could the flowmaster possibly be more restrictive than OEM? my main concerns are weight and keeping the noise level down, any gain in power at all would be a plus but im not looking to maximize power or anything. now if it actually reduces power, that might be a different story
if youre not looking to maximize power like i was, then a flowmaster could be okay. its still very restrictive but probably a little better than OEM. I went through a few different itterations of my exhaust. Ill go through the steps and describe the sound level.
1. I started with stock header, stock cat stok catback
2. I had a 2.25" catback made and retained the stock cat. I used a magnaflow straight through muffler with no resonator. Under normal driving conditions, it was quiet and had a deep, low growl. At WOT it would fart and would very raspy. Very minimal gains up top notcied.
3. Replace the stock header with a longtube header. This didnt make it much louder during normal driving. Very deep, manly sound that was smooth until the top of the RPM range (6000-7000). Then it would rasp out again. This setup is perfect for most people. I noticed minimal gains down low, if any, and a small increase from mid to up top.
4. (Heres where the hunt for horsepower took over) I removed the cat. This made the entire thing much louder and wayyyyy too raspy. It drove me crazy but there was a noticeable gain through the entire RPM range.
5. Removed the magnflow muffler and replaced it with a magnaflow resonator. This didnt change the sound level, it changed the tone. It made it much lower and took out most of the rasp. This setup easily provied me with the most HP but the drone at 70mph can drive other people crazy. My passengers hate it most of the time. Its forced me to drive much easier on the car when Im not racing so Ive actually saved money on gas haha.
All iterations of my exhaust were tested in a race against the same miata every single time. My buddies stock 03 miata. We would do 3rd gear pulls from 1500rpms until redline and compared distances before and after using go pro cameras and gps things. It wasnt perfect but it helped me understand where the gains were being made. Being a poor college student, I cant afford dyno time every other week when i decide to change something.