300ex bore and stroke question

[nick28_89]

hey ex riders....i am wondering what the average bore for a 300ex is. I also wanted to know how big i could go and how reliable it would be....
thanx

[bwamos]

Stock bore is 74mm x 65.5mm stroke.

The 2 most common bores are:

80mm x 65.5mm stroke = 330cc (required big bore sleeve)

76mm x 65.5mm stroke = 297cc (does not require a new sleeve).

Both are very very reliable.

Sometimes the 330 will require some case work for clearance at the sleeve.. but usually not. Just depends on how they fit up.

Sparks has a 350cc. I'm sure it's just as reliable as the 330.

I've seen up to 390cc on bore alone.. but I can't attest to how reliable they are. Some people here run them and I haven't hear of any issues.

A 80mm - 82mm w/ a +4.5mm falchion stroker crank would be sweetness.

But... as with any 300ex mod.. you're modifing an oversized lawnmower motor. ;) You're never gonna get 450r performance out if it even if you go to 600cc.

[2muchquad]

You're never gonna get 450r performance out if it even if you go to 600cc.

This is so true.More hp is always fun but its only a necessity at the pro level.Spend your cash on suspension and a good steering damper and get in shape.If you are fit you'll be smoking most 450s at the end of the race be it track or woods in no time.:D was out riding last sunday and there were a couple 450s out and with my 385 i was doing everything they were,climbing all the hills etc.What i do like is the stares i get because anybody with a semi trained ear knows mine isnt a 300.;) Im not gonna sit here and even try and pretend i could run side by side with a piped 450 but on the track and real world situations i hold my own.A drag race is the ONLY time i would be at a dissadvantage.My 385 kit has been reliable for me too.

[dork]

my 300ex runs with 450s:D . my buddy has been running the fst 380/390 kit for 3 years now, no problems to speak off. just keep the oil fresh.

[bstuart]

I ran a 385 for 3 years and sold it. As far as I know, its still running strong. I think the key for this motor is an oil cooler. And like a prev post said, good maintenence.

[bwamos]

Originally posted by dork
my 300ex runs with 450s:D . my buddy has been running the fst 380/390 kit for 3 years now, no problems to speak off. just keep the oil fresh.

A good rider in the woods on a modified 300ex can keep up with a 450 yes. Tight woods and the MX track is more skill than machine.

I wasn't talking about that. I was talking performance wise the 300ex will never compete with the 450's. The technology just isn't there.

If you hopped on a modified 450.. you'd smoke those other guys on their 450's ;)

[2muchquad]

if all one did was ride wfo up and down the road like some maniac then a 450 is the way to go.But for real world riding a built 385 isnt at much disadvantage.I can go where the 4fiddys go and if wheelie popping lowend is what your after a 385 can do that too.Actually it has more lowend than a 450.These new hi po 450 mx derived motors have lots of midrange torque but people call it lowend.A 450motor wouldnt be of much use in a utility quad with a snow plow attached to it,thats real lowend there not gearing.So almost anything can beat anything on a track where skill is more important.there im done:D