Dual mode exhaust question
Thread Starter
Burning Brakes
Joined: Jun 2009
Posts: 1,065
Likes: 7
From: Madison, MS
Dual mode exhaust question
I searched but could not find an exact answer. I have a 13 gs and it has the stock, non npp mufflers on it. If I install a set of 2012 dual mode mufflers from a grandsport but do not hook up the dual mode function, will the mufflers be in the closed position or open?
Burning Brakes
Joined: Feb 2012
Posts: 977
Likes: 28
From: Lynchburg VA
It takes vacuum to open them and electricity to shut them. The valves are electrically powered closed, but by 3500 RPM the Vacuum force exerted on the valves overcomes the electrical actuators and the valves open. If there is no vacuum they will not open. This is why you need to by NPP in a box to have Dual Mode Exhaust on a non RPO Code NPP Corvette.
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,108
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
It takes vacuum to open them and electricity to shut them. The valves are electrically powered closed, but by 3500 RPM the Vacuum force exerted on the valves overcomes the electrical actuators and the valves open. If there is no vacuum they will not open. This is why you need to by NPP in a box to have Dual Mode Exhaust on a non RPO Code NPP Corvette.
Melting Slicks
Joined: Mar 2011
Posts: 2,708
Likes: 83
From: Arkansas
Actually, they are spring loaded in the open position by design. In an oem setup, vacuum forces them closed and an electrical signal opens them below 1250rpms and above 3500rpms. They are closed in-between to reduce highway drone under normal driving.
Yes OP, they will be open all the time if you install them without hooking them up.
FWIW! I pulled the fuse the instant I got the car home from the stealership and they've been that way since.
Yes OP, they will be open all the time if you install them without hooking them up.
FWIW! I pulled the fuse the instant I got the car home from the stealership and they've been that way since.
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 26
From: Austin Texas
It takes vacuum to open them and electricity to shut them. The valves are electrically powered closed, but by 3500 RPM the Vacuum force exerted on the valves overcomes the electrical actuators and the valves open. If there is no vacuum they will not open. This is why you need to by NPP in a box to have Dual Mode Exhaust on a non RPO Code NPP Corvette.
It takes engine vacuum to CLOSE the flaps. The force used is vacuum, the vacuum is switched by electricity.
Easy to check. Look at the flaps with the engine off (no vacuum), they are open.
Look at the flaps with the engine running (vacuum!), they are closed UNLESS you ELECTRICALLY turn off the vaccum.
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Burning Brakes
Joined: Feb 2012
Posts: 977
Likes: 28
From: Lynchburg VA
You are all correct I was in a hurry between projects in the garage. I only came in long enough to do some Forum Research. I happened upon this thread and in my haste to help out I typed exactly the opposite of what i was thinking.
Last edited by jsucraig; Oct 4, 2014 at 11:02 PM.
Burning Brakes
Joined: Dec 2011
Posts: 876
Likes: 116
From: HOMESTEAD FL
This is why they are open when the car is off... also when you fire it up there is a split second where it roars then quiets down as it closes... So they are OPEN when power is off.
SPEED SAFE, AIR RAM
SPEED SAFE, AIR RAM