Silencing my exhaust woes, PLEASE chime in

[Modern Motorsports Ltd]

Well I'm not sure if I almost have dream exhaust or not.........KEY issue for me is being quiet with little to know resonance at cruise in the city of highway. (ringing in my ears due to major chemo years back, I like loud but it doesn't agree with me!).

 

I just got my car back from 3.5 wks in the shop for various works, including all new exhaust.

 

Specs as it is now (one pic in my hybridz gallery when it was partially done):

 

Hooker shorty 1-5/8's headers, 2.5" collectors

-dual 2.5 from collectors

flex section on each side

then 2.5" again with a 4" OD magnaflo bottle (14" long case)on each side

this then comes into a single Y pipe right at rear U joint of driveshaft

Y finishes to 3" which then passes over rear crossmember

single 4" OD Vibrant 'bottle' as it comes down from rear crossmember towards rear muffler location

 

1st rear muffler they used was a magnaflo straight thru centre in/out , was too loud at cruise rpm and too barky on any throttle tip in (most would have loved it like this), idle was quieter, 2500+ rpm was reasonably quiet, up to 2500 it had a lot of resonance

 

2nd rear muffler is now a dynaflo super turbo 16" case, offset in, centre out, very quiet idle, and cruise above 2300rpm with nice on throttle sound mid level, not annoying but present, not a typical V8 sound at all and not high resonance, but different.......BUT THIS SYSTEM HAS A resonance from 1200-2200 rpm at light throttle/cruise that may even be louder than my original system.

 

I'm quite frustrated as the shop was just supposed to take care of design/completiong of what was mandated to be an 'optimized for quiet' exhaust system. The original straight thru magnaflo could not be deemed optimized for quiet in any way and I've looked online/phoned many and really want the forum's inputs as I'm sure some have cured the chevy lower rpm cruise 'drone' previously.

 

The work they've done on the exhaust is fine looking quality all mandrel stainless work. I'm hoping a muffler alone can zing out this resonance. Present system dynoed at 280 rwtq and 280rwhp with my mild mill so that's OK. I hear some lifter noises so some tuning could be done. IF I lose power with this rear muffler thats FINE, SOUND IS KEY and thus quiet desired so I still have my hearing another couple decades from now.

 

I've read some old threads but nothing is jumping out as the solution.

 

One exhaust guru out of province rang in with some word of mouth info that chevy V8 resonance had been dured in a couple nice setups with IPC turbo mufflers........which I've since chased down as Midas's own product line and they don't appear (in phoning anyhow) to come in any 3" configurations. He fealt the system was great, just a matter of trying different rear mufflers.

 

ALL input welcome!! I would love for this to simply be a matter of finding the right muffler!

 

All connections are slip fit, some with clamps (either end of bottles) so it's relatively easy to slip in other components to try before permanent slicing/dicing the SS piping etc. Dual mid-car mufflers would be great but not too much room, would cats cure this instead of the mid car bottles without killing major power? How much would an H pipe help and if so what size and where???????

 

(my new tranny cooler, radiator were installed, engine mounts revised, tranny mount revised, header wedges fitted/working OK).

 

THANKS in advance!

 

Ross (Frustrated! someones built this wheel before!) C

[pparaska]

Ross, my guess is that you'd need to change the bottles in the dual part of the system. Something that's made to be a resonator. The rear muffler is probably not going to have a huge difference on the resonance, unless its very restrictive.

 

Just a gut feeling... good luck.

[Modern Motorsports Ltd]

Thanks for the thoughts Pete, what type of resonator are you thinking? Ones I have already are termed 'resonators' by some but I'm not sure if they do have packing in them or just a perforated tube...I'm not sure how you're thinking they should differ?....I had really wanted 6" OD resonators in their mid-car but at the rear driveshaft Ujoint it's too narrow for them to fit the dual mufflers side by side......now I'm curious if a single piece dual 2.5 in and 3" out muffler beneath my driveshaft would serve the purpose better....

 

Concurring with your advice, I've personally experienced, as have a few friends, mid-car resonators work great at curing resonance/drone (both on L6's and V8's)........these were all on cars that had Y pipes that merged fairly shortly and then on the single pipe the resonator was placed. Some of the resonators were not a very large case either, so I'm not clear why mine are not working to take out this resonance. (I'm positive a pair of 6" round mufflers midstream would work if they could fit them in). My dad has a large resonator (6" OD at least on his 3" single section alongside driveshaft with his OEM Lt1) works great, 300rwtq dynoed.

 

PS, what do you think of a pair of magnaflow hi flow cats in place of the midstream bottles/mufflers...I have to think cats have to have a rather notable impact on resonance with their air obstruction...(ie. anything but straight flowthrough), cats would likely slip into present system without a lot of work

[Guest greimann]

One thing about exhaust is it is very hard to the home hobbiest to predict how it will sound until it is built.

 

I think your resonance has a lot to do with the total length of the system and pipe diameter. The resonators and mufflers just fine tune and attenuate the sound. I have a couple of 2 1/2" cats in my system and they don't do much muffling. Along with the 3" Dynomax super turbo, the system is beefy but not annoying. Of course annoying is also a matter of opinion. Also, since my car is a 2+2, I've got about 9 extra inches of pipe in there too.

 

I think you are going to have to experiment......

[fl327]

best muffler i have is the powered bazooka sub in the hatch, exhaust

what exhaust?

[BRAD D]

A couple of turbos will quiet that right up

 

Ross I got my CV adapters, Look nice thanks

[Pop N Wood]

I thought the glub glub glub sound came from the headers themselves. That is the one advantage of cast iron exhaust manifolds. Would some type of thermal tape on the headers cut their resonance?

[Modern Motorsports Ltd]

I thought the glub glub glub sound came from the headers themselves. That is the one advantage of cast iron exhaust manifolds. Would some type of thermal tape on the headers cut their resonance?

 

I've heard ringing due to headers before, I'm quite positive this is not header related. Sounds coming from rear drone and not front. Nice thing with stainless piping though is you can wrap it if you want and it won't go brittle like aluminized can and has in some setups I've seen. My headers are reasonably beefy and coated, front end is quite quiet, letting me hear all the engine noise that I haven't for a while now.

[Mike C]

Ringing or "tinging/ticking" noises are from the header. As noted, the drone is a combination of tubing diameter and muffling. My '84 Corvette droned badly @ 1400-1600 rpm with the stock exhaust. (factory tube headers into a single monolith cat, then back out into two pipes and into separate rear mounted mufflers. I went to a Dynomax exhaust that had a balance tube where the rear twin pipe started going back out. This I thought was odd since the exhaust was already "balanced" in the cat. It did wonders for the drone however. The best thing you can do is add pipe AFTER the muffler. This is very difficult with a rear mounted muffler and not having the VW beetle effect to your exhaust! Why don't you remove whatever tip you have and try a resonating tip? It is a cheap and easy trick if it works. BUT might be significantly detrimental to power but the very tip is where gases are the coolest and require the least diameter. You could even try a 2 1/2" muffler at the very rear instead of the 3" for the same reason. Beyond that, you may want to try a crossover of some sort closer to the engine.

[DavyZ]

... Beyond that, you may want to try a crossover of some sort closer to the engine.

 

Ross, this is what I was thinking, but I'm not even sure that this would make enough of a difference to justify the cost.

 

I have to admit, the system looks great! I hope it gets resolved though, since droning can make you mad at speed...

 

Davy

[Owen]

Ross,

My engine output is similar to yours. Setup-wise, I have block huggers coming into dual 2.5" pipes into dual 2.5" bullet style Dynomax mufflers. Then into a Ypipe 3" single out into a Random Technologies hi-flow catalytic, and then to my muffler 3" in 5" out.

 

It still may be loud to you, but the what really helped me was the twin bullet mufflers, sound level went way down. From raspy high pitched to deep grunting. Haven't really noticed a drone but I haven't been driving it for a while.

 

Anyone know if a balance pipe makes any difference on a system which goes from dual to single? I've heard it does on straight duals...

 

Another thing people do is get a resonator and flip it around so the raised lip of the fins inside are facing the engine. Don't know what this will do to

performance tho...

 

Owen

[jhaag]

Ross: just as food for thought, here are a couple of web sites that talk about the acoustics of vehicle exhausts. This information might be valuable in case you aren’t able to solve the noise problem through use of different mufflers or resonators. On the other hand, being knowledgeable about engineering, you may know all about this already.

 

1. Saveguard. It’s a UK “manufacturer and supplier of high temperature resistant textile products and acoustic and thermal insulation materials used mainly in fire protection, thermal engineering and vehicle exhausts.†http://www.saveguard.co.uk/

 

Their “Acousta-fil material has been designed for controlled expansion on initial contact with heat and is intended to fill complex voids with acoustic insulation media to a pre-determined density." http://www.saveguard.co.uk/exhausts/index.htm

 

There is a great photo of the material at http://www.saveguard.co.uk/acoustafil_image.htm

 

I’ve thought about using this in a home-built side exhaust system to control noise and heat. I contacted them and learned they don’t have a North American supplier but they said they’d be happy to ship. I didn’t ask about costs.

 

 

2. Aerotech Engineering http://www.aerotecheng.com/ . Even though they do "computational fluid dynamics analysis consulting for motorsport" they have several heat shield products that can be used for noise attenuation and acoustic damping. Click on ‘products’ and then click on ‘material properties’ for each to see their data on noise attenuation. It’s another UK firm and I don’t know if it’s available in North America or what the costs are. http://www.aerotecheng.com/CirrusGIIIx.htm

 

 

3. At the “How Stuff Works†site

( http://auto.howstuffworks.com/muffler2.htm ) there are a series of descriptions of canceling out sound and several other muffler-related articles. It might be fairly elementary to someone that has studied headers/exhausts as much as you have.

 

4. The Australian National Occupational Safety & Health Commission site

http://www.nohsc.gov.au//ohsinformation/ohssolutions/noise/soundf.htm describes sound movement in ducts and exhaust systems. I found it interesting but it might be elementary to some people.

 

John

[fastzcars]

Hi Ross. Have you thought about sound proofing the interier cabin with dynamat or brown bread? Maybe you can reduce what you hear that way? Just a thought. Maybe double up on the sound proofing stuff.

[zgeezer]

Ross, Sound control in the cabin is THE issue for me. You might consider putting inserts into both header collectors b/4 you begin replacing mufflers. I understand the earlier 240's drone even with the stock I-6 and I would expect that heavy dampening of the roof, passenger/driver floor panels, and the back storage area would help. It made a big difference on a 444 Volvo with straight pipe I drove a few years ago.

 

gw

[clint78z]

Might I suggest something like this Ross, it's a variable butterfly much like on the Mitsu 3000GT. I have seen in the US a company is designing these as well, mabey a junker Mitsi will have one for cheap ??

 

http://autospeed.com/A_0883/cms/article.html

[Guest Anonymous]

DELETE

[jeromio]

I have been daily driving my car for the past 8 weeks. I think I have already suffered some permanent hearing loss. The problem is that 65-70MPH (6th gear) translates to 1700-2000RPM. This is the magical sweet spot for my setup that produces brain scrambling drone. It's diving me crazy. My wife and co-workers are having to tell me to stop yelling - I don't realize I'm doing it.

 

I have an LS1 (of course) with stock manifolds (sheet metal) to 2.5 inch tubes. These meet at a fat Y (slow transitions) 3 inch. this immediately feeds a 3 inch Dynomax Race Magnum Bullet Muffler. From there it stays at 3 inches all the way to a Mac Performance 3 inch offset to 3 inch center out muffler. Everything is mandrel bent.

 

The addition of the bullet reduced the noise at idle slightly and seems to have taken some slight edge off the drone, but did not eliminate it. The Mac muffler is supposed to flow well. Perhaps it's just a crappy muffler (it's very pretty though - solid stainless - very heavy). It fills up the spot back there - of course it is small. I also have a 3 inch by 9 inch exhaust tip which is packed and perforated - though I doubt that is doing anything to the sound.

 

My car sets off other car's alarms. And not just in parking decks - out in the open too. Wife drove the car the other day - I could hear her arriving home many many blocks before she pulled up.

 

I've read pretty much every post here on the subject of noise. My next try will be car chemistry inserts. They're expensive though. If they don't work, I will cry, but no one will be able to hear me.