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05 450exc big bore kits

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Thumper Racing sells them. You can also put a 525 cylinder and piston on a 450EXC to make it a stock KTM big bore.

Ed

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Anyone know of a site that carries bore kits for exc's?

+! thumper racing , had a 570 kit on my ATV (99mm jug stock stroke) power was incredible , i can't imagine that on a dirt bike.

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Thumper Racing sells them. You can also put a 525 cylinder and piston on a 450EXC to make it a stock KTM big bore.

Ed

Thanks I've thought about doin the 525 jug and piston. But. I was just wondering what kits they made.. if you put a 525 piston and cylinder on do you have to do anything to the head? Valves, cam ect.

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No they use the same head,valves and cam. You can upgrade any of them if you want and you probably should do the intake valves anyway. You can also use the stock head with the Thumper 540 or 570 kits if you want.

Ed

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Sweet thanks I'll look into that. Do you think it would be a cheaper route for more horsepower to go with the stock 525 piston an cylinder or but a bore kit?

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Cheapest way to most power is to get a 560 (100mm) piston and have the 450 cylinder resleeved with steel sleeve. 100mm sleeves are plenty and just about any engine shop should have them around, a car or tractor sleeve is just fine. Thumper racing 99mm is probably the best option because they use plated aluminium sleeve (99mm is pretty much the biggest you can go with aluminium since cases are 104.5mm), but it requires special 99mm piston which can not be bought from ktm (bought from thumper racing). I wish they made bigger pistons, 100mm stock ktm is the biggest available as far as I know. 560 cases have a bigger hole (107mm or something) and they'd allow use of bigger pistons.

Before you do anything for the head, you'll have to have at least 41mm carb or it's just waste of money. Also stock cam pulls way too low. I'd way leave the head alone, just not worth it. A stock 560 is scary as hell already and it has the same head as exc.

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I looked into this too and am going to go up once i decide its time. I have a 525 which is actually a 510-dont know why they call it a 525, the 540 is a little more than the 525 for power and the 570 is supposed to be about the same amount more over the 540 as the 540 is over the 525. 570 is a power house, 540 might be what Im looking for.

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Well crap my 450 has plebty of good power, and the 525's are a powerhouse.. a 560 or a 570 has got to be awesome :thumbsup:

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I think when mine (2007 525EXC) needs to be rebuilt I am going to go with KW valves,540 kit,a 806 cam and get the carb bored to 41mm. I think that may be what I'm looking for.

Ed

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