accel
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I posted my self installation experience here awhile ago.
I also mentioned there was no or almost no drone. Maybe I didn`t know what it was. So, really, inside the cabin it was quiet so that I could hear and talk to passengers without raising my voice. It was not about loudness. It was some frequency inside and outside that sort of has some accumulative effect. It eventually feels like it's pushing into your ears. You do not notice it for the first couple of days, you hate it after a week, by the second week you get headache even after 15 minute drive. I didn't want to drive the car and was ready to revert back to stock mufflers.
It all started from my belief that I could make my stock exhaust marginally louder by sawing off stock tips and replacing them with tips of maximum possible exit diameter and length - kind of like musical instruments - flute, clarinet, saxophone - have deeper and louder sound with diameter and tip increase. I was hoping (and still believe) that tip alone would impact the sound level of sound system to some extent.
But then I thought that while I still had BBK varitune installed I might as well play with its tip and to see if it would make some difference. Stock GT pipe diameter is 2.5", varitune muffler exit is 3" and final single wall tip diameter is about 4".
I know some people weld some extra resonators behind aftermarked mufflers and that eliminates the drone. I didn't want to involve any welding and make the system any heavier. I also didn' want to change the system in any permanent way so that if I do not like results, I can return/sell varitune and rollback to stock.
I acquired 2.5" perforated pipe. Some exhaust adapters 3" to 2.5", ceramic wool of several formats (some loose wool, and some very dense wool), and steel wool (loose) with the intent to change characteristics of the exhaust tip.
Exhaust 2.5" -3" adapter was the thing that let me bolt 2.5 perforated pipe in and insert it into 3" muffler exit pipe. I then played with sound absorbtion materials to see what kind of configuration would have any impact. You'll see the final design I settled with. I also tried the following:
a) just inserting perforated 2.5 pipe into 3" muffler exit all the way almost to the end of the muffler tip. No impact of any kind.
b) wrapping the above pipe into very dense 2mm ceramic wool. Packing the place where 3 to 2.5 inch transition is very tightly. This basically transforms perforated pipe into a non perforated pipe. The drone outside is still present. You can feel it outside the car and inside the car with windows down. After closing windows I could tell that even the frequency was still present, it was greatly reduced.
d) Putting some thick ceramic wool around the end tip of 2.5 perforated pipe to seat the gap between the tip and the pipe and filling the rest of the void with some loose ceramic wool. I was also putting some sticky exhaust foil in the end (to seal the space between pipe exit and the tip) to make sure gases will not push the wool out as I drive.
Dramatic impact. The headache frequency is eliminated outside and inside. You could still feel maybe a tiny bit during engine cold start, for a minute, outside only, but after warmup it's gone.
I was happy as hell. After driving the car like this for a while I could definitely tell that the drone was coming back. I attributed it to ceramic wool being sealed by exhaust gase deposits/moisture.
e) in the design above replaced loose ceramic wool with steel wool. Left thick ceramic wool seal between the exhaust tip and 2.5" pipe in place.
The frequency is permanently and long term eliminated.
The foil fix wouldn't stay in place though... It stayed ok in (d) but apparently steel wool lets gases flow through much better and destroy the foil collar. Remains of foil somehow held wool in place though. In this configuration it was still killing that drone frequency just as good. So I replaced the foil with some non sealing solution and it stays in place.
I enjoy driving the car again!
P.S. forum says my pictures are too big to attach. So I'll pos the article without the pics and add them later when I resize them.
I can feel that this also killed some sound, but db measuring app does not support my assumption. It shows decibels at the same level. So this just eliminated particular frequency range. I still feel it being a little quieter.
I do have sound pipe removed. Inside cabin sound volume is pretty close to stock exhaust plus sound pipe.
P.p.s With the space between 2.5 inch pipe and the tip being not sealed, the whole system is probably less restrictive then just 2.5 pipe. So I think it should be still less restrictive than stock.
I also mentioned there was no or almost no drone. Maybe I didn`t know what it was. So, really, inside the cabin it was quiet so that I could hear and talk to passengers without raising my voice. It was not about loudness. It was some frequency inside and outside that sort of has some accumulative effect. It eventually feels like it's pushing into your ears. You do not notice it for the first couple of days, you hate it after a week, by the second week you get headache even after 15 minute drive. I didn't want to drive the car and was ready to revert back to stock mufflers.
It all started from my belief that I could make my stock exhaust marginally louder by sawing off stock tips and replacing them with tips of maximum possible exit diameter and length - kind of like musical instruments - flute, clarinet, saxophone - have deeper and louder sound with diameter and tip increase. I was hoping (and still believe) that tip alone would impact the sound level of sound system to some extent.
But then I thought that while I still had BBK varitune installed I might as well play with its tip and to see if it would make some difference. Stock GT pipe diameter is 2.5", varitune muffler exit is 3" and final single wall tip diameter is about 4".
I know some people weld some extra resonators behind aftermarked mufflers and that eliminates the drone. I didn't want to involve any welding and make the system any heavier. I also didn' want to change the system in any permanent way so that if I do not like results, I can return/sell varitune and rollback to stock.
I acquired 2.5" perforated pipe. Some exhaust adapters 3" to 2.5", ceramic wool of several formats (some loose wool, and some very dense wool), and steel wool (loose) with the intent to change characteristics of the exhaust tip.
Exhaust 2.5" -3" adapter was the thing that let me bolt 2.5 perforated pipe in and insert it into 3" muffler exit pipe. I then played with sound absorbtion materials to see what kind of configuration would have any impact. You'll see the final design I settled with. I also tried the following:
a) just inserting perforated 2.5 pipe into 3" muffler exit all the way almost to the end of the muffler tip. No impact of any kind.
b) wrapping the above pipe into very dense 2mm ceramic wool. Packing the place where 3 to 2.5 inch transition is very tightly. This basically transforms perforated pipe into a non perforated pipe. The drone outside is still present. You can feel it outside the car and inside the car with windows down. After closing windows I could tell that even the frequency was still present, it was greatly reduced.
d) Putting some thick ceramic wool around the end tip of 2.5 perforated pipe to seat the gap between the tip and the pipe and filling the rest of the void with some loose ceramic wool. I was also putting some sticky exhaust foil in the end (to seal the space between pipe exit and the tip) to make sure gases will not push the wool out as I drive.
Dramatic impact. The headache frequency is eliminated outside and inside. You could still feel maybe a tiny bit during engine cold start, for a minute, outside only, but after warmup it's gone.
I was happy as hell. After driving the car like this for a while I could definitely tell that the drone was coming back. I attributed it to ceramic wool being sealed by exhaust gase deposits/moisture.
e) in the design above replaced loose ceramic wool with steel wool. Left thick ceramic wool seal between the exhaust tip and 2.5" pipe in place.
The frequency is permanently and long term eliminated.
The foil fix wouldn't stay in place though... It stayed ok in (d) but apparently steel wool lets gases flow through much better and destroy the foil collar. Remains of foil somehow held wool in place though. In this configuration it was still killing that drone frequency just as good. So I replaced the foil with some non sealing solution and it stays in place.
I enjoy driving the car again!
P.S. forum says my pictures are too big to attach. So I'll pos the article without the pics and add them later when I resize them.
I can feel that this also killed some sound, but db measuring app does not support my assumption. It shows decibels at the same level. So this just eliminated particular frequency range. I still feel it being a little quieter.
I do have sound pipe removed. Inside cabin sound volume is pretty close to stock exhaust plus sound pipe.
P.p.s With the space between 2.5 inch pipe and the tip being not sealed, the whole system is probably less restrictive then just 2.5 pipe. So I think it should be still less restrictive than stock.
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