I'll throw in my two cents ...

* The Big Gun Quiet Core IS quieter than the race core, but slightly noisier than the Vortex Insert (I think most full Evo X systems sold today come with the Race Core and Vortex Insert).

* I believe that a "little bit" of back pressure increases the overall compression, but I don't fully understand the theory ... only that it probably requires a lot of tuning to get it optimized for a particular engine speed ... HOWEVER ...

* ... adding any aftermarket exhaust, opening the air intake with an aftermarket air filter, changing to a high flow snorkle (or removing the snorkle / airbox cover compeletly), changing to a 13T front and/or larger rear sprocket, and doing the crankcase breather mod, all combine to make the engine rev faster into the upper RPM range, so it would be hard to stay in the lower end RPM range anyway (except in higher gears).

* Exhaust upgrades alone provide improvements, and intake upgrades alone provide improvements, but the BEST improvements come when you upgrade BOTH intake and exhaust (or in otherwords: 1+1=3).

The general comment I'll make is this: Pretty much ANY exhaust improvement is better than the stock setup, and the full systems are probably all over priced. Read the comments, but get whatYOU think is a good deal, and you'll be happy.

Mike

 

I'm surprized nobody has mentioned the weight loss. The factory boat anchor just had to go. Not only did I gain a couple horses, it actually sounds like a bike now. Get a Muzzy/Big Gun full system and be done with it. My 2 cents.

 

Oh yeah, forgot to mention that you lose something like 8 pounds by switching to an aftermarket system...

 

+1

 

Plus you lose the catalytic converter. I think that if I was going to stay with stock displacement I would be looking at the Two Brothers slip on and keep my stock header and heat shield. 06-07 Kawasaki KLX250S Two 2 Brothers s/o exhaust. Good luck and hope this helps.

 

well I am glad to see another KLX250S specific slip on.. maybe we can expect a lot more aftermarket stuff.. for some reason I am really stuck on the FMF- but want a full system and they don't have one yet

anyone know how this bike is selling?? the more popular the more AM goodies

 

I can't answer your question as I would like to know the answer as well. But there's no doubt that the statement is true. Pipes need to be tuned to the engine for best performance and the tuning can only help in certain RPM ranges. The Muzzy web site has a really good explanation of their race pipes vs their street pipes and they really steer normal riders to their street pipes because they will give the best performance for that type of riding. The race pipes are designed for constant high RPM and they've tuned them for that and they won't perform well on the street. I found that interesting.

See FAQ #1:

http://www.muzzys.com/support/faqs.html

At any rate - just imaging no back pressure. That would be equivalent to running without a pipe at all. Performance is horrible in that situation. That should be a strong indication that bigger headpipe does not always me better. Removing the header completely would be equivalent to an infinitely large headpipe.

 

I like the looks of the 2 Brothers slip-on, but it seems a little pricey. Our headpipe is very small, which may, or may not matter to you. If you keep the stock headpipe, you'll get to keep the heat shield. If you buy a full system, you'll have to fabricate a heat shield, or do without.

I did a search for "back pressure". From what I can tell, it is more applicable to 2-strokes than 4-strokes. I did find that any back pressure makes the piston work harder, and that equals a loss of power. It seems to be a lot more complicated than I thought, as you must factor in pipe size, pipe length, pipe curves, sound waves, rpm range, etc. At low rpms, the gasses cool quicker and move slower, which may create more back pressure depending on the other factors. It seems on drag bikes, a sectiion of straight pipe was cut off until the bike ran best (at a particular rpm). It's a good thing my KLX250 isn't trying to win any races.

Since my bike has more pep than stock, runs cooler without the catalytic converter, and sounds cool, I think I'll just forget about trying to squeeze out another tenth of horsepower or so, and just go ride. I hope I don't **** off any treehuggers with my loud pipe...

 

There is nothing wrong with a small head pipe. It gives more low end torque. It's not a theory it's a fact. I have been changing pipes on bikes for 30 years. I have tried slip-ons and full systems on the same bike and each have advantages. Every full system I have tried over the years give the most peak power at the expense of low end. That is ifyou get if jetted or mapped correctly. Every slip on I have ever put on a bike has improved performance without low end torque loss. If you want any pipe to do what it is supposed to do you will need to work on the intake and jetting. More air in and more air out equals more HP. An engine is justa big air pump that turns a sprocket. My zx10r has a full system I didn't need any more low end on that bike. I put a slip-on on my KLX because I didn't want to loose any bottom end.

 

This is gonna be Harley stuff as far as back pressure is concerned, but we've experimented with drag pipes which are basically wide open pipes of a given diameter. We added a 1" diameter washer in the end of the pipes with a stud welded to it so that we could turn the washer to any position and lock it down. Drag pipes typically move your power to the upper RPM range (WFO) thus the "drag pipe" name...add the washer and you create back pressure to move the power down the rpm range slightly. This must modify torque as well as HP....(do a search for torque cones).
You can go way overboard with freeflow exhaust and defeat the purpose. I dynoed my sportster race bike with 1.75" drag pipes and the engine loved them at high rpms, I put a set of 2" drag pipes on her and she fell on her face.
2strokes are a whole different animal. A guy on my race team (Land Speed Racing) bought a Cagiva Mito 125cc 2 stroke bike to race. It was bone stock and he set the record at something like 76mph in a standing mile. I took the exhaust off just to see what was what, and found a restrictor at the head end (factory piece) I offered to bore the restrictor out to the same diameter of the headpipe, but the owner didn't wanna go there. So...I made a duplicate piece with the larger hole so he could try it if he wanted to. He did try it, and I'll admit that I didn't have a clue what it would do...but what it did was 124mph!