building a mx 300ex, got questions

[markvette]

getting ready to build my 12 year old a 300ex to race mx. he has raced mini quads for 4 years but has outgrown them. got a lot of questions.

1. i hear 400ex plastic can be made to fit, what has to be done, do you have to change the gas tank.
2. it already has lsr plus 3 a-arms so i plan on some works black wodow shocks for it since he is sponsored by works.
3, what is a good mx cam ?
4. is the 330 kit worth the money
5. what is a good pipe.
6. stock swinger or is a plus better for mx
7. graphics, we like flames and i need the 300 to match my older sons 400ex/yz426 hybird, it has maier yellow plastic with k and k flame graphics.
8. any other suggestions for a good 300 mx setup would be appreciated.

Mark

[FMFTRX250r]

Id go with a Web cam/Sparks Exhaust setup....for your son id stay with the 295displacement range to keep him in Aircooled classes at the nationals...


i myself always liked the stock swinger length..and it seemed pretty strong.....


if you got the cash..put yellow fullbore on it..and trim it... it will look trick...


the head is super restrictive on the 300's....porting and big valves do wonders...some of the fastest 300ex motor came from a guy named Scott and Pro Fab ATV.....i dont know if they are still around or not anymore...

[Sjorge450R]

everything you said sounds good. And Yes the 400ex plastics do fit, but will need custom mounts made up and a little trimming.

[kd5sfq]

My thoughts are probably a radical departure from most but we all know about the value free advice. Sometimes you get pearls of wisdom and other times you get a blarney stone. The bottom line is you should take everything with a grain of salt and do what you think is best.

My son races a 300ex and is going on his 3rd year. I don't think a 330cc is worth the money for MX because it's not national legal and even if you don't plan on running nationals it's power band isn't that great for MX. The highest I would go personally to have a reliable engine is a 310 kit and even then it takes much work to get it to rev fast. I would recommend running a Jag oil cooler if you do any engine work. If you do that and change the oil every other race and the engine should last a season of more.

A good cam, high compression piston, porting, oversized valves, 400ex carburetor, rev box and good exhaust will make any 300ex worthy of respect on an MX track if and only if you have a good suspension. I do the wrenching myself but I have Dee at Rage Racing do the porting and machine work for us. Dee is the engine builder and mechanic for John Natalie Jr.. Dee is also President of the South Texas Quad Racing Association and is a good friend of mine.

There isn’t that big of a difference in power between brands of exhaust on a dynamometer according to Dee. Sometimes you can modify an exhaust by cutting it by two to four inches to eek out a fraction of a pony or so.

A stock swingarm works good but you need a good rear shock.

I recomend that at first you spend most of your racing budget on a good suspension. All the power in the world is useless unless the quad and rider can handle an MX track. PEP or Elka is a better choice for shocks... I don't know anyone who races in the front of Youth Production or any other class for that matter that runs Works shocks. They are ok but not near as competitive. They will wear a rider out… Been there, done that... I wouldn't run Works for MX anymore even if they were free. I do have Works pro series on my 400ex that I trail ride on though. Someone told me that PEP can rework Works to make the better... Don't know if that's true.

Remember that you must put zero preload shocks on the front before you can put them on the back. ZPS shock are the only way to go. Stock rear shocks or a raptor shock on a 300ex and MX racing is a very dangerous combo. They are preloaded and can throw a quad to high on jumps. They also make it very unstable in the rough stuff because they kick the rear end of the quad funny.

The bottom line is that a good rider on a good suspension with a stock engine will more than likely beat a good rider on a crappy suspension with lots of engine work. I see that happen all the time. Last weekend an Open C rider on a stock Z400 with a great suspension beat a field of 450cc quads with fair suspension. He won the race in the corners and on jumps.

Our graphics seen below was custom made by:

http://www.goforitgraphics.com/

I hope this was helpful.

Best of luck!

[WildWestRacing]

Excellent reply!:)

[kd5sfq]

Another pearl about building and racing a TRX300ex MX that is worth mentioning is that it needs to go on a diet. The dry weight of the 300ex is 377 pounds while a 450R is only 350 pounds. Some of the Blasters running MX only weigh around 200 pounds.

The power to weight ratio is what racing boils down to once everyone has a high performance engine. Team Suzuki and several pro riders even go so far as to replace all the stock nuts and bolts with ones made from titanium. That is way to radical for the youth classes because of it’s extreme cost.

It’s amazing how much weight can be shed with a little out of the box thinking. MX tracks are dirt so rock skid plates are not of much benefit. You don’t need a parking brake. Reverse is a luxury. 400ex spindles are lighter. You get the idea.

As you can see by this photo, I lighter 300ex is more nimble and race worthy.

[holister]

here are some stuff we did to our trx300r

Frame: 1998 stock gusseted
A Arms: burgard +2
Swingarm: burgard +2
Steering Stem: burgard +2
Stbilizer: PEP
Axle: lonstar +2/+4
Carrier: burgard
Locknut: lsr antifade
Hubs F|R: stock
Bars: moose
Throttle/Clutch Lever: fly racing
Grips: oury
Nerfs: ac racing
Bumper: ac racing
Grab Bar: ac racing
Front Shocks: elka dual rate remote rezzies
Rear Shock: works w/ eibach springs
Brake Lines: galfer
Rotors F|R: galfer
Rims F|R: front itp rear itp beadlock
Tires F|R: front holeshots rear turf tamers

Body:

Plastic: maier race cut
Graphics|Seat Cover: verde powersports
Number Backgrounds: none
Handguards: none
Bar Pad: fly racing
Fuel Tank: clarke

Engine|Drive System:

Cylinder|Head: ported polished
Bore & Stroke: .80
Displacement: 289cc
Carburetor: 400ex
Air Filter|Box: K&n outerwaer
Pipe|Silencer:supertrapp shorty
Clutch|Plates: tusk heavy duty
Gearing F|R: 14/34
CDI|Killswitch: rick's motorsports pro design
Cooling: oil cooler
Other: extended footpegs, motor built by norman racing, race cam

[markvette]

thanks for all the replies. im not new to quad racing or wrenching on them, just new to the 300ex. my oldest son raced a 400ex which now has a yz426 motor in it. we done most the work ourselves putting it together. i know suspension will be first then the motor. billy holt at wrh racing is a personal friend of mine and can do the port work. he ported the 426 head for us and it made a big difference. i know what you mean by the zps shocks, we have them on the hybird and my son swears by then. again thanks for all the replies, it gives me a good direction for the quad now.

Mark

[elementryder]

i race mx localy and dont know how much $ i want to spend on a 300ex you can check my sig to see what im runnin