300ex bores...

[400exrider26]

my friend wants to mabe bore his 300ex that is completly stock out... he is getting a pipe too before the bore... what sizes can he bore reliable? before he needs a new sleeve? what are common sizes that mabe have kits for the engine? what bore size makes the best power all around? thanks

[hardkoratvmxr]

you can go .20 .40 .60 .80 reliable before he will need a new sleeve i believe. If he wants a slight increase in power i would get the .20 but if he wants to make his 300 a true 300 go .80 and it will still be reliable.

[400exrider26]

what sizes are those .20, .40, .60, .80 making the 300? what is a very reliable size? im thinking eventually he will get a pipe, airfilter, cam, high comp piston, etc... but he is not sure if he wants to bore it out or just get a stock bore high comp piston...

[bwamos]

Depending on the current wear on the sleeve. He may not need a bore at all.

Just hone the cylinder and put in an 11:1 compression stock bore piston and a stage 2 hot cam. If you want to bore.. go with a 297cc setup (known as a true 300). It will be a 2mm (0.080") overbore. It will keep you in the sport class if he gets a wild hair and wants to race.

It will run on premium pump gasoline. 91 or 93 octane. Will rev very well (may want to get the rev limit increased, the 300ex has a very low rev limit) and be very very reliable. Combine that with a good FULL system pipe + filter, and you'll be seeing a very decent increase in power.

WB/HMF/Sparks/Yosh/etc.. all make good pipes. Just stay away from Cobra. ;) Sparks works best with a little more motor work. I'd reccoment the WB E-Series full system, or HMF w/ WB header.

For a litte more money he can look into some minor port work to get it really rockin. But you can port it later as well as long as you stay under the 300cc mark.

[300exrdr]

i have a 300ex and im going to bore it to 330cc. that is a common size for a 300ex to be bored to

[bwamos]

Originally posted by 300exrdr
i have a 300ex and im going to bore it to 330cc. that is a common size for a 300ex to be bored to \

The 330 is a great setup. But, beware. If you decide to race, you're going to be stuck racing with the 450's. If you stay with the 297cc you can race in the sport class.

[kyleschonert]

I thought the limit would be 350. At our fair races it is 101-350B and C. BUt i dont think they care much at these ne way. ANd all the places i race their are 350X motors, and storked out 300's. Everything. Doesnt that rule mainly just matter at the Nationals?

[kyleschonert]

thanks.

[bradley300]

Originally posted by bwamos
\

The 330 is a great setup. But, beware. If you decide to race, you're going to be stuck racing with the 450's. If you stay with the 297cc you can race in the sport class.

you are thinking of youth production at the gnc mx. the gncc sport class is 350cc limit. if he wants to race a national mx, he's gonna race w/ 450's no matte what unless he's 13 to 15 years old. if he's 16 or older, he can race the gncc sport class with warriors, blasters, 300ex's etc.....

[bwamos]

That must be nice.
Out here we are limited to 300cc's or less in the sport class. Missouri (MHSC). 200cc 2-stroke or 300cc 4-stroke.

330's, 350x's & Warriors are stuck racing with the 450's ;)