Resonator necessary?

[bradbig]

In doing the work to get my 73 on the road, I need to do some exhaust work. Is the resonator really necessary? It's rotted and has holes in it. What would the effect be of removing it, and adding a straight pipe to go from the Y to the muffler? Will removing it negatively affect performance and driveability? Or will it be too loud and buzzy sounding?

[azruss]

I just replaced the exhaust on my 80. It had the factory cat and resonator with a glass pack. Had a nice sound and not overwhelming. The new system kept the stock cat, but the resonator went bye, bye with a stainless high flow muffler. the sound remained the same. gets louder when warmed up, but would be able to carry on a conversation behind the car when idling. I do not consider it loud.

[MrJD]

Straight pipe = no backpressure = bad performance and TERRIBLE sound. Trust me, I know. I just went through an exhaust build. My car with nothing but a straight pipe = would barely even idle... much less run worth anything.

[Landhawk]

Straight pipe = no backpressure = bad performance and TERRIBLE sound. Trust me, I know. I just went through an exhaust build. My car with nothing but a straight pipe = would barely even idle... much less run worth anything.

What did you do to correct this? Does the resonator serve to create backpressure? I thought it was just to reduce sound?

[carl]

The resonator is just a small glass pack muffler and you can certainly run without it. It may change the loudness and tone of the exhaust but if you run a stock muffler or an Ansa you should be just fine. I seriously doubt removing it could affect idle.

[So Cal Mark]

back pressure is a bad thing and is a real detriment to performance. Engines do not need backpressure to run properly. The only benefit from backpressure is to quiet the exhaust note

[MrJD]

back pressure is a bad thing and is a real detriment to performance. Engines do not need backpressure to run properly. The only benefit from backpressure is to quiet the exhaust note

I'm not going to get into a discussion of pulsing and exhaust velocity, but I've never seen a small engine happy with virtually no backpressure. This fiat of mine seems especially susceptible to this, as when I ran it with nothing but a straight pipe it ran, well, terrible. Doing nothing other than changing to an appropriate muffler made all the difference in the world.

[toplessexpat]

FWIW - On the 1800 I've got a 2.5 pipe from the bottom of the header to the backbox, which is a Magnaflow. It's loud, it's fun.

A

[timinator]

I'm not going to get into a discussion of pulsing and exhaust velocity, but I've never seen a small engine happy with virtually no backpressure. This fiat of mine seems especially susceptible to this, as when I ran it with nothing but a straight pipe it ran, well, terrible. Doing nothing other than changing to an appropriate muffler made all the difference in the world.[/quote]

Has nothing to due with pulsing or velocity. When you remove the back pressure the A/F goes lean. You either need to go richer or advance the timing. Due neither the engine runs poorly. If you have a points type dist. it won't produce a strong enough spark to fire a lean mixture in the first place. Basic engine tuning is rich at idle, lean at cruise, and rich at WOT. Make the entire range leaner and it won't idle, buck at cruise, and burn down at WOT.

[azruss]

many years ago i read a book on engine tuning and performance. it explained the need for back pressure this way. the intake and exhaust set up waves. high performance motors (meaning in those days 1 hp/cu in) the intake gases were drawn into the head while the exhaust valve was still partially open. some of the unburned mix would head out the exhaust but would reverse direction because of the back pressure and go back into the head. this effectively gave you a larger volume of gases in the head giving more fuel to burn on firing, thus more power. the purpose of a tuned header was to equalize this effect evenly across all cylinders. most street cars are built with too much back pressure. The VW bug being a classic example. Those aftermarket "extractors" did nothing more than lower the back pressure

[kustom]

FWIW, I've had a few different mufflers on my 81. From large and quiet, to small glass packs that became loud and buzzy around 2500 RPM. Performance was good with all mufflers, regardless of having a resonator installed or not. My muffler shop actually allowed me to clamp on different mufflers, and go for a spin around the block to test out the sound. I really like the sound of my car right now, but it can be a bit loud at times with a mid size glass pack and no resonator. I think I will stay with my current muffler, but throw a resonator back in.

[bradbig]

OK. Well, this makes for very interesting reading, and I'm still not sure what to do. There seems to be educated opinion on both sides of this question. I spoke to my muffler/exhaust guy, and he suggested that the car had both a resonator on it, and a standard muffler on the end, so it's probably best to replace old with new. He did give his opinion that he thought I'd find the exhaust noise unpleasant without the resonator. He also felt the engine was probably designed and engineered to have both a resonator and a muffler, and probably would perform better. So, I'll go that route. Thanks for all the input.

[vandor]

I tried running with only a performance 'straight-through' muffler, and it was too loud for my taste. Maybe OK for short around town runs, but it makes your ears bleed on long trips. These cars have so much wind noise on the highway, you should not be hearing the exhaust.
I added a resonator and it's a lot more civilized. If you use one be sure it does not have 'spikes' on the inside, pointing toward the middle, we tried one and it was very restrictive.

[spiderdan]

Is a resonator necessary, hope not! When I bought my car it didn't have one installed. 4-2-1 straight pipe to Ansa muffler, and I love it!
Does it give a few more HP? Maybe yes, maybe no...but I don't care. IMO the sound that comes from my exhaust contributes to the pleasure I get driving my Spider. Although my car is a head turner on it's own, I do understand the pleasure those Harley guys/gals experience when they crank their hogs. When I floor it, I love that throaty roar that comes out of her butt. When I ease on the pedal, she can purr with a classy rumble. I like having the choice. I asked my mechanic (25 years fixing Fiats) if I needed a resonator? He replied, if did need one, he would have installed one. Good enough answer for me.
Then there is the safety aspect of my loud muffler. I drive country roads regularly on the way to my cottage, specifically the Gatineau parkway, (local conservation park, 36,000 hectares). There is lots of white tail deer in that park and lets just say that Bambi hears me coming. And then there are the bikes, the parkway is full of them. No need to blast them with my air horns when they are riding side by each. They hear my downshifts and move right on over. Although I do like watching them jump when I do blast the horn.
In 13 years, I've only been pulled over once for noise, by a cop on a Harley. At 1st he thought it was a modified rice burner type exhaust. I explained that in 68, it was a factory optional exhaust system that was designed for the Abarth models. (ya I know what you're thinking...I used to sell very well used cars) He looked the car over, checked my papers, saw my gray hair (it's good not to be a kid sometimes) and he kindly suggested that I could drive her a little bit quieter on residential streets.
He gave me a wink as he was mounting his Harley and said..."nice car"
IMO the sound coming from my exhaust is a big part of the overall pleasure I get driving my Fiat.

Bradbig, don't know what it will sound like on yours without one but give it a try and see how you like it.
It's all about what turns your crank