Why is a stock kx250 so much more powerful than our klx250s or even 350s?
 

I assume is has something to do with the 2 stroke vs 4 stroke comparison? I rode my buddies 2011 kx250 and tried riding it just like my klx350 and I was overwhelmed by the power that it puts out. It was insane!

2011 KX250 :confused: Typo? Did you mean 2001?

Anyway, that's a totally apples-to-oranges comparison. At face value, there's the two-stroke vs four-stroke difference of course. But besides that, the KX250 engine is designed to make power to compete in motocross, while the KLX250/300 was designed for mild trail riding.

I suspect if you ever get a chance to ride a KX250F you'll find similar results: it will make way more power than your KLX350 (though your 350 will have way more torque).

FYI, and a little bit off topic...as a rule of thumb with four stroke engines, horsepower potential is a function of cylinder head flow capacity, while torque potential is a function of displacement. Of course there's a lot more to the story, but there's volumes written on it. That's why a well prepped KLX351 doesn't make much more peak power than an identically prepped KLX250 (same heads, cams, etc), but the 351 makes loads more torque (more displacement).

seriously? 2-stroke vs 4-stroke.... lutz already mentioned this but i wanna review it just to make the water more clear

i guess the best way to explain it is kinda like this... u got a 2 stroke ridding along side a 4 stroke, both guys are crackin along side one another at 4000 rpm's (lets assume simiar weights, gearing, displacement etc. for the sake of less things to argue about)

the 2 stroke fires a solid 4000 times per minute
the 4 stroke fires a solid 2000 times per minute, call me crazy but thats half the power strokes... in the same amount of time!
(check my thoughts on this, i believe i did math correctly lol)

this is not all... but a solid foundational reason 2 strokes make the power they do... and wear faster etc... im not goin into all the details, the lists are to long. The point is there is half and many moments of "force" created in 4 strokes vs 2 strokes.

Less moving parts and they fire every time the piston comes up vs every other on the KLX

I think I understand...the 2 strokes work twice as hard in the same amount of time? Which is why everything wears faster and why 2 strokes have different powerband locations?

On a two stroke the gas is also the oil, so less parasitic losses and from there it gets more complicated, the design and shape of the expansion chamber affects performance, as the real good ones send a little exhaust charge back in the cylinder. I'm no genius but when I raced years ago we'd refer to this as comming on the pipe and that was the powerband in a two stroke.

Yea pretty much holmes, let me give u some very common facts to help us all in engine deducing... i know some are obvious buy hey it can't hurt.

1) One revolution of the crank = 2 strokes (for a typical 4 bar linkage system)

2) A stroke is not specific to work... ie. it could be an exhaust stroke or a intake stroke... etc. (6 cycle engines have a stroke for water injection for example)

3) The amount of cycles that are denoted for an engine (2-cycle, 4-cycle, 6-cycle, blahhh blahhh blahhh), refer to the number of strokes relative to 1 combustion cycle... ok, so let me explain a little better cuz once I do it will makes so much sense...
For example: a 2-stroke engine has 2 strokes for every 1 combustion cycle, and since we know 1 crank revolution (the premises for RPM's) is equal to 2 strokes, it therefore completes 1 combustion cycle every revolution.
However, a 4-stroke engine has 4 strokes for every 1 combustion cycle, and since once again we know that 1 crank revolution is equal to 2 strokes, it now takes 2 crank revolutions to complete 1 combustion cycle.

So yea in short 2-cycles fire there happy little pistons twice as much as a 4-cycle, considering they are both running at the same RPM's for the same duration of time... I dont mean to be that guy; but hey u would all surprised how many ppl who think they know alot about such things really miss these simple facts that help us understand our machines better. Im an going to school to be an engineer and just last spring i fu*ked this simple stuff up on my exam.... ( i was trying to relate the crank RPM's to a O2 sensor instrumentation system, and i forgot to divide by 2, thus the O2 sensor was looking for combustion cycles typical to that of a 2-cycle engine, even though the problem stated it was a 4-cycle egine)

anyways hope this helped, that is wat my real goal was lol :)

For visual reference:

4 Stroke -=-=-=-=-=-=-=-=-=-|=-=-=-=-=-=-=-=-=-=-=-=-=-=- 2 Stroke
https://upload.wikimedia.org/wikiped...oke-Engine.gifhttps://upload.wikimedia.org/wikiped...e_Zweitakt.gif

Awesome example. So why does a 2 stroke engine have such a huge header compared to the pencil sized headers that 4 strokes have?

If you look at the 2 stroke you will see that the "TUNED" pipe is resonating the back pressure and forcing all of the unburned fuel back into the cylinder (supercharging) the cylinder. the length of the pipe has alot to do with the rpm that the motor makes power in. typically the shorter the pipe the higher the power band. AND the fatter the pipe the wider the power band (to an extent).