim) benefit that a 4T has over a 2T will evaporate.

Now, I'm reasonably clued up on the concept of resonance and how it turned the 2T motor from a stationary, generator motor into the thing of beauty that we all know and love and why we all worship at the alter of Kaaden, Degner and Blair but, damnit man a 4T's got valves! Why do you need a resonant pipe to duplicate what the valves are already doing?

and the result is that the engine "sees" the header as not having a fixed length.

Not arguing against you Noel but the whole point of an expansion chamber is that it is tuned for a fixed frequency (in the case of a 2T) how can a tuned cavity do the opposite?

As others have mentioned it looks like its all marketing BS. Gotta have one to match my new Oakley sunnies.

[Daryl Jones]

"damnit man a 4T's got valves! Why do you need a resonant pipe to duplicate what the valves are already doing?"

Performance 4-strokes have a considerable overlap period where both the inlet & exhaust are open at the same time.
Just like a 2-stroke.

The first purpose of the 2-Stroke expansion chamber is to create a negative (sound/pressure) wave to extract exhaust gasses and to reduce pressure in the crankcase and inlet tract, allowing atmospheric pressure to push more air/fuel mixture into the engine than would occur otherwise.

The second purpose of the expansion chamber is to create a positive (sound/pressure) wave, timed to push fresh charge, that has entered the exhaust port & header pipe, back into the engine before the exhaust port closes.

A similar, but obviously smaller, effect can be produced  for 4 stroke engines with an expanding & contracting chamber in the pipe.

As far as full expansion chambers for 4-strokes goes, I spent a fair bit of time with Lotus's Sim program, designing pipes for the mighty SL100/125.

In my attempts, the full expansion chamber did not ever produce a higher output than a tuned length pipe.
What it could do for the little Honda was produce an almost completely flat torque curve across the entire rev range. 
Might be good for 4-Stroke trial engines, but not MX.

Cheers, DJ

[Daryl Jones]

and the result is that the engine "sees" the header as not having a fixed length.

Not arguing against you Noel but the whole point of an expansion chamber is that it is tuned for a fixed frequency (in the case of a 2T) how can a tuned cavity do the opposite?

Noel's answer is pretty good, and is backed up with my attempts to create a full 4-Stroke chamber producing a flat torque curve..

IF KTM designed this, it is possible that it has been 'tuned' to be effective below the optimal engine speed.
This would allow a 'wilder' cam, with greater overlap for peak HP, but then allow the engine to operate below that RPM.
Effectively producing more peak HP & widening the power-band.  Paradise.

Don't know, just throwing it in the mix.

Cheers, Daryl.

[evo550]

These have been around for years as aftermarket systems, fmf has a patent out on the powerbomb which must be about 15 yrs old by now. Looks like KTM have decided to fit them standard.

[sleepy]

Maybe KTM have come up with a new type of engine. A hybrid 2 stroke / 4 stroke engine with valves and port. It would be a 3 stroke or 2x4 = 8 stroke.

[Daryl Jones]

Maybe like this one?



DJ