Originally Posted by Klxster

Here is where you start to open a "can of worms".. I own a Q4/Powerbomb system, a PC4/Megabomb system, and a full KLX300R exhaust system.

If you are certain that you will eventually buy a performance header to "augment" a performance slipon, there are things you should know right now.

1. Not all slipons will fit both the stock header and the aftermarket headers (FMF's or the FSW). The performance headers are a larger Dia. than the stock header. Improper mixing of a performance header and slipon is a total waste of time and money - Don't ask how I know(lol). One of my Dyno tests proved this point..

The FMF slipons (Q4 and PC4) correctly fit the stock header and correctly fit the FMF headers (Megabomb and Powerbomb). So, add a FMF header to a Q4 or a PC4 and additional gains in power are "available" - you must change the airbox config and carb setup to take full advantage of the "available" gains.

The FMF header(s) drawback is the lack of, and/or expense of, proper heat shields. Uline carbon fiber shields are about the only "good" shields for the Megabomb. "ARL" found a way to attach the stock shield to the FMF headers though..


2. Only the entire KLX300R system can be used on the KLX250 - you cannot piecemeal the KLX300R system onto the KLX250.. Performance available with the KLX300R system with performance end cap is same-as KLX250 header + slipon.

3. The Four Strokes Works (FSW) header: It will only correctly fit certain slipons - I believe it mates correctly to the FMF slipons..


4. The rule of thumb about slipon mating - If a slipon requires the stock seal in the stock headers' slip joint, it will not mate correctly to any performance header. Such slipons carry the exact same "nipple" size as the stock slipon. DG's, Delkevics, are like this. FMF's and some others will require the removal of the stock seal in the stock header bell - these are the slipons that will fit correctly to a performance header as well.

5. Performance header + matching slipon: Compared to stock header + slipon, this combo "offers" more TRQ higher in the RPM band (6.5k-10.5K) and less in the low/mid range.

6. Stock header + slipon: "Offers" more TRQ below 6.5-7k RPM than #5 and less above.

7. If MCM (Marcelino Cam Mod) is a future mod, it enhances TRQ below 6.5k and offers about the same TRQ above - compared to standard cam timings.

What I have just said saves you hours/days of research in here - but you can verify all with said research..

So, in summary, your choice now needs to be based on what you intend to do in the future. A DG is cheap compared to a FMF. I ran stock header + DGR + MCM + lidless airbox + lidless carb setup - It is a loud, crazy powerful TRQ monster that runs outta breath by 9k RPM. For over a year now, I am running Megabomb + PC4 + MCM + lidless airbox + lidless carb setup. This is power everywhere that pulls to redline. One member running the same has reported top speeds with stock sprockets @ over 100mph (Don't try that at home, he is a professional amateur..)


DGR is loud. DGO is pretty loud. PC4 is my favorite - quiet when driving "normal" , mean "howling" when terrorizing the hoods. Q4 is very quiet everywhere compared to all the others. Most all other slipons are reported to be pretty loud. The Delkevic is loud only once the baffle is removed. The stock KLX300R system with performance endcap is also fairly quiet - comparable to the stock header + Q4.

While adding a "quiet tip" can be done on most all the above, the net effect is to restrict/constrict the exhaust flow which defeats the whole purpose, and the money spent, on improving performance.

Originally Posted by Klxster

PC4 = Power Core 4..
Gonna keep the stock KLX300R exhaust system, sorry..

Originally Posted by Klxster

PC4 = Power Core 4..
Gonna keep the stock KLX300R exhaust system, sorry..

Originally Posted by Klxster

I am aware of reports of melting airbox's - apparently it is possible to install a slipon in such a way that it is too close to the airbox. I chose not to do that - you should choose not to do that as well. Also, I do not know if the air injection system played a part in those "melting reports" but removing it from the bike, along with proper jetting, drastically lowers exhaust temps.

The PC4 needs no tweaking, not sure where you got that info..

I did run one weekend with PC4+stock header+MCM+lidless setup - While I did not Dyno test that "mod combo", I am convinced that the increased power levels were more "evenly distributed" from idle to about 9.5K RPM compared to the smaller Dia. midpipe on the DG slipon.. It is a little louder than when used with the MegaBomb header - The Megabomb/Powerbomb headers have a quieting effect..

Since you've asked about my thots on drilling the starter jet, I assume you've read enough of my posts to know how I feel about peeps molesting their KLX's with drill bits. There is no need to drill anything, anytime, ever. Even the 2206 kit has been found to work better if you do not drill the carb slide as per the instructions. However, the starter jet drilling is a benign "drilling" - it only affects the amount of fueling during "full choke" operations, nothing else.. Also, the members that tout this mod are members I trust (IDRIDR, TNC, etc).. The only other "drilling" that I find almost acceptable is the opening up of the crankcase vent port on the airbox.

Your best lidless carb setup will depend on your average riding altitude. It will use the needle from the DJ2206 kit or the DJ2152 kit, a properly sized main jet, etc etc..When you get to that point, I can provide you the exact recipe for your lidless power enjoyment.