Flowmaster 40 Deltas too LOUD! Please suggest...

[mcintyrederek]

Hi,
1986 C10 LWB with 350 and a mild cam, full length headers.  My exhaust needed to be replaced (all of it) and my good friend who owns a muffler shop suggested Flowmaster 40 Delta Flow mufflers.  He went from the collectors and came back just behind the transmission and installed an H pipe.  Everything behind the headers is 2".  From there goes to the mufflers and straight out the back.

The truck sounds FANTASTIC.  It has that Flowmaster sound that everyone loves.. but.. it's TOO LOUD in the cab!  Driving with the windows and back glass open gives you a resonating humming, deep tone and afterwards, and ear ache.  Driving with the windows up is tolerable not comfortable.  My buddy did an excellent job installing and welding, so I don't want to hurt his feelings by telling him how bad the noise is in the cab..

I have plenty of room from the mufflers back up to the H pipe.  Would installing something in line BEFORE the Flowmasters quiet it down some?  Would installing a set of cheap 2" glass packs up close to the front eliminate some of that resonation, or make it worse?

I'd like to keep the nice tone out the back but definitely need it quiet in the cab.  What can I add to the system to help this..  I'd really rather NOT change the mufflers.  They're brand new and the job he did looks like nuclear power plant welding.

Thanks for any suggestions.

Mack.

[benr21]

You could put in some cheap cats or put in some resonators. Or just put more sound proofing in your cab. That actually be the best route. It will drown out the noise.

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[mcintyrederek]

Yes, I should have mentioned the headliner is gone, the carpet, all the padding, and everything else is gone, too.  It's just a bare-bones metal cab with some undercoating used as floor liner.  I'm sure that probably has a lot to do with it also.  Truck sounds great on the outside but on the inside it's like hum city.

Mack.

[Stewart G Griffin]

How far back are the mufflers?

[Greybeard]

I had that problem too way back when. I never solved it. But with new tech it should be a easy fix. Newer cars have a sound/heat barrier above the exhaust system- a simple sheet metal tunnel over the exhaust pipes might help some by radiating the sound waves down as well as acting like a heat sink. If you ever drive barefoot in the summer it will also keep your right heel from getting too well done.

I never wanted an interior in my truck because it's easier to just flush stuff out with the garden hose after wheeling. I didn't have AC anyway. So mud and crud was no problem and getting out (and back in) in knee deep mud didn't make me cringe as much knowing the cleanup was easy. I also played in deep water so having a cab full of water that reached waist level at times (when I misjudged the water depth and drowneded) did not cause too much stink later on. Seats actually dry out pretty fast, carpet doesn't since it lays on metal. 

[mcintyrederek]

The mufflers are sitting up close to the bottom of the bed, about halfway between the back of the cab and rear axle.

Mack.

[mcintyrederek]

I don't have an interior in my cab either, just metal coated with bed liner.  Someone told me that if I put the spare tire back under the truck, it would cancel out the resonating  ?!?!?!?  Hard to believe but worth a try!

Mack.

[Usareke]

Glasspacks... Lol

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[travisr1988]

Do you have tailpipe on it or did you dump it under the bed?

Also, a crossover will quiet it down a little but tailpipes will quiet it down quite a but. When I ran my temporary exhaust I had the mufflers just behind the cab and dumped right after the mufflers (thrush welded) and I had a crossover and it was so loud in the cab. When we did the final exhaust we started at the headers again and hung the mufflers behind the cab in front of the axle and ran tailpipes out to behind the rear wheels. That without a crossover was significantly quieter, then we added a crossover which quieted it down more.

[Greybeard]

On my old truck I had no crossover, my mufflers were Thrush turbo's (have them on my current truck too) and they dumped out in front of both back tires- straight out. Don't remember exactly where the mufflers were placed under the truck but far enough forward to let the tailpipe turn and exit from in front of the tires. It was a resonating SOB! I drove that tin can from St. Louis to Colorado pulling a trailer. By the time I got to the west end of Kansas my head was throbbing my ears were ringing, I felt like i had been run over by a truck, and my body buzzed like it was electrified. And worse than that all I had was a stand alone 8-track player with bad speakers and with one tape that played (AC/DC). It was set to repeat. I was driving in the cold and snow so the windows were up which helped with reducing the resonating. To say it was a fun trip would be an understatement. 

[mcintyrederek]

Yes, the tailpipes are all the way to the back bumper.  And yes there is a crossover pipe just under the tailshaft of the transmission.  I know that connecting the crossover pipe as close to the headers as possible would have been best, but not an option right at the moment.

The Flowmasters are right up under the bed of the truck.  Everything resonates.  I mean, it's not horrible and man is sounds great but it's there.  It hums from about 35 MPH to maybe 55 then goes away.  Convenient.  Under 35 it's put-put-put with that nice metal clangy sound the Flowmasters are known for.  35 to 55 it starts humming.  55 and over, the resonance goes away and it's all road noise.  It's a 2.73 rear end so that means it resonates from around 1500 to 2000. 

It sounds too good on the outside to be mad about it.  But it sounds too droney in the inside to just leave it alone.  I'm afraid adding glasspacks before the Flowmasters will make it even more of a humming sound since the fiberglass is supposed to cut out the HIGH frequency noise, not the low.  Should have gone with the 50 series instead of the 40 I guess.  I don't have $200 to go back and re-do it so I guess I'll just live with it and be happy the truck runs as good as it does.

Mack.

[Greybeard]

If you have tubes headers therein is the problem not the mufflers. Once the sound of the explosion is channeled out of the heads it those nice tight turns in the tubes and that is where the resonation originates from. Downstream is simply the force of the moving gasses carrying their own sound. It makes sense actually. Consider the gas is under extreme pressure when the valve opens, that allows the nearly sudden reduction of pressure which creates sound (think of air coming out of a balloon- magnified). Some of that sound is absorbed, and thus transmitted, to the outside of the header tubing and since this sound is at it's maximum volume that translates into a lot of sound. Now consider the cast iron manifolds the factory uses, same thing only the cast iron does not transmit sound as well as steel does....resulting in a quieter exhaust. That is why the more expensive cast iron exhaust system is used. Remember also that a stock exhaust system still has essentially the same tubing from the exhaust manifold rearward. So adding a fix to the tubing is not the cure.

Wrapping exhaust tape around the header tubes near the head and down as far as the collectors is one way to fix the problem, at the risk of greatly shortening the lifespan of the headers due to excessive heat buildup and rust. Heavier header tubing works a little too. Cheap priced headers are cheaply priced because the tubing wall thickness is thinner. I have a thirty year old set of 454 headers in the basement that weigh close to twenty pounds each, the Hookers I put on my truck for the small block...about seven pounds each. 

There is nothing short of lining the interior of the truck that will totally eliminate the noise, but knowing the vast majority of the sound is coming from the engine compartment is a good start. Of course, not all the sound is coming from up front but most of it is, thinner exhaust pipes are used today because they are now coated for rust prevention. Anything with a thin wall will transmit sound easier than something that is harder to create/transmit vibrations in, like thick steel or cast iron.

The name of profitability today is to make things as light as possible while still making the potential customer love it even though it won't last (I am getting a Masters in Business, this is what I'm being taught). With the exception of automobiles, this is an industry standard now. Thinner/lighter is better. Well, even in automobiles it's true, check out all the stamped steel or plastic parts that used to be forged steel or cast iron. Thinner is better even though it's lifespan is shorter. I'm not a believer in that theory. However, the buyer is supposed to beware and send feedback to the companies in order to voice disapproval. That does not happen however.

[jg1977c20]

welcome to the club - i have the original 40's so i feel your pain - i'm thinking about the 50's too but my 40's are only 2 years old maybe 1 more year -lol i think were just gettin older ?

[Greybeard]

I'm kinda in agreement with the gettin old thing, I still have my 1984 Harley and it still has the first set of pipes on it after I chucked the stock ones. They are 28" open goosenecks. My wife tells me they can be heard from ten miles away. I know they made my right ear ring when I passed cars at 70 mph or rode next to a barrier of some kind and very few of my buddies could stand to ride next me on my right side for very long. Even after 32 years of that I still love it however. But my trucks and cars...not so much anymore.

[mcintyrederek]

Thanks again for the comments.  I was afraid now that someone would say the new headers are probably where most of the noise is coming from.  The thump thump sound at a lopey idle is not only a sound, it's vibrating the floor board.  So, when running at 2200, it's a HUMMMMMMM....  Golly, opening the windows and heaven forbid the back glass, the resonant hum at certain RPM's will make your eyes water.  I could kick myself in the butt for not installing new cast iron manifolds.  I'm not running the thing for performance, neither do I care about loud trucks.  I just ordered the headers because they were cheaper than cast.  Lesson learned.

I think I'm still going to try something in conjunction with the Flo 40's..  I have room to add something else right after the headers but way before the mufflers..  just to see.  The headers I put on were made by Flow-Tech, they weren't high $$$ but they are very heavy, full-length.  This would explain why I can hear the pulses under the hood now and I've never been able to before.

Thanks for the input.

Mack.