Just wondering if those of you who have a test pipe have experienced any discolouration of the rear bumper bar particularly on the White evos.? Just wondering because my previous nissan 240sx (i think thats what it is in the states) had serious yellowy soot/crust deposited over a period of time.. Is this more of a tuning issue or non cat issue??

any significant odor also??

cheers

 

I can't say anything about the discoloration as I have a GG. But you can smell it.

 

State of tune will have quite an effect as will how often you get into full throttle which is where the car will run the richest. I have a GG with a test pipe so it's somewhat hidden but my original tune ended up being around 10.8 in the midrange literally painting my bumper with soot and brown coating. I ended up leaning my car out into the 11.3 to 11.5 AFR range and it's light years better compared to before. At Watkins Glen I still was belching fireballs shifting out of 4th at high RPM but the back bumper only had a few black spots here and there with the tips only slightly discolored.

I would try and aim for a safe tune around 11.5 AFR's on the street and maybe dial back the timing slightly if you are beating it up on a road course track. My mileage numbers seem to have improved a bit as well, not a ton, but every bit helps. Staying with a high flow cat will light up some of the unburnt fuel before it exits the tailpipes and along with a tune would still be the cleanest burning option.