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440 bore vs 426 bore

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Hi all, I have 2000 xr400 That i would like to bore out to a 440 or 426. I have never done this to any of my bikes and would like some feedback on this. (eg, over heating,how much hp power,life of the cylinder after the bore and general overall reliability of the 440 or the 426 ?

Thank-you for your replies. :cry: :canada:'A

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Just got the 426 with 11:1 compression done. I've put 60 miles on it.

HOLY CRAP! Its so awsome. Huge increase in horsepower. I kept stalling because I'd wack the throttle, and it would stand up, and I'd fall over sideways. It pulls longer and earlier in each gear, which makes them feel much wider. It made me faster on a lot of trails.

Starting is a one kick affair, even cold. It can be a little tough to kick though occasionally.

Heat... my bike got hotter than it used to, but it doesnt seem too bad. I'll probably see about some bigger cooling fins and a temp dipstick.

Reliability is supposed to be on par with stock. I'll tell you in a few thousand miles though [:cry:]

Anyway, its totally worth it. I love mine. I've got to go check the sparkplug now, because it seemed a little lean. That might account for the increase in heat.

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Dwight's answered this one a hundred times so I'll help him out.

The 440 has no overheating, reliability or other issues. It's a great way to make a monster out of the 400. It kicks butt. But........you have to sleeve the bike. Another option to gain h.p. is the 426 kit that me and a few others have had Barnum and other shops do. It requires an overbore, but is cheaper than the 440. I started with the 416 then went to the 426. The 11:1 compression piston runs great on pump premium. Either one of these kits gives great performance with no sacrafice in reliability. The 440 definitely has more of a kick than the 426, but not that much. There's no substitute for displacement.

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That was keithco, but....

There is a cylinder sleeve. Basically a round tunnel thing the piston goes up and down in. In order to get a bigger piston (increased cc's) you need a bigger sleave. You can "bore" out the current one (basically drilling out material) or you can get an entirely new one set at 440 cc's.

I went 426 because I didnt want to buy a new sleeve.

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So I can use the exciting sleeve and bore it out to fit the 440 piston. Is there any worries related with this or is it best to press a new sleeve into the cylinder so you have the correct wall thickness instead of thinning the orginal sleeve? :cry:

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Resleeving is a safer way to bore out to 440. If you bore the stock cylinder out to 440, the cylincer walls might be too thin. So, with the sleeve you have a stronger set up. Then, if you have a problem, you can resleeve. The main reason people go with the 426 over the 440 is expense. Well, there's some other reasons as well. But for the sake of time, I wont go into em.

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Okay Kiethco, remember you you opened up this can of worms. :cry:

Why would people go to the 426 instead of the 440 kit disregarding the expense? Why i ask because i have just ordered the 440 kit for my bike. I have looked into this for a bit and came to the conclusion that i would do 1=440 bore kit 2=aftermarket exhaust 3=re-jet the stock carb. If you have a moment I would like you to explain the reasons where the 440 bore has it's down falls so i might be-able to prevent future problems. And thx-you in advance :cry:

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If you havent put an aftermarket filter, pulled the snorkel and the baffle, and rejetted, there's no reason to spend money on a big bore. If you havent done this yet, DO IT NOW.

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I have done those suggestions, and thx-you for them. I guess why i want more power is that i sold my wr426 with every thing done to it like exhaust,jetted,air filter ect,ect. I bought this bike from a estate sale for so cheap that i couldn't pass it by. So here i'em jumping with two feet to make the bike my own. Also I have installed a street legal kit and want some more top end.

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The 426 really, really increased bottom, with (of course) some top as well. Actually, it feels very similar to a WR426 I rode (jetted, piped. See my mods also, in sig), except it hits way earlier. The WR seemed to have more mid and top, while my bike is all bottom. Suits me just fine :cry:

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Ive heard that the 426 kit revs faster than the 440 kit. I think I heard this from Barnum but Im not sure.. I got the 426 in my bike like a lot of others and really like it. Ive actully beat a crf450 with it but there might of been other reasons why I won. Makeing the same power as a wr426 would be about right. So far this is the best mod Ive made to my bike. So why dont you join the 426 club :cry:

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I have a XR250/300 and 2 XR4's one 416 and one 440. Both are ported. The 440 is noticeably more powerful, but I don't think you would be unhappy with either one. The 440 I have was built for a sponsored XR's Only rider and it has everything including the addition cooling fins welded to the head. I've head that cooling can become an issue. Call Gary Hazel of Thumper Racing and he'll give the pros and cons of each choice.

RH

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Speaking of extra cooling, what options are there?

Ride faster!

You'll be happy with the 440 kit. I think Rob likes to do the 426 kit because it's what he sells. That doesnt mean he doesnt like the 440 kit, he'll do either one, or sell you the parts for both. Rob uses his experience to tweak alot of power out of the 426, I have porting, valve work and carb work. These all make any 4 stroke much more efficient. Like I said earlier, and you old street racers and hot boat guys know this, there is no substitute for cubic inches. The 440 kit gives you more motor, period. It's just not the only way.

OK, who'd idea was it to open this can of worms. I swear I can see D'wight back there laughing. :cry:

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I went from a 400 to a 416 and now i just got i back from a boring it out again to a 440 ( broken timing chain so i figured why not bore it out again if i have to replace the piston anyway?) I have put about 15 hours on the 440 and have not had any problems. It has alot more snap then the 416. YoungGun sorry dude I also have a Wr426 ands its quicker then my XR. Its also got the same lowend power but keeps its grunt all they way up to 11,000.

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I've got the 440 kit with mik pumper, and a WR400 bumped to 444

down low both are close, the WR has more though, lot more snap & throttle response, and the WR will keep pulling a LOT farther into the RPM range.

I only have the XR440 because it came moddified with street plates (very hard to get in georgia)

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I rode with a crf450 set up for the woods and it just didnt seem like it had all the power as people make it sound. My brother rode it and said it felt like mine without the extra weight. I havent raced a crf450 on an actual track since my motor has been bored and I was keeping up and passing them so I just guess the xr fits me the best and that is what Im fastest on. :cry: I had a chance to trade my xr in on a yz426f and didnt do it because it wasnt the bike for me at the time. The KTM 525exc is looking pretty good now. :cry: Maybe in a couple of years. :cry: But back to the real question. Yes the 426 is a good kit. :cry:

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I believe I could keep up in terms with outright acceleration (ON FLATS) with a CRF450. I was NEARLY keeping up before. On hills, I'd still be decimated. They do still have 10+ more horsepower.

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Crf450 still only has 40 something hp and the cr250 just has a little over 40. Maybe 42-43hp.

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