engine mods

[riderssb250x]

hey guys what do you think about these engine mods for a 250x the fst 288 kit i belive with a sleeve a 400ex carb and a hotcam? how will this work will i gain alot of power or do i need a port and polish? also if i went with a 330 sleeve for the 250x what would i need other than it like could i use stock valves and springs?

prety much i wana do a bore kit a 400ex carb and a hot cam but dont want to do valves springs and a port and polish how will this run?

[bwamos]

I think that's what you are already looking at. The 292cc kit would have the 80mm piston and bigbore sleeve in it.

You'd see a significant increase in power. You can always send the head off later and get it worked on.

You could get a mild port job fairly cheap, now, though. No need for anything crazy.

[maddmatt02]

yeah, the 250x and 300ex are the same bore, its the increased stroke that gives you the extra cc's stock so a bore that would be 330 with a 300 crank, wont be 330 with the 250x crank. if you get the 12.2mm stroker crank (which is a +4mm 300 stroker) then that would put you at 349cc's with the 80mm bore, crank sint too bad, its about 300 bucks, and it says nothing about the case needing trenching or anything, but maybe they just dont list it and it does need clearancing inside the case.

another thing to check out, and Ive never heard of it done, but maybe you can get a nice cheap stock 300 crank off ebay, and see if you can drop it into the 250x cases and use a 330 kit and have a true 330.

not sure what differences there are bnetween the 2 to keep the piston from slamming into thew head, because there is a 8.2mm difference in stroke between the 2, and Id figure maybe the 30 had a taller cylinder to accomodate the longer stroke, but the 80mm kit has the same part number for both, so it leads me to believe maybe the case is a bit taller on the 300 so with the same cylinder height the head is still further from the centerline of the crank.

[riderssb250x]

So i would get a decent amount of power with the mods im looking at?

[maddmatt02]

yeah although I am with bwamos about the head, if I was gonna do a higher cr big bore, larger carb, and a cam, Id definately have some port work done.

[JohnT_98300EX]

Originally posted by maddmatt02
yeah although I am with bwamos about the head, if I was gonna do a higher cr big bore, larger carb, and a cam, Id definately have some port work done.

have to agree with matt on that. more fuel flow and more displacement would just "bottleneck" in a stock head.
My plan;
Port and polished head
Sleeve and bore
Then over next winter the motor comes out to clean and paint the frame. At that time (seeing as the motor is out anyway) have the case split and a stroker crank installed.
I'm leaning toward Powerroll 'cuz they offer a low (10.5 - 1) compression ratio. After all, this is a trail rider and I have to be able to run real world pump gas.
I hope to give the warrior riders in my area fits next spring.

[2muchquad]

The 250x crank is NOT compatiple with the 300ex crank.The 300ex crank is longer for the starter gear behind the stator.I have a 250x motor with the 12 to 1 wiseco piston and a wb #1805 grind cam and a exhaust and it runs good.Its got plenty of get up and go for the woods.I have the 76mm piston kit i will install when its time for a rebuild:)