Don't worry about it. These guys are all missing the point. It's actually the flux capacitor in the muffler bearings that make all the difference in the power curve on the KLX. Last year when I was in Mexico winning the Baja 1000 on my KLX...solo...I ran into this world renown tuner who told me, "snorkels?...snorkels?...we don't need no stinkin' snorkels!" He's famous...perhaps you recognize him?

But seriously, these discussions are fun and interesting.

 

Lol. I don't recognize this man, but your post is amusing anyway.

Amusing, but with a sense of truth: things in practice don't always work as they do on paper (or as common sense would make us believe they should). I've learned lately this is particularly true of aerodynamic processes in engines. Attributing the power curve to the flux capacitor or to extraterrestrial manipulations is sometimes not so to stupid.

 

Good work, Mikko.

My empirical testing agrees completely with your model.

Ron

 

Ray, not knowing how old you are, and maybe because you're from Canada, my use of a famous line from the Humphrey Bogart movie, "Treasure of the Sierra Madre" may be lost on many here. The older I get, the more I forget that for some odd reason people are a whole lot younger now.

I appreciate discussions like the one on this topic started by Finn. With technology at the level it exists now, you'd think we could snap our fingers and have a definitive answer...and I'm not saying his assessment is incorrect...maybe just incomplete...maybe. It's super interesting and often very educational...but a little fun never hurts either.

 

Wow! makes my head hurt too. I'm going with TNC's muffler bearing comment
Dan

 

Oh crap, dan!...and that's one of the new depleted uranium muffler bearings...sweet! You can tell because of the lead-lined rubber gloves that guy is wearing.

You know...I hope someone comes up with some real input on Finn's post here, because I'm out of material. Really...I'm serious...this is an airbox/intake post, and I promise to quit blathering, Finn.

 

Hi everyone!
My bike is a KLX250 injected and I think the bank results are very similar to the American version of the carburetor.
I bench tested the standard snorkel and snorkel KDX200. I also completely removed the airbox cover despite the intense noise, modifications have rejected because the power gain does not compensate for the annoying noise. Snorkel in my opinion is very restrictive standard, giving an improvement KDX200 snorkeling. Is the one I have installed and the results are satisfactory.

Here a graph with the standard bike: 19´62CV, Kgm 1.996


Here with the airbox lid fully removed. 21´26CV, Kgm 2160. Almost 2CV difference!!



KDX200 + snorkel here with UNI filter= 20´22CV and Kgm2.001:

 

Here's one "real input" as bit more food for thought.

In even a modern stock engine (not talking about race engines here) practically all the restriction is between intake valve and the valve seat. That's where the air velocity is greatest and all the cylinder charge has to pass through that narrow opening in an extremely short period of time.

From there on, backwards toward the outside air the intake system starts to behave more like a sound instrument, it's more about resonances and waves. To simply talk about "restriction" caused by different elements like the back fire screen or the snorkel is almost meaningless.

If the components were grossly undersized, yes they would restrict the intake efficiency. But they aren't.

How does a bigger diameter header change any of this?

Peak torque happens at the RPM when cylinder fill is most complete.
For the optimum cylinder fill we want to time the high pressure wave from the intake side (resonance all the way back from the airbox) to arrive at the intake valve at the same time when low pressure wave from the exhaust (resonance of the exhaust system) just comes in from the exhaust valve and both just a hair before the valves close.
The pressure waves push & pull last bit of charge into the cylinder and valves closing right after that event trap in the extra charge.
If you get that timing right (three things must happen just in the right order) you get great cylinder fill and lot of power.
Obviously the timing is right only at one RPM. That's the RPM of max torque.

When you change the header diameter you change the resonance frequency (or flow speed, different side of the same coin) of the exhaust system. That changes the timing of exhaust pressure waves (at other RPMs the pressure waves work AGAINST effective cylinder fill).
The waves from intake and exhaust are "connected" during the valve overlap and that's what causes the interaction between changes to the exhaust system and the intake side.

--
Mikko

 

"Jeff Ward", very cool dyno plots.

What's bit confusing to me is that the top graph is called "MOTO ORIGEN + ECU DESLIMITADA" (I'm not sure what language that is but "deslimitada" would appear to translate to English about as "non-limited" or "non-restricted")
That plot you said is 100% stock.

The next one is labeled "MOTO ORIGEN" but that one you say is same as the one above but this time with removed airbox lid. Or de-restricted airbox.

The middle plot also shows the signature of what I'm talking about.
the 5000RPM torque dip being filled by the airbox design.
Other plots show that torque dip, because the 5000RPM resonance is not there anymore to fill it.

The price you pay for that good mid-range is that that the torque does fall-off more rapidly than w/o a snorkel, or with the KDX snorkel.

With all due respect Jeff, I think your two first plots have got mixed up.

--
Mikko

 

Mikko, I wonder why the term "ECU" is used in that first graph and not in the second? Is it the ECU that is somehow unrestricted?...but that wouldn't make sense...unless it's some kind of programmable ECU. Some of his description maybe needs some clarification. Yeah, that word "deslimitada" appears to be Spanish, and it seemed to mean unrestricted, full power, and other similar concepts.

I get your take on the synchronicity of the intake and the exhaust and the working balance between them to help or hurt the fuel air mix and the combustion process. Complicated as crap. Good stuff.