I would like to straight pipe my car but i'm not sure what type of piping material I should buy or what size of piping. I have a 1.8l gas engine non-turbo'd. I can measure and weld the piping i'm just not sure what size of piping would be best for both sound and power.
My car has a manual transmission.
I would stick with mild steel exhaust tubing and use 18 gauage or 16 gauage (thicker wall) to weld with a MIG welder. If you use "aluminized" tubing - available from the big box aftermarket suppliers, that’s should be okay but just remember to thoroughly grind the 1/2" or so of heat-affected area where you will weld. As for diameter, going more than 1/4" in diameter larger than the stock pipe diameter (1 3/4" vs 1 1/2" for example), is excess weight and money. A small amount of "backpressure" is needed in the exhaust system.
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