Catalytic Converter

[ORFORD2004]

Did the Resonator provide improved performance over the CAT?

I don't know but the turbo did

[timinator]

Theoretically would the removal of the converter increase performance on a FI car? If so, could the same performance increase be achieved by removing the innards of a catalytic converter and reinstalling? Not that I would ever do such a thing........

You are asking the wrong question. Leave the cat and lose the muffler. The law says nothing about needing a muffler. The cat does a great job of quieting the exhaust. The muffler is the restriction you don't need. Your engine needs a long enough tail pipe to keep atmospheric air from going back down the pipe and keeping the cat from lighting off or effecting the o2 sensor. Put a turn down on the end to keep it from droning.

[wizard124]

When i bought my car, it needed to be smogged. I took it to a local Fiat shop. He stated the original cats tended to rust out internally, restrictive, and not too effective.
He welded in a California compliant one that he recommends.
I have no complaints. It has passed smog twice. Has a nice tone with the original exhaust system and is not loud or annoying.
Search my posts on this subject to find the manufacturer and model number.

[rridge]

The original cat on my '81 Spider was the GM type, a stainless steel shell filled with large ceramic beads that looked like water softener salt pellets. These early OEM type cats are known to be restrictive. Most expired a long time ago. Some simply had the beads emptied from the same port used to fill them and were left in place.

The Fiat vendors and most muffler shops have sold modern generic cats since the mid-90s at least. You can spot them by their size. The OEM cats are as large as the resonator. The modern cats are half that size and usually have a short section of pipe connecting the cat body to the flange on each end to make up the difference in length. They are not restrictive unless damaged by a poor running engine.

Richard

[carl]

Allegedly removing the cat was worth 5hp but I have never seen any documentation to this fact. Someone needs to schedule a trip to the dyno to verify. I do know my spiders always sounded better without the cat. Modern cats flow much better than the crap that came on cars originally in the 70s.

[Dawgme85]

At the time I had the head on my '77 1800 rebuilt and port matched I also installed a 4-2-1 manifold and downpipe. During the installation, the original cat became "lost" and I had a new muffler installed (nothing special, basic muffler shop replacement). When I picked the car up from the muffler shop, the shop manager remarked, "it's kinda loud", which I was ok with. However, over the next few days living with it, I came to agree with his assessment and ended up returning to have a low-restriction cat installed, even though the car is not subject to emission-testing here, due to its age.

The addition of the cat toned things down just enough, although it still sounds like a swarm of bumble bees under acceleration. Definitely Italian!

Regarding any performance change due to the new cat, when combined with the head work and manifold change, I just can't say how much power was lost. All I can say is that it's lightyears ahead of the way it ran previously, so I'm ok with the overall results, even if the cat subtracted a horse or two when all was said and done. I suspect adding a resonator would have produced more or less similar results.