On a separate topic, I recently had a dyno test done to quantify the results of all of my low rpm torque mods.
Nothing was done to increase the horsepower, only low rpm torque.
I use my bike in my business as daily utility transportation.
With stock supermoto gearing, 50 mph is 5,000 rpms. I live in a rural canyon,
so that's about as fast as I ever go, so the engine rarely runs over 5,000 rpms.

Here are the numbers.

Stock KLX300SM done by Cycle World on youtube:

23.9 HP @ 8,080 RPM
15.6 TQ @ 7,750 RPM

My Modified KLX300SM

26.2 HP @ 8,020 RPM
18.3 TQ @ 6.420 RPM

While my engine only made only 9% more horsepower,
it made 17% more torque while lowering the peak torque by 1,330 rpms.

My engine produces as much torque at 3,500 rpms
as the stock engine produces at 7,750 rpms.



These are the mods:

FMF Megabomb Header
Shorty Muffler with a DRZ400 End Cap
25% Longer Exhaust Pipe Extended Into the Muffler
40% Longer Intake Pipe with Velocity Stack

Delete Secondary Throttle Control Plate
Delete ECU Controlled Primary Throttle Spring
Delete O2 Sensor
Delete Pair Valve
Delete All Smog Equipment

EJK Fuel Controller
Oversized Snorkel

My dyno chart is clearly deliniated in whole numbers for Horsepower Torque and Rpms,.and is very easy to read.
This is because I'm not trying to hide anything.

 

I no longer feel the need to try to figure out what's going on between the ears of that BDSB guy.
He is developing products for the KLX300 and trying to sell them. As such, all his "supporting dyno data" is suspect.
He will not, or can not, produce an ECM that is reprogrammed for popular mod combos.

He is continuing to direct owners to cut slits under the heat shield of their stock mufflers ! This is shear lunacy. This destroys an expensive part and bathes the heat shield with hot exhaust gases - the shield was not designed to function in this manner and under certain conditions would certainly become very hot.

Sadly, his personal philosophy regarding performance modding means that the expense of creating a truly "unleashed" KLX300 goes way up due to the fact that his ECM will not fuel a lidless airbox + performance exhaust system. A piggy back fueling device must be installed and dyno tuned to refuel ONLY WOT operations for such a mod combo.

 

I agree. The cheapest stock muffler goes for $130 on ebay. Why destroy it, when you can get a new Delkevic muffler with a midpipe for $210.
And those dyno charts look like a Shell Game.



I keep the stock one intact and use another muffler for all of my exhaust experiments. I found that lengthening the exhaust pipe inside the muffler produces more torque while also lowering the torque peak.




And so does lengthening the intake.





While the screen needs to be trimmed, the velocity stack fits nicely inside the stock air filter.

 

I like the veliocity stack idea!

I smoothed out and rounded the outlet on my bike?

How come you didn't remove the entire backfire screen?

 

I like the veliocity stack idea!

I smoothed out and rounded the outlet on my bike?

How come you didn't remove the entire backfire screen?

 

Removing the airbox cover on a KLX250 does absolutely nothing except make more noise, and it actually hurts the engine quite a bit. On my Japanese 250, I had it removed, and the bike was overheating like crazy on uphills and losing power.
Putting a 5.8 kOhm resistor into the IAT (Intake Air Temperature) sensor at 20°C improved things a bit, so now I’m planning to install a 6 kOhm thermistor. Our bikes have a stock 2 kOhm sensor at 25°C with a 3500 Beta coefficient. If we triple it, we get a 27-20°C lie to the ECU in the 35°C to -5°C range. But if we use a 6 kOhm thermistor at 25°C with a 3950 Beta coefficient, we’ll get a smoother 27-23°C drop instead.
Long story short, don't remove the airbox cover without adding more fuel.
Shoutout to all the 'expert tuners' out there who still haven't figured out how to talk to real human beings. Sending thoughts and prayers to your social skills. ✌️




To really open up the KLX300, I think you need an exhaust, removing the airbox cover, and adding more fuel—or even a bigger injector if you are going to run the Japanese KLX250 ECU. The 250 ECU has shorter injector pulse widths, so it won't supply enough fuel for the 300 on its own.
My bike's ECU part number is 21175-0820. There are other part numbers listed on webike.japan, but I'm not sure how they perform. Usually, the 2007-2012 models had a different number, and this one is for the 2013-2016 models.
Also, the KLX250 camshafts might actually be better than the 300 ones.

 

Unsure why you quoted my post and then yammered about unrelated topics. Perhaps to get my attention ?

The IAT modifier table - more specifically, the values within that table - are what you are trying to invoke with all that spoofing you are doing.
IAT modifier tables offer a very limited amount of enrichment. They are valued (set up) to keep the engine safe. They can help, a little bit, to better fuel mildly modified induction + exhaust tracts that cause slightly lean fueling, but cannot provide performance fueling.

Your musings about "opening up a KLX300" is correct. The details of which have been established in here many years ago.

 

You are looking at the IAT sensor from a closed-minded, one-way perspective. Yes, you are absolutely right: the IAT modifier table has a limited range of enrichment, maybe 6% to 10% max [BoosterPlug]. No one is arguing with that.
But what you completely failed to understand is that the system works both ways, and you are completely forgetting the biggest variable: the injector size.
Nobody forces us to use the stock 220cc injector.
Think about this simple math
If I need a +15% total fuel increase for a modified engine (Big Bore / Open Airbox / Exhaust), and I try to get it only through the IAT sensor, I will fail because the IAT table doesn't have that much room.
But what if I install a +22.7% larger injector (270cc)? Now my baseline is too rich.

This is where the magic happens: instead of using the IAT sensor to add fuel, I use a custom thermistor with a coefficient under 1 (<1) to trick the ECU into thinking the ambient air is extremely hot (+50°C).
The ECU reacts by pulling fuel back by about 5% to 7% via the IAT modifier table.
Final result: +22.7% (from the hardware) minus 7% (from the software) = +15.7% total fuel increase at Open Loop.
By scaling the hardware (injector) and fine-tuning the offset via software (IAT spoofing with a precise Beta coefficient thermistor), you get a perfect Air-Fuel Ratio (AFR) across the board. In Closed Loop, the O2 sensor handles the rest.
Why on earth would anyone spend $200-$300 on a fragile, aftermarket fuel controller box that can fry in the mud, when you can achieve the exact same global offset with factory reliability for $5 using hardware scaling? It's just simple math and physics.

 

Closed mind ? Nope, just trying to help you and the membership to understand the reality of what you are posting.

1. IAT modifier tables have values for BOTH fueling AND ignition. Namely, it pulls ignition at higher temps. Your "both ways" premise, while technically correct, cannot be used to lean AFR without retarding ignition, rendering the option moot.
2. Replacing the injector with a "larger" one: The ECM has many tables that allow it to properly operate a injector. Without reprogramming the tables with the pertinent data for the "bigger" injector, the ECM will not operate it correctly. Namely, the Scaling factor will not be correct for the new injector. This causes unpredictable fueling errors throughout the RPM and load range, especially idle fueling. There seems to be "biggy" injectors that have proven workable throughout the years but without data as to what they actually accomplish.
3. A dyno session is the only way to know what is needed on a modified EFI KLX. It cannot be assumed that any particular mod combo will need 15% more fuel.
4. Most assume a "module" has been set up / tested / verified for certain mod combos - therefore the money is spent instead of the unknown results of spoofing the IAT sensor signaling.

I am done with this subject.
Have a good one.

 

You are shutting down the discussion because your generic textbook theories just ran into real-world testing on this specific platform. Let’s clear up your misconceptions:

1. Ignition Retard: On the KLX250/300 platform, ignition timing is strictly tied to the Engine Coolant Temperature (ECT) sensor for overheat protection. The IAT sensor on these bikes does not retard ignition between ambient shifts of -10°C and +35°C. It is a simple air density calculator used for fueling trims .
2. The "Unpredictable Fueling" Myth: There is nothing unpredictable about basic physics and math. My practical tests completely busted your skepticism. I tried two different setups:
3. A -30°C spoof (+10% fuel) resulted in a slightly rich cold start (smell of unburnt gas) but a super smooth, stable ride once warm.
4. A -26°C spoof turned out to be the absolute sweet spot. It completely compensated for the lean condition caused by the open airbox, restoring full power and eliminating the overheating on uphills without causing any idle or fueling errors.

The factory ECU handles this global offset beautifully. You don’t need to reprogram the whole scaling factor for mild hardware stepping when you know how to balance software offsets via exact Beta coefficient thermistors.
You can stay "done with this subject," but the math works, the bike runs flawlessly, and it cost me less than $5 instead of a $250 piggyback box. Cheers! ✌