Hey I see this is an old thread but hopefully I hear from some one, just looking for the outside diameter of the exhaust pipe for an 04 GZ250

I am pretty sure it is a 51mm. If you decide to modify the exhaust, be aware that you may have to change out the jets in your carb as it will change the back pressure of your exhaust system and will cause it to run really doggy.

"I dont feel safe with it"

My.eyes just rolled over twice.

If you feel unsafe because of the volume of you pipes stay home. Good grief

"Needs backpressure" isnt a thing people. Its called scavenging. Backpressure implies that the exhaust is restricted intentionally beyond peak performance. If suzuki could make more reliable power with a louder exhaust, they would.

Mine is drilled. Why? Cuz I wanted to. Idgaf if you like it or not because its mine and not yours.

The bikes need jetted from the factory so whats the difference