Thrush Welded/Flowmaster knockoff sound?

[hillytim69]

Hi guys I have been away from the garage for a while (other projects) such as a new baby girl last week... but finally had an exhaust put on my 75 Stepside with the 383. Now can hear things a little better. I've never ran Flowmasters or chambered mufflers in the past, usually just ran Super Turbos or cheap turbo muffs. This time i thought i'd try something different and got the Thrush Welded (Flow knockoff) mufflers. I have a mild 383 10:1 compression, Summit headers into 2.5 piping then mufflers and turndowns before rear axle. I don't mind the tinny sound but is it normal to hear a bunch of pinging/rattle noise on part throttle accel? It kind of sounds like detonation but i really dont think it is. I run 91 octane non-oxygenated gas and retarded the timing a bunch by hand and it always sounds the same. Of course i have no floor mat in the cab and a couple holes but still... Do you guys think I'm hearing exhaust pulses banging around all over the place under the truck or what? I'm thinking I'm gonna put some stock manifolds and y-pipe on with a quiet muffler and see if it goes away. I really don't think its from the engine or detonation but it sounds similiar. Maybe I'll advance the timing to make it ping and testdrive to see if its a different noise. If this is what the Flowmaster/and flow knockoffs sound like I don't like it. Opinions welcome. I told my wife if this thing blows, I'll have to do a big block but I don't think thats gonna happen. With all these kids now I'll be spending most of my time behind the wheel of the Odyssey minivan.

[travo77]

i have that same flow knockoff muffler with turn down before axle on my durango and it sounds like a normal muffler to me

[olblue81]

Originally Posted by hillytim69

Hi guys I have been away from the garage for a while (other projects) such as a new baby girl last week... but finally had an exhaust put on my 75 Stepside with the 383. Now can hear things a little better. I've never ran Flowmasters or chambered mufflers in the past, usually just ran Super Turbos or cheap turbo muffs. This time i thought i'd try something different and got the Thrush Welded (Flow knockoff) mufflers. I have a mild 383 10:1 compression, Summit headers into 2.5 piping then mufflers and turndowns before rear axle. I don't mind the tinny sound but is it normal to hear a bunch of pinging/rattle noise on part throttle accel? It kind of sounds like detonation but i really dont think it is. I run 91 octane non-oxygenated gas and retarded the timing a bunch by hand and it always sounds the same. Of course i have no floor mat in the cab and a couple holes but still... Do you guys think I'm hearing exhaust pulses banging around all over the place under the truck or what? I'm thinking I'm gonna put some stock manifolds and y-pipe on with a quiet muffler and see if it goes away. I really don't think its from the engine or detonation but it sounds similiar. Maybe I'll advance the timing to make it ping and testdrive to see if its a different noise. If this is what the Flowmaster/and flow knockoffs sound like I don't like it. Opinions welcome. I told my wife if this thing blows, I'll have to do a big block but I don't think thats gonna happen. With all these kids now I'll be spending most of my time behind the wheel of the Odyssey minivan.

Maybe I'm just lazy, but instead of swapping exhaust to see if the noise goes away, I'd just slip on different mufflers (swap meet, friend) and see if it goes away. If you have the room, you could even just take the turn downs off and put 2 mufflers on each side temporarily till you diagnose.

Do you have an adjustable vacuum advance on the distributor? Maybe you've got too much vacuum advance causing part throttle ping and you need to dial that back a bit.

Oh and make sure your headers aren't leaking cause that can sound like pinging if the leak is small. When I installed mine I had to run the motor to get them hot and then tighten them again to stop the leaks at the head. And the cheap headers I bought leaked at the collector so I had the muffler shop weld the transition to the header and the exhaust pipe to the transition.

[hillytim69]

I'm pretty sure the Durango has Catalytic converters and/or resonators that would soften the exhaust note before it reaches the muffler. Hey Olblue81 I'll try what you said. i was already having second thoughts about the manifolds anyway. I'll get a couple cheap turbo mufflers and put them on back of the existing muffs. Also couldn't i run with the vacuum advance disconnected just to test? otherwise I do still have the adjustable one somewhere. I "fixed" my Skipwhite HEI by putting my GM module and coil and vac advance on it. I don't really know how to adjust the aftermarket adj vac. advance either, an allen wrench but which way is which??? Thanks for the ideas. I also noticed a miss on full throttle 1-2 shifts (TH-350) or when hitting the throttle hard then backing off a bit to reduce tirespin but i think the carb needs some tuning for this engine. its an edelbrock 1902 series Q-jet. I will follow up when I can.

[olblue81]

Originally Posted by hillytim69

I'm pretty sure the Durango has Catalytic converters and/or resonators that would soften the exhaust note before it reaches the muffler. Hey Olblue81 I'll try what you said. i was already having second thoughts about the manifolds anyway. I'll get a couple cheap turbo mufflers and put them on back of the existing muffs. Also couldn't i run with the vacuum advance disconnected just to test? otherwise I do still have the adjustable one somewhere. I "fixed" my Skipwhite HEI by putting my GM module and coil and vac advance on it. I don't really know how to adjust the aftermarket adj vac. advance either, an allen wrench but which way is which??? Thanks for the ideas. I also noticed a miss on full throttle 1-2 shifts (TH-350) or when hitting the throttle hard then backing off a bit to reduce tirespin but i think the carb needs some tuning for this engine. its an edelbrock 1902 series Q-jet. I will follow up when I can.

Pulling the hose off the distributor and putting it on the air cleaner stud will make the vac advance inoperable and will help diagnose whether it is a timing issue. My Crane Cams adjustable one has instructions in my toolbox somewhere. I'll see if I can find them.

[hillytim69]

I've been researching this online tonight, I never realized there were so many different parameters in stock vacuum advance cans. I knew they all interchange but other than that I don't know what I got on there right now. I always just ran what ever I had in the past and got lucky I guess.

[Kaysenmc]

I have this same mufflers on my 87 and have the same sound.. not very happy with them, and definately not the same sound as flowmaster. They will soon be coming off for a turbo muffler or true flowmaster

[munice]

i had a tinny, rattling sound in my exhaust (had exact same thrush muffs installed) and upon tapping underneath when the truck wasnt running I found it to be a broken baffle in the pass. side muffler. i took it back the next day and they swapped it out for free. My guess was one just got dropped in the shop or something...

[grinch4om]

I had 2 chamber flows on my rat, loved the sound but at cruising speeds I couldn't hear the radio...found a stock 3" in and out muffler , put 2 on and it sounds good but real quiet at speed...if I just cruised the truck, flows all the way but since I have to drive it and I MUST have radio...these work great. if anyone wants the part number, I can get it for you

[grinch4om]

maremont...103211...44.99 at the zone fits a 93 C-3500 diesel

[USSkoval]

I have the "Force" mufflers on my Suburban and it's the same deal. They look like a Flowmaster, but the sound is way off. However, after about a year of use, the sound started to change for the better and I like how they sound now. Still different from a Flowmaster though.