Initial thoughts on performance exhaust

[Dawgme85]

I recently installed an Auto Ricambi performance muffler on my '77 Spider. So far, I'm pleased with the results, but thought I'd share some thoughts on my experience. FWIW, the work was done by a local muffler shop.
A bit of history:
The car had a 4-2-1 manifold installed a few years back and, as a result, I had to have some modifications done to the exhaust system at that time. During the manifold swap the catalytic converter was removed (Washington state doesn't require emission testing after 25 years), but it needed to have a new muffler installed. After the new muffler was installed, the car was a bit too loud, so I had a new cat put on, which toned things down just enough. At this point it sounded pretty good. I referred to it as a swarm of bumblebees at higher revs. This was about 5 years ago.
Things were fine (except for occasional contact between the exhaust and the rear axle lateral link on hard bumps) until this summer, when I installed lowering springs. Now the exhaust was riding on the lateral link, so I knew a new exhaust was in the cards. Eventually, the muffler bracket broke where it was attached to the muffler, so I ordered a 2" performance exhaust system (center and rear) from Auto Ricambi, thinking it would install easily, if we removed the cat in the process (I was pretty ambivalent about keeping the cat, although my mechanic friend suggested keeping it so as to avoid stinky exhaust fumes).
When it came time to install the new system we discovered that the center section wasn't long enough to attach to the 4-2-1 downpipe (apparently, the downpipe was shortened when the new cat was installed). I now had a decision to make; ditch the cat and extend the downpipe, or keep the cat and just use the rear muffler? After discussing with the installer, who recommended keeping the cat (to avoid stinky exhaust fumes (!)), and realizing that the cat diameter (2") matched the new rear muffler, I chose the latter. The new system was fabricated and installed and off I drove.
Within a few minutes I realized 3 things: 1) the exhaust was louder and throatier, 2) the car seemed to have more power, and 3) between 25-3500 RPM it sounded like a bass drum inside the passenger compartment. Gone was the swarm of bumblebees at high RPMs. Apparently, the larger diameter exhaust moved the tone into a range that resonates with the trunk and/or top. Totally unacceptable, IMO.
I returned to the muffler shop and we ended up installing a12" resonator been the cat and the muffler, which helped a bunch, and I'm now happy with the setup, although I haven't yet been able to hear it with the top down. I'm confident it'll sound really good with the top down, however.
The bottom line is as follows:
1) 2" diameter exhaust will deepen the exhaust note, compared to a (relatively) stock system, and produce drumming/droning/resonance in the passenger compartment with the top up.
2) a resonator will tone things down, somewhat, but the resonance will remain.
3) if I was doing it again, I would probably opt for a 1.75" system.
4) a modern, low-restriction cat will prevent potentially obnoxious stinky exhaust fumes.
YMMV

[So Cal Mark]

cats do not eliminate fumes, in fact an overly rich mixture run through a catalyst will create a sulfur smell

[Dawgme85]

As I understand it, the catalytic converter converts hydrogen sulfide (rotten egg smell) to sulfur dioxide. Hydrogen sulfide is a byproduct of the combustion process. I don't recall noticing it in the pre-catalyst days, but that was quite a few years ago. Given the low back pressure of modern cats, I'm OK with not tempting the wrath of my odor-sensitive co-pilot. I still have my fingers crossed that she won't complain about the exhaust change. As it is, I will probably have to keep her out of the spider until top down weather returns in the spring, then ease into top up driving!

[chrisg]

exhaust note is such a matter of taste & even that varies with time. Performance & it's function, of course, is the opposite.

One of my favorite 124 exhausts was done when I was a poor, scrounging Fiat enthusiast....I has a Kirk 4-1 short header that ended in a 2" pipe & I ran the 2" pipe (welded, off-the-shelf pieces...so there had to have been turbulence & losses in the bends) to a 2" straight in-out (you could see through this muffler...as in, "turbo" muffler meets glasspack) Dynomax stainless steel muffler that I caught on a crazy sale at Summit for something like $35. Lovely high end, plenty of growl & grumble, no weird resonance, but as you might expect it was loud, especially with IDFs at the other end. It routinely set of car alarms in parking garages, but it never caused complaints of droning or resonance & there were no odor issues of note.

The fun thing about these cars is that in the classic sports car way it appears the entire exhaust system was almost an afterthought in terms of creating adequate space for it with the chassis design. Or maybe we're doing it wrong & we need to be lifting the cars instead of lowering them!

[carl]

I have the Auto Ricambi sport exhaust but mine includes the resonator. No cat and the exhaust sounds fine.....you really do need a resonator. While a cat is not a muffler per se, it is loaded with a matrix and will naturally perform a bit of muffling. Old wives tail is that removing the car on a spider frees up about 5 horsepower but I have never seen an dyno test to prove that. Also a modern designed cat should be much better flowing than those originally put on spiders.

[jon8christine]

I have the Auto Ricambi sport exhaust but mine includes the resonator. No cat and the exhaust sounds fine.....you really do need a resonator. While a cat is not a muffler per se, it is loaded with a matrix and will naturally perform a bit of muffling. Old wives tail is that removing the car on a spider frees up about 5 horsepower but I have never seen an dyno test to prove that. Also a modern designed cat should be much better flowing than those originally put on spiders.

When you installed the AR 2" exhaust did you do their 4-2-1 header too? Did you see a performance gain from it?