Help me with my C15 for better mileage ??

I am trying a new forum after I tried other things and told people perhaps it was snake oil because I saw absolutely no improvement and was severely blasted by the outfit sponsoring the website.

C15 2006 13 speed 3:36 ratio.

First got the truck was at 435 hp. Cat shop said I could turn to 550Hp since it had 1850 ft tq tranny. Did it and seen some more power but nothing to brag about. Mpg stayed the same. Last fall bought Bullydog and now that was a response !! But still no change in mpg. This spring put a roof fairing on this truck that is a day cab and no change in mpg. Dropped from 13 gear at 65mpg and 1300 rpm to 12 gear and 60 mph and 1400 and no change in mpg. Was told I had really bad tires as far as rolling resistance (were 168) and bought new virgins with 116 RR some places show it as 98 RR. Again no change in mpg. Asked my regular shop to check CAC and they said it was fine but that is all we discussed on that.

I see the mufflers say Catlyst on them and are original at 450,000 miles. I see that flow through mufflers can help but being a day cab and I have outgrown noise I am afraid it might be too loud. Some say not noticeable but Jake is louder but how much louder ? I can't hardly hear the Jake with oem muffler now. Remember we have a day cab with twin stacks behind the cab. Some say the ECM will know there is less back pressure and adjust for it anyway.

We pull flatbeds half the time about 78,000 and vans about 65,000 and half the time return empty. We travel in a 100 - 250 mile radius to a single point destinations.

I consistently average 5.5 every 3 months and this winter only dropped to 5.3 mpg. Occasionally I will get 6.0 but sometimes even in a snow storm or loaded both ways - real odd. Days you think you should get good mileage you don't. In the summer when you get out you could never hold your hands on the fuel tanks they are so hot. Some say that is all you are going to get - good engine just likes fuel. I would like to get 6.0 average.

My biggest question is would the flow through mufflers help and are they going to be too loud ?

 

muffler's help. a haney tune will help a lot also.

 

I don't mufflers are gonna improve the fuel economy at all. 5.5 with an acert is pretty good but do you know if cat shop verified the part # on your injectors when they went from the 435hp setting to the 550 alot of times techs just jack the ecm wide open not realizing they are getting everything out of balance. I am positive on the single turbo E models the turbosfrom a 435 to 550 are diff. had one go down on a 550 had a 435 on shelf looked the same driver never was happy. Bought the right turbo and problem solved. Also a fuel cooler in the return line would help i think cooler the fuel tighter it compresses better it burns. Even a minor almost un noticeable cac leak can affect economy.

 

this is what a wise man told me about a fuel cooler. it may help some in the first part of day when you start a trip. but it wont make a difference after your tanks get low. the fuel will still warm up to what the water temp is in head or close to it. all a cooler will do is cool the fuel in tank some but not where you need it in the head. as long as the fuel doesn't get hotter than water temp. you wont gain anything.

 

I have the same issue with the same motor even tho mines is an 3:55 rears... seems like no matter how fast I go, or I heavy I am I'm constantly in between 4.8 - 5.5, C-15 Cat 435 that was turned up to 500...

 

Fuel temp in the head has nothing to do with it. There is a sensor that measures fuel temp and after the fuel warms up it adjusts how much the injector injects. Read up on fuel temp wires in tech section.

 

The mufflers will help a little with MPG and turbo lag. Also I run dual exhaust on my '06 379 and the high flow mufflers were not load at all except a little noisier on the jakes...still quieter than a single turbo engine. I would check the simple cheap stuff first. Run the overhead, boost leaks in the intake bellows, and fuel pressure (that is a major issue on the ACERT engines even though they have the same fuel system as the 6NZ engine). Also the ACERTs like lower RPMs...like down around 1150-1250 for cruising. Another thing is your shorter runs will result in lower.

 

At this point any gains will come from driving technique. Cruise in the 1200-1300 range, easy on the pick up and coasting long before you have to brake if it can be planned. I've found the C15 Acert will get 5.5-5.8 all day long, but getting above that 6.0 is a #####.

 

they never messed with injectors just hooked up computer and made out the bill.

 

I think if you truly checked IFTA records on all CAT C15 motors, you would feel alot better about your mileage. That's just where most of those motors will be for mpg IMHO. Focus on higher rates to compensate for lower mpg is your best option.