The other thing to consider in the big picture with intake and exhaust is you will only get coming out essentially what went in. For instance if you have a restricted intake (plugged filter) you can open your exhaust all you want but nothing will improve. The other way is run perhaps a K&N to allow more air in but if your exhaust is plugged your not going to gain. Don't get me wrong there are other factors involved such as air volume, air/fuel ratio, back pressure etc.

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