pcard

I am trying to reduce the noise level as much as possible on a 1970 SX with L31 engine (dual exhaust), without robbing too much power.
Can anyone suggest any modifications that can be done to a stock exhaust system, or any new systems that would be quieter.

Reason - I live in a town with strict noise regulations.

Thanks for your help, Peter.

jo75olds

Well with my new 455, Dual Exhaust, I will be putting a more conservative exhaust systems (will cut into power) but I plan to put the electronic exhaust cutouts on as well (runs straight pipes on a flip of the switch)

I also live in a town with strict noise regulations, this way you can have the best of both worlds

http://shop.quicktimeperformance.com...ct_detail&p=47

oldzy

Single exhaust!

Shizzy

adding a crossover can help. maybe add a set of resonators in the system to see if that quiets it down a tad?

Rickman48

There's some hi-po resonators out there - before the exhaust tips will work.

pcard

Thanks to all.

GreekDog

what are you gonna end up doing?

pcard

GreekDog: At this point I am going to continue researching. I will also get in touch with some auto engineers for input, maybe contact some of the aftermarket companies. Noise suppression is not a simple thing and if not done correctly can mess up your tune (heh heh - no pune intended). Unfortunatley most folks like to be heard as well as seen, so the market caters to the majority.
I will update this post when I learn anything.

joe_padavano

Call me a cynic, but I'd be cautious that an aftermarket company will answer that the right muffler is the one that they sell...

By the way, unless you get past the uninformed "tech support" people, don't expect to get anything useful. Just try asking the tech support folks at header manufacturers about Supremes.

pcard

Yes - I have a healthy respect for tech support too - I was one in a prior life. I was going after the engineering department; I have often found those guys love to talk about special projects.

pcard

Here is an interesting link.
http://www.ozhonda.com/forum/archive.../t-125186.html

pcard

Just an update. I have had some good results from simply Googling "low noise mufflers" and "car muffler noise reduction".
Some points:
mufflers reduce noise over a range of frequencies, and the best one will have been tuned for your particuar car/engine. So if you want to go quiet, find a supplier who matches a muffler with your car/engine. In general the bigger the muffler the better it is at absorbing noise.
A resonator is also specifically tuned for a particular car/engine, but only handles a very small range of frequencies. It is designed to target the particular resonance frequency of your car/engine (hence the name).
To go supper quiet, you can install two mufflers inline: use two different types to cover a broader range of frequencies. One straight through and one with interiror returns works best with manageable backpressure.
All backpressure is not bad, and in most stock cam setups some backpressure can actually helps increase low end torque. This is sensitive to valve lift and duration apparently (I do not understand why). So to optimize fuel economy you should go with a variable muffler which supplies backpressure at low RPM, but a straight through at higher RPM for the highway.
I am taking a very close look at the products from Walker and their sub DynaMax. By the way SummitRacing has Walker Quiet Flow, but they are still selling the old aluminium products, which are now apparently superceded by the Walker Quiet Flow SS stainless product.
Muffler design has traditionally used passive noise absorbsion. New technology is coming out with active noise suppression directing the flow to feed back on itself and cancel the noise out.
I found a pretty cool technical paper on muffler design if anyone is intersted (there are a few out there).

Oldsguy

No doubt that is correct and useful, I can't help but think that when our cars were new on the showroom, even with dual exhausts, they weren't that loud. With full mufflers and full bended pipes all the way back designed to fit your car similar to OEM I would think the car would be almost as quiet as it was originally (exhaust noise wise). The local law might be very actively enforcing noise abatement but if you car is 'originally equipped' and you drive judiciously I think it would be very difficult for a citation to stand up in court.

redoldsman

I don't guess I have ever seen this much discussion about quiet mufflers. Usually is somebody wants really quiet, they just put stock mufflers on. I have never heard of mounting two mufflers inline. Mufflers and resonators yes, but not two mufflers. There is a company that makes a muffler with a remote control that will switch it from quiet to loud. I don't remember the name of it but they were over $300 each. Too rich for my blood.

Shizzy

are we talking the city or the development you live in? If the car has factory exhaust I don't see any issue. Any cop pulling you over for noise is going to have a rough time writing you a ticket if there are two mufflers and possibly a set of resonators under the car. If it were me, I'd take any ticket written out and head right to the Cop shop to have them check the DB's. I'm sure it would be well under required.

if its just the development you live in I would just suggest a quick but quiet entrance/exit any time you are driving. I live on a busy street and I have no issue with loud vehicles or stereos as long as they don't sit in front of my house for minutes on end. if its just 10 seconds for them to drive past my house then whatever.

455man

Like Shizzy said the law would have to measure the decibels with a meter. I used to get pulled over all the time with my header into 2 1/2 dual turbo mufflers because of noise. Really I was a target. Young kid with long hair, yellow and black car with a big block in it. Anyway a judge/law professor told me they would need a decibel meter to hold up in court. I never got a ticket for the noise, they just checked my DL and registration. Sometimes wanted search the car and almost seemed disappointed when nothing illegal was found and let me go.
Your research is interesting but I would have a hard time believing two mufflers inline would not decrease horsepower. These Olds seem to like better flowing exhaust. The dual pattern cams with the larger exhaust side makes up for the poor flowing exhaust. I've always been told to open up the exhaust on even a stock Olds for more power.

pcard

I agree about the noise check requirements - though it is unpleasant to have a young officer of the court try to play important - had enough of that on my motorcycle - ruins my ride.
I also agree that two mufflers would be overkill, l and they would take away some HP for sure. I just wanted to share my findings.

If anyone can explain how backpressure improves low end torque on specific cam setups that would be interesting. Maybe has something to do with turbulance in the cylinder.