Exhaust crackle and octane?

[440]

Just curious about how octane affects crackling or backfiring on deceleration.

The accepted idea is to use the lowest octane that doesn't ping under acceleration. I can run 87 in my truck without pinging but on decel it crackles, pops and carries on. Same with 89.

If I run 100-110 octane it decels crisply without any backfiring.

[BLK 68 R/T]

Just guessing here - crackling/backfire=un-burnt fuel in the exhaust igniting after it has been expelled from the combustion chamber? higher octane fuel has a better combustion, which therefore decreases the amount of un-burned fuel entering the exhaust? again this is just my theory 

[Troy]

Octane makes fuel harder to burn (less likely to detonate when hitting really hot stuff).

My Mach 1 crackles when I let off the gas quickly but I always thought that's because it was too lean (it has a stuck idle needle). I never researched it much.

Troy

[440]

It has never bothered me before nor does it bother me now. I'm just curious as to why it happens.

From what I gather when you back off the mixture goes lean and the fuel doesn't completely burn in all cylinders. When one fires it then burns the excess fuel in the exhaust.

Is it only because the higher octane is harder to ignite in the exhaust? Interesting .. 

[c00nhunterjoe]

Typically this is caused by an exhaust leak allowing air to be drawn into the exhaust. Dkesnt have to be a big one.