2009 gpx250 exhaust headers into 2005 model compatibility?

[Willy2021]

Hi.

I have a 2005 GPX250 (Ninja 250) and I want to fit a 2-1 exhaust header (as the ones from a 2009 model).

My GPX is a Cafe Racer custom and I want to go for the single exhaust system setup rather than the factory twin exhausts.
I don't mind if the 2009 exhaust headers are not the same “from the Y pipe backwards” as I expect that given the different chassis, however, I do want to make sure that they will fit in the engine side of course.

If you see the photo, the section marked RED is important and must be compatible on the engine side, whilst the green section is not as I can easily fit a custom tube all the way to the muffler, I hope that makes sense...

Thanks in Advance,
Willy

[DannoXYZ]

Hi Willy, it can be done, depending upon how much work you want to do vs performance results.

Issue is way they attach to head is completely different between generations. Also factory pipe sizes are not compatible with other gen's cams due to high-end Hp tuning of pre-gen vs. mid-range Tq on new-gen. You'd end up with too many compromises in specs even if you cut and welded pipe-ends to fit new-gen exhaust onto pre-gen bike. Result will be both loss of high-end Hp pre-gen is known for as well as no mid-range torque of new-gen.

Check out this exhaust comparison thread. Your GPX has same exhaust as 1st-gen 86-87 EX250: https://www.ninjette.org/forums/showthread.php?t=338180

For best combination of looks and performance, you'll want to build one of these pre-gen 2-1 exhausts: https://www.ninjette.org/forums/showthread.php?t=13852

[Willy2021]

Wow! so many factors to consider DannoXYZ
Your feedback was very helpful!
Will update on how I go in the future, many thanks again!
Willy

[DannoXYZ]

What you can do is re-use factory 2-2 exhaust and convert it to 2-1 (use just front portion before crossover pipe).

1. first remove crossover pipe from factory exhaust


2. rotate #1/left so that pipes are parallel on right side

3. chop pipes near where crossover used to be

4. use true merge collector to join with outlet of roughly 2x cross-sectionsl area. Two 31mm inlets = 1x 43mm outlet


5. finish with single-outlet and muffler

[Willy2021]

Very good option sir, you have really helped immensely with your feedback.
The term “Legend” should be added next to your current username.