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Discussion Starter · #1 ·
When we are in "normal mode" only 2 exhaust valves are open.
Does it stay this way even when we run the rpms up through 6k?
or does the car automatically open all 4 valves at a certain rpm range?
Somebody asked me this question last weekend and I wasn't sure the answer..
 

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That's not how it works . . . The mufflers have 2 circuits each and one valve each. When in normal mode (quiet mode) the exhaust runs through the outer tip, which in effect is a normal muffler circuit. When the exhaust valve opens the the exhaust now has an unrestricted path through the muffler past the valve and the inner tip. The valve opens normally at about 1/3 throttle at lower RPM's and requires a bit more throttle at higher RPM's. It is almost like the ECU detects a load condition to open the valve. I also notice the valves open a little sooner when the car is cold as compared to when it is running hot.
 

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... I also notice the valves open a little sooner when the car is cold as compared to when it is running hot.
I think this was already mentioned on a previous thread, but you can cycle the valves closed before starting the car by holding the clutch in for a few seconds. If it's quiet, you can actually hear the valves cycling open. I was so glad when I found this out, because I leave fairly early in the morning and I was starting the car full blast in my garage with all the fun reverberation sounds. Well fun for me, not the neighbors lol.
 

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Discussion Starter · #4 ·
That's not how it works . . . The mufflers have 2 circuits each and one valve each. When in normal mode (quiet mode) the exhaust runs through the outer tip, which in effect is a normal muffler circuit. When the exhaust valve opens the the exhaust now has an unrestricted path through the muffler past the valve and the inner tip. The valve opens normally at about 1/3 throttle at lower RPM's and requires a bit more throttle at higher RPM's. It is almost like the ECU detects a load condition to open the valve. I also notice the valves open a little sooner when the car is cold as compared to when it is running hot.
Dave I appreciate your detailed explanation, but if you were to dumb it down for me... so if you are driving in normal mode and you get on it the exhaust db levels will be the same as if you are in sport mode, and then return to quiet mode once the rpms come down.. do I have that right?
 

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It looks to me like ECU is looking at vacuum values to determine the opening. The vacuum values being closely related to load it makes sense that it takes less throttle to get them going on the lower end of the RPM spectrum.
 
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