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Discussion Starter #1
Just changed the rear muffler on my 33 to get a slightly louder exhaust note ( sounded like any other car ) but now the exhaust is popping quite significantly under deceleration. What causes this? and what can I do to minimise it? or should I bother at all.
Thanks
 

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it is the nature of alfasuds to give a fast popping at revs under deceleration
but if it is a slow occasional one, its probably signifies an air leak in your induction.
 

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The popping sound on the overun is *the* characteristic of the Alfa flat 4 engine! I used to drive my Alfasud around with the a stupidly loud exhaust system, and driving through a tunnel, carpark, etc was just bliss!

My theory on the popping sound is that its the unburnt fuel burning on its way out of the cylinder - even with your foot off the accelerator the engine is still sucking in quantities of air saturated in petrol, and it "pops".

~Benjamin
 

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What, don't you like it? :D

It is caused by unburnt fuel detonating in the exhaust. You can see an extreme example of this in V8 supercar racing - watch how flames come from the exhaust on the overrun.

Lumpy cams with lots of overlap are the culprit. On the twin carb suds this is quite pronounced. I imagine the injected boxers are much quieter as they were tuned much 'cleaner'.

Your new exhaust is contributing as it will be more free flowing, and it's larger diameter will amplify any sounds in the exhaust.
 

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mate are you mad leaveit. my sprint pops like nothin else i love it.... i like to call it burble and crackle....hehe
 

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My serie 3 33 does it too.. when i bought it id didn't do it but when i took it to a mechanic and adjusted the carbs and timing it does it! I like it, but a friend of mine told bme that i could be bad timing, could it be?
 

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Discussion Starter #7
My Sprint

has a nice crackle to the exhaust but doesn't have popping any where near as loud . Is the 1.7 different in the valve timing?. As for the noise as long as it's legal it's fine by me!.
 

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Love the popping. Its the highlight of my sunday drives...


Its really part of a fantastic sounding engine.

1. You get that great gruff and rorty note on acceleration....

then

2. You get the popping on the over run.

4 cylinder 'Bliss'
 
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