Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB - View Single Post - I need a quiet exhaust system 2.5-2.75"

johnmk · 04-05-2016, 11:22 PM

Hello folks,

I'm having the ptuning turbo kit (w/ GTX2867R) installed in a few weeks, and need to figure out what to do about the exhaust. I'm concerned about noise, inside and outside of the vehicle, as I drive in a lot of neighborhoods where excess noise would not go over well. I'm also not a fan of needless noise myself, nor are my passengers. My goal is a sleeper vehicle with a modest boost to power.

What I'm reading seems to indicate that the larger the exhaust diameter, the louder the exhaust. Also, since my turbo goals are no higher than 300 horsepower, I don't see the need for a 3" (76mm) exhaust. The sweet spot appears to be around 2.5" (63mm). I think 2.75" (70mm) would be tolerable as well. The stock exhaust being, if I read elsewhere correctly, 2.25" (57mm). I'm not 100% sure that's right though but I can't imagine it being any higher than 2.25". These metric conversions appear quite odd to me, by the way, since I would think the car's specs would be conceived in metric. Why would a non-US car company bother with such odd values as 57mm for an exhaust, when 55mm or 60mm are cleaner values? I wonder if the stock exhaust is really 55mm (2.165"), but anyway, I digress quite unnecessarily here. :-)

The ptuning turbo kit dumps the wastegate into the exhaust, by the way. I'm not sure if that's relevant to my central question in this thread, but it could be if a small diameter exhaust system restricts exhaust flow at a bad time -- I don't know if that's a concern, or not.

I'm considering the Invidia Q300 cat-back exhaust, but diameter appears slightly to the low side of my goal (2.5 being ideal, I think). At only 2.36"(60mm), it doesn't appear to be that much of an upgrade from stock (55mm), though 60^2/55^2 = 1.19. So Q300 has almost 20% more cross-sectional area and should flow at least a bit more air than stock. The Q300 being cat-back, how would I mate it with the ptuning turbo kit components?

Is there something a bit roomier than the Q300 that's also quiet and can be mated with the ptuning turbo kit? I guess anything I get will probably need to have a suitcase-style muffler.

Here's the exhaust system that ptuning have designed for use with their kit.

http://www.ptuning.com/subdir/itemde...&ModelDesc=BRZ

It looks top-notch, but IMO the emphasis appears to be on performance and not noise-suppression. Those mufflers seem awfully small. Is size a fair way to predict muffler performance, in general?

Anyway, please folks. Help me out! There are a dizzying array of options out there and I must decide soon, or my install schedule has to slip.

Thank you so much for your time folks.

-John

04-05-2016, 11:22 PM	#1
johnmk Fidei Defensor Join Date: Mar 2016 Drives: 2015 Subaru BRZ Limited - Black Location: Sequim Posts: 34 Thanks: 1 Thanked 3 Times in 1 Post Mentioned: 0 Post(s)	I need a quiet exhaust system 2.5-2.75" Hello folks, I'm having the ptuning turbo kit (w/ GTX2867R) installed in a few weeks, and need to figure out what to do about the exhaust. I'm concerned about noise, inside and outside of the vehicle, as I drive in a lot of neighborhoods where excess noise would not go over well. I'm also not a fan of needless noise myself, nor are my passengers. My goal is a sleeper vehicle with a modest boost to power. What I'm reading seems to indicate that the larger the exhaust diameter, the louder the exhaust. Also, since my turbo goals are no higher than 300 horsepower, I don't see the need for a 3" (76mm) exhaust. The sweet spot appears to be around 2.5" (63mm). I think 2.75" (70mm) would be tolerable as well. The stock exhaust being, if I read elsewhere correctly, 2.25" (57mm). I'm not 100% sure that's right though but I can't imagine it being any higher than 2.25". These metric conversions appear quite odd to me, by the way, since I would think the car's specs would be conceived in metric. Why would a non-US car company bother with such odd values as 57mm for an exhaust, when 55mm or 60mm are cleaner values? I wonder if the stock exhaust is really 55mm (2.165"), but anyway, I digress quite unnecessarily here. :-) The ptuning turbo kit dumps the wastegate into the exhaust, by the way. I'm not sure if that's relevant to my central question in this thread, but it could be if a small diameter exhaust system restricts exhaust flow at a bad time -- I don't know if that's a concern, or not. I'm considering the Invidia Q300 cat-back exhaust, but diameter appears slightly to the low side of my goal (2.5 being ideal, I think). At only 2.36"(60mm), it doesn't appear to be that much of an upgrade from stock (55mm), though 60^2/55^2 = 1.19. So Q300 has almost 20% more cross-sectional area and should flow at least a bit more air than stock. The Q300 being cat-back, how would I mate it with the ptuning turbo kit components? Is there something a bit roomier than the Q300 that's also quiet and can be mated with the ptuning turbo kit? I guess anything I get will probably need to have a suitcase-style muffler. Here's the exhaust system that ptuning have designed for use with their kit. http://www.ptuning.com/subdir/itemde...&ModelDesc=BRZ It looks top-notch, but IMO the emphasis appears to be on performance and not noise-suppression. Those mufflers seem awfully small. Is size a fair way to predict muffler performance, in general? Anyway, please folks. Help me out! There are a dizzying array of options out there and I must decide soon, or my install schedule has to slip. Thank you so much for your time folks. -John Last edited by johnmk; 04-05-2016 at 11:34 PM.