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Discussion Starter #1
Dear all,
During the restoration of my Spider I took off the exhaust system. I have always wondered what the strange, what looked like expansion chamber was in the system.
The exhaust I believe was fitted in California before I imported the car to the UK in 2009. I was amazed to see what was inside!
I would be very interested to hear if anyone knows what it is and why it was fitted. I have raced cars for many years and to my mind all it did was cause a severe disruption to the flow of gases. It was fitted with the scoops facing into the gas flow just after the secondaries.
Have a look and see what you think.
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I have no expertise on the matter so I should probably not reply but as a guess, I'd suspect that it is an aftermarket catalytic converter. California smog rules are more stringent than most states so this car may have needed a little boost to pass the smog test.
 

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Those are baffles for noise control.
 

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Definitely not a cat. Looks like some sort of resonator that was welded in to replace the cat.
Yep, it very well could be the opposite of a compliance effort. Not uncommon, I seem to recall cat converter replacement pipes ads in car magazines.
 

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My understanding is that the box that was in the same place as the cat was a resonator and its purpose was to prevent resonant noise that can cause a booming sound.
 

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Jim steck describes it as the school bus resonance. I had it at about 2700 rpm on my GTV6. They are produced by standing waves in the exhaust.
 

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Looks like a cherry bomb muffler to me

Pete
 

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1978 Spider
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Looks like a cherry bomb muffler to me

Pete
bingo!!! that's a "glass pack"...aka "cherry bomb", well they are usually painted bright red, thus "cherry bomb"...

standard cheap noisy muffler for American teenagers. I had my Ford Torino glass-packed in high school. High flow and high noise.

the 'correct" way to install is the scallops facing the exhaust flow in order to duct the gasses into the fiberglass to absorb noise (ha ha). But most people install them backwards to improve airflow (and noise) even further.
 

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1978 Spider
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Since the car came from Cali...maybe the PO was hoping to use the glass pack to visually "simulate" the catalytic converter to pass inspection?

Anyway, probably a lot of work for nothing. You probably marginally increased flow and noise by removing it. Those are very free flowing as-is...
 

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I would gather your car was rather loud before the teardown?

Good pictures
 

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Discussion Starter #14
Hi all,
Thanks for the interesting comments. The car was actually very quiet before the restoration, the only discernible noise being intake as it ran with K and N filters, that sound of course is simply wonderful! The exhaust system had this element, then the standard silencer, the tail pipe silencer and then the very end was a 1 into 2 straight through chrome twin exit with wadding around 1 inch perforated pipe . That was badly fitted also with a step restriction from 2x2 inch to 2x1 inch. I have included a couple of pics of what was at the end and what it has now, I think it looks much neater, very personaI I know. The body work was cut out for the old pipes before I had it!.
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Cheers
 

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Yep, a cherry bomb. My 66 Chevelle fitted with an aftermarket 454 sporting dual quads, a tunnel ram and headers ran 'em in high school. That car was too loud even for me with straight pipes so I ran dual Cherry bombs bought at pep boys to help reduce the noise slightly. (Ah the good 'ol days when life was easy).
If you want a good song reference for your "muffler" listen to the john cougar mellencamp song "cherry bomb".
 

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1978 Spider
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that cut out fort the dual pipes looks kinda rough...get some door edge molding or door edge guard to "trim it up" make it look a little smoother? Or would that make it stand out more?
 

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It looks very similar to a resonator that we used on power generation system's in the Air Force, the spiral was to "promote a swirling in the exhaust and cancel out a broad range of sound waves" but they never really helped as far as i could tell. Kind of like those fan blades that fit over your carbs and increase fuel mileage on older cars. That never did much but sounds good in advertising. Buy i wouldn't swear to that but that very similar on the inside to them.
 

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1973 Alfa Romeo Spider Veloce
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Here is a video comparing a straight pipe to glass pack exhaust. Perhaps the small Alfa engine wouldn't make that much of a difference? Certainly would like to hear your alfa with the straight exhaust. Getting close to choosing a new exhaust system on our 73 veloce spider
 
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