Probably head design. Usually that's the limiting factor on most production engines. Look at the 454 that came in 90s chevy duallies, 190hp 250 lbs of torque, change to oval port aluminum heads and you have yourself a 300hp 500ft of torque 45 freaking 4

 

I'm with you Wreckster.. Happy to do some modding but curious about what in its' design is limiting the output.

Durielk, I want my 40+ HP and I want to get it using only a paperclip, a rusty metric crescent wrench, and a few hammer blows.

 

Turbo... want your 2 stroke like hit? Lol.

 

I don't quite get this, because with constant rotating parts the plain bearing set has less friction than with ball bearings. If it wasn't you'd see cars using ball bearing cam and crank bearings - they don't.

A properly set up carburetor can deliver fuel very close to that of injection so I'm not seeing a 10% gain there. Now if the carburetion is significantly off, that's another story. 90% of the issue with carbs versus injection is ease of starting, ability to adapt to modifications up to a point within their maps, and somewhat instant fine tuning.

What a shame there isn't an "intellegent" injector conversion like they have for high performance street rods. They have throttle body injectors that "learn" what is needed as they run!

Then the thing about valve springs? Too heavy? How did you figure that? They have to keep valves from floating upwards of 12,000-14,000 rpm (missed shifts). Then your comment on ports, just how big do you think it takes to fill a cylinder about 1/4 the size of an oil can? Start looking at and reading some magazines like Hot Rod, Car Craft and such to see what they have with the various engines. They don't run huge ports on small blocks, like they do on big blocks and the header tube size differences are big too. Small cannot be forced to take more than it can draw unless you do a turbo or supercharger and then the ports and such become even less important since the flow is forced.

(Edit: In a side note, the reason I recommend the car magazines is that there are no similar bike magazines doing work like that so you have to kind of interpolate the information. A big block car engine is only about 1/3 bigger than the small block, yet there are huge differences in how and what is done. They are four strokes and thus the same thing applies to trying to make a 250 run like a 450 - even with a big bore.)

I will say when we sold bikes and some guy wanted to make his 600 perform like a 1000 supersport we would tell them the best mod was to pull the axles out of the wheels, raise the bike up and away, lower a 1000 supersport minus wheels down on his wheels, put the axles back in and go. Actually it really should have been "take off the air caps and put them on a big bike"

The point - as TNC aptly put it - there are limits and reasons why the KLX250 is what it is. Play a bit, but remember going for big gains makes things break or more difficult to ride. You want a lot more - buy bigger higher performance, built to do it. You'll spend way too much to make a KLX250 run like a KX250F.

 

Roller cams!!!!!! haahaha


The problem I think we'd run into is having the transmission last, pushing 35+ horsepower on a transmission built to stand only 19 might be an issue. I think the best we can do is get the bike running the cleanest and best it can. No flat spots, no surging, easy starting etc. This of course has to do with jetting. Make it run clean, make it run crisp, and the lack of power will be less important I think.

 

And maybe the clutch more than anything else. Kawasaki is well known for overbuilt clutches, but the KLX clutch is only decently adequate for moderate power gains.

 

So from the posts so far, I take it we have no one around that has analyzed the engine from a performance engineering standpoint. E.G. - flow benched the head in order to identify the most offending aspects of the design - Dyno checked various cam profiles. Performed alterations in ports/ bowls/combustion chamber in small increments to find the "holy grail".
I guess no one has ever completely modded the stock bore with cams, carb, exhaust, etc,,
It seems that if the WR can make its' 26-27 hp stock, we ought to be able to make at least 25hp modded....?

While I enjoy all the opinions that cast shadows and create emotion. I'd rather acquire intellectual knowledge I can use.

 

That's what I'm interested in. I know plenty about how capable it is currently, but why is it exactly it doesn't have more potential? What if it were as simple as swapping heads for the kx250? Or maybe just some carefull porting?

 

I don't think many people test things on the KLX mainly due to the following -

1. Its a cheap bike, most people don't throw thousands of dollars at upgrading and, more to the point, testing the upgrades to quantify on paper the results.

It would be great to have run my stock bike on a dyno and then again after my big bore install and here again when I upgrade the carb and exhaust and then again if I ever get a set of Web cams. But the cost of the dyno pull would be money taken out of my already meager upgrade budget and add that to the fact that I don't even know where the closest place with a dyno is, its not gonna happen.

I know the bore kit increased power, and it was worth every penny in my mind. I've seen results and they were satisfactory.

I think most of the KLX crowd is of the same mindset.


That being said, it think that some might be surprised at how much power a modded KLX can put down, its just that there are only a handful of examples to look at, which makes the overall picture a bit fuzzy.

 

I don't think there is room for a roller cam... now if you redesign the head for 5 valves, maybe we could work that in.
When do you want me to get started?