motor rebuild, time to start modding! what mods are the best? who makes the best?

[livetoride249]

i already have my 300ex bored 0.50 over with a JE high compression piston. i'm thinking i should port/polish it now. hone the cylinder. are there any mods i could do to the cam? any good cam out there i should buy? also who makes the best pipe for pit/trail riding? should i gear it differently? any airbox/intake mods i can do? i want this thing to be as fast/ faster than a stock 400ex. they're already wicked light. also where do you find those 450r race hoods? normally i race motocross in NESC i'm a B rider. i just want this 300ex to ride in the pits. money is not an object, this is going to be my winter project. i'm not worried about a-arms chasis/susp etc. just want more power! and how to keep it cool as well, i dont need it over heating

[m0t0xk1d]

Ill help a fellow mainer out. Where in maine are you from?

Well anyways the best pipe for a 300ex is the sparks racing pipe or the TC supertrapp shorty.

I saqw in your other thread you had an 81mm piston. i believe that equals out to be 300cc? im not sure but i know its more then 300cc.

Sparks racing offers 2 cams; one for all around riding or one for motocross. however for the sparks cams you need to buy hardface rockers and HD valve springs. Web Cam shafts has a lot of good cams and with some of them you dont need HD springs or hardface rockers. Hot Cams has a stage one cam also.

14 37 is a good gear ratio to just have fun. i would get a big gun rev box also. lets these bikes rev out alot more.

You can get several hoods that can be made to fit a 300ex. none of which are made for the 300ex. maier-mfg makes a few hoods for the 450r that fit and same with 250r hoods. Quadtech makes some hoods for a 450r that can be made to fit. Fourwerx carbon makes a hood for a 250r that looks SWEET on a 300ex. Gen - X makes a hood for a 300 on custom order. you would need to contact them through email or phone to have them make one for you and it lookks just like their hoods they make for a 450

Porting really opens these bikes up. they are very restricted stock and a good port job help. I had mine bike ported by BCS Performance in mass and definitely noticed a huge difference. BCS does a great job

400ex Carb is also a very popular upgrade for a 300. the 300s are under carbeurated stock and 400 one really helps.

[shiley55]

Powroll.com.

[m0t0xk1d]

dont go through powroll. build it your yourself powroll doesnt compete with company like sparks and tc who have built many 300s that have won championships

[livetoride249]

Originally posted by m0t0xk1d
Ill help a fellow mainer out. Where in maine are you from?

Well anyways the best pipe for a 300ex is the sparks racing pipe or the TC supertrapp shorty.

I saqw in your other thread you had an 81mm piston. i believe that equals out to be 300cc? im not sure but i know its more then 300cc.

Sparks racing offers 2 cams; one for all around riding or one for motocross. however for the sparks cams you need to buy hardface rockers and HD valve springs. Web Cam shafts has a lot of good cams and with some of them you dont need HD springs or hardface rockers. Hot Cams has a stage one cam also.

14 37 is a good gear ratio to just have fun. i would get a big gun rev box also. lets these bikes rev out alot more.

You can get several hoods that can be made to fit a 300ex. none of which are made for the 300ex. maier-mfg makes a few hoods for the 450r that fit and same with 250r hoods. Quadtech makes some hoods for a 450r that can be made to fit. Fourwerx carbon makes a hood for a 250r that looks SWEET on a 300ex. Gen - X makes a hood for a 300 on custom order. you would need to contact them through email or phone to have them make one for you and it lookks just like their hoods they make for a 450

Porting really opens these bikes up. they are very restricted stock and a good port job help. I had mine bike ported by BCS Performance in mass and definitely noticed a huge difference. BCS does a great job

400ex Carb is also a very popular upgrade for a 300. the 300s are under carbeurated stock and 400 one really helps.


thanks! i'm from casco/naples area. right around the jugtown trail system. i'm 20 minutes from windham.

[livetoride249]

also i was wondering, could i do a motor transplant. i was thinking of just doing a stock rebuild for the 300ex motor. then sell that with the carb and air box as a kit on ebay. then use that money and buy a cr250/trx250r engine or a CR500!! motor. would that fit at all, i know im going to have to make new mounting brackets and everything but could it happen? could this be done?

[ballzdeep38]

also i was wondering, could i do a motor transplant. i was thinking of just doing a stock rebuild for the 300ex motor. then sell that with the carb and air box as a kit on ebay. then use that money and buy a cr250/trx250r engine or a CR500!! motor.

Why not just sell the whole thing and buy a 250r???:huh without widening it and upgrading the suspension its going to be a lot to handle on stock suspension. they are already pretty "tippy"...

[livetoride249]

the 300ex is a 97 i couldn't get 1200 for it. 250r's up here don't go for any less 2500ish. i wrote money's not an option so i could see what people had to say, who had the best stuff. i already have works susp on it now, and i'm making a set of wheel spacers.

[mx Eli]

janssen make's a really nasty 300ex motor

[Arctic Cat Dad]

Are u sure sparks and tc are the best pipe for the 300? The Looney Tuned Exhaust was the best in all the dyno runs we tested.Also webcams grind # 240 which is there 4th cam on the mod list works great for us with a 14:1 JE piston.Also webcams will build u a wicked crank if u send them yours. While u have the head off some oversized Kibble White valves really help. Believe me this engine screams.