Cold start question
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Instructor
Joined: Jan 2018
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Cold start question
I have 2018 z06 a8 , borla attack with 1 npp valves on each muffler and cat back delete x pipe . and I am stumped on what I am hearing at start up. Cold starting in sport mode, with the npp valves opened( I done this with remote to make sure), the sound is incredible, but after about 15 seconds the sound decreases idle goes down, and it as if a ( unknown valve is closing) but my npp’s remain open.i know the engine runs richer to start, I don’t think the rpms change that much from what I am hearing. I know that I seen earlier c7 z06 that had 4 npp valves close to the mufflers, but mine only had 2. Could there be another sound damping valve upstream in the 2018 exhaust that I am hearing closing? Even with fuse 42 removed it does this. Wish I could figure how to keep those mysterious valves open because it sound so so so good!! Thanks for any help to dissect what I am hearing.
Last edited by Tray333; Aug 5, 2018 at 08:12 PM. Reason: Spelling
Drifting
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Race Director
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From: Bluffton SC via Canton Oh
I think we’re all saying the same thing...... but my understanding is it is running rich to get the cats heated up ASAP to curtail the pollution stuff.
I run corsa extremes and actually idle in the garage with the door down to keep peace with the neighbors until it warms up.
I run corsa extremes and actually idle in the garage with the door down to keep peace with the neighbors until it warms up.
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mine is a manual and it does the same.
I noticed it does it more when its lukewarm rather than a real cold start.
meaning if i went for a drive, then about 2 hours later start it up again.
Melting Slicks
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From: Eastern WA
Tech Contributor
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From: Charlotte, NC (formerly Endicott, NY)
It is just the way the engine sounds as the idle speed is dropped as the engine warms and fuel mixture leans out. Drive around at low rpms and nail the throttle wide open and it gets loud right now.
Bill
Bill
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I have an M7. And because i have a catless xpipe, the car screams as we all know. So sometimes when i'm approaching an overpass, i like to stab the throttle under it just so the exhaust can scream with NO intention of accelerating.
I'm not doing this at idle speed in 7th gear or anything like that.
But i would be in like 5th with the rpm's around 2100-2300rpm etc. Then i just stab the throttle pretty good so the exhaust can scream. The car does wanna lurch foward a bit but obviously the rpm is too low to actually get going.
Is that bad what i'm doing? LIke prematurely wearing my clutch?
Safety Car
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Thread Starter
Instructor
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Thanks to all the responses. So just so I can get it strait in my mind, this “imaginary” valve closing damping sound I think I am hearing from cold start is caused by fuel, ecm timing, and idle speed, but no mechanical butterfly valve. It does make sense, just wish the car would idle like that all the time, sure does sound good.
Race Director
Joined: Nov 2012
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Thanks to all the responses. So just so I can get it strait in my mind, this “imaginary” valve closing damping sound I think I am hearing from cold start is caused by fuel, ecm timing, and idle speed, but no mechanical butterfly valve. It does make sense, just wish the car would idle like that all the time, sure does sound good.
your car can sound like that all the time.
long tubes and an aftermarket axleback, without the npp..
my old c6 with long tubes no cats had the most amazing cold start idle, even with the stock cam.
Last edited by Z0HS1CK; Aug 7, 2018 at 12:23 PM.