LS 376/480 - Backfire Issues?
Thread Starter
Instructor
Joined: Dec 2012
Posts: 155
Likes: 5
From: Illinois
LS 376/480 - Backfire Issues?
I posted this on the C3 Tech Forum, but thought there might be an expert on this Forum that doesn't comment over there --- I have an LS 376/480 crate engine in my 1970 Corvette restomod. The engine runs great, but I'm experiencing a "popping" and "crackling" sound when I decelerate while the car is in gear. Sometimes, I even get one or two "backfire" pops. What is causing this? Can it be tuned out of the engine? The car has a stainless steel Magna-Flow exhaust system that has been installed by a pro, so I know there's no flow obstruction or other problems. Could it be inadequate air intake through the K&N filter setup? Help ...
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Ive seen something similar with spark plug choices. If its too long it will cause ignitions with out actually being fired. I had all kinds of popping like that with torque master plugs I ran once. Great under full throttle but a royal pain at cruising and slowing down.
Le Mans Master
Joined: Feb 2005
Posts: 6,475
Likes: 564
From: Clearwater Florida
I posted this on the C3 Tech Forum, but thought there might be an expert on this Forum that doesn't comment over there --- I have an LS 376/480 crate engine in my 1970 Corvette restomod. The engine runs great, but I'm experiencing a "popping" and "crackling" sound when I decelerate while the car is in gear. Sometimes, I even get one or two "backfire" pops. What is causing this? Can it be tuned out of the engine? The car has a stainless steel Magna-Flow exhaust system that has been installed by a pro, so I know there's no flow obstruction or other problems. Could it be inadequate air intake through the K&N filter setup? Help ...
Last edited by C409; May 30, 2015 at 08:09 AM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Yes, If you tune so that DFCO enables sooner on decel, there will be no fuel while decelerating, to cause the combustion.
Uh Oh. A "professional"? That always raises a red flag for me! I'd carefully inspect the entire exhaust system for leaks, from the manifolds (including any AIR plumbing) to the mufflers.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 155
Likes: 5
From: Illinois
The "pro" who did my exhaust is a real craftsman, so I'm not too worried about the quality of his work, but I'll still have it checked. This guy has 40+ years experience as is the "go to" shop used by all the classic car people in my area. He is the only one who touched my car and he did the whole system from front to back, with beautiful welds (no clamps or connectors anywhere). Everyone who's seen it says, "Man, your exhaust is a work of art"!
Racer
Joined: Dec 2007
Posts: 416
Likes: 3
Well anyway, if it's not a mechanical problem it can be tuned out. DFCO, throttle follower, decay rate, etc. Closed throttle timing. Although I do believe it's normal.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 155
Likes: 5
From: Illinois
Did you ask him what might cause it? 40 years is a long time, one would think he'd have been asked that before.
Well anyway, if it's not a mechanical problem it can be tuned out. DFCO, throttle follower, decay rate, etc. Closed throttle timing. Although I do believe it's normal.
Well anyway, if it's not a mechanical problem it can be tuned out. DFCO, throttle follower, decay rate, etc. Closed throttle timing. Although I do believe it's normal.
I appreciate your input and help!
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Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
It's normal in that most if not all C5's and C6's will do it. My C6 did w/stock exhaust...more noticeably w/mufflers.
A couple people have already told you how to fix (eliminate) it....
A couple people have already told you how to fix (eliminate) it....