340 3" exhaust unbearable

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Jbombr

Jbombr

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Hi guys first post here. At my wits and with this. "Mild build" 340 727, heads, XE268 cam, headers, airgap, msd etc. Timed as always around 18&35. Changed my leaky temporary 2 1/4 exhaust for my fabbed 3" now the thing resonates so bad I can't get it out of the driveway. Under wot it sounds like the general Lee but anything lower and you can't hear the engine over the low low frequency resonation. Changed the welded body turbo style mufflers in the pic to my former rolled seam turbo that were on it (2 1/4) but little change. I have full 3" proper turbos coming to hopefully help.

I know 3" is a little big but fits future plans. Will some resonators/glass packs ahead of the mufflers help? It is full back to the bumper.

Any ideas?

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Your joking right???
The issue is with the pipe size allowing more sound to pass. How is this a mystery?
A 2-1/2 system is enough for that build, as stated.
If your planing on stepping up the game to where you need a 3 inch system, then plan for a lot more noise over what you have now with the more radical engine.

Welcome aboard!
 
Sorry not kidding. Was just looking for some help as to maybe I'm wrong with the cutouts after the H. Or maybe that being in the wrong postion. Loud yes, please. Currently the low frequency resonation at idle is incorrect for any sized system. The resonation is way way louder than the exhast tone itself. Its rubber mounted and not hitting the body or chasis.
 
Yeeeeeaaaaa, The cut outs are about where there supposed to be. You myself would have done them right at the muffler. But when there capped, it should t be so bad.
 
I run full 3" - TTi headers, mufflers then resonators - no X or H right now.. I wish you could hear it, really has a great rumble! So yea, if you can find some resonators to squeeze in there - they'll probably help.
 
At cruise or part throttle,I can barely hear my TTI supplied dynomaxers. Full 3 inch duals with their TTIs. No crossover anymore. And no drone whatsoever.I only have 420 or so buckeroos, but when they get to pulling, then everybody knows it's me. Needless to say, I take it easy, close to home.
Oh yeah; factory turn-downs.
I gotta ask what kindof hangers are you using? And how radical is your 268 engine.

Hey I gotta tell you what I did just after highschool
See; this Azzhole cop pulled me over for noisy mufflers. This was in about 74/75 and there were no noise laws yet, but I didn't know that. Turns out he wasn't as big an azzhole as I thought, cuz he gave me some time to fix it and told me to bring it around to the station and he would reduce it to a warning.So I went home and grabbed a big corrugated card-board box and cut a couple of 16 inch squares out of it. The day before my appointed time,I rolled those up tight, cut them to fit and jammed them up the pipes. Then I drilled a whole straight through the pipe and cardboard and out the other side, into which I stuck a nail. The next day after I passed his noise inspection, I rolled around the corner, stopped, pulled the pins, jumped back in and goosed it. Babamms that cardboard was street-litter!
To be fair the car was really loud. 65 Valiant wagon 340/904/fenderwells into dual 2.25s into really short THRUSH straight-thrus out the back under the rear axle. It was a straight shot from the end of the header to the rear bumper. Yeah it was loud.I was 23 and didnt give a a a hoot!
Card board is cheap
I made another pair to idle around the neighborhood with;but I didn't wind 'em up as tight......
Man, that brings back sweet memories.
 
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Thanks guys. It was loud before and is loud now, just the loud is burried behind this much louder heavy heavy low WHUAH WHUAH WHUAH WHUAH WHUAH !!!!!!!! Oh and there's a small rumpety rump rumpety rump in there. That's the good noise.
 
The hangers are rubber strap w/ fabric weave in the layers. U bolted behind the mufflers and then again at the tail pipes near the bumper. I'm going to drop the whole system and let it hang mostly by the collectors tonight and see. It has about 1/4 clearance below the body all along. Engine shake may twist it up into the body is my last resort.

If my crossover and cutouts aren't postioned wrong then it has to be a mechanical interference that I can't see.
 
Well it's not mechanical. Dropped the system. Has plenty of clearance, the racket is at 900-1700 rpm (under load or not). Coming from behind the cutouts. Sounds like a set of 12" subwoofers. The exhaust note is there but greatly overpowered by this harmonic that shakes the cabin light out of its socket.
 
I Think that is called a chassis excitation. I had that on a 69 Barracuda 6 cylinder at exactly 50 mph. The car was impossible to spend any time there. 50mph with 2.76s and N-50s(don't ask) was just about 1800 rpm. My solution was to not drive 50.That was 1977, and I was newly married. She had the furniture and apartment. I had wheels, and was extraordinarily handsome.lol
My chassis excitation wa s caused by the tires. It had not done it with the previous set.It was just as you describe except at speed.
"heavy heavy low WHUAH WHUAH WHUAH WHUAH WHUAH !!!!!!!!"
It went up into the seats and steering column, and pounded my eardrums.
 
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get rid of the turbo mufflers and put Hooker Aerochamber mufflers on with 2 1/2" tailpipe. you will be happy with the result.
 
I run the tti x pipe but in 2.5 diameter and dynomax super turbos. I know there is a good exhaust system behind the healthy stroked 340 .. I get alot of compliments on the sound and I don't think it's bad. But maybe my marbles are already loose
 
Do you have tail pipes now? If not, that's the problem. The sound exits where the exhaust pipe ends. If it ends under the car, the sound exits under the passenger compartment.

I agree with putting tail pipes on it, but I don't agree with down sizing them. That goes against putting bigger pipe on it to begin with. Once it has tail pipes, then the sound will exit behind the car, where it belongs.
 
Ya you bet, I've got the full over axle exiting to the back just past the bumper. Trying a different muffler setup tomorrow to rule those out.
 
fishmens67 said:
get rid of the turbo mufflers and put Hooker Aerochamber mufflers on with 2 1/2" tailpipe. you will be happy with the result.
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Thanks! I've read great things about those on here. May be my next step as I've got it isolated to the mufflers now.
 
Jbombr said:
Thanks! I've read great things about those on here. May be my next step as I've got it isolated to the mufflers now.
Click to expand...
find a set of Black Widow Mufflers and you will be VERY happy.

If you cannot find them, let me know I have a very close friend who has an exhaust and performance shop and is a distributor for Black Widow mufflers.
 
I (have before and currently) run Aero chamber before and it have noticed a large difference between a mello 318, a warmed up 360 and 400. Also warmed up in a minor way.
 
Drone is a problem. I had a pretty good case of it. Muffler, H pipe, X pipe may help solve it and maybe not. I tried different mufflers including Dynomax VT mufflers that are suppose to control drone but they only reduced it 12db and it was still annoying. After my journey was done and what I found along the way an H pipe may have been a solution. I ended up using a branch resonator on each side which killed the drone. There's a post in this section on my whole journey with the problem and how I solved it. Here's a link Suggestions for muscle car sound muffler without drone
 
AJ/FormS said:
I Think that is called a chassis excitation. I had that on a 69 Barracuda 6 cylinder at exactly 50 mph. The car was impossible to spend any time there. 50mph with 2.76s and N-50s(don't ask) was just about 1800 rpm. My solution was to not drive 50.That was 1977, and I was newly married. She had the furniture and apartment. I had wheels, and was extraordinarily handsome.lol
My chassis excitation wa s caused by the tires. It had not done it with the previous set.It was just as you describe except at speed.
"heavy heavy low WHUAH WHUAH WHUAH WHUAH WHUAH !!!!!!!!"
It went up into the seats and steering column, and pounded my eardrums.
Click to expand...

Ma Mopar started putting those heavy rectangular cast iron dampeners on the passenger rear floor boards to help calm this noise issue. I'm sure some of you have encountered these......
 
buck351 said:
Drone is a problem. I had a pretty good case of it. Muffler, H pipe, X pipe may help solve it and maybe not. I tried different mufflers including Dynomax VT mufflers that are suppose to control drone but they only reduced it 12db and it was still annoying. After my journey was done and what I found along the way an H pipe may have been a solution. I ended up using a branch resonator on each side which killed the drone. There's a post in this section on my whole journey with the problem and how I solved it. Here's a link Suggestions for muscle car sound muffler without drone
Click to expand...

I have a 340 with 284/484 cam X heads, dougs 450 headers, 2.5 inch pipes with a cross pipe like your first picture followed by Dynomax VT mufflers, and it sounds great, load when I get on it and nice when I don't and no drone.
 
I have a tti 2.5 x pipe with flowmasters mufflers for sale. 72" long
Prefer pick up but may be able to ship.
Was looking $300. Plus ride if need to ship.
Fastenal ships store to store reasonable
Tiffin oh 44883

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