I'm all ears.

 

Ok..
Air filter - this is a constant in the equations of induction airflow, as such it's effect on airflow velocity can be ignored.

A). Pressure gradient between the opening presented via a given slide/butterfly valve position combo (CVK), and the ambient air pressure at the entrance of the snorkel.
B). Pressure gradient between the opening presented via a given slide/butterfly valve position combo (CVK), and the surface of the air filter material (Lidless airbox).

The gradient is higher in A (due to restrictiveness of the snorkel). Lower in B.(very little restriction to airflow).

The higher gradient throughout the induction system, in A, causes a relatively smaller volume of air (than in B) to flow faster thru the system. This faster flow, drawn by the higher pressure gradient, occurs throughout the system.

The lower gradient in B (lidless airbox), causes a higher volume of air to flow relatively slower throughout the induction system.

Within an envelope, Higher velocity airflow thru an induction system will enhance lower RPM cylinder filling (via inertia) and lower velocity / high volume airflow will enhance higher RPM cylinder filling.

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For whatever reason, the stock KLX is delivered with an induction system and a exhaust system that favors lower rpm power BUT with cams and cam timings that favor mid-range to upper mid-range power.

So: Add the MCM to a stock engine and you enhance power below 6.5k rpm and may lose a tiny amount of power above. The bike becomes a "tractor" with all systems optimized for power below 6500 rpm.
Add a lidless airbox, full performance exhaust system, and proper CVK setup, and you will "unleash" the mid to upper power capability of the engine - but will have lack-luster low-mid power levels

Combine MCM with the above for power that is enhanced over most all of the operational range - making an incredible change to the riding experience.

 

You seem to be treating the snorkel as if it’s a cold air intake pipe with a constant diameter all the way to the throttle body. It’s not. Your velocity measured at the tiny snorkel opening is not going to be the same as the velocity if measured deep inside the airbox, the same way if I blow through a straw right now that the air speed won’t carry to the other side of the room. Air intake flow also isn’t constant speed, it occurs in pulses due to the intake valves opening and closing. Each “pulse” is going to pull from the air that’s already been inside the massive airbox for a moment, not directly from the snorkel that’s far away from the throttle body and pull smoothly like a vacuum cleaner.

Again, you’re basically talking about the snorkel like it’s a velocity stack that is directly responsible for the intake air speed through the throttle plate, but it’s not because anything you may have read before about tuning intake charge speed most certainly did not have a shoebox left in place between the inlet and the TB. No engine builder is retaining a factory airbox on a car and just grafting a different inlet size to the box to tune volumetric efficiency.

 

You guys can argue all you want, about all you want, but the dyno's don't lie. Put up your dyno testing and leave the speculation to the 'great frog' in the lake.
Those guys did the tests, where are yours?
And, yes if you move enough air through the straw, you will feel it on the other side of the room.

 

I think I've said all I need to say on this. I do understand your angle(s) of perspective, but those angles require that you recharacterize my response - put words-in-my-mouth - and then draw conclusions from your recharacterization(s).

"cold air intake pipe" ? Blow thru a straw ? Velocity stack ? shoebox ? And concluding with "No engine builder is retaining the ......." ?

Perhaps using a more "down to earth" approach would be me saying " If one is going to (or compelled to) ruin an engines' power output (something no engine builder would ever do) via a highly restrictive exhaust and intake system, (as Kawa does with the KLX) , properly matching the induction system functioning to the exhaust system is a good measure to provide the best possible overall power curves. - this induction system matching would be required to favor high velocity airflow in order to enhance the lower half of the operating envelope ( as the upper half is killed by the exhaust system.) Kawi achieves this with a long snorkel that creates a constant high velocity airflow within the induction system via an enhanced "suction" being constantly applied to it. Thankfully, Kawi did NOT redesign the entire airbox to achieve this - they left us a workable airbox and cam system such that relatively simple "uncorking" unleashes very large power increases (when fueled correctly)..

Imagine a shoebox with two straws stuck in it. Now attach a suction (pulsed or constant) onto one of the straws. Measure the velocity of the airflow thru both straws.

Note that the entire discussion and subject is predicated on the assumption that conditions (via engineering and component selection) are kept within an acceptable "performance envelope". E.G. Attach inappropriate suction (which exceeds the envelope) to the shoebox, and you destroy the test thu broken straws and collapsed shoe boxes. Likewise, the KLX induction system must operate within an acceptable performance envelope with components that are matched/engineered correctly - don't replace your snorkel with a straw and don't significantly alter the functioning of either the induction system OR the exhaust system expecting a good result.

Nuf said..

Ok, done with this..

 

My two cents, for free....

KLXster, I think you meant DOHC in an earlier post, not SOHC, no doubt you know what you are talking about. And I agree whole heartedly that the MCM timing should be done on both intake and exhaust for sure. Only doing one would make as much sense as only porting only the intake or exhaust and ignoring the other. You're in there, just do it! Plus disengage the KACR easily done by removing the spring or having it pressed out of the cam. It is unnecessary for starting with a proper jetted carb and should be the same with the EFI, although I cannot say the latter for sure, but I do know the former. I've started my 250 in single digit Fahrenheit temperature with it starting near instantly. Summer, the choke may not even be needed, only 30 seconds at the most. Do the MCM and disable the compression release, it just isn't needed.

Now in understanding the cam overlap (aka Lobe Separation Angle LSA), from what I have been able to learn from the one source I actually found information, the less the overlap, wider LSA (stock Kawasaki timing), the more absolute low end will be had. The more overlap, narrower LSA (MCM timing), the more mid and high range power is to be had. Hot Rod demonstrated that in the article they wrote (click here), which is online. They did three cams identical in lift and duration, only differing in the LSA. They did similar overlap to what the original KLX had and the MCM, but for a Chevy small block. Sure you may say that's different, but it's not. They're both four strokes only differing in displacement and number of cylinders, Hot Rod never differentiated between their engine and any other, it is true for all IC engines. The increased overlap, narrower LSA, had increased power output from mid range up.

Why don't we feel the drop in low end with the MCM you may ask. Thing is few of us actually use the true low end rpm of our KLXs after we have ridden them for maybe a day. We are all mostly running the mid range and upper, running a minimum of around 4000 rpm in general and usually operating higher in the range than that. Personally unless I'm just rolling slow in traffic I am never under 4000 rpm. So that low overlap low end power is down below where most any of us actually ride and few dynos are usually charting.

I would actually venture to say the reason for Kawasaki's timing - emissions. Less overlap = less emissions, less chance for unburned fuel charge to blow out the open exhaust during overlap. That is one way to clean up their act. They also do the pair valve to reduce emissions, but it doesn't hinder performance. The cam timing does.

So based on Hot Rod's explanation and my ventured guess on why Kaw times the bike as they do, doing the MCM, like KLXster says, should be the first thing done. Especially since both Marcelino and KLXster have proven out the results on dyno runs. First thing I did. I also jetted and use the KDX snorkel, since there is a possibility of sloshing water in the air box, keep it off the filter.

 

Except the dyno charts I've seen here for the MCM show a decrease in HP and torque after about 6,500 rpm. Which is odd, because like you said, cam overlap/lope is meant to increase power at high RPM yet the MCM, which increases overlap, causes the torque curve to be *less* flat and drop off harder in the upper end of the RPM range. Is it possible that our head just don't flow well enough to support the additional overlap?

I was thinking the MCM was a no-brainer to do this spring, but lately I'm second guessing if it's worth it. Like you said, we ride our bikes at high RPM. I'd like some added low RPM grunt for single track trails, but I also ride on the street where with my 13T front sprocket I'm cruising at 7,000 to 8,000 RPM a *lot* and I don't want to sacrifice anything in that area of the tach.

I'm also skeptical of people citing these allegedly monstrous gains from the MCM. Looking at the dyno graphs posted to this very forum, the numbers are very minuscule. Like this for example, this is not convincing at all that the MCM is going to transform the bike into a torque monster. It's just making the bike hit peak torque a little lower in RPM, it isn't actually adding any torque though. This graph shows the engine just running out of the breath sooner: : https://www.kawasakiforums.com/forum...timings-44296/

It reminds me of how modern turbo four cylinders from the factory tend to have good mid-range punch but then also quickly fall flat as RPM increases. People think they're powerful because of that quick peak, but it really isn't a desirable powercurve. The falloff in the MCM graph after 6,500 is basically the antithesis of what tuners aim for on a dyno so I'm a little confused why people here are aiming for this. I'll probably still try it myself out of curiosity, to feel what you guys are feeling, but the numbers appear to be pretty wonky on paper, I gotta say.

 

Are you riding a dirt bike or a supermoto? If it's dirt, you'll never see the increase in high rpms' cause most don't use that in the dirt, unless flat tracking.
It's a 250, your never going to see any HUGE change.

 

Mix of dirt and street but at different times. I have a dirt specific setup I switch to with 90/10 knobbies, rim locks, and a 48T rear sprocket. MCM might be beneficial there but I don't wanna have to go MCM and then revert to stock cam timing again when I switch back and forth. The thing is, off-road if you need to get up higher in the revs to get into the meat of the powerband you can do that with clutch control. On the street though you just have what you have, so I think keeping the stock cam positions is a better all-around setup because sacrificing anything up top would be make bike even more of a dog on the road.

In terms of not seeing any "HUGE" gain on this 250, I agree, but people on this forum really talk it up like these gains *are* huge, like going lidless with a slip-on is gonna knock your socks off. My bike in terms of powertrain is still stock so I can't say from experience, but I doubt how drastic these changes really are or if it's worth putting any money into this thing for exhaust and EJK over just riding it as is and accepting what it is.

 

Big Bore & Carb, the only way to go!