my annoying attempts to reduce resonance from my exhaust stacks...

[Forrest Nearing]

so I put some 5" miter cut stacks on my truck exiting about 10" above the cab or so.



pretty rowdy inside the cab...



so I lined the roof sheetmetal with lead sheet. cut the resonance in half! now pretty much everything I'm hearing is the back glass vibrating. if I had a club cab, I don't think this would even be an issue, but right at about 70mph it starts wearing on you on the highway... it sucks cuz w/ my 5" straight pipe, I could cruise at 75mph without much discomfort. the stacks just have a different resonant frequency.



so I bought a pair of curved top stacks off ebay cheap hoping that it would direct the sound waves back... I installed them facing to the rear of the truck.



with the windows up, there's no change, but I like the way they look better, and as an added bonus, you can actually drive with the window down without going deaf, and it's louder outside the truck now.



SO, after getting in from OKC the other day, I decided I was going to put a resonator on it... Yesterday, I cut down the old 20" long 5" muffler that came w/ my 5" exhaust system and turned it into an 8" resonator. it actually came out really well...



I installed it and went for a drive... took some of the sharp edge off the exhaust note, still had good turbo whistle, and still had all the resonance



so I yanked that thing off and put a 12" long dynomax bullet right after the downpipe... took most of the sharp edge off of the exhaust note, ate up tons of turbo whistle, slightly cut interior resonance everywhere BUT the peak point, and there is sounded worse...



so I gave up for the day, came in, and started searching the net for a suitable muffler. I was very tempted to buy something louvered like the Diamond Eye that Rip sells because I think they might yield more turbo whistle, but due to price, being able to listen to a sound clip, and being able to call Summit at 11PM and order it, I settled on the Dynomax 22572... welded ultra flow that Jannetty uses on his systems... 20" long 9" round case. it might be a tight squeeze on my little single cab, but I did some measuring. SHOULD be alright, but if there are clearance issues, they won't be anything a BFH won't cure :-laf



then this morning I promptly went out and straight piped it...

 

[Jeff Clark]

Dude, you go through exhaust systems faster than I do.

 

[KLockliear]

Just wear a helmet and ear plugs... works for me.



#ad

 

[RBratby]

that truck looks :--)

 

[Forrest Nearing]

I've gone through 10-12 different variations between stacks, under the truck, back to stacks, etc. in the last year...



I braced the stacks to the front rail a minute ago... seems to have helped a little, but rush hour traffic wouldn't allow me to get it up into the 70-75 range for very long.



Keith, if I had twins on it, I don't think it would be any problem w/ that second turbine chopping it up... care to make a donation?



Forrest

 

[metal tech]

Forrest, here's another option if this new part doesn't work out for you. JCL Spiral Baffles, if you've seem that Moroso muffler that has a spiral core these are the same except that they install inside the exh pipe. They do make sizes up to 6" or so. I haven't tried them, but with the drone my 5" straight pipe puts out, I'm looking for something that will reduce it. JCl does have a web site, and since they do market toward OTR trucks they might have some info that could help you out.



Al

 

[Forrest Nearing]

Al,



I've seen those inserts, but never heard of JCl... but the place I saw wanted like $300 for a pair... NOPE! LOL!



I'll do some diggin' on JCl and see what I can find.



Forrest

 

[Forrest Nearing]

yeah, that's the same ones I've seen for sale elsewhere... that dynomax cost me $85, and I always build my exhaust systems to be completely modular... I'll be able to swap between the muffler and straight pipe in under 10 min.



I love the straight stacks... around town they're awesome... but on a long haul they SUCK!



Forrest

 

[metal tech]

yeah they are a bit pricey. Maybe they would only sell singles. I've looked at the Dynomax race Bullet 6" OD, 5" thru. It seems that placement is very important when installing mufflers to reduce the drone.

 

[Forrest Nearing]

I've played with placement too w/ my old 5" system... I put a 12" long dynomax bullet right on the downpipe about 2" from the turbo... I wasn't impressed.



the biggest thing that helped my 5" straight system was welding all the connections and putting a few very stiff exhaust hangers on it.



honestly, I wouldn't waste your time on the dynomax bullet... it takes the sharp edges off the exhaust note and eats up a lot of turbo whistle, but it leaves the heart of the booming resonance...



my 5" straight system was no problem... at 75 it'd let you know it was there, but not bad at all... 80-85, you didn't want to be there for long... 90+ it smoothed out, but I don't drive that fast... with the stiff hangers and all the lead sheet I've got lining my cab, it really was a great setup... rude obnoxious outside, and very livable inside...



when I FIRST put it on, I had band clamps at every connection, re-used the stock hangers, and had no additional sound deadener in the truck... it resonated so bad it was rediculous. 65-70 was pretty annoying... 70-75 sucked... and the peak resonance point was 2500rpm... at heavy throttle at 2500rpm, the sound was SO bad, it literally hurt your ear drums... I'm not talking annoying give you a headache loud, I'm talking ice pick in the ear drum loud!



the lead sheet cut half of that or more... getting everything welded up and braced up good and tight was the cherry on top.



I've been tempted to put the 5" system back on, but I've got time and money wrapped up in these stacks, and I'll be the first to admit that I'm addicted to turning heads



Forrest

 

[NIsaacs]

Forest,



This is just a guess, as I am no expert on straight stacks, but maybe it has something to do with the 5" diameter and the length above the cab. The twin 5" may not have enough flow volume and creates the "singing in the rain barrel sound" I have a set of twin straight 4"x72" on my CTD powered Ford, with very little sound in the cab with the window up. I have to open the rear slider or side windows to get any sound. The outside sound is mellow for the most part, with that big truck sound under power with a cool turbo. As the turbo heats up, as in up hill pulling, the tough pulsating sound will go away and become a smooth growl. I like the cool turbo sound the best





"NICK"

 

[Forrest Nearing]

Forest,



This is just a guess, as I am no expert on straight stacks, but maybe it has something to do with the 5" diameter and the length above the cab. The twin 5" may not have enough flow volume and creates the "singing in the rain barrel sound" I have a set of twin straight 4"x72" on my CTD powered Ford, with very little sound in the cab with the window up. I have to open the rear slider or side windows to get any sound. The outside sound is mellow for the most part, with that big truck sound under power with a cool turbo. As the turbo heats up, as in up hill pulling, the tough pulsating sound will go away and become a smooth growl. I like the cool turbo sound the best





"NICK"

good point, but I wanted full 5" for twins... I'm wondering if your 72" stacks just resonate at a different frequency ( higher RPM )



also, is your truck a single cab? if I lean my head forward so that it's up over the steering wheel, I can barely perceive any resonance at all... I've got so much lead sheet in the interior, the only thing that's vibrating is the back glass, and on a single cab, my head is only a few inches from it... I'm confident that if I had a club cab, this would be a non-issue.

 

[NIsaacs]

Forrest,



You are probably right on the RPM'S thing. I very rarely go over 2300, usually 2100. It might have something to do with a different cam profile also. My "O1" sounds good with the stock pipe to the resonator, then 4" back to the tailend. My "91" has a straight 3" all the way back, but sounds kinda raspy, I don't care for it much. My Ford is a regular cab.



"NICK"

 

[KLockliear]

and the peak resonance point was 2500rpm... at heavy throttle at 2500rpm, the sound was SO bad, it literally hurt your ear drums... I'm not talking annoying give you a headache loud, I'm talking ice pick in the ear drum loud!

Forrest

Well there's the problem Forrest... you're lugging that thing. I leave the line a bit higher than that with our truck. :-laf

 

[Forrest Nearing]

the highway patrol doesn't like it when I run 2500+ in OD



Forrest

 

[work2muchplay2little]

Two things basically eliminated the drone from my stacks; twins and about a 36" section of flex pipe. I am straight piped from the secondary turbo back and the flex pipe is the final piece before it turns upward to go through the bed. Of the two, the twins made the biggest difference.

 

[Forrest Nearing]

I've got 41" of flex pipe...



I'm still workin' on the twins!



Forrest

 

[Forrest Nearing]

Update:

wow, you wanna talk about ticked off?



UPS running slow for the holidays... didn't get started till ~5:30... no problem...



was a little worried when I saw that the muffler wasn't a continuous ID all the way through. it expands out in the center... but I didn't have time to return it and get something else before the x-mas road trip.



so I put it on...



sounds AWESOME... OUTSIDE the truck...



inside?



I give up... interior resonance w/ this thing is worse than either of the others... figures... :{



it's a shame because it really sounded sweet outside... cut the thunder big time, but left TONS of turbo whistle...



but it created a brand new resonance around 65mph that wasn't even there before... and the resonance from 70-75 was worse, and it had a new resonance at 80mph...



I don't know if it's because it was clamped on instead of welded in and didn't have stiff exhaust hangers, but I didn't/don't care... I was ******... I coulda bought two bottles of whiskey for what I paid for this thing, and I'd be in a much better mood...



I pulled it into the driveway, and ripped that thing off w/ the stuff still good and hot... threw the straight pipe back on it and went for a drive...



on a positive note, it now seems quieter inside than it did before (because of how terrible it was w/ this thing on it)



so that's it... I give up... I'm just gonna have to get the twins on ASAP :-laf



anyone wanna buy a muffler?

 

[Slingblade]

Forrest,

I just got one of my stacks connected this last weekend. I'll get the second one connect in a couple weeks. They are routed under the truck. Just not much time right now. Anyway, the resonance in the cab is BAD! I have the quad cab and it's hard to get used to the sound. My seat, roof, back window vibrates. The wierd thing is first thing in the morning is the worst. By thie time I pull into the parking lot at work it seems real mellow. I ran around the side with it running to see if I lost a piece of pipe it was so quite. After work same tone. After I warmed it up good alot of it was gone. I like the sound outside. It turns alot of heads, but with a west the east coast trip next month I am having second thoughts. Do you think the second stack will drop the noise/resonance down to a more acceptable level? I was thinking about mufflers on these to cut the resonance out. Seems like you tried this without success. Kind of stumped. I guess I could just grap a handfull of foamies from work to protect my hearing.

 

[Forrest Nearing]

you might like those earplugs on a cross country trip! LOL!



honestly, if you add a bunch of sound deadener, I think you'll be fine...



when I first got this truck, it had stacks on it, and it was HORRIBLE inside... now it's not bad at all, but it's just annoying... I honestly believe that if I had a quad cab, it wouldn't be a problem for me.



I just think this muffler isn't a good muffler under the cab. the way the muffler is designed it's like a big heimholtz (sp?) resonator with two small resonators at each end... but the center is hollow, and I think the muffler itself is resonating and that's transfering up through the floor... if it was mounted back under the bed, it would be a non-issue...



now, with your quad cab, I would take some measurements, and see if you can fit a 51" Donaldson under there... or even just go with a magnaflow or other popular muffler that's 30-40" long... like the Walker 21741... I was just VERY space limited, so I ordered the largest diameter muffler I could find... I was under the impression that like every OTHER ultraflow on earth, this was a constant diameter perforated tube w/ glass packing... wrong...



weld as many connections as you can, and use some good stiff hangers... run flex pipe between the downpipe and muffler, and you should be in business.



Forrest