Just installed a 60mm test pipe and mugen exhaust. After a couple of days I'm hearing a blow off like noise after I let off the throttle hitting redline in first and second. Haven't tested higher gears yet. Weird thing is it doesn't occur when I shift at 7k. I don't see any black soot on the flanges but will get underneath the car this weekend to get a better look. From inside the car it sounds like it's coming from the test pipe area.

 

I narrowed the sound to the test pipe area. Checked all the connections and none have the black soot so no apparent leaks. Check the tq on all bolts and they seem to be good as well. My last guess is maybe the flange from test pipe to header is thinner which doesn't compress the springs enough causing them to vibrate at high rpms? Sound plausible? If so, I think the next thing to do is to put a few washers in between the flange and spring bolts to see if that makes a difference.

 

are you sure a blow off type noise or more like a pop or bluff? it could be you backfiring or back pressure from your tp and exhaust set up

 

Sounds like a release of air to me. I'll do some video.

 

from what i read here is that when you hit redline to a certain point spark cuts off and only fuel is being injected. the unburn fuel will get pushed through the exhaust pipes making sounds

 

Same thing happening to me. Also happens when I rev-match from fourth to third and from third to second. At first, I thought something was loose but everything checked out. You might be right with the spring idea. Let me know if that works for you. BTW, my setup is berk header to test pipe + 3" single combined.