310 Big Bore performance

Anybody tried the Luke's racing 310? As I understand it, the 290 hurts the over-rev capability of the 250F engine but it also give much better HP gains than the 263 kit. If you add the stroker crank to the 290 you get something like 310. So I'm wondering if the 310 is the best way to go if you are looking for the best overall performance. I read that the Thumper racing 320 on a CRF250F was the best overall kit for the honda in Motocross Action I think it was. They compared it to a factory 250f in performance. So if I bolt an Athena 290 and the hot rods +3 stroker on my WR what else would be necessary to make the engine scream? Bore the carb? Stage 2 hotcams? Porting? Or would the perfomance with just the Athena and stroker be a big gain across the power band. I'm looking for performace that will keep up with the 450F's and KTM 300's in hare scrambles racing. The real question is does the stroker bring back the ability of the engine to rev out or does it take the other mods to do so?

Thanks for your help

I have not done it but have been reading up on it. With the stroker you need to change the ignition timing and mess with the carb. You will also need to look into porting to allow more fuel/air the engine will need. Try talking to Jesse Williams and see what he has done

The article on the TR 320 was actually in Dirt Bike. But the more I read the more I am leaning away from the steel sleeve path used by Thumper racing. Why not use the new technology if its available? Going steel sleeve seems like a step backwards. Then again as far as plated bores go, some of the kits on ebay say they have "custom or re-cast" cylinders but I think they are just overbored, replated yamaha cylinders. On the Honda, from what I have read here on TT it sounds like you can't go over 263 and have any reliability with a bored re-plated cylinder. On the yamaha I don't know, but would err on the side of caution and go with a cylinder designed to be a 290. I'll give Jesse a call as you suggest.


i have done 263s and 269s on kxfs, but to do that much work why? just get a 450 it would be cheeper and have better relability.

It could all be done for less than a grand if cams or porting aren't necessary. Saw a kit on fleabay for $750 so the cost is not much (I will do all the work myself) The extra power would not be the "rip your arms out" kind of 450 power and the bike would be lighter than a 450 and should be much easier to handle for an hour long race. All the same justification KTM had for building their 350. I just don't want to put all that effort into it and end up with a tractor or an out of balance engine.

The WR seems to be very reliable, my motor has probably 80 hours on it and the valves are still in spec. I don't like to highly modify engines that much based on lots of bad experiences. The big bore seems like the easiest approach without ruining the reliability. There are tons of kits out now. Saw a 288 today which was a 263 big bore with the +3 hot rod crank. That may be a better setup than the 290 or 310 since the piston is smaller and the engine should still rev well with less vibration and balance issues.

From what I've read, you will want to send the crank out to get it balanced or risk vibration issues.

using an ductile iron liner is not backwards technology.the iron liner will hold a more precise shape when under stress and having it nikasiled prevents wear also there is less heat generated to the cooling system and more pushing the piston .it does add weight .

Cylinder Works 262 kit plus a hot rods +3 crank =285cc for $775.00. The piston is smaller than a 290 so you keep rev capability of the 250 engine but still get the added displacement. Anybody tried this combination?

I'm sure someone has. I see post on TT from ten years ago about big bore kits people are installing. But never seem to hear how they worked out other than "awesome power" etc. So I guess they all worked out pretty good, If they had problems they would sure as hell be complaining.

check this thread: http://www.thumpertalk.com/forum/showthread.php?t=112366 It's old and TR probably fixed the probelms with iron liners they had back then. But I never said it was backwards technology, I said it seemed like a step backwards, meaning its been around since dinosaurs roamed the earth. Still Cisneros makes some good points about the liner. I looked around the TR site and couldn't see anywhere that they say they nickasil the iron liner. Guess its an option and could fix the honing issue Eddie brings up as well as add longer life to the bore.

XC, all things being equal, the stroker will tend to make the engine more of a tractor . More pull off the bottom with less and slower revs.

I had a TR big bore kit in a DRZ400 that was un-plated iron. The cylinder got a ridge worn in it very quickly. It should have been plated.

I emailed Hot Rods last week and asked them about the ignition timing and balancing. The answer was, No, the stroker crank does not change the ignition timing or the camshaft timing. It does increase compression by about .5 and Yes, the crank is balanced from Hot Rods for the stock piston but you can have it balanced if you use a different piston for better performance.

Cool! That's good to know

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