So the riding season is almost over in upstate NY. I figure I have until the end of october if I am lucky maybe a day here or there in November.

Now it is almost time to get my winter projects planned. The winters are long and cold up here. It is a perfect time when 3ft of snow is falling outside to tear into my bike and do a bigger bore upgrade. I am wondering what is the difference in HP's between someone with the klx 300 cylinder and the 331 big bore kits.

I spoke to KustomKraft and they told me the reason they are more expensive than Bill Blue and thumper is because they start with a brand new klx300 cylinder, which they provide, and bore it out then re-nikasil the cylinder verses taking a 250 cylinder and putting a sleeve in it.

getting a klx300 jug, piston,pin, gaskets and the rest needed to put a klx300 cylinder on is about 470.00 us. The thumper racing kit is 530.00 to have them press in the sleave and bore the cylinder. The Kustom Kraft is almost 800.00 Bill Blue is 490 shipped to my house with my cylinder or add 125.00 to use one of his.

I have a pumper carb, big gun exhaust, and snorkle from the kdx. Still need to get a better air filter and mine is filthy... Went into a puddle that swallowed my bike to the handle bars. The water rolled over my lap.

Post up the dyno sheets. I would like to see if the big bore kits are worth the extra $$$

 

Your set up is similar to mine but I have the genuine 300cc kit.
BG full system, 33mm Mikuni pumper (bored to 34 by BB) and no air box lid.

Here is the dyno chart.



I'm happy with that.

But, if I didn't have the 300 kit already, I would go for the 331 kit from Bill.

 

My 250 already runs surprisingly healthy already so it's going to be fun trying this 330 kit. I'm using stock cams and stock carb and pipe to start with, then will swap to a KLX300 header and muffler.

Thereafter I may go for one of Bill Blue's TM33-12 Mikunis he sets up with special adapters and mods. I've ridden a 330 with his carb and man, it was healthy! Bill suspects the KLX crank is balanced to the 300 piston, and just works OK with a little buzz with the 250 piston, and he says they vibrate less as 300s than 250s. That's good. It's not like I'd be deviating so far from the 250 piston weight, more like adding a bit to the 300 piston weight. By the way, the J&E piston, wrist pin, rings, and circlips weigh 241g.

I bought the Kustom Kraft 330. It's sitting right next to me. Afterwards I talked to Bill Blue. Nice chap. Very knowledgeable. Talked to Marvin a Kustom Kraft and found the same thing.

Bill L.A. sleeves the 250 cylinder and doesn't like Nickasil, says Nickasil chips and is more $$. I've never had Nickasil chip, only chrome, and nobody chromes cylinders anymore. Marvin doesn't like to bore the 250 cylinders and Nickasil them for the 330 kit. Something abou tthe water jacket is different? I think the 330 kit will work good either way, whether you pay for that 300 cylider and re-Nickasil or not.

Being a 2-stroke guy many years, it was really weird to get the J&E piston and the 330 cylinder and do a fit check. An .0015" feeler just splipped in between skirt and cylinder, so nice and tight there. But the camming (tapeer of piston at top) and modern, short piston make the piston crown loose like a toothpick in an oil drum, especially side-to-side. Weird. It'll take a little getting used to these 4 strokes!

I favor lugging the motor and strong mid range, and don't generally run the motor over 7 krpm, so the direction I'm going to up displacement and stay with modest other bits should be quite favorable.

We shall see.

 

So are you using the Kustom Kraft or are you planinng on going with the Bill Blue setup? I have the bill blue carb, he also makes a blocking plate to plug off the air injection at the front of the block. Bill is very helpfull and responds quickly.

Steve

I am curious what kind of gas mileage the will get afterwards.

 

Who has a dyno sheet with either a bill blue or kustom kraft 331 kit? What kind of power are you making?

 

the 300 makes around 24 horse stock, the big bore kit makes around 26. you'll gain around 2 horsepower with the bigbore over the 300 kit. there is a dyno graph around here somewhere, you'll just have to find it. I do remember it though.
also, there was a dyno of two guys with a big gun and one had a muzzy. the two put out around 22 horsepower with the stock jug and other minor mods.
I think NB had the bigbore kit dyno readout somewhere.

 

According to Dynojets readings the stock 2009 250s has 18.07 HP stock and 19.27 with their kit installed (I assume stage 2 kit). And the 300 has just a shave over 20 HP all stock, and with their stage 2 kit its just a shave over 22 HP
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CRF450X

 

It all has to be done on the same dyno or it's meaningless. There's a dyno graph for the 300 right in this thread that shows 26 hp.

It doesn't mean a thing unless you run the same bike with 250, 300 and 331 and same exhaust on the same dyno.

Were the dyno jet numbers using the stock exhausts? That would definitely limit the potential increases in HP.

 

Well that may be sound advice to give someone under normal circumstances but did you even take a look to see what other mods he has listed right in that very same post? It's not a stock machine. Therefore, your post is moot.
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COACH PURSES

 

My best, somewhat educated guess is that you'll get around 3HP -> 300cc, and another 3HP -> 331cc, ballpark. So if you go 331cc, you'll see about a 6'ish HP gain. I think the pipe and carb mods will net you around 3 HP also. So if you do all that, tweak a little hear, a little there, you can expect in the ballpark of around a 10'ish HP increase over stock. You can probably squeeze a few more out with port & polish and cams ala Shadetree.

If I recall, mine dyno'd out at a hair under 27 HP. Unfortunately, I don't have any "before" runs to compare. And as tremor pointed out, it's not terribly scientific to compare the results from different dyno machines since there are a lot of variables such as calibration, compensation for temp/humidity, as well as even the operator. Rear tire can make a big difference too, and of course, how well the carb is tuned also has an significant affect.