To provide members with guidance on performance mods, and the combos that have been dyno proven..
This top post will be added to as needed - Check back periodically.


SECTION 1. EXHAUST CONSIDERATIONS AND CHOICES.
SECTION 2. KLX CARB SETUPS.
SECTION 3. KLX300 (EFI)



Section 1. Exhaust Considerations and choices:
This exhaust information pertains to KLX250 parts and accessories - the subject of KLX300 parts and accessories is in a separate section below.

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.
Not all slipons will fit both the stock header and performance headers: 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..
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THE LIST - Updated as new information is found.
Slipons that are known compatible with performance and stock headers:
TBR,
FMF,
HMF ( https://www.kawasakiforums.com/forum...ad-pipe-21871/)
Big Gun is very likely compatible..
DanMoto makes a great looking slipon that is cheap and will mate to any header properly - Kawasaki KLX 250/300 S/R 1994-2014 Off-Road Slip-On [OF-00011] - $108.00 : Danmoto, Motorcycle Racing Parts & Accessories

Slipons that are known incompatible with performance headers - : Delkevic, DG, Yoshimura, some (maybe all) of the Delta slipons
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Notes on performance Headers:
At this time, similarity of the Big Gun header and the Delta "Torq Head Pipe" ( - DELTA - EXHAUST SYSTEM) to the FMF headers has not been member verified. However, it is quite likely to be so and is quite likely that they interact with slipons in the same way as the FMF's...

Four Stroke Works headers and slipons are in the KLX300R section below and should be considered "same-as" KLX300R exhaust components regardless of the FSW application ( KLX250 or KLX300).

The Delta "Torq Pipe" EDIT 4/22/2020: A member bought the Delta system - the header and midpipe are mismatched in size. The header carries the larger dia. slip-bell but the midpipe (slipon) has the small (AKA stock) nipple ! Whether this is a simple mistake in part numbers or if all Delta slipons carry the small nipple remains to be known. Mismatches such as this are a total waste of money(power is lost). The Delta header does NOT increase low rpm power - it is a typical step-design peformance header that should increase mid and top end power..

ChinaBomb Headers: Member information/installation (Thanks @Rickybobby2 ) reveals that the header bell is the exact same size of a FMF slipon nipple. This means the ChinaBomb headers WILL NOT FIT ANY SLIP-ON without work. Necking down to fit a stock or small nipple aftermarket slipon (Delkevic, DG, Yoshimura)will cause a power loss across the board. The bell must be expanded slightly (from a shop capable of expanding such a small dia. pipe) in order to fit FMF and Same-As FMF slipons - which is the only option for using a Chinabomb if a increase in performance is desired. https://www.kawasakiforums.com/forum...werbomb-46904/


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The FMF header(s) drawback is the lack of, and/or expense of, proper heat shields. FMF has finally made one for the Megabomb-with unknown effectiveness. "ARL" attached the stock shield to the FMF headers. - Vid here: Link to attach kit here:Flatland Racing: Universal Heat Shield Mount Kit (Set of 3)

While E-Line does not list a shield for our KLX250+Megabomb, I know they can make up shields that they don't list. They do list attach kits: Pipe Guard/Heat Shield Replacement Brackets - Replacement Mounting Kits


The rule of thumb about slipon mating - If a slipon requires the stock seal(gasket) in the stock headers' slip joint, it will not mate correctly to any performance header. Such slipons carry the exact same 1.25" dia "nipple" as the stock slipon. DG's, Delkevics, Yoshimuras, are like this. FMF's, TBR's, HMF's and some others will require the removal of the stock seal in the stock header bell . They will fit tightly into the "naked" stock header bell and only require a smear of high temp sealant to fully seal.. These are the slipons that will fit correctly to a performance header as well.


Performance offered by exhaust combos:
Performance header + matching slipon: This combo "offers" more TRQ higher in the RPM band (6.5k-10.5K) and less in the low/mid range.

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

If MCM (Marcelino Cam Mod) is a future mod, it radically enhances TRQ below 6.5k and offers practically the same TRQ above - compared to standard cam timings. (Dyno shows .5 -.75 lb ft loss above 6.5k rpm.)
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There is one other consideration - the midpipe. The performance compatible slipons have a "biggy" midpipe dia. compared to the noncompatibles. And when used with a stock header, the "step up" to the biggy midpipe occurs at the header/midpipe connection instead of past it. So slipons that carry the stock nipple size, actually further enhance low/mid TRQ over the others at the expense of upper mid/top end TRQ - again, when used with the stock header. In my experience, the FMF slipons + stock header provide increases that are "spread out" more in the RPM range. A DGR+stock header pulls hard from idle and starts to shed TRQ a little quicker up top.. These are small differences to be sure - but this info is needed to help with parts selections.

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 after 9k RPM. For over a year now (to post date), I am running Megabomb + PC4 + MCM + lidless airbox + lidless carb setup. This is big power everywhere that pulls hard to redline (10.5k RPM). One member running the same has reported top speeds with stock sprockets @ over 100mph on level ground (Don't try that at home, he is a professional amateur..lol) Either of the combos (correctly set up) are profound increases in performance - utterly giving you a "new bike" performance-wise.


DGR is loud. DGO is pretty loud (thanks Josh128). 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 (thanks Houstons4). The stock KLX300R system with performance endcap (or stock end cap removed) 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.

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KLX300R exhaust components on the KLX250


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

2. The Four Strokes Works (FSW) header for the KLX300R will fit when used with a KLX300R slipon - including the stock KLX300R slipon (thanks Dpippin). And you can order the FSW header with a heat shield!

3. As far as we know at this time, the power potential of any combo of KLX300R parts is the same as a similar KLX250 parts combo. I personally believe a FSW header + stock KLX300R slipon (w/o end cap or with performance Ebay end cap) could offer a cheap alternative to a KLX250 FMF PowerBomb + KLX250 Q4 in terms of performance potential. I would have to assume that cheap stock KLX300R mufflers are available at the local motorcycle wrecking yards or on Ebay..

4. Again, the stock KLX300R system with performance endcap (or stock end cap removed) is also fairly quiet - comparable to the stock header + Q4.

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Other Notes:
The Barker system offered by Bill Blue (Page 2) has an interesting "megaphone" shaped midpipe. It produces great gains with a stock bike and could make best-to-date power levels when used with a lidless airbox and lidless CVK setup. 25-26 horsepower stockbore KLX's could be possible. The Big Gun system as well as the slipons are a very interesting option as they seem to come with accessories that usually cost extra (end tips, etc) - but at an advertised 98 db, the slipon will be loud!

Edit 10/2018: At this time the Barker system has been member tested and shown to provide at least the power potential of a full FMF system. 1- 2nd gear power shifts at redline can wheelie the bike..


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SECTION 2. CVK carb setups and additional performance options:

Firstly, a decision must be made on the airbox.
The two choices are to run the airbox lidless (best power levels possible), or run with the airbox lid on ( and either without snorkel or with the KDX snorkel.)

Throughout the years and throughout the world, a great many KLX's are running the "Lidless Max Performance" setup - with ZERO reports of being more susceptible to water and mud intrusion. The shrouding around the top of the airbox has proven to be effective in preventing any unexpected contamination - contamination that a snorkel would have prevented. For instance, drop your bike in deep water, and it doesn't matter how your airbox is configured, everything is going to get flooded !

Still, some will prefer to leave the lid on. Which will require a KDX snorkel or removal of the stock snorkel.
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MCM: https://www.kawasakiforums.com/forum...rcelino-35904/

The cam retime will significantly increase low and mid range TRQ on any klx (dead stock, or modded in any way). It is not experimental, it is a many years old proven mod. You do the mod correctly, you get the results:https://www.kawasakiforums.com/forum...timings-44296/

Help in doing the MCM can be found at the beginning and the ending of the MCM thread ( No need to read the whole thread ), and by using KLX678's MCM document https://docs.google.com/document/d/1...m3gkMeNUU/edit , as well as my PDF on my signature line: https://redirect.viglink.com/?format...&txt=MCM%20PDF

Deal with the KACR issue by simply pulling off its' spring.
DO NOT USE ANY VIDEOS (YOUTUBE) AS NONE ARE COMPLETE AND OR CORRECT !!!!!!!
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Help and knowledge for doing a "CVK carb session" : https://www.kawasakiforums.com/forum...s-fixes-43146/

CVK setup when using a lid on the airbox is simple - buy the DynoJet 2152 or 2182 kit (they have identical components) and install as per directions.

CVK setup with a lidless airbox: The owner must make sure their carb is running a stock slide lift port and a stock slide spring, and rectify any deviations with a lift port fix and/or a stock slide spring acquisition.

There are two dyno proven, and time tested recipes. Prior to installing the lidless recipe, a bike must be running perfectly. Installing a lidless recipe into a faulty carb will guarantee failure and cause significant downtime.

Option 1: When using the stock header (or full KLX300R (stock) system with performance endcap). This combo makes the most power possible, below 7000 rpm, but less above.
Option 2: When a full performance exhaust system is installed (header and slipon). This combo makes the most power possible from 6000 rpm to 10,500 rpm, but less than option 1 from idle to 6000 rpm.

NOTE: The best overall performance, and the most power possible with the stock KLX engine and CVK, is Option 2 with MCM.

Here are the threads that describe and prescribe the Lidless recipes:
https://www.kawasakiforums.com/forum...-system-42926/
https://www.kawasakiforums.com/forum...-slipon-43039/

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SECTION 3 KLX300 (EFI)

9/14/2023 : It has been shown thatsimply removing the secondary throttle plate, on a stock KLX300 will result in a huge boost in midrange power. The stock fueling will trend toward being lean but not so much as to be an issue - do not mod intake or exhaust tracts, from stock, in any way or wide open operation ( WOT) will become too lean. This should be done ASAP by all owners of stock KLX300's.

Here is the video showing the difference in power this simple and free mod will unleash - it has been verified that the engine is stock with stock fueling:

This post will be updated as new information becomes available.

 

Got the 6db restrictor for the DG-O. Thinking about moving up to a 3 db as I believe there was a "seat of the pants" difference between full and the 6db. As long as the 3db is at least the same dia as the header, shouldnt be much difference in power from full. The 6db looks to be *slightly* smaller than the header dia.

The full DG-O sound was just too much for me. Caused headaches even for 30 minute rides...

 

By the time the exhaust gases reach the end of the slipon, they are cool and low velocity. Expelling them effectively requires a larger Dia. than elsewhere in the exhaust system. A restriction at the end of the slipon causes the cooler, low velocity gases to re-compress before exiting - this restriction becomes a "game changer" for the whole exhaust system in terms of being able to provide power potential with "as designed" tuned and enhanced gas flow.

If the noise of a performance slipon/system is unacceptable, a "quiet tip" may be the most cost effective way to get relief - but there will always be a price to pay in terms of power lost.

 

The Four Strokes Works (FSW) header also mates with the KLX300 silencer/slipon

 

Thanks Dpippin, I've updated the top post with your knowledge.

The FSW "stuff" we can use seems to be "tagged" for use with the KLX300R. Their KLX250 stuff is only for '94-'96. So the "golden rule" still applies - entire 300R system only, no piecemeal (due to midpipe length differences)..

 

Added info about the TBR slipons based on the install instructions - http://www.twobros.com/Cust_Service/...104xV_Inst.pdf

Notice the requirement to remove the stock seal in the stock header in order to fit the TBR.. This is exactly as the FMF slipon instructions..

 

Really fantastic write up. Thank you! Do you know if the slip ons and headers are compatible between the 06-08 klx250s' and the 09 and greater? Or is the 06-08 compatible with the 300r? I've been looking for answers in the forum but haven't found it yet. If this has already been answered in another thread, I apologize-- just give me the link.

Btw, I actually talked to Bill Blue this week about his barkers exhaust. He says that on the dyno it increases hp by 4.9 (with the quiet insert in) as compared to other performance exhausts that only increase it by 2-3hp. He said he's never dyno'd the Barker without the quiet insert.

 

Since the Barker system costs as much as a Megabomb+PowerCore 4, it would need to produce same or better numbers.. Reviewing the charts, there is a "spot" whereby my bike (MCM+Lidless setup+Mbomb+PC4) makes right at +5 hp over Houstons4's stock bike - BUT, the gains are mostly in the 3-4 hp range.. If the Barker system can add another 1-2 hp throughout most of the useable RPM range, it certainly would be worth the money.

If anyone buys or has the Barker and wants it dyno tested against the Mbomb+PC4, we should talk..



About '06,'07 system compatibility with '09 up - This has been answered in here.. I think I remember that they are all compatible..

 

https://cdn.shopify.com/s/files/1/0475/8121/files/Barker_s_2012_KLX_250SF_-_Bill_Blue_-_Stock_vs_Barker_s_Modded_Bike.pdf?1236

I found this dyno of Barker vs Stock. I don't know if that helps. Thanks for the response! I'm positive my question has been answered on here somewhere... I just can't find it! I've spent several hours looking for it at this point. Thanks for your response!

 

This is the chart she is referring to. I had to reduce the quality to get it here. Follow Steffs' link for a better viewing".


All run data is present - it's a valid chart. What we don't know is the details of the bikes' carb/airbox setup. Still, the curve for the "stock bike" looks right. The "enhancement" curves are believable for a non-MCM bike. The peak numbers are exactly what I would expect with a non-MCM+lidless setup + Full FMF system. What I can't guess at is the shape of the curves between this Barker system and a Full FMF system.

Notice the TRQ/HP is enhanced everywhere but, as expected, really "takes off" above 6K. All-in-all, a very impressive result. If you don' know Dyno charts very well, let me assure you that the bike went from "zero" to "hero" - Tame to Dangerous(That power surge above 6K will have it come over on top of you, out on the trails, if you are stupid with the throttle and the situation..)

Just had a long conversation with Bill Blue. I'll post a new thread about this conversation but info on the Barker System I'll post here.

He always runs his test bikes with the lid on and usually with a KDX snorkel. This means that the Barker system could produce a new "standard" of horsepower and torque on a stockbore with a lidless airbox and lidless carb setup! The megaphone midpipe and the obviously properly sized header could produce 25-26 horsepower KLX's.. We need to produce this data!!!