Wouldn't it be cool if the C7 exhaust stayed as loud as it is when it first starts?
03-07-2014, 09:59 AM
#1
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Wouldn't it be cool if the C7 exhaust stayed as loud as it is when it first starts?
Dang it sounds awesome when it starts cold in the garage in the morning. I would love it to stay that loud all day what about ya'll?
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03-07-2014, 10:00 AM
#2
03-07-2014, 10:19 AM
#5
Race Director
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03-07-2014, 11:20 AM
#6
Race Director
Yeah, there definitely no way to be stealthy when starting the car. If you want to attract attention its great but when I go to work at 7am my 93 yr old neighbor gets blasted out of bed since my garage faces his bedroom. 
03-07-2014, 11:22 AM
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tlippy (12-06-2016)
03-07-2014, 11:24 AM
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St. Jude Donor '11-'12-'13, '16-'17-'18
03-07-2014, 11:33 AM
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What OP is trying to say is that after the car warms up, the exhaust note changes, which it does on my car too.
NPP is always open / set to OFF but something with the metals or something along those lines make the exhaust quiet down after 1 minute or 2.
Has nothing to do with the valves opened or closed.
03-07-2014, 11:48 AM
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St. Jude Donor '11-'12-'13, '16-'17-'18
What OP is trying to say is that after the car warms up, the exhaust note changes, which it does on my car too.
NPP is always open / set to OFF but something with the metals or something along those lines make the exhaust quiet down after 1 minute or 2.
Has nothing to do with the valves opened or closed.
It seems to be pegged to throttle position, vehicle speed and engine revs. I need to do a more empirical assessment of the details however but it is quite obvious the NPP isn't "open all the time"
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bjones7131 (12-06-2016)
03-07-2014, 11:55 AM
#12
Melting Slicks
The C7 flapper valve is electronically controlled in lieu of vacuum controlled. In sport mode the computer is constantly opening and closing the flapper. In track mode it is open more of the time, but still not constantly.
Last edited by Steve Garrett; 05-29-2016 at 10:59 AM. Reason: Merged Posts
03-07-2014, 12:05 PM
#13
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I disagree. Even when set to OFF, there are times the butterflies still open and close, at least on my car.
It seems to be pegged to throttle position, vehicle speed and engine revs. I need to do a more empirical assessment of the details however but it is quite obvious the NPP isn't "open all the time"
It seems to be pegged to throttle position, vehicle speed and engine revs. I need to do a more empirical assessment of the details however but it is quite obvious the NPP isn't "open all the time"
With the setting on "OFF" The valves are open at idle.
As to what you are referring to, yes my valves close at certain RPMs especially low ones in 4th gear.
OP Is stating it would be nice to sound as raspy, throaty and deep as when you initially start the car.
Go listen for yourself and listing to the sound levels decrease with engine temperature.
03-07-2014, 12:06 PM
#14
Instructor
I 'll bet if you took off your mufflers to gain access to the butterflies on the engine side of your mufflers, there would be 2 screws holding each butterfly valve in place. (I think it's the same on the tailpipe end butterflies too)If you removed the butterfly valves you would get loud exhaust all the time and no check engine light. ( if you were to remove the wire to the electric motor that operates the valves)
Then you could still use your in car controls (tour, sport, track...) to make the car quiet or loud. But in V4 mode you would here the 4 cylinder drone sound when your exhaust was set to loud.
My brother and I did this on the throttle bodies on our ZX-14's. It helped a lot on the low rpm torque.
Then you could still use your in car controls (tour, sport, track...) to make the car quiet or loud. But in V4 mode you would here the 4 cylinder drone sound when your exhaust was set to loud.
My brother and I did this on the throttle bodies on our ZX-14's. It helped a lot on the low rpm torque.
03-07-2014, 12:19 PM
#15
Drifting
While you are correct, not in the case of what OP is stating.
With the setting on "OFF" The valves are open at idle.
As to what you are referring to, yes my valves close at certain RPMs especially low ones in 4th gear.
OP Is stating it would be nice to sound as raspy, throaty and deep as when you initially start the car.
Go listen for yourself and listing to the sound levels decrease with engine temperature.
With the setting on "OFF" The valves are open at idle.
As to what you are referring to, yes my valves close at certain RPMs especially low ones in 4th gear.
OP Is stating it would be nice to sound as raspy, throaty and deep as when you initially start the car.
Go listen for yourself and listing to the sound levels decrease with engine temperature.
Cold startup is awesome. Then it ramps down very noticeably after about 15-20 seconds over a span of just a few seconds.
There are 2 sets of valves on the NPP: ones forward of the muffs and ones in the tailpipes. Non-NPP has only the forward valves. I believe these front valves are to manage backpressure in certain conditions as well as taming 4-cylinder fart mode.
I also notice that even though my NPP is set to "open" all the time, there are throttle conditions (low RPM tip-in on upshifts especially) where the sound is quiet and then something "opens" at about 1700 RPM-ish. So I -think- this is the effect of the forward valves.
This tip-in behavior does -not- change with drive mode selection. At idle and most acceleration conditions, it's clear that my rear NPP valves are open.
I also wonder if this behavior is different between A6/M7; mine's M7.
Last edited by xp800; 03-07-2014 at 12:24 PM.
03-07-2014, 12:21 PM
#16
Pro
What OP is trying to say is that after the car warms up, the exhaust note changes, which it does on my car too.
NPP is always open / set to OFF but something with the metals or something along those lines make the exhaust quiet down after 1 minute or 2.
Has nothing to do with the valves opened or closed.
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AdventurePoser (12-06-2016)
03-07-2014, 12:28 PM
#17
I bet the engine mixture, timing, etc. is different during cold start because the cats need to be heated quickly for EPA compliance. This would account for some of the difference in exhaust note.
Cold start "sounds" can be humorous. My 2006 GMC Duramax pickup has a fast cold warmup mode if it is below 32 degrees. Unlike gas engines the diesel starts at its 600 RPM base idle but after about 30 seconds it will begin to ramp up 100 RPM at a time until it finally reaches around 1200 RPM. While this is going on the turbocharger exhaust vanes are moved to their most restrictive position and the Allison transmission is used to load the engine but its output shaft is still locked. It sounds like a little jet engine on takeoff at this point. When my daughter was about 3 I had buckled her in her car seat in the back and then ran inside to grab the cell phone I had forgotten. During this time the engine went into its fast warm strategy and Anna thought the truck was leaving without me
Cold start "sounds" can be humorous. My 2006 GMC Duramax pickup has a fast cold warmup mode if it is below 32 degrees. Unlike gas engines the diesel starts at its 600 RPM base idle but after about 30 seconds it will begin to ramp up 100 RPM at a time until it finally reaches around 1200 RPM. While this is going on the turbocharger exhaust vanes are moved to their most restrictive position and the Allison transmission is used to load the engine but its output shaft is still locked. It sounds like a little jet engine on takeoff at this point. When my daughter was about 3 I had buckled her in her car seat in the back and then ran inside to grab the cell phone I had forgotten. During this time the engine went into its fast warm strategy and Anna thought the truck was leaving without me
03-07-2014, 12:42 PM
#18
Corsa's on my C6, the same thing is noticeable, it is definitely louder idling for about the first 60 seconds.
My non-expert theory is that it likely has something to do with some parts expanding as they heat up.
My non-expert theory is that it likely has something to do with some parts expanding as they heat up.
03-07-2014, 12:48 PM
#19
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Mine is always louder at startup as well. It does not get any quieter when starting even if when I had put the car in economy mode before shutting it off.
I think it has to do with the sudden crashing of all the air molecules inside the pipes as the engine starts and then slowly calms down as the air molecules all get to moving in the same direction out the tailpipe. Just a theory.
I think it has to do with the sudden crashing of all the air molecules inside the pipes as the engine starts and then slowly calms down as the air molecules all get to moving in the same direction out the tailpipe. Just a theory.
03-07-2014, 12:59 PM
#20
Racer
I would go with this explanation. Same thing happens with my C6 LS3 w/o NPP. They run richer on cold start-up.
