What alot of people do not understand is Honda engines are different to most 4cyl setups you need to look at alot of things when it comes to choosing the right exhaust for your car with its given engine size.There are so many papers written by text book tradesmen about exhaust size + header design and so on but not one of them has ever tested there idea's but yes it works on paper and in a engine simulation computer program but in the real world its a fail,the sizes I posted before are a general idea of what I have always found to work on Honda engines and in no way am I saying I am 100% correct it just comes from years of dynoing and testing and racing these Honda engines that we all own.