I'm not referring to the manufacturer's warranty of the bike. I'm referring to the 1-year warranty of the Nikasil-plated cylinder, compared to the 5 year warranty of the Bill Blue Sleeve. I'll cheaper cheaper (Bill Blue sleeve) with a longer warranty every time.....

 

[QUOTE=BlkDakDave;464453]First thanks to everyone for their replies. My question seems to have opened up the discussion with a lot of good information being passed on.
To answer the question why not get the 351cc kit, I have several reasons. I don’t want to have to worry about clutch plates or my stock carburetor that may or may not work. The 300 and 331 kits are dry sleeves while the 340 and 351 are wet sleeves. There really isn't going to be a huge difference in the amount of power but there might be a noticed difference in cooling during our hot south Texas summers. I think I’d rather keep it dependable and stick with the 331.[/QUOTE

Last night I spent some time googling dry and wet sleeves to learn the difference between the 2. Every thing I read said a wet sleeve is better for heat transfer.

 

5 year warranty! I did not know that. I'm sold on a BB kit.

 

Sorry, I misunderstood your point.
I'm not a fan of long term warranty, It's not factor for my decision but I understand it gives some peace of mind!

 

Interesting -different from what I came up with... Will have to do some more googling - Thanks!

 

I'd sure like to see dyno charts of the 331 vs 340 vs 351. I'm sure the 351 would make the most torque but would it really make the fastest engine. I had a KK 300cc big bore kit on a KX 250. It made more torque for sure but with the larger piston it also reved slower. It was easier to ride through technical stuff but in the open desert it "felt" slower than the bike did with the 250cc cylinder. However sometimes seat of the pants dyno's aren't very accurate.

 

KLX 351 Dyno Run - YouTube

 

Id like to know if the second half of this quote is possible? Before I pull the trigger on a 331 kit, am I gaining torque,but somehow losing speed? Thats important to be since I ride pavement more than dirt...

 

My KLX250 would barely make 62 mph (indicated) up a particular hill. As a 331, I have no trouble going upper 70's (indicated), and I haven't tested it to see exactly how fast it will go. 331 is certainly much faster than a 250.

 

On heat transfer as it relates to cylinder, sleeve, and plating designs, I think it's relatively accepted that a nikasil coated aluminum cylinder will usually transfer heat a bit better than a steel sleeve in an aluminum cylinder. But...as always, there are other factors that come into play in a negative/positive way to affect overall performance, durability, etc. Really, as long as the steel sleeved cylinder transfers "enough" heat to operate safely, the heat transfer may not be as big an issue...and the wet sleeved KLX versions seem to be doing that just fine. Conversely, an engine needs a certain level of retained heat to perform at an optimum level. It's a tangled web of overlapping issues, so it may not be correct to focus too much on one element of a given engine's design or component material...unless it's at a failure level, of course.

On that 2-stroke comparison of the 250-to-300 cylinder swap, that might not be a good general comparison to a similar 4-stroke engine. I'm not sure that the volumetric efficiency of the 2 designs always respond the same to displacement variations. But of course, there are notable differences even within the same 4-stroke field of engines that don't correspond. The KLR650 is one of those 4-strokes that doesn't seem to respond as well to a displacement increase because of the valve/cam/cylinder head design, whereas the KLX and many others have a slightly more optimum design to take more advantage of the displacement increase. But we're talking about the KLX here, and I think it's fairly apparent that it responds well to more displacement. I've mentioned this before, but I think there's a reason that Kawasaki went to the 300 displacement instead of sticking with the 250 size. The valve placement in the head actually seems more optimum for the 300, and apparently it has room to respond well to even bigger bores. No, I'm not an engineer, and I didn't stay in a Holiday Inn Express last night.