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500 power in a 250

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Saw this on ebay. If I wasnt closing on my house thursday id buy this for shure. Real rare parts. How often do you see a stroked and psi kit together. Stock engines go for this much with out all this extra stuff.

http://www.ebay.com/itm/YZ250-Engine-w-psipowerinc-genesis-440cc-top-end-CR-500-YZ-250-450-/220941650842?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item3371260b9a

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Very cool, didn't know PSI made anything for bikes.

Not a huge fan of that powervalve setup for bikes, but I'm sure it more than makes up for it with displacement!

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I wonder how much power it makes, it looks insane. I wish he listed the meaurements and if it took a standard piston.

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This would work for the EG 295 kit also

fmf 500 silencer so this motor can breathe

pipe with oversized stinger

That looks like it will drop straight in to a humble YZ frame.

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How do you think the crank would hold up? Seems like it would be an aweful lot of force on a crank not designed for it.

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Crazy!

Unless it's a stroker, to make 440cc displacement that sucker has to be an 88.2mm bore. That is just MASSIVE!

They must have rebalanced the crank to work with such a massive pistion. No way you can make a piston that big anywhere near the weight of a stock 66.4mm pistion.

Adam728, It wouldn't be all that tough to build a programmable electronic controller and servo-motor for a powervalve like that.

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Crazy!

Unless it's a stroker, to make 440cc displacement that sucker has to be an 88.2mm bore. That is just MASSIVE!

They must have rebalanced the crank to work with such a massive pistion. No way you can make a piston that big anywhere near the weight of a stock 66.4mm pistion.

Adam728, It wouldn't be all that tough to build a programmable electronic controller and servo-motor for a powervalve like that.

Auction says it's a 4mm stroked crank.

What I meant on the PV is that it's controlled by vacuum, plus you lose your two sub-port barrels. It's better than no PV, but not as advanced as the stocker.

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Auction says it's a 4mm stroked crank.

What I meant on the PV is that it's controlled by vacuum, plus you lose your two sub-port barrels. It's better than no PV, but not as advanced as the stocker.

I missed that part about the 4mm crank. That's still a massive piston. 440cc works out to 85.9mm x 76mm

I was thinking the same thing about the vacuum powervalve. Some of the snowmobiles (Ski-Doo) use this type and still have the sub-ports.

I haven't seen those cylinders in person, but What I think they do is use a wider PV and route the sub ports so that they blend into the main port sooner. The main valve is wide enough to block the sub-ports when it's closed. That's still not a two stage deal like the stock YZ system though.

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Interesting... but.. if you are going to go to the trouble of frame mods and custom engine parts why not go with a 4t chassis and bigger 380/500 ktm/honda/kawi stock engine.

Parts availibilty on that motor would worry me.

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I'm thinking that a 4mm stroker on a 295.....=310.....maybe the perfect size bike

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The only thing I don't like is when you click to enlarge the pics they don't get any bigger. It's so sexy it would be considered porn I guess. That's cool.

Craigus

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I'm thinking that a 4mm stroker on a 295.....=310.....maybe the perfect size bike

That would work out to be a 310cc. It would be interesting to know how much the porting layout would have to change to make that work.

The interesting thing about the stock YZ250 cylinder is the piston covers about 2.5mm of the bottom of all the ports even at BDC.

With a 2.5mm stroker crank and a KTM rod (129mm vs the YZ 125mm) you would have nearly identical rod/stroke ratio to the stock setup.

Of course you would have to use a cylinder spacer of approx 4mm as well.

Displacement would go from 295cc up to 303cc

The port durations would increase a bit, I don't know if that's a good thing or not, but here are the numbers:

Stock YZ250:

Intake ~ 114.5*

Exhaust ~184*

2.5mm Stroker (with stock ports)

Intake ~ 122*

Exhaust ~ 188*

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I asked him a few questions and here is the response:

"4mm stroked crank, rebalanced, stock crank with KTM 300 rod. will handle with no problem"

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