350x cheap performance

[Fixer_Upper]

I am 13 years old and rebuilding my dads 350x. I would also like to see what performance upgrades can be done to it. I have seen 400ex carb swaps, NOS, and others for a relatively low price. The thing is is that I really want to stay out of race fuel territory, and not blow up my motor. This also goes to say my motor is stock completely except for “race” valves and a air filter. I’m just looking to get a little more juice out of her, for a low price.

[Homeless Dave]

Well, you need a decently high compression ratio to need to move away from pump gas. I assume by race valves you mean that they are larger than stock? If so, I would recommend a better cam, carb (or re-jet the original), and exhaust. That is the best way to pep up a 4 stroke. Those 3 things should be done together will improve flow drastically, but you will still be limited by the head itself until it is dealt with. The power gains might not be huge, but it will be noticeable. If you want to keep the compression reasonable, you could still go with a higher compression piston,, but it does not have to be extreme.

[350for350]

You can also open up the intake for more air flow. Remove the air box lid, that will get you better air flow which helps to make more power. Just remember, if you do this, it will be easier to get your air filter clogged with mud or water.

[Fixer_Upper]

Thanks! I don’t think the valves are any longer, the company that makes them calls them race valves, as in that they’re stronger than stock. Would you know of any company’s that make an exhaust for this that still has the spark arrestor, if not then that’s fine because mine is missing it out of the stock exhaust. Makes cool flames though! The only reason i want it is so there’s a smaller chance of burning my woods down.

[BOB MARLIN]

Look for a Supertrapp on ebay.

[Fixer_Upper]

Ok. I have seen they’re kinda rare tho.

[ps2fixer]

If you want a near stock option for the exhaust that flows better than stock, but not as loud as aftermarket, check out some posts about using the 400ex or 450r exhaust on the 350x. Spark arrestor isn't an issue when sticking with an OEM part since they all have it.


Also, does your exhaust shoot out flames? If so you might need to do some carb tuning, you shouldn't be getting unburnt fuel that far into the exhaust. If it was a short header pipe I could see you having flames, but not a full length OEM exhaust.

I'm not sure how common forest fires are caused from missing spark arrestors. My dad's 1953 Case tractor doesn't have any kind of spark arrestor and at night you can see the sparks flying up. He's ran it like that for years and year and years with tree limbs being hit by the sparks and all, never seen even a hint of a fire starting. Maybe in a super dry climate it's a problem, Michigan is a pretty wet state.


Pretty much engine performance comes down to the core basics, it's an air pump, the more efficient it can get air in and out, and the quantity it takes in and out determines how much power you can get. Just remember, efficiency doesn't always mean bigger. The whole system is a balancing act, bigger you go, the more you loose out on low rpm torque since the whole system is tuned to be peak performance at higher rpm. Same story with exhaust length, shorter = high rpm, longer = lower rpm. Bigger = high rpm, smaller = low rpm. Intake plays under the same logic.

You can see this effect in any racing scene, generally racing equates to going fast, wide open throttle, max hp possible (work over time, effectively max speed), so most engines run short header pipes that are huge. Go the exact opposite extreme and look at any car that's designed to be a gas miser, it has a tiny exhaust and it's the full length. Ideally it would have long tube headers on it, but they are normally cheap budget machines so they get the cheap cast iron style exhaust manifolds (less than ideal, but cost dictates design).



Either case, good luck with the build. The 350x is known as a torquey engine, not sure how race ready you can make it with out major mods. Kind of like taking a long stroke tractor engine and trying to build the engine to race it.