How have I missed this thread. Awesome work man.
I dig the exhaust. I've been thinking of getting some of those silicone bushings when the time comes for my exhaust. I didn't see how they could take the full brunt of the exhaust heat..............now I see they need to be stood off a bit. Drilling holes in the tabs for cooling is brilliant too.
Thanks, Kevin! This is my first attempt at an exhaust system, so I'm learning a TON on the fly.
I'm sure the holes help some, but it looks like placing the grommets about 3-4" minimum away from the tubing is by far more important. My rear (eight!) grommets are all further away from the heat than the front two, and the eight all look pretty much new. They're also further downstream, so the exhaust is cooler back there too. With the wrap in the front, the front two grommets are a little deformed but not melted as badly as they were without the wrap. I suspect ceramic coating would work even better for the grommets.
Not sure what to think about the silicone grommets as far as vibration/noise transmission is concerned. I'll have to destroy the 2000 RPM drone first (and maybe fix other, more important noises that I also can't hear at the moment haha). They are doing a good job holding the weight of the exhaust. I tried to set them up so they're holding around five or so pounds each, but I haven't seen any load limits for them.
EDIT 9/22/19: the grommets are all damaged/deformed; couldn't tell until I took the exhaust apart. I'm going to have to re-hang the exhaust using probably a mix of OEM hangers and something other than these little blue grommets. They're useless to me at this point. More to follow...
So a quick update. I now have about 900 miles down and getting ready to park it for some needed fixes and upgrades. Here's the punch-list:
1. P2098 - Post catalyst fuel trim system too lean Bank 2; erratic fuel trims on both banks (long and short term); lots of hunting and occasional stall/misfire at idle when stopping or creeping through parking lots. So far, I've checked torque on the exhaust fasteners and cleaned the fuel injectors. Looks like the stalling has stopped after cleaning the injectors. Convinced I still have a small exhaust leak somewhere (probably bank 2 / passenger downpipe or header gasket). Also looks like these were 900 rich miles, so hopefully I didn't damage the cats. Going to pressure test the downpipes off the vehicle and look for any hints of soot plumes anywhere...
2. Drone @2k RPM - After reading about all the cool kids with their Fast & Furious rides, and even some old farts like me with other vehicles, it looks like this drone problem is very common, especially for setups where none of the stock components are retained. The OEMs must put magic unicorn farts in their exhaust systems to prevent the drone (or they just build a tuned resonator into the muffler). Unless the specific aftermarket system was built and tuned for a car's exact setup (my mufflers were not), drone is almost guaranteed. The (after-thought) solution is a 1/4 wave resonator tube for each side of the exhaust. I currently don't have room for two, so I'm going to attempt to mount a single resonator tube onto the x-pipe, coming right off the top center of the X, kind of like a Kentucky pony tail
. I've not seen anyone attempt a location like this, but what the hey. If this doesn't work, I'll have to do a major re-work of the system, maybe ditch the x-pipe, make an H-pipe, relocate the mufflers to the middle and put the 1/4 wave tubes in the back. Hoping it doesn't come to that because damn, she sounds so good right now (minus the drone).