Any difference between 09 and 12 exhaust slip on mounting locations? I found a new q4 for 256.00

 

I believe they are all the same... I got my pipe used from a guy with an 07 and it fit my 2011.

 

I have a '99 KLX 300 muffler on a '12, same mounting locations.

 

Would it be best to get a full exhaust or would a slip on alone help the engine breathe, i plan on getting the kdx200 snorkel when i do the exhaust

 

The stock head pipe is too small ID by about 1/4". I would venture it to be possible that more power could be had with the stock muffler and a bigger head pipe if the muffler's lead in pipe is big enough. I didn't look.

Long story short before the long part... Muffler set up is easily available, but the head pipe is too small ID for the bike. A slip on may help, but frequently doesn't do that much when choked down by a small head pipe. Money available, I'd do the full exhaust. Otherwise I'd be a bit torn, wanting to try the head pipe first, but not sure if it would be best benefit.

I used an on-line exhaust calculator and found that the ideal straight ID pipe size for the KLX 250 was 1-3/8"ID x about 21" for the 8600 rpm state of tune. If it had the cam and all for 10,000 peak the ID went to around 1-7/16"ID x about 19". Being within around 1" on the head pipe is adequate, the ID critical for breathing. The tail pipe/muffler should be a bigger ID in the connector pipe.

Those dimensions pretty much matched up to the straight ID aftermarket head pipe I have in the garage. Still need to put that stuff on.

I don't have it on this computer, but TNC gave me some measurements for his aftermarket pipe, which has a stepped design. Interesting set up. My KLX650 has a tapered head pipe increasing in OD from the head to the end of the header pipe.

Side note: In 2003 the hop up tricks for the KLX300R was a pumper carb and a bigger ID freer flowing full exhaust, per the media doing the stuff. Really boosted the performance.

 

Ahh, the stock muffler will not mate to a performance header. And thank goodness for that!

That Q4 will bolt right up to your stock header. The full exhaust will allow a greatly enhanced powerband from 6k-10.5K - I say allow because I don't know how much top end power you loose with a KDX snorkel vs lidless.

One member, that has all the snorkels and multiple exhaust setups, said the KDX snorkel is too restrictive for top end. Another member is quite sure that even lidless is not enough de-restriction due to the close proximity of the seat base to the top of the airbox..

What I know is that lidless, and properly fueled, you'll be around 23hp with a full system, and power that pulls hard pretty much to redline. With just the Q4, around 22hp with power that tapers off about 9200 RPM.. Doesn't sound like much of a difference, but it's night and day in actuality due to the differences in the power curves.

Anyway, if I were going to run a KDX snorkel regardless of anything else, I'd just get the Q4 and rejet..

 

A KLX300 aftermarket pipe is bigger than stock and conforms to results calculated using Wallace Racing's work sheet. Wallace lists the references for the formulas used in their spreadsheet.

It's been a year since I did the plug&play with it so I don't remember exact numbers used, but I did research to find what was needed. As said, around 21" long, 1.375" ID. Stock KLX250 is around 21" long, but around 1.25" ID.

Best exhaust set up requires a full swap out.