KLX 250 ( 300 ) camshaft mod by Marcelino
#955
Discussions on interesting subjects can lead off track numerous times in areas that may relate originally. Part of what makes a good discussion is trailing off a bit then cycling back.
#956
Well, I guess I lied about posting again in this thread, but I just found a KLR 250 manual online, which I said I'd look for earlier. This is the bike that shares its engine with the Mojave and is essentially the technological predecessor to the KLX 250/300 engine. It shares so many similarities (except the valve timing!!) with the KLX I feel this info is relevant to those looking to understand what the MCM does. Note the super advanced intake valve timing of 41 deg BTDC on the first model, and the Mojave matching 31 deg on the later models.
Also of note is the incredible horsepower claim (this HAS to be at the crank ).
So again, these KLR, KSF, KFX engines share similar bore, stroke, #of valves, compression, and liquid cooling with the KLX, while the valve timing and rocker arms between cams and valves are the biggest differences.
Also of note is the incredible horsepower claim (this HAS to be at the crank ).
So again, these KLR, KSF, KFX engines share similar bore, stroke, #of valves, compression, and liquid cooling with the KLX, while the valve timing and rocker arms between cams and valves are the biggest differences.
#957
Concerning overlap: The exhaust valve stays open past the standard close point(retarded), and the intake opens/unseats earlier (advanced) with MCM. So at the top of the exhaust stroke/beginning of the intake stroke, overlap in increased. (This is the aspect of the MCM that gives a "power boost" on top..)
Whatever the stock overlap measures, the MCM increases it. How could it not? Whether your measuring @ .050 or not, you are opening the intake valve earlier and closing the exhaust valve later - increasing the amount of time both are unseated (overlap) around TDC on the intake stroke..
Visually, the MCM rotates/repositions the cams toward each other.. Now if, somehow, a MCM was done backward - repositioning/rotating the cams away from each other - you certainly would loose overlap with, no doubt, lousy performance.
Whatever the stock overlap measures, the MCM increases it. How could it not? Whether your measuring @ .050 or not, you are opening the intake valve earlier and closing the exhaust valve later - increasing the amount of time both are unseated (overlap) around TDC on the intake stroke..
Visually, the MCM rotates/repositions the cams toward each other.. Now if, somehow, a MCM was done backward - repositioning/rotating the cams away from each other - you certainly would loose overlap with, no doubt, lousy performance.
Last edited by Klxster; 07-07-2016 at 08:02 AM.
#958
thanks I may have mathematically calculated the OL wrong for the mod. I did however have them positioned correct. The 1st time I did the int cam only, 2nd time both. FWIW the stock .050" spec is. intake 2.5/37.5, exh 37/5, zero OL, duration 215/212 measured by webcam. The intake closing time is the most important timing event. Stock it is about where it should be. Modded it moves too far, closing to soon for good fill. That's exactly how it runs too, despite any increase in OL. The increase in dynamic compression from the early closing gives it some more felt power down low, but in my case takes away the strong pull at redline on top. This was more noticeable when I put it all back stock. Where I did think it helped was in slow trails, maybe using a gear higher roll on. just my 02, has been a few years since messing with it.
my bike is a 06 250, here's what it looked like new, rejetted with a kdx snorkle and 300 exh system. Sort of my baseline as I played with K&N filter, lid off, big gun pipe, cam phasing, offset timing key later.
my bike is a 06 250, here's what it looked like new, rejetted with a kdx snorkle and 300 exh system. Sort of my baseline as I played with K&N filter, lid off, big gun pipe, cam phasing, offset timing key later.
#959
You should know that, best I can tell from a few years of researching performance modded non-MCM KLX's, they seem able to make about the same peak HP, but 2 lb.ft. LESS torque.
Since the TRQ curves on non-MCM and MCM bikes is a nice bell shape, this +2 lb.ft. at peak creates a HUGE difference in performance.
Also, you should know that a measurement of TRQ @ 9500 RPM between your chart above and my latest run shows you almost to 11 lb.ft. and me at 13 lb.ft.
Since you are looking for power level increases around redline (10,500 rpm) and a TRQ ramp-up closer to redline, I can understand why you could prefer standard timings even though the dyno charts indicate otherwise. The "earlier" MCM midrange "hit" is so strong that it "masks" the fact that more power is also being carried to redline.
Since the TRQ curves on non-MCM and MCM bikes is a nice bell shape, this +2 lb.ft. at peak creates a HUGE difference in performance.
Also, you should know that a measurement of TRQ @ 9500 RPM between your chart above and my latest run shows you almost to 11 lb.ft. and me at 13 lb.ft.
Since you are looking for power level increases around redline (10,500 rpm) and a TRQ ramp-up closer to redline, I can understand why you could prefer standard timings even though the dyno charts indicate otherwise. The "earlier" MCM midrange "hit" is so strong that it "masks" the fact that more power is also being carried to redline.
Last edited by Klxster; 07-09-2016 at 01:31 AM.
#960
Thanks for posting your chart. I'm having a great time analyzing it.. It looks like a DJ128 does a pretty good job of fueling with a snorkel below 8200 rpm. That "lean-out" 8200 - 9200 hurts - probably a lotta MOPOWAH could be created there with an proper AFR.