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Discussion Starter #1
So, getting ready to do exhaust and am torn to do exhaust but am getting conflicting info on 3 inch exhaust. Everyone on the Challenger and Charger forums state that the Hemi actually loses torque with three inch until you crest 450 horespower.

So, those here who have 3 inch on the Hemi, what system dis you do and what gains or losses did you see? I am hoping for a bit more power and slightly better mpg.
 

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My $.02.... it will make a lot more noise, probably only slightly if at all help power at the very top of the rpm band and hurt power at low mid and mid-high rpm.

If you're looking for a little extra power for a few hundred go with a chip or fastman throttle body.

I wouldn't go 3" until either heads/cam or forced induction.

Check what the SRT GC is running....
 

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Discussion Starter #3
I am running the K&N cold air intake with the Traildash 2 tuner already. Waiting to hear back from a member on what SRT headers will work, and then do all the exhaust at the same time, whether it is 2.5 or 3 inch remains to be seen...just waiting to see what others have experienced.
 

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Honestly, I seriously doubt that going to a 3" exhaust will hurt anything. The cats are the most restrictive part of the exhaust anyway, so some larger pipe won't affect airflow much at all. The stock system is also around 2.75", so you definitely don't want to step down to 2.5".

The myth that a larger diameter exhaust will negatively affect low end torque is largely unfounded. Some people say that backpressure is important to maintain low end torque, but that's simply not true. Backpressure will always hurt performance.
 

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Discussion Starter #5
People try explaining it as a lack of back pressure, when in effect, what they are speaking about is exhaust velocity. Properly sized exhaust actually helps velocity by almost helping to pull the exhaust from the engine..and overly large exhaust can be a detriment because then the engine has to push it all without the help of the pull effect. I have had the issue prior and know many others that also encountered going too big too soon. If I were forced induction like my turbo car, bigger is better as it helps decrease spool up time which is why I run full three inch from front to rear and no cat on my 4 banger. From what I have read, the stock is 2.5 on the Hemi, but could be wrong.
 

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It's true that going to too large of an exhaust will hurt the scavenging effect, but the Hemi is definitely at the horsepower range where that's not going to happen with 3".

The stock exhaust is slightly larger than 2.5", though I haven't measured exactly how much. I've heard 2.75", but I'm not positive on that number.

Many aftermarket systems go for a 3" exhaust, including Gibson, aFe, and MBRP. Magnaflow goes for 2.5", and I haven't found any specs for the Borla/Mopar system. So you can go either way, but if you're adding some extra airflow with headers and a CAI anyway, I don't see any reason not to move up to 3".
 

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I plan on installing a set of heddman stainless headers that I purchased last fall. I was trying to find a cat section that is 3" pipe, but haven't found anyone that specifically lists it. The unfortunate problem with the catback systems that are 3" is that they quality is not as good as the Magnaflow.
 

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I plan on installing a set of heddman stainless headers that I purchased last fall. I was trying to find a cat section that is 3" pipe, but haven't found anyone that specifically lists it. The unfortunate problem with the catback systems that are 3" is that they quality is not as good as the Magnaflow.
I would beg to differ with you there Flex;

Have you checked out aFe's cat-back systems?

aFe: Advanced FLOW Engineering | Engineered Adrenaline

I have aFe's 3 inch stainless steel cat-back system for the 4.7L; I've had it for a couple of years now and it's legit.
 

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I have the MBRP exhaust and it, along with a K&N CAI and Superchips TD2 on the 87 octane tune, has not only improved power, but fuel economy. I am getting between 15-16 city and 20-21 highway over at least 5-6 fill ups and constantly crunching numbers. Very little to no drone when MDS kicks in depending on speed. Also, it sounds AWESOME! I would love to put some headers on mine, especially since I have the dreaded broken manifold bolts, but I'm not ready to try to find something that's going to require me changing everything else. Only reason I haven't fixed the bolts yet is because it seals itself up after about 30 seconds of running. It will definitely be happening once it warms up here!
 

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Don't get me wrong, I am not saying that they are all poor quality. Side by side, there is no comparison though. The welds, the finish is much higher quality on the Magnaflow part. I have seen both. If I knew that the 3" system was the better option for more power with other power mods, I would go with it hands down.
 

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Does anyone know of a matching 3" cat section? As far as I know, all the standard replacement ones are 2.5".
 

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I plan on installing a set of heddman stainless headers that I purchased last fall. I was trying to find a cat section that is 3" pipe, but haven't found anyone that specifically lists it. The unfortunate problem with the catback systems that are 3" is that they quality is not as good as the Magnaflow.
Hey buddy, What headers did you buy? I didn't know there were any that fit these things? (hemi also here)

and FYI to those referring to magnaflow as the holy grail, I had a magnaflow rot out in 3 years time in the salt belt, they are far from a top of the line system.

lastly The OE cats on the commander is a 2 mile serpentine... you could probably hack it off anywhere post cat, and notice zero performance gain or ill effects.

I have long tube headers on a hemi truck, with full tune, and bolt ons...even with a tune i noticed little difference from the manifolds, to the headers, to a 2.5 true dual system. It DOES get better mileage than my commander however...on 35's...
 

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Johnny,

There are no headers specific to the the Commander bud. I chose these because they are very tight in design similar to the factory log. If they need a tweak, I can do that as well.

https://www.hedman.com/part-search/?PartNumber=72620

Not sure what you mean by 2 mile serpentine? I know for a fact that when Edelbrock first came out with their headers, they posted impressive gains. That was 28 hp and 34 lb of torque. You won't notice that in a 5000 lb truck seat of the pants.

Edelbrock Hemi Headers - Hot Rod Network
 

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Looks like I could provide some positive input here as to parts.
1. The SRT8 GC manifolds from 06-10 are the best fit for the commander, although transmission housing modification may be required.
2. Any SRT8 GC midpipes, are virtually identical to our midpipes, but are 3" and typically include an X-pipe, I have the Magnaflows with high flow Cats on mine.
3. As for Catbacks, just buy the mufflers you want and have a competent shop build from the midpipes back. I'm finding a lot of people don't do this, and I'm still baffled as to why.
 

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Johnny,

There are no headers specific to the the Commander bud. I chose these because they are very tight in design similar to the factory log. If they need a tweak, I can do that as well.

https://www.hedman.com/part-search/?PartNumber=72620

Not sure what you mean by 2 mile serpentine? I know for a fact that when Edelbrock first came out with their headers, they posted impressive gains. That was 28 hp and 34 lb of torque. You won't notice that in a 5000 lb truck seat of the pants.

Edelbrock Hemi Headers - Hot Rod Network
Woah.... $900 shorties? If its as simple as challenger shorties...there are cheaper options out there.


My serpentine comment was for the catback comparisons, when NOT changing the manifolds. I'm talking about the factory cats/midpipe.
 
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