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Old 05-03-2009, 01:40 PM   #1
bills01
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Default Muffler Upgrade

There have been several threads on after market exhaust upgrades. My problem with most after market exhaust systems for imports is that they look/sound cheap. (jmho) I took my Astra to a local muffler shop and put it on the lift to see what could be done. After the cat, there is a resonator (about 2.5' long) that is a straight through design. Not much to be gained there from a performance stand point. Then the factory muffler. So for $149, he cut out the stock muffler and replaced it with a SS Magnaflo unit. He attached my stock tip, which I think looks nice and maintains the stock look.

The sound level from stock is slightly louder. not really noticeable until the R's get above 3k. Then you know it's there, but still not obnoxious. I noticed a little better pull on the bottom end of rpm range and about a 1.5 to 2 mpg increase. I do 90% of my driving at highway speeds.

If you want a more pronounced exhaust note, have the resonator replaced with straight pipe. Shouldn't cost to much more.
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Old 05-03-2009, 02:42 PM   #2
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Default Re: Muffler Upgrade

not sure i believe any sort of performance upgrades on the muffler. Even if there were, it would be in the upper end of the RPMs, not the lower end. Any muffler will flow the same with the engine being lower in the range, as it's not flowing very much. With a performance one, you'd only notice it's ability to flow better higher up, when you're trying to run lots of gasses through it.

The 1-2 mpg better is probably just you unconsciously driving more conservatively, as there's no way the muffler would give the torque or efficiency gains to get that kind of a improvement.

Other than that: good deal
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Old 05-04-2009, 07:58 AM   #3
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Default Re: Muffler Upgrade

changing to a less restrictive muffler is not going to increase performance nor increase gas mileage very little if at all. u would need to replace the exhaust from the cat back with a larger diameter exhaust system & a performance muffler. u want more? then u require a header.
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Old 05-04-2009, 11:28 AM   #4
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Default Re: Muffler Upgrade

Hey Bill can we get a sound clip or video on youtube of your exhaust? I want an exhaust system also and was contemplating if i should import a irmshmer exhaust.
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Old 05-04-2009, 11:54 PM   #5
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Default Re: Muffler Upgrade

Factory muffler = back pressure
Back pressure = inefficiency

Opening up the muffler reduces back pressure, add to that opening up the exhaust pipe diameter and reduce back pressure even more.

I didn't dyno the car before and after. All I have is seat of the pants feel. The car seems to have a little more "snap" off the bottom. Nothing earth shattering, but noticeable. As to the MPG aspect, all I have is my BC to refer to. I drive a lot of miles. 26k since last Sept. when I bought the car. 95% at 65-70 and along the same routes pretty consistently. (Nor-Cal commuter) I was averaging 29.5 mpg before I had the muffler installed. Now I'm getting a solid 31 mpg. No real change in driving habits. If anything, I drove it harder the first week or so to make sure it was broken in and the sound level wasn't obnoxious.

It was an upgrade that I thought was worth the $150 and 30 mins it took for the shop to install it. No real science here, just my observations.
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Old 05-05-2009, 05:32 AM   #6
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Default Re: Muffler Upgrade

So anything with the sound clips or video? What area of norcal are you from bill cause I have yet so see another astra coupe and seeing a white one would be interesting.
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Old 05-05-2009, 10:46 AM   #7
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Default Re: Muffler Upgrade

Quote:
Originally Posted by bills01 View Post
Factory muffler = back pressure
Back pressure = inefficiency

Opening up the muffler reduces back pressure, add to that opening up the exhaust pipe diameter and reduce back pressure even more.
Sound in theory, except for...

Our engines (and all naturally aspirated engines) need some backpressure.

The 7-8' of tubing leading up to the muffler: still the same diameter as before. Therefore, the breathing ability of the engine is still the same as before, meaning it can't put out all the extra torque needed to increase your MPGs all on its own.

A muffler by itself will only change sound.
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Old 05-05-2009, 11:04 AM   #8
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Default Re: Muffler Upgrade

Quote:
Originally Posted by mdcclxxvi View Post
A muffler by itself will only change sound.
And not in a good way when it comes to 4 cylinders...
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Old 05-05-2009, 11:08 AM   #9
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Default Re: Muffler Upgrade

In reality backpressure can have an effect on certain portions of the powerband as it effects engine scavenging.

I believe that some improvement in performance might have been gained from just this mod.

Some of the arguments as to why it wouldn't help didn't really make since to me. For instance the straight thru stock pipe just isn't as restrictive as the muffler itself so to say that no improvement can be had by just a muffler replacement sounds wrong to me.

Also, Regal told me that write a different file for a 100% stock exhaust and a stock exhaust w/ a flow thru muffler. They also told me just replacing the muffler gives about 75% of the gains that the full tuned exhaust system gives.
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Old 05-05-2009, 11:37 AM   #10
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Default Re: Muffler Upgrade

Wouldn't the benefits of a muffler replacement depend on the muffler being the most restrictive part of the system? Is it definitely the 'weak link' in the system? If the intake box or air filter or exhaust header or catalytic converter are the most restrictive portion of the system air (exhaust) isn't going to get into the muffler any faster so it's not going to get out any faster.
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Old 05-05-2009, 12:33 PM   #11
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Default Re: Muffler Upgrade

and the intake side on the U/Z18XER is much more restrictive than the exhaust side, so take that into consideration
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Old 05-05-2009, 09:11 PM   #12
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Default Re: Muffler Upgrade

What is the inlet diameter on your new muffler?
Did they only replaced the muffler or did they also replace the axle-back part?
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Old 05-05-2009, 09:50 PM   #13
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Default Re: Muffler Upgrade

Quote:
Originally Posted by Robor007 View Post
Wouldn't the benefits of a muffler replacement depend on the muffler being the most restrictive part of the system? Is it definitely the 'weak link' in the system? If the intake box or air filter or exhaust header or catalytic converter are the most restrictive portion of the system air (exhaust) isn't going to get into the muffler any faster so it's not going to get out any faster.
For most people, this is true. But if you really want to get into the science of it, replacing just the muffler can increase exhaust flow. It's this "science" that gets exagerated by the muffler manufacturers.

Simply put, air is compressible while liquids are not. Both are fluids, however, meaning that they "conform to the shape of what they are flowing into/through" (sand is technically a fluid as well). What you're describing -- one bottleneck reducing the flow of an entire system -- is true in fluid dynamics when the liquid is not compressible. One tiny restrictor in a huge 1" oil feed line to a turbo will cut the flow of oil dramatically, regardless of the free flowing nature of the 1" line. It is the friction imparted by that single restrictor that forms the bottleneck that reduces flow.

But when dealing with compressible fluids like exhaust gases, it isn't as simple as "flow is reduced by the sole component offering the most restriction". A two inch exhaust pipe 10 feet long will present more flow restriction than the same sized pipe only 5 feet long. It is the friction against the inner walls of the entire exhaust system that contributes to much of the backpressure, while turns and bends account for most of the remainder. Because of this, exhaust gases speed up and slow down at various points from the exhaust valve to the tail pipe.

So, replacing just the muffler with a freer flowing one and leaving the rest of the exhaust system alone will certainly decrease backpressure. The question is, by how much, and whether or not doing so actually has any true benefits. Exhaust gas velocity can be altered by messing with the exhaust system, and the engine is usually tuned for it. Reduce the backpressure too much and you might even set off your SES light.

We've come a long way since the days of slapping on a four-barrel and some headers and screaming "Yea-haw!"
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Old 05-05-2009, 09:56 PM   #14
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Default Re: Muffler Upgrade

Read, then debate.

http://www.superchevy.com/technical/...exh/index.html
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Old 05-06-2009, 01:47 PM   #15
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Default Re: Muffler Upgrade

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Originally Posted by SaturnSdn View Post
Nice read. I'll admit I 'skimmed' it but noted this...

Quote:
Without data to the contrary, it seems safe to assume that the more a muffler flows, the better. This, fortunately, is not so and here's why. Increasing muffler flow unlocks potential engine power. Once all the potential power is unlocked, further increases in exhaust system flow will not produce any further benefits in terms of power. But what may be good for power may not be good for noise as any excess flow capability can lead to a noisier system. From this we can conclude that too much muffler flow serves no useful purpose and possibly costs more money than was really necessary. The trick here is to use just the right amount of muffler, no more and certainly no less. This allows the full power potential of the engine to be realized at the lowest cost without undue compromise in terms of noise. Now the question is, how much flow is enough?
So the question is, how much (if any) are the Astra's being held back by the muffler?
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Old 05-06-2009, 03:32 PM   #16
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Default Re: Muffler Upgrade

Modern cars .................. little to none.
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Old 05-06-2009, 07:31 PM   #17
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Default Re: Muffler Upgrade

Quote:
Originally Posted by SaturnSdn View Post
Modern cars .................. little to none.
yeah i agree....Plus as mdcclxxvi said i think most of our restriction takes place on the intake end...and even then i don't think our gains are that big even if we tak
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Old 05-06-2009, 08:05 PM   #18
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2008 Astra XR
Default Re: Muffler Upgrade

Do you have the part number for the muffler? Any pictures/sound clips?
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Old 02-15-2018, 11:50 AM   #19
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Default Irmscher i38-08-019 Silencer Box

Irmscher i38-08-019 Silencer Box (Muffler)

Pros

-Somehow still maintaining the sound of the Astra Personality!
-I can hear the kind of boxed soft mellow sound when I try to accelerate quickly
-When I go over 60 mph the wind noise and the tires hitting the bumps become more noticeable priorities
-I enjoy my stereo at much lower volume than before
-There are diffusers, moldings, trims, seals, spoilers, lips, etc., to make it a nice bumper finish

Cons

-There is not exactly fit for the Astra Z18XER 1.8 140ph GTC body
-Bumper work and minor rear bumper cut is need
-The silencer box body is about 1 away from the tire coil spring
-Hangs about < 1 lower than the OEM

Others

-My idle dropped little bit 50-100 rpms now stays steady around at 700 rpm when is warm
-No noticeable horsepower increase
-The same or better gas millage consumption
-The exhaust pipe is weld instead of clamp
-Welder adaptation on the silencer box arm hangers
-Same rubber hangers are used

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File Type: jpg Irmscher01.jpg (102.9 KB, 15 views)
File Type: jpg Irmscher02.jpg (80.3 KB, 16 views)
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Old 02-17-2018, 07:50 PM   #20
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Default Re: Muffler Upgrade

Has anyone changed there exhaust recently? I have been wanting to make my exhaust a little louder but not "fart can" loud. Just a little rumble when going through the motions.
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