At the pump conversations...

[mr.wilson]

At he local fueling hole, it is so easy to strike up a conversation about Dodge trucks. I usually hit up the guy across the pump with have you ever heard of TDR? As of late, the conversations have been a little weird, for example:

"Hey I can tell you an easy way to gain some fuel economy out of your '03" Curious me asked "Well how is that" The old boy from the his side of the pump replys, "... pull the number 35 fuse". I know what curiosity did to the cat, so I thought I would as the most knowledgeable bunch of folks I know too see if anyone else had heard of this.



Another fellow swore that adding the 4" exhaust made no difference to his trucks performance. As he drove away I was pretty sure that it was only 4" exhaust and nothing else, no muffler, no cat. Could that be possible? Other that illegal, is this normal or do you need some type of muffler for back pressure to see an increase in performance from your after market exhaust?



Craig

 

[Cummins Thunder]

You mean the truck was straight piped? It is a rather common thing among Dodge Cummins owners. Too loud for me, but some love it.

 

[BHolm]

Fuse #35 on my '03 is for the ABS module. Pretty sure that isn't going to help anything.



On the exhaust, the trucks already have a 4" exhaust, it is stock. The pre 04. 5 HO's use a 3. 5" turbo outlet otherwise it is 4" in diameter. Turbo diesel trucks do not need a muffler for back pressure. The turbo itself is an exhaust restriction and generally completely uncorking the exhaust will have some benefit. If that is the only change, there likely isn't a difference you can feel, just one you can hear. :-laf

 

[LightmanE300]

Pulling fuses may just disable some feature on your truck. Adding exhaust alone won't increase performance, just noise.

 

[steved]

Adding exhaust alone won't increase performance, just noise.

I disagree with this statement, while you might not see the absolute best gain in mpg that it can give with other mods, it will still give you an increase...



I have more or less straight piped all my trucks and the exhaust by itself DID provide some increase in mpg...



While it will only provide an increase directly related to that which the OEM exhaust was inhibiting, it will still provide a gain.



steved

 

[mr.wilson]

Yeah I think it would be a little too loud for me as well. I had to ask because it went against most of what I know about trucks.



I think the guy mentioned that pulling the fuse turns off the Odometer and confuses the computer to increase the fuel mileage.



Craig

 

[NavyDood]

The pre 04. 5 HO's use a 3. 5" turbo outlet otherwise it is 4" in diameter.

On the 04. 5's it is 3. 5" all the way to the Muffler. Only the tailpipe is 4".

 

[steved]

On the 04. 5's it is 3. 5" all the way to the Muffler. Only the tailpipe is 4".

Umm, my 04. 5 600CTD is 4" from the turbo to the tip of the tailpipe... all factory.



steved

 

[Lightman]

On the exhaust, the trucks already have a 4" exhaust, it is stock. The pre 04. 5 HO's use a 3. 5" turbo outlet otherwise it is 4" in diameter. :-laf

03-04 use 3. 5" from the turbo elbo to the muffler 4" out of the muffler

 

[jjdiesel]

03-04 use 3. 5" from the turbo elbo to the muffler 4" out of the muffler

Lightman's got it right.

 

[NavyDood]

On the 04. 5's it is 3. 5" all the way to the Muffler. Only the tailpipe is 4".

Grrrr... I fat fingered it. What I meant was the 04's are 3 1/2" to the muffler.



04. 5's and newer are 4" all the way.

 

[Turbo1Ton]

03-04 use 3. 5" from the turbo elbo to the muffler 4" out of the muffler

I thought '03's and '04's were 3". My '03 built in 8/02 uses 3" from the turbo through the muffler then goes to 4" on the tail section. I know this because I purchased and installed 3" band clamps when I put on my muffler eliminator.



Jeff

 

[JCleary]

An answer to "freeing up" the exhaust having no benefit:



With our computer-controlled trucks, the ECM is looking for boost to add fueling. Once you've opened up the exhaust, the turbo *will* spool quicker, in fact, perhaps too quick for the ECM's taste. The result is that the ECM pulls back fueling until it sees the boost rise according to its programming. Therefore, the net benefit can be 0hp gained.



This may be especially true on the SO/HO trucks, but I would imagine removing the cat will have the same effect.



Now, on a sustained pull, as in 5th gear up a long hill with a trailer, you maintain about 24psi in an '03. Since it's a sustained pull at max boost, the truck is giving full fueling. The only power loss, or lack of gain would be the initial full throttle application as the turbo spools. The benefit of having an open exhaust here is that your EGT's will be lower, about 50°-100°.



I dynoed before and after installing my "first mods" which were an AFE PG7 with a torque tube and a Banks 4" turbo-back exhaust--Same dyno (Mustang), different days, stock fueling. If I remember correctly, I saw a 3hp difference, but in the negative. You can attribute the difference to a number of factors, but I believe that the mods netted me nothing except a nice exhaust tone and some turbo whistle. Any performance-enhancing downloader or module will make your truck appreciate the open exhaust.



A 4" exhaust is adequate for most of our setups, especially if you have a stock turbo. Have you ever looked at how tiny the exhaust opening is? Maybe 2" plus the wastegate?. I think you'll only benefit from something larger when install bigger turbos and get to 600hp+.

 

[steved]

An answer to "freeing up" the exhaust having no benefit:



With our computer-controlled trucks, the ECM is looking for boost to add fueling. Once you've opened up the exhaust, the turbo *will* spool quicker, in fact, perhaps too quick for the ECM's taste. The result is that the ECM pulls back fueling until it sees the boost rise according to its programming. Therefore, the net benefit can be 0hp gained.



This may be especially true on the SO/HO trucks, but I would imagine removing the cat will have the same effect.



Now, on a sustained pull, as in 5th gear up a long hill with a trailer, you maintain about 24psi in an '03. Since it's a sustained pull at max boost, the truck is giving full fueling. The only power loss, or lack of gain would be the initial full throttle application as the turbo spools. The benefit of having an open exhaust here is that your EGT's will be lower, about 50°-100°.



I dynoed before and after installing my "first mods" which were an AFE PG7 with a torque tube and a Banks 4" turbo-back exhaust--Same dyno (Mustang), different days, stock fueling. If I remember correctly, I saw a 3hp difference, but in the negative. You can attribute the difference to a number of factors, but I believe that the mods netted me nothing except a nice exhaust tone and some turbo whistle. Any performance-enhancing downloader or module will make your truck appreciate the open exhaust.



A 4" exhaust is adequate for most of our setups, especially if you have a stock turbo. Have you ever looked at how tiny the exhaust opening is? Maybe 2" plus the wastegate?. I think you'll only benefit from something larger when install bigger turbos and get to 600hp+.

I agree with your findings, but on the issue of freeing up some mpg, having the engine work less to overcome restrictions in the exhaust can't be that big a detriment... I know I saw an increase in mpg with the exhaust... I also know it seemed to pull harder to the top speed too... but that might have just been the noise too...



And what I'm talking about in restrictions isn't the restriction of 3" vs 4", but that of the cat/muffler/resonators they seem to enjoy adding to these trucks...



steved