Adding a resonator to my 75's exhaust...
 

Hello, I have a mildly modded 75 L82 auto.

When I got the car 1.5 years ago, it had a "pacesetter" catback exhaust installed on the back of the oem exhaust setup. Since then, I had a local exhaust shop fab up a "true dual" exhaust system (I believe 2.25") with an "h pipe". Since the "pacesetter" mufflers were fairly new (and I didn't want to pop another $350 for new mufflers), the shop was able to use those at the end of the system.

While the car runs so much better without the old "smog belt", it is a little louder than I would like it to be (particularly at low rpms/city cruising). The "droning" at times is too much.

Would adding two "inline" resonators after the "h pipe" on the exhaust quiet down this "droning" that I am now experiencing? Anyone have any experience with this? I like my current setup, and am not looking to drop another good chunk of money in the exhaust at this point in time.

Thanks again for the input! :cheers:

The "droning" you speak of is a resonant frequency, so it's hard to tell what will affect it and what won't. The material that the exhaust pipes are made of, the type of hangers used, the tightness or looseness of all the fasteners, including the hangers, to name just a few, are all factors here. A friend of mine had a pretty bad drone, one day he tightened up a loose exhaust pipe hanger, and it miraculously disappeared .


Scott

You are in luck that I have almost the same system you are talking about which seems very rare on the forum considering that I happen to prefer the Monza Turbo mufflers over just about anything that is offered out in the market for C3's running no cats-that is the key word-the cats, not the horrible OEM pancake one, cats helps muffle the exhaust.

I have had the Monza Turbo Mufflers on my 78 since 1989 and still do. I am assuming that you have the Mufflers, NOT the tips only, which I had briefly before switching to the Monza Turbos, and the tips only on the OEM 2-1-2 (no Cat on mine) were WAY TOO loud since they are designed to be used with the OEM cat. With the 2-1-2 OEM system without the cat, the Monza Turbos were pretty much quiet-very little noise at speed, only idle. When I switched to a 2.5 inch true dual exhaust in 2003, the Mufflers got louder but again, not offensive at all-you could just hear them at speed. In 2007, I removed the OEM exhaust manifolds and installed McJacks shorty headers and the system got MUCH louder, but not much drone, just more of a European type sound versus the motor boat sound for most of the aftermarket mufflers like flowmasters/magnaflows. I happen to like magnaflows and do have them on 2 other cars BUT with cats:

1994 Mustang GT with BBK shorty headers, magnaflow X pipe with 4 highflow cats, and the magnaflow cat back system-It sounds great at high RPM's.

2001 Pontiac Grand Prix-stock cat, U Bend delete after the cat, 12 inch Magnaflow resonator and dual magnaflows after the cat-2.5 inch pipe-sounds good, NOT great! Had to add a 12 inch chambered resonator after the magnaflow resonator to eliminate drone-worked great!

I am surprised that you have drone with the Monza Turbos (assuming they are turbos and not just tips) especially with 2.25 inch duals, not 2.5 inch duals. I have no drone with my system and never have. With that said, I would add the biggest resonator in each side that you can fit before the mufflers-magnaflow has 12 inch and I think 9 inch resonators but they are straight through but will help quiet the exhaust down. For more sound deadening look for a chambered resonator (baffles inside) which will knock many decibels off the sound but will reduce flow slightly as well. Remember that the quieter the exhaust system generally the more restrictive it will be-there is no free ride, like everything else in life! Hope that helps!

the more restrictions to flow you add the more you effect power within some range. I have true duals through wire grid bullet cats on each side into flowmaster 40's I think it is. There is a drone at 32-35 mph but I just make it a point not to drive at 32-35 which in a Vette is no trouble at all! Darned if I'm going back to more restrictions once I got that old flat crapped up 2-1-2 pellet cat outta there! I like the deep rumble and when you go 40 mph with mine you don't hear the exhaust anyway as it's well behind you geographically in sound. riding around at 35 mph in the vette sight seeing isn't the best use of the car or the gas it uses either so I don't use it for those kinds of sojurns.

My answer would be not to put anything more restrictive in there. The darned car is supposed to be loud enough so that you hear it a little!

Lance

Another possibility to try would be add a X pipe crossover under rear end.
I am for the right mufflers w/o resonators, but if you need them, then smallest.

Thanks for all the advice!

Yes, they are full mufflers, not just the tips. I am running stock headers/manifolds. The only real mods besides the exhaust system itself are the removed emissions and "re-curved" timing. On a separate note, that alone has added a lot of power. The car is more of a "cruiser" and I'm happy with how much get-up I currently have (clocked the 0-60 at under 6 seconds the few occasions I actually tried it).

I agree, I don't really want to add anything more restrictive. Sounds like the resonators should make a good amount of difference, possibly even little longer ones. This week I may be calling the different muffler shops to see what kind of prices they can give me on getting these installed. When calling, I can also ask to see if they would think adding an "x pipe' after the "h pipe" would make. While it's there, I can request to have everything "tightened up" as well, maybe that will also make a difference.

With the car being more of a cruiser (as well as having the factory optional "performance" rear end ratio and the three speed auto tranny), I just want the noise down a bit. Now I don't exactly want it as quiet as my Camry (haha) just looking to make the droning a little more bearable for the cruises around town with the wife.

I will re-post if I end up getting the resonators installed and let you guys know how much of a difference it ends up making.

Thanks again, you guys here are the best.

Normally only a H or X is installed. The X has a different sound which they should know. Since normally only a H or X is installed their opinion about 'adding an "x pipe' after the "h pipe" would make' can be expected to be worthless. Someone has to try it.

"I didn't think an X pipe would make any difference because I already had an H pipe. But my muffler guy had this x-pipe laying around, and nothin' from nothin'. We tried it. Wow! What a difference. The drum sound has been replaced with a higher pitched roar, and the overall volume is down. I think the wife and I can have conversation now. I'm a believer, and I love my flowmasters again. It doesn't look like much, but it works." Bee Jay

Note that you asked for ideas & that's what you got. X is what I would try first whether replacing the H or just adding the X as I stated earlier (before adding resonators).

The checking & tightening has merit. I would put in on a rack running ...

Resonators do not add restriction to an exhaust system. Exhaust gasses pass straight through a resonator, and only the "noise" enters the resonant chamber.

Resonators are tuned for a particular frequency. While it's a good answer for a particular noise problem, it's difficult (without laboratory equipment) to find out what particular frequency is the problem, and additional difficulty finding an off-the-shelf resonator that matches your needs.

69427..

Actually, your statement that resonators do not add resistance is inaccurate. It isn't a lot but it does add some while further "muffling" in effect some of the sound waves. the more things you put in the pipe that move the sound waves and heat in the exhaust air around changes air pressure to the gas going through them the less horsepower you have net. It's probably pretty small but don't assume there is no restriction, There apparently is.

Here's dialogue from a thesis on the subject from an engineering college: "After the above discussion of the components in an automotive exhaust system, it is obvious that the principle of the engine as a pump is not being utilized to the fullest. Air is not allowed to flow too freely because of restrictions in the form of the catalytic converter, the resonator, and the muffler." Cat and muffler are worse but there is other discussion laying out the resonator's milder restrictions too.

It would be interesting to measure the air pressure at the exhaust end both with and without resonators in the pipe to see how much. I think it would be pretty small and would be fun to find out how much.



L.P.

Sorry, I gotta disagree. You're essentially not adding anything with a resonator, you're just substituting it for a similar length of tubing. Don't confuse the construction of a classical resonator (a straight tube with side connections to a resonator chamber) with externally similar looking mufflers (which often have internal directional changes that cause pressure drops) or glasspacks (which often have flow reducing internal projections). By installing a straight tube resonator (avoiding the venturi tube type if you encounter one) there shouldn't be any backpressure issues to worry about.