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06-28-2013, 02:52 PM
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CC Member
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Join Date: Jan 2007
Location: PHILADELPHIA,
PA
Cobra Make, Engine: ANTIQUE AND COLLECTABLEFORD 460
Posts: 112
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Neutral
460 Backfire out exhaust
Hello all! Its been a while but I'm back on the Cobra track.
I have a mild 460 build, stock bottom end with late model dove heads 9:1 comp. rollers rockers, edelbrock performer intake, 750 edelbrock carb. Mallory hi fire box and distributor Cam : Intake 479 Exhaust 504 duration 270 intake 280 exhaust. Its smooth and strong all the way through the RPMS and when I let off the gas around 5500-6000 rpm it sounds like shotguns going off on either side of the side pipes. I adjusted the valves last night and its doing the same thing. Only seems to do it when its running around 195- 200 degrees. Could it be a breakdown in wires or over am I over reving motor. Oh and how much horse power do you think I am making?
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06-28-2013, 03:55 PM
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CC Member
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Join Date: Apr 2002
Location: Poole, Dorset, England,
Posts: 150
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Not Ranked
Hi Vincent , Dave in Uk, 6k is right on the limit of that combo I would think, what valve springs you running? probably getting valve float causing you some issues, should be around 400 hp, give or take. Dave
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06-28-2013, 04:01 PM
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Stolen Avitar
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Join Date: Oct 2004
Location: Brunswick,
GA
Cobra Make, Engine: BDR 1311 428PI
Posts: 3,044
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Not Ranked
I'd bet on header/collector gaskets. It's a fairly common issue with Cobras. Check your header gaskets and where your headers connect to the intermediate pipes. If air can get in either of those places back-firing on decel will occur.
Steve
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06-28-2013, 05:22 PM
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Senior Club Cobra Member
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Join Date: Jan 1999
Location: MARKSVILLE,LA.,,
Posts: 3,235
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Not Ranked
Quote:
Originally Posted by lovehamr
I'd bet on header/collector gaskets. It's a fairly common issue with Cobras. Check your header gaskets and where your headers connect to the intermediate pipes. If air can get in either of those places back-firing on decel will occur.
Steve
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+1
it doesn't take much of a leak either........and you may even get "some" popping on decel at high rpms without an exhaust leak,the engine is not under a load, basically "coasting" and the fuel is not all burnt as when under a load, so some unburnt fuel will go thru the hot exhaust,burning in the side pipes, causing the popping.......
HP wise guessing 400 to 450 with a lot more torque......
David
__________________
DAVID GAGNARD
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06-28-2013, 06:03 PM
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CC Member
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Join Date: Jul 2006
Location: Redding,
CA
Cobra Make, Engine: FFR chassis and suspension, Mr. Bruce 289 FIA body
Posts: 1,066
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Not Ranked
Exhaust manifold gasket. Mine did the very same thing
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06-28-2013, 06:20 PM
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CC Member
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Join Date: Jan 2007
Location: PHILADELPHIA,
PA
Cobra Make, Engine: ANTIQUE AND COLLECTABLEFORD 460
Posts: 112
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Not Ranked
I just had my hands in it about 10 min ago. I am noticing arching at the front of the motor the same time the back firing happens and its not all the time. I adjusted the timing reved the motor up and it was fine not backfire. After it heated up some more I seen the arching and popping again. I am running a Mallory 6al box with high fire coil but I have a set of 8 mm ford racing wires from summit. Is it possible the wires laying on the motor are breaking down from the heat and causing problems????
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06-28-2013, 06:22 PM
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CC Member
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Join Date: Jan 2007
Location: PHILADELPHIA,
PA
Cobra Make, Engine: ANTIQUE AND COLLECTABLEFORD 460
Posts: 112
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Not Ranked
How do I seal the headers to the side pipes? They are slip on?
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01-04-2014, 07:29 PM
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Registered User
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Join Date: Mar 2002
Location: Crosslake,
MN
Cobra Make, Engine: 67 Shell Valley - Kevlar; 514:TKO
Posts: 181
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Not Ranked
I frankly love the popping. Especially in the dark. It's totally bad ass. I see fire out the exhaust all the time on most al sorts of race cars - drag, Indy, etc ... Why not just enjoy it?....
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01-05-2014, 01:28 PM
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CC Member
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Join Date: Jul 2009
Location: Westerly,
RI
Cobra Make, Engine: Fordstroker 408w custom solid roller-Craft ported Brodix 17*heads-CFM ported Vic Jr. intake-1 3/4 primaries- 575hp-TKO-600RR Liberty upgrade- -Moser 8.8 trutrac-McLeod Street Extreme--QA-1-Wilwood brakes, Classic Chambered 3" Cobrapacks, Avon's
Posts: 645
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Not Ranked
Popping under deceleration [no load] is usually lean carb condition or exhaust gaskets.
Ignition usually acts up under load.
When I was playing with jets one day I went just a hair too lean and I started getting the snap crackle pop. It does sound cool though.
__________________
Lou
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01-05-2014, 05:16 PM
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CC Member
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Join Date: Aug 2008
Location: Memphis,
TN
Cobra Make, Engine: Superformance SP02423 KCR 445W 611hp 599ft lbs
Posts: 321
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Not Ranked
What Ret Cop says....
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01-05-2014, 06:45 PM
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CC Member
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Join Date: May 2002
Location: Pittsburgh,
Pa
Cobra Make, Engine: A&C 460
Posts: 169
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Not Ranked
The header fit on the 460 pipes from A&C are terrible. Leak big time. I have to use muffler sealer once a year. I'm cutting them off and putting flanges and gaskets as soon as I get a chance. When they are sealed, it sounds awesome and absolutely no back fire. Sometimes the flames are cool at night.
Mike
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01-06-2014, 07:47 AM
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Average Guy
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Join Date: Sep 2002
Location: Rushville,
IN
Cobra Make, Engine: red Shell Valley, white stripes
Posts: 579
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Not Ranked
The flames are pretty eye-catching at night. I took my son out for a spin one evening and, on an abrupt deceleration, startled him with a 6-footer. I could see it from the driver's seat. Since then, I've sized the pipe more accurately at the slip joint and now use Permatex copper at the joint. Problem solved.
__________________
When I said I wanted to be somebody, I probably should have been more specific...
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01-06-2014, 10:59 AM
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CC Member
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Join Date: Jul 2011
Location: Shreveport,
LA
Cobra Make, Engine: SAI; '68 427FESO Southern Automotive
Posts: 300
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Not Ranked
Let it pop!!!!!!:d
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01-06-2014, 11:40 AM
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CC Member
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Join Date: Dec 2011
Location: West Chester,
PA
Cobra Make, Engine: ERA #795 427 S/C completed Jan. '14 - '68 FE 427 side oiler
Posts: 1,049
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Not Ranked
Quote:
Originally Posted by VINCENT RUDI
How do I seal the headers to the side pipes? They are slip on?
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Hi Vincent,
You probably don't remember me - I looked at your car a couple of years ago when I got the Cobra bug but ultimately decided to do my own build. Anyway, my car is also slip fit and the recommendation was to use Walker's Acousti-seal #35959. It is available at most parts stores - I got it at Pep Boys. Wear rubber gloves when you use it - it's like tar.
Regards,
Kevin
Edit: Just noticed that Vincent's inquiries are from last June...old thread.
__________________
"Anyone who drives faster than you is a maniac and anyone who drives slower than you is an idiot" - George Carlin
Last edited by kevins2; 01-06-2014 at 11:45 AM..
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