CRF300L/Rally Air Box & Performance Mods

Many riders are investigating and trying different performance ideas for 300L/Rally.
Maybe a dedicated thread is a good idea.

I decided to try and increase the airflow on my Rally by removing the back-fire screen on the OEM filter. As it turned out . . . at 900’, I really did not need more air. Higher elevation may work fine.

Mine seemed to run a bit lean w/out spark screen. I decided to try a pre-filter to off-set the lean condition.

I tried cutting a Home Depot general purpose grout sponge to 3/8” and testing it. It actually works very well at my elevation.

There are many different porous grades grout sponges you can try.

The engine breathes fine . . . reduces the factory lean tune a bit. No idea on mpg etc. I will monitor it.
Walk speed (w/38T rear sprocket) worked great. Definitely will extend your air cleaner element.
It does seem to limit the top RPM a bit.

Wondering if an enterprising company might step up and manufacture an entire replacement air filter made out of foam, that can be oiled after cleaning, with a similar perimeter locater/seal that is used by the Honda paper filter?

With a North American ECU, I was able to re-map after making exhaust and intake changes. My combination is:

550Performance 91Octane reflash service
MotoX Full Stainless exhaust (spark arrestor omitted)
3 UNIvents in the airbox (stock air filter)

Result: noticeable boost in power at all rpms, throatier exhaust (not too loud), and improved low-speed throttle control. It also drastically reduces exhaust heat and cools the combustion chamber enough to nearly stop the actuation of the radiator fan. The gas mileage is reduced to ~62mpg and high octane fuel is required.

With the power boost, changing the rear sprocket from 40T to 38T was a no-brainer. Speedometer now matches my GPS and the lower gears get things going a little faster. The vibration threshold is raised a few miles per hour.

I replaced the rear shock with a YSS gas unit with preload and rebound adjustments. This allowed me to select a spring that is appropriate for my weight. This is a great option for overlanders, as the weak rear spring precludes proper sag adjustments and the flaccid dampening creates a bucking effect over multiple bumps.The price was reasonable and this shock meets all my requirements for rear wheel control.

I also replaced the front spring with a replacement from YSS…again more appropriate for my weight. The result has been improved wheel control and reduced dive under hard braking. Though the stock spring was okay, and much better than the stock rear shock, this mod makes a nice refinement at a great price.

These changes significantly improved the utility of my Rally. It now feels right, sounds right, and pulls a little harder. The remainder of my modifications involved ergonomic changes, the installation of a GPS, and the installation of luggage racks. Future changes include a throttle lock, a Seat Concepts Comfort XL saddle, dry bag saddlebags/duffel, and a small tank bag.

Some details from the owner of 550 Performance on the Honda 300 ECU flash in quotes

"I am the owner of 550Performance. We are a very small outfit, husband and wife team. We do not currently have a website in place, but may add one in the future. We can be directly contacted on Facebook or emailed at support@550performance.com. We monitor both inboxes regularly and will provide timely responses. Our Facebook webstore currently is the best way to purchase products and services.

With the 91 Octane tune we advance the ignition timing to make use of 91+ octane (R+M) / 2. Additionally, we account for any standard bolt ons that you may have, like a header, silencer, larger throttle body, big bore, or airbox mod. The custom tune essentially takes this 91 octane base tune one step further by taking extensive data logs and rebuilding calibrations for your specific bike and its specific hardware, this is essential for dialing big cams. The $59.99 CBR250/300 calibration swaps are basic simple reflashes. Essentially all of the mapping from those models can be loaded into your stock ECU. This is convenient when converting to the CBR250 / 300 specification. With this method you do not need to purchase a new ECU and you retain OEM functionality without repining the harness or having CEL's.

I have been developing these calibrations for about a year and a half. I solely run a custom calibration on my CRF250L with a 300 crank. I am not a fan of piggyback fuel controllers because they can cause more issues than solutions they create. Take the EJK for instance, it adds fuel in the LOW, MID, and HIGH ranges which roughly corresponds to Green, Yellow, and Red zones. The EJK has a very simple algorithm. It literally just adds a fixed amount of fuel to each zone base on your setting. For example: on the MY13-16 250L the Green zone adds 100uS of injector pulsewidth multiplied by your setting. Ex: 4.5 * 100us = 450us = 0.45ms of additional fuel. For reference the bike usually idles at around 2.3ms of injector pulsewidth. At peak power it is about 11ms. Yellow and Red are both 80uS per step. Ex: 3.5 * 80 = 280us = 0.28 uS. So a setting of 3.5 at peak power would be a difference of about 2.5% in fuel. There are a couple issue prone spots with the EJK. First, on quick throttle stabs the EJK tries to replicate an accel pump feature (blue / red zone). This additional pulse can cause stalling issues. I had issues back in the day when I ran an EJK where sometimes coming to a stop the bike would stall out or cough. I reduced the (Red/Blue) and (Green) zones to stock to entirely eliminate the issue. Note: a setting of 0.5 is stock, no change. In addition to this fundamental problem, there are a couple more. The bike runs closed loop from essentially 5% - 80% throttle. So all the fuel you add in these zones with the EJK, the stock ECU is pulling out over an integration process. Takes about a second to two to fully remove any additional fuel. This cascades into another issue. The ECU sees that it is pulling x.xx% fuel throughout most of its operating range. It stores long term fuel trims that can be extrapolated and used at WOT. This essentially means that the EJK could cause fuel to be removed at WOT. The final reason is that this is an addon controller that can fail. If you are relying on this controller to run your big bore, imagine what happens when the controller fails. Instantly you are about 22% lean. If the bike continues to run, this can cause damage to your engine.

The ECU reflash removes pretty much all these risks while unlocking more features and power potential. In addition I have been tuning engines for roughly 10 years. Five of those years were at an OEM powersport level.

Within the next couple weeks we will be additionally offering an ECU core service to go along with our tuning services. What this will entail is a core deposit roughly for the price of a new ECU. We will flash this ECU and mail it to you. Plug it into your bike and you are good to go. Send us your original ECU back and we will reimburse you the cost of the ECU core.

Hope this helps answer some questions you may have and feel free to ask more!



-Maverick"


The ECU still utilizes closed loop feedback fuel. However, I can redefine when it can and cannot be used. I will never recommend to completely removed an oxygen sensor and its feedback, however if you want to go into fuel enrichment earlier I can get behind that. Closed loop is awesome because at cruising speeds and part throttle (when you are not requesting peak torque) you can still retain fuel economy. But the moment you flick you wrist, the fueling can go into fuel enrichment and you are at peak torque. This is the true beauty of fuel injection.


This system is actually very modern. There are quite a few parallels between this and the Africa Twin in how the ECU architecture is setup. This makes sense because when you design ECU firmware you design it so it can be portable. What works on the Africa Twin can be reutilized on a single cylinder engine like the 250L. I am not implying that the 250L's code is based on the Africa Twins, just merely stating what I have observed and would personally do when developing firmware. The 250L's ECU has a large range of authority to correct fuel via fuel trims. On my bike when developing my current calibration I had seen it pulling fuel up to 23% in some cells. That is just my observation, doesn't mean it is the limit. I have also seen it adding up to 10% before so I know that it has at least that range of authority which is pretty huge. In Mark's case, his bike was about 6% leaner when running his hardware setup. This means that there was 6% more air going through his engine than stock. The stock system will account for it. However, it takes time to react and integrate in the extra fuel. Mark's ECU is now custom matched to his current setup. His base maps already account for the ~%6 additional airflow. No time wasted on integrating, the ECU is already at target and the bike is more responsive because of it. The one thing that surprised my when I first learned about it on our ECU's was that it runs full sequential. It uses a phase detection algorithm using the MAP sensor. I had seen it used in the OEM industry before, just assumed that this bike didn't do it and ran batch injection. They are way more sophisticated than they appear.

This may help visualize what your ECU is doing. This is real data from my personal bike when I was doing development work on it. The first chart shows data when the bike is pretty much fully tuned to my current hardware. The band that has been selected is a duration of 0.5sec. In 0.5 seconds It pulls my fueling, which at the start is 3.13% rich [(14.7 * (1 - 0.0313)) = 14.24:1], to 14.7 which is where both I and the ECU want it. The second chart shows earlier data when my tune needed quite a bit of work. The band there is 2902ms or 2.902 seconds. In 2.902 seconds the ECU is able to pull out 9% fuel, (started at 13.37:1). You can get the idea from this. The ECU will do its best to pull your calibration back to target when in closed loop. However, for those brief moments, whether it is 0.5 s or 3 seconds, your bike may be running rich, or lean. The time it is running lean won't necessarily hurt anything, but your bike will not be as response either. It will feel sluggish. The EJK can help offset this by pushing it into the rich domain through it accel pump feature and base adjustment. The ECU then will pull out any extra fuel resulting in a net zero difference. Through remapping I can better match your hardware to your bikes base calibration. I can also dictate when the bike will and will not be in closed loop operation.

The DNA is pricey. $124.50. I would assume removing the OEM mesh screen would have similar airflow (plus, OEM has 2X filtering pleats).
You can buy bulk Uni Filter sheets to use instead of a sponge. It may be more restrictive. Bulk Uni pre-filter material (BF-2/5) would be less restrictive.

https://www.denniskirk.com/uni/bulk...3YXf0r3Z5TEAm11mVNC4BcRt69Tltvr0aAt8SEALw_wcB

https://www.e-dnafilters.com/produc...&utm_medium=dnafilters&utm_source=w_dnafilter

Make: Honda

CC: 300

OEM Air Filter Air Flow: 101.20 CFM

DNA Air Filter Air Flow: 111.50 CFM

DNA Increased Air Flow: +10.18%

DNA Filtering Efficiency: 98-99%


Product Information

• 
  
  
  • This filter features DNA®’s advanced FCd (Full Contour design).
  • To install this new DNA Air filter follow the installation instructions included in the workshop manual.
  • A perfect airtight sealing and trouble free filter installation for the user is guaranteed by using a high quality EVA seal, which is precisely cut and factory installed (glued).
  • A specially made supporting frame is included with the DNA filter.
  • The filtering efficiency is extremely high at 98-99%filtering efficiency (ISO 5011), with 4 layers of DNA® Cotton.
  • The flow of this new DNA filter is +10.18% more than the stock filter!
  • DNA air filter flow: 111.50 CFM (Cubic feet per minute) @1,5”H2O corrected @ 25degrees Celsius.
  • HONDA stock filter’s flow: 101.20 CFM (Cubic feet per minute) @1,5”H2O corrected @ 25degrees Celsius.
  • This DNA® filter is designed as a High Flow Air filter for: ‘Road, Off Road & Race use’.

Coarse Uni Pre-filter material:


View attachment 3294961

The DNA air filter looks like a carbon copy of the K&N air filters I've used in the past. I do see that K&N makes one for the CB300R but not the Rally 300 (yet). Price is more realistic... potentially a future option if K&N is approached and begins production..

550Performance website link:
https://www.550performance.com/products/my21-ecu-tuning-honda-crf-300-l

Received my pre-filters, just have not installed yet.

Purchase options:

• https://cjdesignsllc.com/product/au1436pc/
  
• https://touratech-usa.com/Store/UNI-Snorkel-Pre-Filters-KTM-1190-Adventure-R-1290-SA
  
• https://www.uniflow.com.au/contents/en-us/p6160.html

Reusable zip ties: LINK

Review:

Sell it and buy a 650 whatever. Remember there is no replacement for displacement. Every mod you do to a 300cc makes a whole lot more difference on a 650cc.

Seems that way from the photos, however the K&N filter I posted which is used on the CB300R is intended to be saturated in K&N filter oil. I'm not trying to say this is better but it is not intended to run dry like the stock Honda paper filter.

I believe the DNA filter is also intended to be oiled.

The K&N filters are oiled, used until ready for servicing, cleaned, dried, and re-oiled before use.

I've used the K&N air filter for at least 100+ hrs (with multiple cleanings) in Glamis on a Yamaha 450 pre-fuel injection days with good success. You must be very meticulous with the use of this type of filter during cleaning, and oiling. Certainly not as easy as replacing the stock Honda paper filter.

.

The DNA filter utilizes a different filter media than the stocker…oiled cotton vs paper. The DNA website claims a 10% improvement in flow. However, I can buy a seven stock air filters for the price of one. The cleaning and re-oiling products are also pricey…

I had my ECU reflashed also by 550 performance...Maverick flashed mine so that I could still run low 87 octane (3rd world reasons)...
(BTW his 91 octane reflash means having to run premium as the fuel grades around here run 87,89,91/93)...

So your 38 tooth gears you up over a 40 stock...I can run 83 mph under normal conditions @ about 8500 rpm's.
Redline is 10,500 so I'm curious your reason for gearing up ?
BTW I am returning 71 mpg under normal riding and the computer say 72 mpg...so very accurate.

Hey Mcmann,what is your reason for gearing up from 40 to 38 ?
Thanks

The higher gearing makes first and second gear far more useful, particularly with the power gains I realized with my modifications. In addition, the vibration threshold (around 7000rpm) is reached at 3mph higher speed. Finally, the speedometer error is almost totally eliminated. It’s a great refinement for a bargain price: sprocket and new fasteners cost only about $35.

Ok..makes sense...I have a 13 tooth that I could always throw on to gear me back down quick if I find myself needing the crawling speeds...

Where are your sourcing the 38 tooth and bolts from ?

The 300L, especially in stock tune, doesn't need more air, and the OEM airbox and filter are NOT restrictive in any way. Adding airbox holes or those 1" UNI vent filters will not increase airflow into the engine. There's even YouTube videos and forum posts where people have added bigger filters and additional holes in their 250L airbox and measured airflow with NO difference; the filter on the 300L is even bigger than the 250L.

Adding a high-flowing DNA/K&N filter to these bikes is totally counterproductive. Unless you're chasing minutes running the Baja 500 and don't mind replacing the head/valves after a hundred hours, the OEM filter is the best compromise between air flow and filtration. Paying $120 for no performance gain and letting more dirt past your filter with a DNA filter seems ridiculous to me. Given the varying conditions these bikes have to put up with, and how lean they're running from the factory, I'd doubt that even a full exhaust and richer ECU tuning would require more air than the OEM filter is capable of. Money would be better spent on a less restrictive pre-filter complementing the OEM filter.

But that's just like, my opinion, man.

McMann can answer better than me, but the sprocket is made by JT and one of the contributors to the Owners thread gave me an Amazon link for the fasteners.

Was going to bore a hole in the airbox, with a 2" hole bit and replace the stock snorkel with a 2" flexible 90 degree plumbing pipe, but can't think of how I can gain access without removing the airbox... It will have to wait for another day.

I think the sponge in the air box is amazing. If I still did a lot of dirt roads/sand I'd do that with just a hint of filter oil on the sponge. I've ruined engines with K&N filters.
Thanks for this dedicated 300 performance thread
I just purchased the 91 octane reflash of a '17 250 spare ECU I had. Maverick said it would be OK.
I think that snorkel air prefilter is clever as hell also. With a strategically place hole in the bodywork, servicing it might be quick.
In the very early days of the CRF300L/Rally Owners thread there was a Thai video on a replacement pipe from the air box to the engine. Mega power increase was quoted. Has anyone seen more info on it?

Yeah you have some good ideas there - given how susceptible our bikes seem to be to getting a large amount of dirt in the OEM filter. I was considering those KTM pre filters that fit in the snorkel, but your flat foam idea looks good as well. I might try that; beats replacing the hard-to-get OEM one every 1000 miles.

Clever business, but not advised for deep river crossings