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Anyone have experience with both a 2024-2026 KX450, and '25/26 KX 250 with a Vortex, full PC exhaust, Airbox mod and possibly some gearing?
I am still on the fence about downsizing from the 450 to the 250. Hoping these mods might offer a good middle ground between the stock 250 and stock 450. Looking to get as much extra power out of the 250 as possible without getting into engine work territory.
Really just looking for some feedback on how much extra low-mid can be achieved with the above mods alone.
Response is better with these mods, but it still ends up being a slow-revving character when compared to most 250s. It's smooth but not exciting by any means.
If I were pointing a rider towards a 250, when coming from a 450, the YZ250F is the obvious direction. The CRF250R is also pretty good and both bikes mentioned respond better to the changes you're discussing.
However, if you're dead set on a KX250...yes, those items will help, but I don't know if you will fully be satisfied.
Have you ridden a stock 2025-26 KX250?
What about the BETA RX350 Two Stroke? Dunno if you've a dealer close by.
Not a Kawi guy but thought my input may still give perspective. Running a YZ250F with hi-flow intake, larger lid, 4.1 slip-on, Vortex with TD dual Injector (21-23 gen) and fuel. Had thought about maybe going to a YZ450F for the next bike. Rode the current-gen 450 back to back with my bike and it's still quite a big difference in the amount of power between the 2. Even with the 250F making noticeably more power than stock, it still feels much slower than the 450 and needs ridden like a 250F. I liked the 450 a lot and would probably get used to it and really like it. That being said, I still think the modded 250F is still where I will stay. Basically, my point is that even a modded YZF is not going to bridge that power gap too much. But it does give you some more power to use, if you are using all of it. Verses a 450 where I'm not using anywhere near what it has anyways, so I'm not sure I personally am rewarded with the advantages that a 450 has to offer over the modded 250F.
I’m a 450 guy(kawi) but rode my first yz250f the other day. I had my expectations way overinflated. I had ridden a 25 kx250 and was expecting the yz to be night and day better motor wise than the kx250. I don’t have enough time on both bikes to actually form any real opinion but from 7-10 laps on each bike all I can say is both felt dog slow coming off a 450.
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I have a 25 KX250 and I’ve only ridden it once, got my 2nd break in ride coming up this weekend.
So far I’ve only drilled the airbox cover with holes but after this second break in ride in I’m going to install my full PC exhaust, Twisted Development Vortex ECU, Twin Air airbox kit, and VP T4 race fuel. Also I run a 51T instead of the stock 50T sprocket.
I’m excited to feel the difference vs stock. In my opinion, if you’re racing C or D class, you’re either going to be fast or you aren’t. A 450 isn’t going to magically make you win. Neither is 2-3 more HP. The key is making the bike as comfy as possible for YOU.
I’m 200lbs, so everyone would say I’m too big for a 250F. But I enjoy riding a 250F more and I don’t get to ride but once a week so if I can get more laps then that works better for me. If I have to ride a 450 to win the Unlimited C/D class then I shouldn’t be on a 450 to begin with imo.
Also it’s funny everyone says the kawi is kind of slow, just because it’s not as fast as the previous year model 23-24.
Its actually not far behind the KTM/GasGas and slightly ahead of the Yamaha in terms of power.
Kind of a middle ground bike. Throw some mods at it and you’re right up there with the top bikes power wise.
and I know peak HP doesn’t really matter but even comparing the KX numbers on the first chart, it actually stacks up pretty well.
Thanks for taking your time to provide your insight, ML. I’m thinking about a new 250F and these are the three at the top of my list.
250f’s rule, regardless of color. Enjoy the small bore!
when it comes to HP .... there's no replacement for displacement.
I am curious how that PC 250 that was at the '26 intro performed. Keefer and MXA said it was much better with only a remapped ignition (IDK if it was stock or vortex), PC exhaust, twin air powerflow kit, and a PC high compression piston. I would like more of a detailed review for it.
It was a ton of fun. That’s all mxa said lol.
We have one with a PC Full System, Twin Air Intake, Twisted Vortex mapped for Pro6. It’s decent, but definitely not the same as a 21-24. I am a die hard Kawi guy and prefer the 250s as well, but IMO it needs more power even with those mods. A HC piston would probably help, but it’s a ways off my 24 with the same mods power wise.
FYI, for you all that have Twin Air Intakes, we just finished the airbox wash covers for them.
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The best mod to my 22 YZ250F was a 24 300SX. Lighter, more agile, smooth power and turns without push or tuck. Shoot, my mod'd/upgraded 200SX has parked my F'er in the garage.
The issue with the RX350 is that it won't require $2k in engine mod's and have $2k repair bills. Lets ponder what could go wrong with making a 250F run harder...
Dude, unless you are light in weight the 250's live in the revs. Why not a 350SX or 300SX. Too much engine breaking on the 350 for this Smoker. My 300SX is lighter than my YZ250F and the power is as easy to ride.
Did you go up to a 51 or 52 tooth sprocket? Helps a ton in my opinion.
If it feels any faster than my roached 2020 I’ll be happy lol
Yes, went to a 51. Haven’t tried a 52. The chassis is must better and it does turn better but the power is definitely different than the previous gen
Haven’t tried the 52 either but I really want to.
And that’s interesting to hear. I’ve ridden people’s 22’s and 23’s and always liked them aside from their suspension being too soft for me.
I’ll take your word for it and the testers that it’s a little slower than the 21-24’s.
My 2020 was fun but tbh I felt like it was kinda slow unless I revved the shit out of it. The 25 with a little more torque may be what I’m looking for.
Haven’t tried a HC piston so that might be something I do around the 40 hour mark
Pit Row
That’s wild man. It always perplexes me why manufacturers feel the need to change a good thing. For 25 they should have just did the chassis/suspension not changed anything else.
What year is your YZ ?
I recently rode a 2025 yz250f with an Dual injector kit, XPR vortex, FMF full pipe, and T4 back to back with my stock 25 350sxf. Like others have said, the 250 still needs to be ridden like a 250. However, I will say that bike felt so lively and awake, I was actually shocked. It was a blast to ride and felt so light and flickable but if you want to ride it fast you will be shifting it. The 350 feels more like a tamed down 450 to me.
The thing was so fucking loud it was hurting my ears also. No way I could ride that bike w/o earplugs. If I was going 250 route I'd deff go w/ the yamaha and a vortex setup.
Hey All!
Been a while since I was able to get back here. Thanks to everyone for posting their experiences and opinions. I have NOT had an opportunity to ride a newer 25+ KX250. I do have a couple of hours on a '21 KX250 with Vortex that my nephew raced for 2 years.
I recognize that not everyone will agree with this approach - but I am seriously considering the 22+ CRF250r alongside the KX250. This is because with the CRF250r I can get an Athena 290cc kit. There is currently no 290 kit for the '25 KX since the engine was redesigned for the '25 model year. Only up to 2024 is available for the KX.
I am fine with the spending the money on a big bore kit, but I do not want to get into porting, cams, etc. I would run a full exhaust and the mapped GET ECU available with the kit.
Bit concerned about the KX's more lethargic feel off the bottom. I would like something a bit more exciting than the 24 KX450.
Kawi is rumored to release a KX 325! Which I could see that likely being based on 250 cases. This could show up before you dial in your kitted CR.
My 250 is the prior gen ('21) but the 450 I rode was the current one (I think '24 or 25).
To the OP, the only thing I sometimes worry about, going that big bore route, is if the bike loses that light rev that makes 250s fun. I guess I just don't have experience with big bore, as each time I threw money into a 250f it was something like this or a GYTR kit etc. That being said, I tell myself that I'm just going to get a 450 next time and then I can leave it stock. Maybe I will finally do that. But modded 250s have sort of been my sweet spot lately.
Omg just ride the damn bike. Inhectors ignitions airboxes? On a bike already close to 10k. And you wont ride any faster . The A 250 class must be tough where you race
Coming off a 125 it feels fast lol. XPR has a template for the airbox cover holes on the site. I’ve been running keefers map and a Rev3D screenless cage with twin air filter. 116L chain with a 51t rear sprocket. Chassis feels nice and planted. For the price I think it’s a hard bike to beat.
Here's an option for you:
Right! but but... nah, way too much investment that usually gets sold off bc it still isn't what you were wanting. IMHO, if you're no longer on a 250cc and racing is a focus. It's best to start smoking with a 250, 300 or 350RX(Beeetah). Preferably carb'd for convenient and cheap tweaks for response and desired powerband.
The kawi is a good bike but you should ride the honda before you make a decision. We were set on switching to the kawi from yamahas, couldnt get a kawi at the time so went with the honda and he has been VERY happy on the honda. The first thing he said on day one was this is the easiest bike to turn ive ever ridden (excluding 125's). Hes been able to get really good starts as well and the bike looks fast. I know what the dyno says but thats not what translates to the track in my opinion. Aside from all of that, as the mechanic, i am very pleased with the honda build quality. Its a solid and well thought out bike. This is the first honda ive owned since the 06-08 generation 450.
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