2015 WR250R big bore

Anybody know why Athena's big bore kit only includes 2008-2013? What options are there for 2015 big bore?

Same same...

I am thinking about getting the same kit. just trying to get some more feedback on it, look at some reviews. also see the pros and cons about installing the kit. do you know how much Hp and Torque gain from the kit? I also read a review about the athena big bore kit, that we also need a black box on top of the kit which for black box he says its $500. I think he is referring to the ECU.

They just haven't updated the application charts.   The kit fits the 2015.  The full kit comes with a controller that's not adjustable.

Thumper racing also makes a 290 kit if you call them. It's not on their website. They have a piston made for them that is lightened. It's only a few grams heavier than stock, which makes it closer to the factory balance. It's less buzzy up high than the Athena kit by all accounts. You can send your cylinder in to be worked on, so it's less expensive than the Athena kit. Does require a programmer though. They have options for that.

If you already have a programmer, you can send it to them and they'll reprogram it to work with the larger displacement. Dobeck does the same thing. If you have an FMF, EJK or AFR+, you send it in and they reflash it to work with the displacement.

+1 on the thumper racing, they're customer service had me sold

IMO only go with the 280 kit its much cheaper than athena, makes the same horsepower and retains a plated cylinder and a low mass 3 ring piston just like yamaha intended!

Thumper's 290 kit is a bit more money, its only made to order so its always a few weeks out and its an iron sleeve, I believe they want a core before they start mean while your bike sits disassembled. With the 280 kit you send the stock barrel back when the 280 arrives.

Per their website and speaking with them, the 280cc kit uses a sleeve, and the 290 kit uses a plated cylinder unless they've changed that to a sleeve also. They work with Dobeck or the other controller manufacturers to get a tune for it. The big bore kits only require remapping of the fuel to work with the larger displacement, and the Power Commander can also adjust spark so it can be tweaked a little more.

Per dyno graphs I've seen and people I've spoken with, the 280 kit is 4HP everywhere pretty much. The 290 kit adds a little more. Either big bore kit can be used with the stroker crank and the 290 kit will yield 306cc.

There's a local guy that purchased the 290 Athena kit with a new bike a few years ago from our local shop. The shop guys told me he's happy as can be with the bike, and he's put a lot of miles on it. I still haven't met up with the owner yet. Still uses the stock muffler, just wanted more grunt for road and trail. He just had the local shop install the Athena kit with the included controller. Didn't do other power mods.

I'm really wanting to big bore my bike for some more trail grunt, but the main thing is I want a little more oomph to pop the front end up over stuff. Just want to be able to get the front end light over junk in the trail and bumps. If I could lift the front end up with throttle when I needed it, that would be great.

Still think that Yamaha should have built a 300cc version for the U.S. market.

when I spoke with thumper back in september I was told the 280 is plated and the website now mentions it, the 290 is a still a sleeve because they cut into the water jacket.

both of their kits keep engine vibes down

They've changed it on the website. I was looking at it a couple months ago and it was still showing them having the customer send in a cylinder to be sleeved with an iron sleeve for the 280 kit. I was told the wall gets a little thin to be boring and replating when I spoke with them last.

I've seen the Thumper Racing piston used in the Athena cylinder also. That's a different cylinder than the stock Yamaha, and is cast to be a big bore. Still a plated bore.

Whichever way you go, it's still a better power curve, no doubt.

Going to call them today and talk about their options. My wife said she wants to get me something neat for Christmas, and I'd love to have the big bore kit.

I love mt Athena 290cc Kit. It makes a huge difference in ridability.