Larger motors in big red 250

[jeffatc250r]

Who's done it? Pros and cons? I know the 300 can go in with an output shaft swap. Any other options? 400 350?
Im only asking because id like a lil more go outta mine, its really my only hangup with the machine. And no, it isnt all worn out, its actually a low hr rig.
So does the 300 really make a difference?

[6speedthumper]

I've never done any swaps with this bike, and don't know of any others besides the Fourtrax 300 engines. If more go is what you want, why not look into the big bore kit offered by Fourstroketech? I believe theirs is a 310 big bore, they offer cams, can port it, and with a good exhaust and carb combo it'll really wake up. Hell, just a better carb and exhaust would make a nice improvement in the power department. I want to say that FST even makes a big bore/stroker kit, too.

[jeffatc250r]

Thanks, ill look into that. Id like the exh to stay, kinda a key part of the rig being stealth

[kebby28]

I have heard of people putting the 300 fourtrax in but have never seen the bikes complete or whether or not they liked it. I am interested though...

[Afrothunderkat]

Thanks, ill look into that. Id like the exh to stay, kinda a key part of the rig being stealth

Ohhhhhhhhhhh, so sneaky.

My big dick loud exhaust got rammed off. Got a stock pipe on now. Time to join the sneaky club.

[aldochina]

I probably have a few top ends floating around if you want to play with a bore, port and cam. Keep your low hr stuff original.

[dustrunner]

just wondering if a 300 piston and top end would be a direct swap ? or how about a domed piston on the 250 ?

[Mickey Dunlap]

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[big specht]

http://www.fourstroketech.net/#!__pr.../vstc1=atc-250

Here you go Me and kizer were just talking about the big reds just needing a little more power on the hills . I would keep the stock exhaust too. I like it being quiet

[kebby28]

http://www.fourstroketech.net/#!__pr.../vstc1=atc-250

Here you go Me and kizer were just talking about the big reds just needing a little more power on the hills . I would keep the stock exhaust too. I like it being quiet

Thank you and Mickey. I have been wondering about this for a long time. Now, they only list it for the sx here. Will that work for my es?

[Mickey Dunlap]

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[big specht]

I wonder how hot it will get when doing woods riding or crawling in the rocks. I know mine gets hot sometimes when woods riding. How big is your big bore?? and does this require any case clearanceing ???

[Mickey Dunlap]

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[dougspcs]

I've been quietly following this thread along and I like some of where this is going..maybe a project for the future.

Now Mickey brings up a good point about the oil cooler..it's always been my concern that the SX/ES didn't have one. Now under most riding conditions this engine stays comfortably in the Goldilocks zone..but under some extreme condition like the day long mud events I like to do it could really use one.

I've finished out my days ride with the engine fins so packed with mud you can't even see them..and after the mud has hardened and dried I know the engine is stressing and hot during the 8+ mile run back on the road from the trails.

Anyway, my question..anyone have pics of how they have adapted a cooler to the ES/SX engine? Or have a link to a kit to fit it? I searched the previous threads and found lots of talk, but no real detailed information.

Engine upgrades or not, I want one or two!

[Canyon Man]

I love where this thread is going. I will be ripping my 250 es apart soon for a rebuild and the timing is perfect for this