The post is still relevent, mods or not...his mods don't look like anything that are out of the ordinary? A pumper carb and BG pipe aren't going to make a huge difference. Also, I only cited that as one possible example. Dynos still vary a great deal from machine to machine, regardless.

If you have some sort of issue with me, send a PM.

 

I sort of wish I had done dyno checks stock and then after each mod.
The dyno check for me was just to check on jetting.

It's true that on it's own, the raw hp figure is just a number.

What I can add is that the difference between the stock 250 and the 300 wasn't much.
A bit more low down maybe, but on it's own, not very impressive.
I did that mod first because I worked a deal with the shop to include it.

The other mods came after the 300 kit and had much more affect IMO.

I have seat of the pants comparisons between my bike and a bike with the 300 kit and no other mods.
Mine smokes his in every meaningful way.
He has now re-jetted the carb but still has the stock pipe.
Better, but still a long way short of mine.

Has anyone gone from a 300 to a 331?
I'm certainly thinking about.

 

Yeah, I suppose what I'm getting at is that most people I know, who have added the 300 jug have also rejetted, and added some sort of higher flowing exhaust, opened in airbox, etc.

I added the 300 jug AFTER adding a pumper and aftermarket exhaust and can tell you I felt a very noticeable seat of the pants change, so I'm sure the stock exhaust and A/F delivery was holding back a lot of potential in your case.

The effect of adding the 300cc jug was roughly equivent to going down a tooth in the front when it came to how well the bike handled hills or accelerated through the gears. Aceleration is 6th felt like how 5th used to feel with 250cc.

I've heard similar comments to mine, but those also came from people who had added aftermarket exhausts, rejetted and opened the airbox prior to bumping-up the displacement.

 

Did that here. Here is my non-scientific, seat of the pants, upgrade scale - how I thought each mod roughly did.

 

I have no dyno runs but can give my seat of the pants experience. 99% of my riding is fairly difficult off road and the bike started as a 300 not the 250S. I use 14/50 or 13/50 gearing. I first went from a stock 300 to a stock 300 with a pumper carb, FCR35. Before the carb I was very frustrated with the power delivery of the bike and was very close to selling it. The addition of the pumper carb transforms the bike to how it should have come from the factory. I will say it is the best mod, maybe tied with suspension, that you can do to the KLX. I then went to a 331 but at the same time added cams. I started off riding around some dirt roads and easy fairly flat trails just "breaking her in" getting the oil changed a couple of times. At first i was disappointed because I couldn't tell much difference than what I had with the 300. Granted, I wasn't ringing her out either. I then went and did some of our usual rides and that's when I could tell things actually changed. With the 331 and cams the bike has noticeably more grunt just about everywhere especially low and mid range. It also seemed to rev out slightly higher than before as well. I found many of the technical hills that I was doing in 1st or 2nd gear with the 300, I was able to ride a gear higher. In situations were I new I had to shift down before, the bike would just amazingly grunt through it and keep going. I don't think I will be using he 13/50 gearing any longer.

For comparison, a riding buddy has a KLX250 off road not the S model. Over the years we would always compare the bikes after doing different mods. Except for the bore size our bikes were set up almost exactly. He is a little lighter than me so he has softer springs in his suspension. With both bikes tuned the the 300 out performs the 250 almost like the way I explained the difference between the 300 vs the 331. At the same time I did the 331, he also did the 331 to his 250. To him, the differences were obviously much more dramatic and he was very ecstatic with the change. He thought he was on a new bike as opposed to a 12 year old bike. Just to add his bike is in super shape for being 12 years old. He opted to not do the cams. I will and he will say the cams add a little to the party but don't expect a huge difference. My bike seems to rev out just a little longer in the usable power band than his.

 

Wrong again bud. Those mods are signifigant. When a bike is corked up like these ones are throwing a pipe and a carb and removing the airbox lid will do a world of difference. It's like opening the freaking flood gates on these bikes. Several HP at least, and several HP is alot considering you only have 20 HP to start with.

To comment on the second part about dyno's variance, I said that that was good all round advice, they do vary.
________
Shower amateur

 

lol ..... is it winter time already?

Whoo Hooo can't wait for some cool weather.

 

It's not even summer yet. It 's coming though.

 

It absolutely pissed with rain today.

 

I don't think there is really right or wrong here 'bud.' Does there have to be for you to feel OK?

Maybe I need to say this another way. I'm well aware of the effect of allowing max flow and getting the jetting right.

I treat it like eveyone has done the exhaust, airbox and jetting to optimize each displacement. Why do it differently? One bike's stock exhaust could be more restrictive than the other, so how can you treat that like it's an even playing field? Uncorking both of them and dialing-in the jetting makes the most valid comparison.

Remember the title of the thread. We are trying to answer the HP difference between 300 and 331cc. Running them both while corked-up doesn't give a fair representation IMHO, because you don't know exactly how corked up each bike is relative to its displacement. I could see it if we were talking about the same displacment when comparing other mods, but we are not.