New exhaust and Bad Mileage

[Flat_Lick_Dodge]

I replace the 4" exhaust with a 5" turbo back and it seems like the mileage has decreased. Has anyone else noticed this. Also, Does the 05 600 need any type of backpressure to run more efficiently on the bottom end. I am a Cummins newbie. I have read on this site for a week or so and have tried to answer all of my questions from prior posts. I made a 380 mile round trip today and hand calculated 15. 64 mpg. Before the exhaust seemed like it was easier on fuel. I was going about 75 to 80 mph most of the way about 2250 to 2300 rpms. I had the BDDL set to performance mode. Any Help would be appreciated

 

[nickleinonen]

need any type of backpressure to run more efficiently on the bottom end.

nope...



my fuel economy has gone down hill ever since i started with mods...



exhaust first fuel economy went down [loud pipe heavy foot syndrom]

gauges next. again economy goes down [lets see how much boost i can make :-laf]

bhaf next. again economy goes down [lets see how loud the turbo is at full boost ]



no fueling mods yet, but they will probably result in another fuel economy loss [how much smoke can i make ]

I was going about 75 to 80 mph most of the way about 2250 to 2300 rpms

going at that speed isn't going to help fuel economy either

 

[rbattelle]

Can you post a copy of your fuel log?



-Ryan

 

[JCleary]

I lost some mpg too when I added an exhaust and intake, and I know it's from heavy foot syndrome.



I did, however, get it back when I installed the Quadzilla Xzillaraider 140. I went from an average of 15. 6 to 16. 8 with the same driving style and conditions. I can't wait to see what it's like when I put the 285 BFG's on for winter. I bet I'll be back in the 18's.



Not that I care that much... Watching mpg's is mainly for entertainment. I bought the truck to drive it. If I wanted fuel economy I would have bought a 4-cyl Toyota.

 

[Jengle]

Mine lost a couple mpgs when I added the intake and exh. but gained it back when I run the box on med. settings. I think its finally broken in at 57k. I saw a slow climb in mpgs that seems to have steadied out now. The last 12 tanks have not been under 20. That's hand calculating and mixed driving with a red light blast every now and then. Overhead shows about 18. 8-19. 2 when I am in the 20s. I found that if I make it to 400mi at the half tank mark, I am over 20.

 

[DPKetchum]

5 inch exhaust is TOO BIG unless running BIG H. P. Dyno graphs show a loss of H. P. /torgue on the low end with 5 inch. I would have just changed the muffler. I went to a 4 inch and saw a instant 1 to 2 mpg increase.

 

[JVolpe]

I think Mr Ketchum is right, now you will have to add injectors, tst, new turbo and FASS to get that mpg back up to where it should be.

 

[Graphic man]

They say you need about 400HP+ for a 4" exhaust

i would guess you would need 600-700 hp to handel 5"

in this case bigger is not better

 

[Flat_Lick_Dodge]

I didnt really put the exhaust on for the power and sound ( however It does sound good) its loud inside though. I put the exhaust on to help keep the egt down. It seem to drop the egt a little. I can still get the egt to hit 1100 about 90 mph though. I am probably going to put the original exhaust back on after I drive it a while. I might take the cat off though.

 

[DPKetchum]

The cat is not very restrictive from what i've read. Its the stock muffller. They say the cat removal is good for about 75 degrees. 1100 degrees at 90 mph is not bad. Do a search on Donaldson mufflers that can be had at your local Frieghtliner dealer. Your truck came with a full 4 inch. Mine was only a 3. 5 stock.

 

[PHeadings]

Doing 75-80 MPH at 15. 6 is not to far off.

 

[DBeardslee]

I have 5 inch from stans headers and it has a Donaldson that has a solid plug in the middle of it, they say that it lets about 2400 cfm through and I only have 30000 mile on the truck with a couple of mods and I average 19 to 20 real consistent. If I drive 70 to 80 on the freeway I will drop down to 18. 5 to 19 depending on the hills. Mine is pretty loud outside :-laf but in the cab it is not to bad, pulling the passes at 70+ I do get a bit of droan and it is louder but that is what I wanted.

 

[hasselbach]

5 inch exhaust is TOO BIG unless running BIG H. P. Dyno graphs show a loss of H. P. /torgue on the low end with 5 inch. I would have just changed the muffler. I went to a 4 inch and saw a instant 1 to 2 mpg increase.

no its not. with a 9 cm exhaust housing, it doesn't matter what is behind the turbo. The turbo is so restrictive, that anything down pipe doesn't matter. . I've run 4 and 5 inch set ups with absolutely no changes in mpg or peak torque on the dyno.

 

[hasselbach]

The cat is not very restrictive from what i've read. Its the stock muffller. They say the cat removal is good for about 75 degrees. 1100 degrees at 90 mph is not bad. Do a search on Donaldson mufflers that can be had at your local Frieghtliner dealer. Your truck came with a full 4 inch. Mine was only a 3. 5 stock.

on the flow bench, the cat is pretty restrictive in our testing. we saw more than 100 degree drop when removed on several vehicles. the pressure drop within the cat is pretty substantial.

 

[DPKetchum]

Well LOTS of posts on 5 inch in the past with the dyno graphs showed otherwize. There is such a thing as to BIG.

 

[hasselbach]

Well LOTS of posts on 5 inch in the past with the dyno graphs showed otherwize. There is such a thing as to BIG.

show me one dyno pull. . the turbo doesn't care about sizing. something else was the problem. turbos don't work on sound waves or exhaust pulsing which the 5 inch would change. a normally aspirated motor might move the torque curve upward on big pipe, but every motor we've ever dyno'd showed exhaust piping didn't matter on th big side of piping. we've dyno'd lots of diesels too with 5 inch vs. 4 inch and never seen any difference with the stock turbo.

 

[DPKetchum]

Interesting how this was a discusion many times here on TDR and many many posts about size and loss of torque with 5 verus 4 unless 500 h. p. plus was being made and not until now has any one mentioned that 5 verus 4 about no loss of low end power. I read this site daily and have for several years. I just didn't make it up. The original post was about loss of fuel mileage with ONLY the edition of a 5 inch exhaust. Seems reasonable to me that it was the reason it went down. Same as the MORE air/Bigger exhaust with no other mods causes these engines to defuel faster and loss of performance and economy or so I've read unless I saw it in a dream. This is NOT the first post about 5 inch on basicly stock engines and loss of MPG.

 

[jwilliams3]

When my truck was near stock. I added a 4" straight pipe and intake and with the boxes turned off my truck dynoed lower than with the cat, muffler and stock air box. This was on a Mustang dyno.

 

[DPKetchum]

I've read that time after time when the 3rd generations started being tested. Then when they went to FACTORY 4 inch systems the only thing needed for a mildly bombed truck was a muffler change. I wonder if it hit some of the vendors in the back side. No more complete front to rear exhaust being sold. I've read for MANY moons that a five inch was way over kill unless a serious drag or sled pulling truck. At least until recently and now there OK to use! Makes you wonder!

 

[DBeardslee]

I tell you what, if you like the 4 inch and the power and economy that you have use it! If you want 5 inch because it looks good and sounds good do it! But it all comes back to the nut that is behind the wheel, we all drive different and there is no question about that! When I put the 5 inch on mine the fuel economy didn't go up or down it stayed about the same, now that I am learning how to take my foot out of it and leave the attitude on 1 I am getting better mileage, but I do like to hear it rattle off the buildings :-laf So I believe it is all personal preference. I have seen big rigs that are putting better that 600 horse to the ground and all they have is 5 inch like the rest of the rigs on the road, so right back to preference. I hope that this does not make anyone mad I just wanted to add my 2 cents