Honda CRF 300 Rally Airbox modification

Fitted the connector pipe and after a good few hours of riding on and off road I can say it has made a difference, not a great deal of power, but it has made the engine livelier, more perky. It breaths better and therefore is a good deal more responsive.
Take your time and this is not as difficult as others say, it is just that there is no manual :)
Did a few non scientific tests with a friend on a stock CRF300 and there was a pick up difference (we did before and afters...).
So, worth it?...Yes, 100%

[@dodgierogie68]

i have the cbr intake but i ended up cutting the original tube flush on the inside of the airbox,was a def improvement,im running the 550 stage 1 and black widow muffler

[@jeffwkirby]

Yes, I considered cutting off the inside but I wanted to maintain the profile of the cone which should help improve 'velocity'...but as you say, an improvement for sure.

[@Impedancenetwork]

I just did this modification tonight. Man that was a miserable experience. I had to put a lot of downward pressure on the throttle body and at the same time push up and forward on the air box then I had to put a bolt in the airbox mounting hole to keep the airbox in place while I push the CBR air boot onto the throttle body. Man what a pain in the ass! It took me an hour of pushing, turning, contorting, resting, grabbing a beer and trying again and again to get everything lined up. I finally got it, but man it would go so much smoother with someone putting the bolt in while you push the airbox and the throttle body. I only have two hands but you need three. While you have the bike tore apart you should block-off the pair valve, remove the evap canister/Air Injection solenoid and the Evap purge control valve. I weighed all that and it was 2 lbs of environmental garbage that is not necessary. I blocked off the pair valve with the 550 performance block-off plate. Installed the stage 1 ECU and the Yoshimura exhaust. I also removed the snorkel off the rear air box and installed the high flow reusable air filter by 550 performance. I definitely noticed a difference in my bike's top end speed and the acceleration from zero to 70 was faster. I'm not sure if all my effort and money was worth the small performance boost. It's not huge but you will notice better performance. With the RSC clutch lever, double-take mirrors, hand guards, crash guards, skid plate, Yoshimura full exhaust, Fancy decal kit, Yoshimura tail tidy, red anodized zeta foot pegs, Lithium Ion Antigravity battery, front and rear LED turn signals, tail luggage rack, race tek suspension, I have spent $4550 + bike $5400 = $9950. If I were to do it all over again I would have just bought the CRF500L and fixed cutting out issue with a tune. I did not enjoy that airbox modification.

[@jeffwkirby]

Agree with all that you wrote. I did have help! As for the spend...the same for. Spent a fortune but I do enjoy the bike.

[@240LTS]

... I am getting ready to do the CBR intake mod and I also am not looking forward to it. I thought it was this video where the gap that fits onto/into the air box was widened to give the boot more play/space to be tilted down to fit w/o so much tension? I have watched so many videos on this I can't remember. . I received the Yoshimura RS4 full exhaust, 550 Stage 1, (91 octane). The DNA air filter and service kit comes from Europe and was stuck in customs for a while. Still haven't received it. Supposed to be here this week. . "While you have the bike tore apart you should block-off the pair valve, remove the evap canister/Air Injection solenoid and the Evap purge control valve." That makes me nervous not fully understanding all of it. I know Jake the Garden Snake did a video on it. Does removing all that really make a difference? Yeah, I'm a little concerned doing all this. I hope all this $$ and time is worth it. . Jeff.

[@jeffwkirby]

@@240LTS good luck!

[@stuivey1]

Hi mate , was there a part number on the velocity stack. I want to send my ECU off to Maverick just wondering if you did ? An who you sent it with from the UK ?

[@jeffwkirby]

Sorry for the delayed reply. The stack can be ordered from Maverick as well, details are on his site. As for shipping, I used DHL. Cheap and reliable.

[@overlandmotorcycletours4785]

Hi thanks for sharing this, is the new inlet pipe from a CBR 300 ?

[@jeffwkirby]

Yes, I got it from 550 Performance in the States. Worth looking at their other parts as well.

[@overlandmotorcycletours4785]

@@jeffwkirby Cheers ill check them out

[@dgrig2]

How did you grind/cut the diameter of the new tube to fit the original airbox hole? I like that method vs cutting the airbox.

[@jeffwkirby]

I used a Dremel with a small grinding disc, about 3cm in diameter. It really is very easy, just go steady. I practised on the old tube first. To enlarge the hole in the air box, same Dremel, fitted with a small routing bit. Slow and steady, keep looking as you can't put it back on!!

[@dgrig2]

So what was the final dimension of the whole on the box?

[@dgrig2]

​@@jeffwkirby Watched it again and around 58-59 and a bit oblong. Thanks this is a helpful vid.