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Tailpipe removal with turndowns at axle


Stickman03SS
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I have a question about exhaust system performance. I had a Dynomax Ultra Flo X muffler installed yesterday. It is dual 3 inch inlet and outlets with a built in x-pipe. We removed the stock muffler and tailpipe as one unit in case I want to put it back on someday. The mechanic installed 3 inch turn downs directly to the muffler dumping just in front of the axle. First thing I noticed is that it is very deep rumble at idle, but incredibly noisy in the cab with alot of drone and vibration. I also noticed that it just does not seem to run as good, especially on the low end. I won't mention backpressure, but have I hurt the scavenging effect of the exhaust system by having it so free flowing? Will putting the original tailpipe back in with this new muffler help on overall caily driving performance? Would it be better to put on 2.5 inch true duals from the muffler back? I am assuming doing one of those two things will quiet the system down quite a bit. Have I changed the flow enough to need the engine tuned? Thanks for any info you can offer.

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I have the same muffler and dumped at the muffler with turndowns as well. It will mellow out after a while but my exhaust guy tried different length extension pipe between the factory pipe and the new muffler to move the drone in the rpm range. 10" was the magic length. And the drone also improved as the muffler broke in. Also moving the muffler back 10" really changed the in cab sound not near as loud. But it is a loud muffler dumped. As far as loss of low end power or not running as good I did not and have not experienced that. But a tune will wake your truck up. My .02

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I personally don't like dumping the exhaust under the vehicle. It makes it much louder in the cab than if you run some sort of tail pipe out from under the truck. I'm not familiar with the muffler you have but if it's a straight through muffler, the noise and vibrations from dumping the exhaust under the truck might make you think it's running rough when it really isn't. I ran my truck with the exhaust dumped before the axle for a month or two and hated it.

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If your stock then yes you hurt a little of the lowend TQ. 3" duals are to big. 2.5" dual exhaust will support up to like 600hp no prob. 3" at wot will be ok. I've seen this for years on this site. Bigger is not always better in exhaust.

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Thanks for the input guys! I have seen the muffler mellow a bit the last day or so. I am getting in touch with my tuner (he did my 6.0 swap tune in my 75 K5 Blazer) to see when he can work me in. I am either going to have 2.5 inch duals put on or have the original tailpipe put in with this muffler. Being stock, I don't think the original tailpipe will be too small and I want to see what it sounds like with basically a muffler swap (what I wanted to begin with, but things got lost in translation). I will let you know how it turns out. I will say this......the ultra flo x muffler is a very throaty muffler, which I like. My Blazer has Flowmaster Series 50 Delta Flows on it now after having original series 40 on it. The 50's have a nice deep tone and sound great with the top off the Blazer. The 40's were a bit too tinny to me, but I know that mufflers are definitely a personal preference thing.

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I personally don't like dumping the exhaust under the vehicle. It makes it much louder in the cab than if you run some sort of tail pipe out from under the truck. I'm not familiar with the muffler you have but if it's a straight through muffler, the noise and vibrations from dumping the exhaust under the truck might make you think it's running rough when it really isn't. I ran my truck with the exhaust dumped before the axle for a month or two and hated it.

Agreed. Turndowns under a truck always got me a lot of drone in the cab.

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Exhaust continues to slowly mellow, but not sure if it will get to where I want it. We will see. What I continue to see and feel is times that the engine seems confused and pretty flat. It almost feels like the timing and fuel maps are just a touch out of sync. Still need to get in touch with my tuner, regardless of the current issues, as I know a good tune will supposedly wake it up quite a bit. Wish I had the funds for long tubes right now, but unfortunately I don't. It did throw a couple codes the other night, but it was at wide open throttle at nearly 6000 rpm. They were the rear O2 sensor voltage low code (P0137 and P0157). I cleared the codes and have not seen them since. I it returns, I will put in new O2 sensors precautionary. Been watching them on my Torque App and not sure if I see anything fishy, other than they are slower to come online. My Blazer only has the front O2 sensors and no cats, so I can't compare the two. We will see. I just now something is not quite right at this point. Thanks again for the input.

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