Stock Exhaust
- Thread starter Pittdawg
- Start date
- Dec 5, 2011
- 538
I can confidently recommend a magnaflow muffler on the I6 now. From the first time I started up the engine after swapping in the magnaflow the sound was spot on but I immediately noticed a loss of low end power. I was concerned that I opened up the exhaust too much and lost too much velocity to properly scavenge the exhaust gases but each day after the install I slowly but surely felt power coming back. While butt dynos are often inaccurate, I now "feel" like I have more power, or a better way to explain it is it "feels" like my engine climbs rpms quicker. Oh yea, I also upgraded my tune to shift level 2 so it gives you a little kick in the pants during gear changes now too.
sounds pretty good, on our 5.3 i want to try a stock muffler off a duramax to see if it flows better and sounds ok.my wife is the primary driver and it has to pass her ear test.
- Dec 5, 2011
- 538
limequat said:
No the newer models (07+?) take several hours with the battery off to reset unlike the earlier years which just take minutes. It's been several hundred miles now so I don't think it still needs to be reset.
oh05ext said:
Is the Duramax a straight throw muffler or is it all chambered and baffled like our stock muffler? Is your goal to keep sound down as much as possible? If so, the 22 inch Magnaflow muffler I used is really not that loud and if you go with a decent sized resonator (mine is pretty puny) I bet it would be very tame.
i havent done much reasearch on the flow of a duramax muffler.i figured for a diesel its gotta flow better than a gas truck.i think its probably gonna get a big resonator adn muffler soon and chop off that flat part over the axle and a side exit.like i said it just has to pass the wife test.lol.which means no usually
Sounds good. As for you resonator, you said it was Vibrant performance, is it the bottle type or the ultra quiet and what length is it?
- Dec 5, 2011
- 538
- Dec 5, 2011
- 538
I lost low end and mpgs initially. Finally, 2 weeks later, my low end and my mpgs came back plus much better midrange power. It used to fall flat shifting into overdrive but now the power feels much more linear. The low end came back after a week but it has taken two weeks to get the mpgs back. Im down from 16.5mpgs with 3.42s and stock 245-65-17 tires and stock exhaust to 16 mpgs with 4.10s 265-65-17 tires and Magnaflow muffler. The added power and grip are greatly appreciated in favor of a minor .5 mpg loss.
- Dec 5, 2011
- 538
I still have minor droning at 2000-3000 rpms. With my 4.10s, those are freeway rpms and my 17 month year old son likes to sleep in his car seat 
I am installing an 18 inch resonator in favor of the 12 inch resonator hoping to resolve the minor droning. The droning is very very minor but I am hoping to erase any hint of it.
I am installing an 18 inch resonator in favor of the 12 inch resonator hoping to resolve the minor droning. The droning is very very minor but I am hoping to erase any hint of it.
- Dec 5, 2011
- 538
The droning is getting progressively worse 
I took some family members to visit my grandmother for her 91st bday today. I took a stretch of the freeway with a lot of grades and to be frank, the droning was fuc#%$& terrible on the uphill grades. I was so embarrassed when my mom was asking me what was wrong with my truck and why was it giving her a headache
I'm going to have the exhaust shop move the 12 inch resonator upstream, basically wherever it will fit and install the 18 inch resonator coming out the back. I'm hoping the two together will help but I'm now concerned that those bottle style resonators just may not have enough sound absorption material to make a big enough difference.
Also, although the majority of my low end came back, there is no denying that the 3 inch magnaflow shifted the powerband up by approximately 700-900 rpms, i.e. with my prior mods and stock exhaust, the power really came on just after 2000 rpms or so and now it is much closer to 3000 rpms. I'm hoping the addition of 18 inches more of smaller diameter tubing helps shift the powerband back down a little.
Again, the muffler sounds amazing from the outside but as the muffler has broken in, droning under load is becoming a major issue and I have to spend money I don't have to fix it
I took some family members to visit my grandmother for her 91st bday today. I took a stretch of the freeway with a lot of grades and to be frank, the droning was fuc#%$& terrible on the uphill grades. I was so embarrassed when my mom was asking me what was wrong with my truck and why was it giving her a headache
I'm going to have the exhaust shop move the 12 inch resonator upstream, basically wherever it will fit and install the 18 inch resonator coming out the back. I'm hoping the two together will help but I'm now concerned that those bottle style resonators just may not have enough sound absorption material to make a big enough difference.
Also, although the majority of my low end came back, there is no denying that the 3 inch magnaflow shifted the powerband up by approximately 700-900 rpms, i.e. with my prior mods and stock exhaust, the power really came on just after 2000 rpms or so and now it is much closer to 3000 rpms. I'm hoping the addition of 18 inches more of smaller diameter tubing helps shift the powerband back down a little.
Again, the muffler sounds amazing from the outside but as the muffler has broken in, droning under load is becoming a major issue and I have to spend money I don't have to fix it
- Dec 5, 2011
- 538
Just had the 18 inch resonator installed in place of the 12 inch resonator and had the 12 inch resonator installed upstream. Initial thoughts are that drone is reduced but not completely gone. It's probably good enough though to not throw more money at it.
gmcman
Member
- Dec 12, 2011
- 4,672
Pittdawg said:
I know this thread is dated but I wanted to throw in my $.02. This theory is actually backwards. You need the larger pipes at the rear and the smaller diameter near the motor. You don't actually need smaller tubes at the motor, but the hotter the exhaust, the easier it flows. This is why normally on 2-valve heads the exhaust is smaller than the intake. When the exhaust cools near the exit it's more dificult to push through the pipes which is where larger plumbing can help.
Hower if for a scavenging effect then I think the slightly smaller piping near the exit may increase velocity and create a suction but I'm not sure on that.
- Dec 5, 2011
- 538
gmcman said:
You're half right. The cooler exhaust gas is more difficult to push through the pipes because the gas velocity has decreased. The easiest way to get the velocity back up is by decreasing pipe diameter. Going to "larger plumbing" just exacerbates the situation, i.e. cools the exhaust gas more and decreases velocity further.
What a lot of people don't understand is that the larger plumbing is really only a benefit in higher rpms when your motor can pump out enough air to take advantage of the extra space. At lower rpms, your engine pumps out much less air and therefore if your plumbing is too big you decrease velocity too much killing your low end. As a point of fact, up until I installed my 3 inch core muffler, I had modded my ride strictly for low end and figured I could give up a small amount of low end for mid and top end with the larger muffler. Well, that is exactly what happened but it made me realize I spend much more time under 3 rpms then over and started to miss the low end power I had before.
The 18 inch res I installed today is actually 2.25. So I have 3 inch dp to 3 inch core muffler to 2.75 inch stock pipe to 2.5 inch res to 2.25 inch res at the tail. Not a big difference but it already feels as if the low end is closer to stock and the mid and top end still seem stronger.
bigytwotone
Member
OK well i just installed a thrush glass pack muffler on the truck and wow sounds so nice out side and good inside at low RPM but give it any gas and OMG the noise inside is horrible so im going to be doing some research and see if i can find some way of making it drone less with out changing the muffler.
Oh I remember cutting that muffler. P. I. A. But yeah, you have to match diameter to engine size. Since the 4.2 has power across a fairly good sized portion of the rpm band, I went with a 2.75 Flowmaster 44 on my TB. Incredibly loud but considering I was a seventeen year old high school senior it worked for me. But I noticed that the flowmaster didn't drop my MPGs like the magnaflow on my 4.3 did, which was by about 1 or 1.5. Also I didn't notice any notable power gains from either muffler.
