Does the Power/MegaBomb make the difference or would you guess any wider header would do? e.g. a stock KLX300 unit or a Chinese Megabomb knock off?

 

Tax, the 300 header is really not different. I have a '07 KLX300R. the header piping is the same, the midpipe is a little larger. The 300 system(with performance endcap) on a 250 will likely perform similarly to a 250 header+FMF slipon. The FMF slipons also have a larger midpipe - they require the removal of the stock seal in the header in order to slide that bigger midpipe into the headers' bell.

As to Chinabombs, Powerbomb, FSW, Barker, etc - We cannot show proof of effectiveness compared to my Megabomb. But, in general, any larger-than-stock header (with a correct, matching slipon) will enhance upper-mid to top end power curves with a softening of TRQ below 5.5-6k RPM. The Megabomb is suppose to do this without loosing low to mid range TRQ - it seems, at this point in our knowledge, that it is not entirely effective at doing that. Using a full performance exhaust system does significantly change the fueling requirement - so a carb re-do is also required in order to produce the benefit.

I've learned that I spend very little time below 5k RPM (I've checked). So "maxing-out" low RPM TRQ is wasted on me.. We should all pay attention to the RPM range we ride in and make decisions from those observations. These charts and the ones to come will show proof of the options available..

 

BTW, I know of only one other KLX running exactly the same set of mods as mine - that is Scootr. Yall can bug him about his performance..lol

 

???

KLXster - you sure you arent hitting the bottle?!

Your post states the green line is your bike and has the MCM-- the red and blue lines are Houstons bike and dont have it.

Seriously, how can you say the difference is due to the header when the valve timings are radically different? You cant say that with any confidence at all unless both bikes are running the same valve timings.

 

Man, this is a gigantic assumption on your part. Gigantic. The only way to say it with any certainty at all is to re-dyno your bike with the stock header, unless you already have. You just cant assume stock timings do anything to enhance upper RPM power. I distinctly remember you posting a while back when you first got the powerbomb that you were disappointed in the difference.

Im running stock valve timings and I can tell you even when I was running full exhaust nothing good happens over 8500 RPM. I have serious reservations that changing the header is going to make my bike do an about face over 8000 RPM and make Houstons graph look like yours, without seeing like for like bike dynos to prove it.

 

Well I always try to be "easy" with how I phrase my posts - as there is so much more to learn, which will no doubt change the recommendations for mod recipes as we learn it.. Houston and my charts will increase our knowledge quickly..

I don't think you are understanding that I am only looking at Houstons' curves when I say that it appears the TRQ tapers off too quickly after 7.5k. If this turns out to be true, the stock header is the only culprit.

When it comes to cam timings - it is science, not conjecture. Stock timings favor upper mid to top end power production - you can look up the timings and do the research yourself. MCM is advancing the intake event and retarding the exhaust event. This creates TRQ lower in the RPM range but it also increases valve overlap (which serves to create power up higher) regardless of what engine we are talking about - again you can research this yourself. What it does to the rest of the TRQ curve, we are about to find out. I have posted many charts with my bike+stock header+DGR+MCM+lidless - I have only to get the raw data files from my Dyno shop to show the evidence..

I don't recall ever feeling negatively about the effects of my Megabomb+PowerCore4 on my performance - quit the contrary, what I have always felt is now proven - it's power in a class all its' own. If you find a post where I "dis" my FMF exhaust system, post a link to it so I can delete it.. Afterall, with the help of friends and family, I have recently stopped sniffing glue..

To get all the top end "goodness", I am quite sure you have to run my exact recipe for "full performance exhaust". To my knowledge, this is not something you've ever done.

 

The green and blue lines have nearly identical slope after 7000 rpm with both losing about 2 ft-lbs from peak at 8500 rpm and another 2 near 9700 rpm.
I'm surprised at how closely blue and red converge at high rpm.

Your point about where one needs performance is a good one. I spend most of my riding on the trails, below 6500 rpm and a lot in the 4500 to 5500 range.

 

Houstons4, next results yet?

 

Not yet, Dyno test guy can't get me till next Wednesday.

I can say after tweaking the mixture screw over the weekend I've increased throttle response some and I'm now pulling unassisted wheelies in first gear. I was surprised the mixture screw made the impact it did (I dialed it in for a while, playing with idle drops at rich and lean). I'm certain getting accustomed to where the power now hits at the low end has helped a ton also.

More to come.

 

If I can, I'd like to share some knowledge - hopefully I won't bore anyone..
The settings and components of the CVK, as well as the airbox config, all work together - modifying any one will have an effect on all the others. With my carb setup recipes, for instance, and with our testing/charts, we have learned that raising the clip position can create more throttle response and power below 6k - but doing so leaves more of the needle inside the needle jet when the slide is fully raised. This could effect a leaning of the top end fueling. The extent of the leaning effect is determined by the contours of the needle near its' tip. Check out the pics of the DN0352 needle (DJ2206 kit) - it has a long, straight section at its' tip which should mitigate top end leaning with higher clip positions.

Using the stock spring to make more power could seem counter-intuitive to some. At lower RPM's, the stiffer spring creates more velocity in the intake tract due to slower slide response - which creates more TRQ. But, on-the-other-hand, it could also make the engine sluggish by being too slow to react - (which, it turns out, it doesn't when running lidless-see below ). What is interesting about slowing down the slide is that it will create an extended "accelerator pump shot" from the pilot systems' transfer ports. These tiny ports flow A/F when there is high vacuum between the butterfly valve (which is connected directly to your right arm) and the slide. This high vacuum event occurs when you whack the throttle and lasts only for the milliseconds it takes for the slide to begin opening from whatever position it was in before you whacked the throttle open. So, slow down the slide response time and you increase the duration of the high vacuum event(s) - creating an extended flow from the transfer ports, therefore, a bigger "simulated accelerator pump shot"..

Another (dumb) way you could slow down slide response is to add a restriction to the airbox airflow. The slide is raised by the difference/gradient/delta between the air pressure at the carb bell (inlet) and the air pressure in the carb barrel at the engine-side of the slide. Reduce this delta with a lid/snorkel and the slide slows down. BTW, since ALL other fueling circuits also function based on this gradient, the entire fueling curve is altered. This is why an owner has to first decide how he will run his airbox (lidless, lid sans snorkel, lid and snorkel etc) and set up the CVK accordingly.

Running lidless radically increases this delta, causing the slide to respond "vigorously". In fact, with the lighter DJ slide spring, in conjunction with the DJ needles, it is showing to be too aggressive and can create overfueling in the low to mid RPM ranges. Hence, the need for the stock spring.