The choice to MCM is a simple one. If you spend your riding time above 5500 rpm, and don't mind loosing more below this, do not do the MCM - just add a full performance exhaust system (header and matching slipon), a lidless airbox with the correct lidless CVK setup ( For EFI, deleting the secondary throttle valve and running the API ECU with a proper tune).. This creates a 25+ HP KLX but with weaker-than-stock power below 5500 rpm.

 

Totally agree. Application is key. If the bike was used for proper dual sport, MCM is the way to go.

It was an interesting exercise to understand valve overlap put into practice. Appreciated the opportunity and lesson.

Thank you.

 

Actually to get what you want doing high performance cams would do the job. The cam timing, lift, and duration will control the rpm peak,.where power is obtained. That was demonstrated in a Hot Rod article on the valve overlap, they did three cams with identical cam lobes, cam timing, only varying the intake-exhaust lobe center angle. More angle, less overlap, more low end, but less peak power and less power through out the mid range. Less angle, more overlap, less low end, but more peak power and more power through out the mid range. With overlap some of the fuel charge will escape through the exhaust at low rpm where time is longer, but at high rpm the overlap along with the intake and exhaust waves will allow more charge to be jammed back in the cylinder as the intake waves push from one end and the exhaust reverse pressure waves will jam back in at the last moment. May sound confusing, but think about it. All exhaust will create some reverse waves, even a straight pipe has some. That is part of the design of headers. But the horsepower peaked within a couple hundred rpm on all three.

Looking at KLXster's dyno runs will show that as well with hp peaks at around 8500 rpm in all, but his modifications show power increase in the mid and upper range. Marcelino showed the same thing.. Reving to 10,000 rpm is the capability for the engine to rev beyond the horsepower peak, something racers will do when they are just short of a corner and rather than upshift they will over rev, because the shift will actually lose time. Common in MX and road racing, especially after the advent of rev limiters. Cams designed for higher rpm will do the trick to push the power peack up in the rpm and gain more horsepower above what can be attained with the stock ones, all modifications done. Of course there will be a loss at lower rpm due to the same physical/mechanical aspects to gain max hp will affect hp at the low end. Think drag racing with lumpy cams that won't idle well or pull from low rpm. As for low end, you clearly aren't going to try to lug your KLX around in the 2500-4000 rpm range much, so a bit of loss there is no big deal. Personally I seldom am under 4000-4500 rpm unless kind of trolling along in town, short shifting because I see slow traffic ahead or the traffic light is or will be red by the time I get there so why hurry up and brake hard.

Just sayin' KLXster has the tricks and knowledge for the CV and gaining on the EFI, some others here have the tricks for the TM36-68, but the rev limits are set by the cams, at least that's what I've gotten from what I've seen and read.

If the MCM is done completely, it will increase overlap, enabling better cylinder filling at higher rpm, giving more horsepower as KLXster pointed out. It is the nature of intake-exhaust overlap, which you did not maximize when skipping doing the exhaust, because others didn't do it trying to keep the compression release. Doing this they are losing part of the overlap and thus part of the power increase. Unless you put the bike on a dyno or find another way to verify the change in performance you may not feel it. Often when a bike performs better, pulls stronger, it may not feel like it. Kevin Cameron pointed that out in a Cycle World article commenting about when doing some jetting. His rider came in after one change, Cameron asks "how did it feel?" Hid rider, a name pro, said it felt much slower... the lap was four tenths faster than their previous best. The jetting had the bike working better and easier to ride, which felt like he was going slower.