Running fine without checking air fuel ratio's is a disaster waiting to happen.

For $100-$150 you can get a power run on a dyno which will check your AFR's at a minimum. Too lean or too rich will mean you have to spend money building another motor.

In regards to your exhaust question, a 2.5" exhaust will be a power restriction, but will offer less noise. If your goal is not to be too loud, then go for it. If you want power, 3" exhaust is what you will want.

If it was my car, I'd be looking at getting a tune put on it asap to ensure the safety of the motor and to enjoy it.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]