11:1 Piston & Cam vs 330 Big Bore?

[Nrgy]

I want to uncork some more power out of my 300ex so friends and family can have more fun with it, and also because I just want a bad little 300. (not interested in upgrading to a bigger bike as I also have a 450r) However I also want to maintain reliability without having to rebuild or tear down to diagnose problems all the time.

I've done the standard stuff so far: UNI filter, no lid, X-4 Sparks pipe, rejet, rev box and currently 14/38 gearing on 22's.

I want to go one step further and can't decide if I should do a standard bore 11:1 piston and Stage 1 Hotcam, or just do the JE 330 Big Bore on eBay? The price is about the same for either setup. Other than perhaps a 400ex carb, I probably wouldn't go any farther such has headwork and the like.

My main goal for the bike is speed. I have a lot of places I can open up the quad for long distances so top end is fairly important to me. I appreciate any suggestions!

[jay80]

How do you like 14/38 gearing? I have a '87 250x and just did a fresh rebuild, wiseco .060, pipe, air box mods, 400ex carb. Its quick for a 250x. I'm running a 450r swing arm so it just squat's down and shoots out of the hole. 1-2 shift it will lift up a little bit. Still have 13/38 and tops out like 55ish, I'd like to hit 60-65.

[Nrgy]

I mostly ran the 14/38 gearing and stock 22's with just the filter mod. I just got the pipe and rev box so I haven't tested this combo yet, but with the filter and gearing at around 4,500' I could top out just under 60 mph on GPS.

Obviously I lost some bottom end but not enough to be a problem for just trail riding. It's not much of a wheelie machine now though...I have to work a little to get the front end to pop up from a slow idle in first gear. But I'm guessing with the new pipe and a proper rejet this could help out a bunch. Should know tonight :)

If you bumped up to a 14t I'd say you'd hit your 60 mph mark and still pull strong down low considering you currently get lift on your 1-2 shift. Ultimately I want to run 14/36 gearing with 20's.

[smr]

looks like your playing it smart. I have worked with just about every combination of engines on a 300ex. I just don't think the big bore is worth it. Punch that sucker out to .080 over and install a 400ex carb. With all the other tricks you've done that will compiment it very well.

[Nrgy]

Well, I ended up getting the 330 big bore. I just couldn't resist the price, it seemed like too good a bang for the buck. However, I bought it thinking it was going to be a simple bolt on with the new jug and sleeve. It's not. And it requires more than just a trimming of the case. It requires quite a bit of material to be removed, so I ended up having to take it to a machine shop to have them do a proper job and split the cases.

So this $300 big bore will end up costing me double that. Hope it's worth it now.

I also broke down and ended up sending my head in to get ported & polished to take full potential of the big bore as well. I'm excited to get it back together, hoping for a night/day difference.

[toomanytoys]

Back in 2001 I had Four Stroke tech build me a 352cc bored and stroked 300EX. I sent him the engine and said do the works to her. I put a pretty large amount of cash into that engine.

She was a screamer. I had to run 16/38 gearing to keep the front end on the ground through the first 3 gears. It was a monster.

[Nrgy]

Yeah I bet that motor was a monster! It was kinda tempting to get a stroker for this motor as well but I was already putting more $ into this then planned.

But I finally got the engine put back together and it fired right up. I went down to a 36 tooth sprocket in the rear, so I'm currently running 14/36 with 22's. And boy is this setup noticeably stronger now. I haven't let it rip yet but it pulls this gearing with ease.

Can't wait to really open it up and see what it's capable of now. I can already tell this is a whole new ATV.

[toomanytoys]

The 300EX is a great little quad.

I never told my friends I put the poke and stroked motor in there, and it suprised them when I was pulling away from much faster bikes, and would take my best friends piped/jetted/k&n 300EX By leaps and bounds in a drag race..

[Nrgy]

Haha yeah, I have to say it's been fun modifying this underdog 300ex. I put on a new front end suspension and spaced out the rear in addition to the engine work, so this should feel like a new quad once I take it out.

I have to say, in stock form the 300ex was a bit underwhelming/disappointing. But it sure has potential.