Can anyone offer advice as to why my muffler exploded last night?

73 F250 Camper Special, 390 w/ 600 cfm Edelbrock carb and Performer Intake manifold. The engine is otherwise stock, minus the Edelbrock air cleaner. Exhaust is/was dual exhaust exiting passenger side just ahead of the rear wheel. Kinda ghetto fabbed, PO just welded both mufflers together rather tahn hanging each pipe individually.

Also, any advice on a cheap muffler to replace with? I'd love an FM40, but not so much the price. What about a Spintech or other basic turbo muffler?

 

an exhaust leak can help ignite some unburnt fuel. A header leak often makes little popping noises on decel for instance.

 

Mine would occasionally buck and pop on acceleration or cruising. It was going through a particularly rough spell of it when the muffler popped.

It felt like it did it once or twice afterwards, but much smaller.

 

Raw fuel getting into the exhaust, have you checked to see if all the spark plugs are firing all the time?

 

Don't put another muffler on until you figure out why it did that

 

My Mustang blew out both of the mufflers after dropping the ignition at about 4,800rpm on a wide open throttle blast thanks to a loose +12v to the coil. I still had my foot in it and it sucked a huge amount of fuel and air into the exhaust. The ignition came back at about 900rpm while it was still spinning down and it blew the heck out of my roll crimp cased mufflers (older Hooker Super Comp Mufflers.) I was told the fireball was quite impressive

My $0.02? Ignition or Fuel

I'd start with the ignition system: plugs, plug wires, points, distributor cap, coil, rotor, etc. That fuel is getting past the engine unburned so try to figure out why that is happening. If your ignition is intermittent like in my example above, you will have the same problem. Confirm your timing as well.

Second is fuel, usually the carb. If you dump enough fuel through the engine, its going to 'wet' your plugs and they won't fire. This is a pretty extreme case and you have to be running really, really rich to make this happen, but its still a possibility. A decent way to check this is to pull the spark plugs and check the colors of the insulator right below the electrode. Check out this site for a really nice plug chart. Huge black cloud on acceleration or unburned fuel smell in the exhaust at idle is another give away.

 

I blew the mufflers off my Bronco when the roll pin on the cam gear of the dist. broke and as the engine was spinning down it pumped fuel into the pipe and did fire a couple of times.

 

It does smell rich. The plugs and wires are all new, did them same time as the 600cfm carb.

Note on the carb, it is an electric choke model, but the wire running to it looks pretty small and weak. Were these originally electric choke? Could that be an issue, maybe the choke isn't warming up fast enough and making it run rich. It seems to run better once the engine warms up, fewer occurrences of the bucking and popping.

It sounds like my plans to buy a DUI have been bumped up some though to ensure proper ignition...

 

spintech is not a turbo style muffler, and it's even more expensive than flowmaster if i remember right. Thrush makes the welded two chamber muffler, which is identical to the original 40series, but about half the price.

 

Here's some pics, finally. I cut the two pipes off in order to keep from having an imbalance in backpressure. Or something like that...








Video:

 

Figure out what the problem is, and imo redo the entire exhaust headers and all. No need for cats on these trucks (or any for that matter)

 

There's need for cats on vehicles that came with them. Federal law... I've thought about adding cats just to clean up the exhaust a little bit. But that would be down the road once I've got the engine fully checked over and running how it needs to be. I'll probably try to diagnose the problem of course and put two new mufflers on, then when I have cash for it, get some headers.

 

I believe it depends on your state. Here in TX, anything older than 25yrs doesn't have to pass any emissions testing, and gets the standard lights/horn/brakes inspection and that's it. As long as it honks, shines, and stops, you can do whatever you want to it. Never had any cats here. I'm a dog man myself lol.

 

It wasn't until 78 that cats were installed on these. Also, same as Sleepy, here in ohio if it's over 25 years old you do whatever you want with it. I use historical plates, and never need an inspection, and let let my FE roar with a good unrestricted exhaust. Screw the EPA.

 

Mandating cats on all vehicles that came from the factory with them is a federal thing, not state. I don't intend to argue it, that's just what it is. And yes, our trucks came factory without, so we needn't worry, I just think about installing some on mine for my own reasons. Get rid of some of the stink. I'm not looking for max power, it's an old work truck. The 5 hp I might lose is not a worry for me.

Now, once I fix the explody muffler problem, what would you guys recommend to maintain the awesome sound of an uncorked 390 while retaining my hearing and keeping the lynch mob of neighbors at bay?

I've been told that it might be an issue of improper jetting letting the engine run too rich. My plan is to get that taken care of and see what happens. If it still has the same issue, I'll also do a new cap and rotor and ignition coil. It already has new plugs and wires. I'm hoping that rejetting the carb will do the trick since I don't have the money for a DUI distributor/coil right now, and I don't want to spend money on a cap and rotor and ignition coil that will be getting swapped for a DUI as soon as I have the cash if I don't have to.