The diameter of the header is always a compromise. The smaller the diameter the the better it is for the lower end and larger the diameter the better it is for the upper end. That much is a fact, regardless of what the engine is, as long as it is an internal combustion engine.

Given that everything else is equal, the smaller diameter stock pipe will indeed produce more bottom end than the larger aftermarket Muzzy or BG header. Also the Muzzy and the BG will produce more power at the upper range than the small factory header. I believe for most off-roaders, the power in the upper range is more desirable, thus the change to the full system. Either way however, the differece is probably a matter of 1-2 horsepower in the case of the KLX engine.

However everything is not equal, and my su****ion that the inside of the stock KLX header is probably rough and has crappy inner welds, restricting flow has been confirmed by that article posted above. There is no question that the bigger diameter header produces more upper range power. Whether the crappy inner weld erases any low end torque advantage of the smaller diameter header, I don't know for sure.

So in summary,

1. The smaller diameter header producing more low end is not an hypothesis. It is an indisputable fact. It does not matter if the engine is a 50cc moped engine or a 7 liter V8.

2. Whether the stock KLX header produces more low end torque than the Muzzy/BG header is still a mystery. We do not know if the crappy inner weld negates the smaller diameter advantage. The reason the people in the posted article chose the bigger header was simply a matter of peak HP. They obviously do not care about low end torque. They only care about peak HP. I would agree with that as how often is a 250cc engine going to spend time in the lower RPMs?

Just so I don't sound hypocritical, the reason I went with the HMF slipon was time. At the time of my purchase, there was a long wait for the full system with both the Muzzy & the BG being on backorder with no release date, and I'm the type of person, once I decide, I want it done right away. I of course weighted the pros and cons. I would of course save money but would probably lose one HP at the upper end(when you only have 17HP, 1HP is a noticeable amount). In the end I decided to go for the slip on because I did not want to wait so long.

 

IG, when will you realize a KLX 300 muffler with no butt plug or a DRZ muffler has nothing to do with the KLX S muffler? The KLX S muffler is hopeless.

Drilling this that & the other is not the same as a KLX 300 muffler & once you do get it opened up enough to be comparable you have defeated the spark arrestor--where as the 300 muffler with no plug still has the arrestor intact.

I regret ever posting that link for you. I laugh everytime you think the KLX S muffler is worth anything more than a paper weight. If you were talking modern sportbike or MX mufflers, that is different, but the KLX S muffler--no way no how.

 

LOL, in case you missed it we're talking about headers, and I found that link before I ever knew about this forum a few weeks before I bought my KLX in '06. Of course I know the KLXS muffler is junk but we're comparing oem headers vs full exhaust headers. Of course a slip-on will flow better than the oem muffler, it's the stockheader that is still holding that new awesome muffler up thus begging to have a larger pipe to breathe out of. Sinkoman has the right idea scrapping the oem header, but I just do not want him disappointed in the HMF since he is already questioning the fitment of it before he even buys it. That's like buying a new car but wondering if it is going to start. It shouldn't be necessary and I know how much he loves his bike and want him as happy as i was with my exhaust.

 

Your right, my mistake. I could of sworn this was in reference to a slip-on.[sm=bangbang.gif]

Oh, & RC runs what he runs first because he is paid too, second because it works WFO around an MX track.

 

Yeah, I could swear the thread was entitled '2 Bros slip-on on Ebay' or something to that effect.

I would say that not very many of us will be screaming around an MX track like R. Carmichael. The magazine hack who wrote the article said "it accelerates harder at all speeds," but they didn'ttry just the larger headpipe without the pumper...nor did they try the pumper with the smaller headpipe. They changed both pipe and carb as a set, soall they really found out was that the combinationofpumper carb and larger diameterheadpipe gave them those results.

The FACT that a smaller diameter headpipe will give you more low-end torque was not some kind ofspeculationcooked-up in this forum. Anybody who isknowledgeableabout the subject wouldneversay that.
I rode my bike with a pumper and stock pipe while my exhaust was being made.I felt more low-end torgue in that configuration, but the midto top-end was choked-off.

I prefermore mid to top-end and knew I was going to large bore, so that'swhy I have a fullsystem, but there area lot of people who are very happy with their slip-ons.....but then again there are people who areNOT happy that othersARE happy with a slip-on, so we have to listen to this repeatedly.

 

Is bought a new 09 KLXs 250. Done 450 miles. Is it to early to be fitting an after market exhaust.

 

No. Get a Two Brothers slip on. Everyone will mistake your bike for as 450.

 

So you think the bike is run in enough to be able to have a new pipe fitted??

 

Yup! To be honest you can fit one from new, many do.

 

Thanks for that