So during a typical start up, the car had a major backfire. It was so loud that my ears were ringing for about 20 minutes after the backfire. Since it was so loud, and I was in my garage with the door open I assume that it was from the intake, as if it was from the exhaust it would not have been so loud.

I plan to check the spark plugs, compression, and distributor (to make sure it is not lose)... is there anything else I should check to make sure nothing was damaged and ensure this does not happen again? Are there any typical culprits of an intake backfire from 455s?

Thanks!

Timing and/or internal carb leaks or stuck carb floats!

Probably timing related...done anything to it lately? Dist, timing chain?

I have not adjusted anything, that is what seemed odd to me. It ran fine the day before, sat over-night and then did this around noon the next day.

Does it run ok now?

I have been affraid to start it, I don't want to further any damage. I figure I will do a quick compression test and replace the spark plugs (since they will be out). I am also going to check/change the fuel filter.

Anything else I should check before I crank it over? I figure you guys are the experts on these, I am a fairly new owner with just enough mechanical know-how to be dangerous.

I'd try to start it again first before anything else. If it does it again and wont run, something may be broke, i.e. timing chain, dist. drive gear or something in the valve train possibly.

Had that problem with my old Holley on my 400. Carb leaked down fuel into intake and tried to start and massive backfire...and blew powervalves.

Mine was fuel leak related....did not happen after rebuilding carb.

Have same prob with my holley d/p if pump to much before crank'n.
Boom...then flames...

Forgot about that...if it's a Q-jet it may have leaky bowl plug(s) if it was never epoxied when rebuilt.

haha well, I don't THINK there were flames; but I don't know because the hood was down and air cleaner was on.

However... you guys are making me wonder. I have a speed demon carb, which is similar to a Holley. The garage always smells of gas after I park the car so I wonder if I have a leak too, I just assumed the gas smell was because the carburator system is a wet fuel system so there would be fuel in the intake. If I have a leak, that may have been what caused the detonation.

I still want to check compression to make sure I don't have a valve that is stuck or a broken timing chain. After that I will turn her over with power and see what happens.

Backfires are not usually a big deal. Most occur when fuel ignites when the intake valve is partially open and the spark plug fires the cylinder. Imagine this situation.... you crank the engine drawing fuel into each cylinder. The engine does not fire right away (i.e. cold start) and you let off the key. The engine stops just at the point of ignition to whatever cylinder, but the motor backs sightly due to compression kick back and the intake valve comes back open slightly igniting the fuel in the intake making the loud bang. I would crank the motor again, and if it replicates a back fire again, there are more serious problems, but my guess is that it will start just fine. Your timing may be a bit too far advanced too.... Sorry fot the loooong post.

For those that may be curious, I started up the old Firebird last night... cringing with a little fear, but confident that the majority of you were right. Sure enough she started up just fine. I gave her some gas, sounded good, so I took her out for a little ride to see how she would handle the road. Sure enough, she ran like a champ. Ironically, I think the Firebird ran better than in the past, so maybe the backfire cleared out some carbon or something!

Thanks for all the advice, you guys saved me a few hours of work checking the distributor, compression, etc. It has been a long time since I have experienced a backfire, so I was a bit nervous.

Thanks again