460 Backfire out exhaust

[VINCENT RUDI]

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?

[keane]

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

[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

[DAVID GAGNARD]

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

+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

[Bill D]

Exhaust manifold gasket. Mine did the very same thing

[VINCENT RUDI]

How do I seal the headers to the side pipes? They are slip on?

[kevins2]

Originally Posted by VINCENT RUDI

How do I seal the headers to the side pipes? They are slip on?

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.

[VINCENT RUDI]

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????

[Jahred]

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?....

[RET_COP]

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.

[Pman1961]

What Ret Cop says....

[gman]

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

[Dirty Harry]

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.

[Tutosnake]

Let it pop!!!!!!:d