When I let off the gas, my exhaust sounds like it's rumbling and popping. I have an internally stock 305, w/o any emission controls, headers, 2-1/2" Y-pipe, 3" cat back (w/o cat), Holley 670 Street Avenger, Edelbrock Performer EPS and MSD Street Fire non-cc HEI.

Any ideas out there?

 

Because it's normal.

 

Your not running enough horse to warrant a three inch exhaust first of all. Secondly you may be running too rich...

 

lack of back pressure will cause this.

 

Thank you for your thoughtful replies. Now that I think about it, this may have first started after I installed a 3" cat back exhaust when I first bought the car.

 

In my opinion a free flowing exhaust + manual trans will do this. A lot of race cars do it. There's nothing wrong with your car or anything, but with a manual transmission the engine acts a little differently under sudden coasting or engine braking scenarios than automatic cars do. You'll notice it a lot on the T5 5.0 Mustangs too. Just one of those perks of having a good exhaust on a manual trans car.

(Mine does it too).

 

Ive had white brother's and supertraps for my motorcycles and atv's. The way to tune those is to install a bunch of discs and then start remove them until the popping sounds is gone or almost gone.

 

It does put me at ease that nothing is apparently wrong with the engine. It does run really nice now, considering how it ran when I bought it stock with a bad auto tranny.

 

This is incorrect.
Backpressure is a bad thing in a 4stroke. 2strokes like a dirtbikes need some.
3" single catback is fine on a 305. The car may have a some unburned fuel lighting off in the exhaust due to a inj dribiling, timing issue, valve hanging open or a exhaust leak. Even a few other things can cause it.

Just a fun lil story. Back in the day of carbed cars we would go down the road in my old beater 76 chevy truck, shut the key off while still in gear, pump the gas pedal a bunch, turn the key back on then it would blow the mufflers apart!!! fun stuff right there.. lifetime warranty mufflers rock!!

 

I love that sound. On my old 305 I had in the 'bird, it was stock exhaust hacked at the front of the car with a small glass pack and I'd rev it and do a lot of engine braking just to hear that rumble and pop going down the road.

 

yeah its nothing bad my v6 did it after i cut the cut out

 

My Z28 does it as well, when I'm accelerating hard an suddenly let off it to slow down I tap the pedal hard it will rumble nice also when shifting down gears

 

I am on board with TT-TOP350 on this. I have seen this on many carbureted engines with free flowing exhaust. The open exhaust doesn't cause it, it simply allows you to hear it. The cause of the "pop" is unburned fuel combusting in the exhaust. The cause of this is generally either ignition misfire, lean misfire during decel fuel cutoff, leaky decel fuel cut off in the carb allowing fuel to pass, an exhaust leak allowing oxygen into the exhaust close to the hot manifolds, or leaky exhaust valves. Leaky injector(s) or a valve train issue will also cause it on an EFI car.

My Beasty did this one time when I first put the new valve covers on. I knew right away that the valve covers were interfering with my rocker arms, causing the valves to stick. A change of the rocker arms and verifying that the valves were okay solved the problem. I love the rumble of my exhaust on decel. I hate when cars pop. It always makes me think of an old beater truck.

 

You have a rumbling American v8. Smile and be happy about it. Some people have to put up with 4 cylinder imports that sound like kitchen appliances.