We need a thread that lists knowledge regarding the 2021 ( and up ) KLX300 performance enhancements that are easily duplicated by all - meaning knowledge that is using aftermarket components or free mods. Please feel free to post any/all that I may have missed and I will add to this top post.



@Nigel has created a PCFC tune for slipon + STP delete + KDX snorkel.

@billp91311 reports that the Dynojet PCV tune for the "KLX300R + slipon" , when loaded onto a KLX300 PCFC, works well for Slipon + STP delete.

@Olderider is running lidless, Barker System, STP removed, and EHS Racing tuner. His power levels are at or a bit above 27hp. EHS Racing offers a tuner with tunes developed for the most logical mod combos once the STP has been removed - including Lidless + Barker System

Secondary throttle plate ( STP ) removal should be the FIRST mod done to a stock KLX300 - it is a "game changer" performance wise.

Pinit Racing offers a performance ECM. When they complete their programming project, their ECM will not require STP removal. Currently dyno testing shows 26hp and massive midrange increases over stock. At this time, they suggest mods that destroy a KLX300 airbox and silencer - I do not recommend doing this - There is certainly no evidence of effectiveness in doing so at this time.

6/15/2024:
Best Dual Sport Bike sells the Pinit Racing ECM - their current programming significantly enhances power production above 8k rpm over stock programming.

IMHO, at this moment in time, the logical mod progression on a brand new bike should be the following :
1. Remove the STP ( Secondary Throttle Plate) - Enjoy a significantly enhanced power curve.
2. Next add (Install) a BDSB/Pinit Racing ECM - significant power jump over #1. Approx 26 hp. NOTES: DO NOT install a performance slipon. DO NOT touch the stock airbox and snorkel. The Pinit ECU cannot fuel such mods.
3. Next buy a performance slipon that retains the O2 sensor. OR buy a Barker complete exhaust system with the O2 bung option. Buy a DynoJet PCFC. Remove the airbox lid. Have a local dyno shop tune (using the PCFC) to refuel open loop operations ONLY, to 12.6 - 12.8 AFR. This will fully unleash the power possible with a stock engine using the stock injector. Power will jump from the 26hp you already have with step #2, to approx 30 with the Barker system.
NOTE: : NEVER EVER disconnect the O2 sensor. . It must be operational for proper closed loop fueling.

10/22/2024:
@tsc has a thread where he has/is dyno testing various performance mods. He is currently producing approximately 32 hp.

Through his efforts, we have dyno proof of a few "items of interest" :
1. Use of a knobby tire during dyno testing will render the results useless and is a total waste of time.
2. KDX snorkel vs Lidless airbox - the KDX snorkel will cost you 2.5 - 3.0 hp. Also, the KDX snorkel loses power over the entire RPM range compared to lidless.

 

EHS racing has a fuel tuner for the full barker exhaust , secondary throttle plate removed and air box mods lidless.
They also have tunes for stock bikes with secondary throttle plate removed and different air box mods like snorkle removal.

 

There is a sub-forum for the KLX300R. One thing I've tried to do was promote this forum for the 300s because other than the displacement and EFI all of them are very very similar since the first KLX250R in 1994. I've especially been pushing the forum at ADVriders forum where there is so much segmentation when someone doesn't look, plus it's easier to look through the topics here rather than searching one long thread. Maybe the administrators here could re-title that sub-forum to reflect the new 300S and 300SF as well as the R.

 

I have asked the same thing. We need the 300ds 300sm sub forum.

 

@Olderider , went back thru your postings on this - included your info on top post.

 

Always striving for more knowledge, I spent a few hours researching the current state of CRF300L performance upgrading. What an eye opener !

Apparently, regardless of how much money is thrown at, and into ( specifically cams), the Honda, it cannot make 26hp !
The reason? The 300L airbox design. There is an internal snorkel that snakes inside the airbox - from the throttle body into the inside of the airbox. This internal snorkel limits power production in the upper RPM, REGARDLESS of any other mods/tuning done to the engine. Apparently this snorkel can be removed and replaced with a CBR300 component - but the process of doing so is incredibly difficult. Also, the other end of the airbox must "opened up" as well , or the whole operation fails to produce upper end power.

Add to this that DynoJet offers a PV3 for '21 and '22 300L's. While this may sound great, it is not. The PV3 is THE tool for accessing all (or most all) of the internal tables - allowing tune development from the ground up. Problem is that only a few shops (Maybe only 3 as of now) in this country have the needed "combination" of a properly updated and upgraded PV3 capable dyno, PV3 training/skills, and most importantly the knowledge needed to know what the hell they are suppose to be doing with all the tables/data they now have access to !

So, KLX300 owners have a serious advantage over CRF300L owners - we can easily make 27+ hp with what we know at this time, and they cannot.

 

Updated top post.

 

First of all, thanks to KLXster and all the rest of this knowledgeable community for the amazing help you brought.

I'm on the process of converting my klx250s (EFI European model) to 300, adding the 270 cc injector to the equation in order to avoid, if possible, the need of a an ECU programmer.

I also ride with a klx 300 snorkel as only other mod.

My question is about the STP removal.

I saw in some other of your posts totally recommending it for big bore mods, but I'm unsure if 300 would be "big enough" to fall in to the category.

Also, and as a bonus question I'd like to ask if a more open slip on muffler would be recommended.

Really excited about all this.

Thanks in advance from spain (900 feet ASL)

 

Any update on your upgrade? My understanding was the 250s and the 300 used same size injectors and the injectors being the limiting factor going to a 331 or 351 big bore.

I may remove my air box lid and add my 02 sensor back in and see how I'm feeling later. Also looking at a BDSB/Pinit Racing ECM

 

Also interested in how this worked out.
If the injector is the same, are the fuel maps different?