Milage and mufflers and air filters and cams and such

[Boldt's Wagon]

I am posting over here in the towing and hauling forum as this thread might be of most interest to the silent majority and we'uns who burn the most fuel. The majority of diesel owners do not increase the HP of their engines (BOMBing)or just do a modest increase. I would separate the BOMBing factions into less than 280 HP and greater than 280 HP. We of the modest BOMBs just want a reasonable performance or towing ability without equipment failure. The other faction of BOMBing is into drag racing, sled pulls, dyno bragging rights, etc. and pay for the fun with busted parts. The high performance faction develops the BOMBs that we can put into use. Cam plates, electronics, injectors and transmission improvements can be used by all. But, I am not looking for further HP increases, I am looking to increase my miles per gallon.



In the past I thought that that air flow improvements with exhaust and air filter changes would have no benefit to us old farts pulling our RVs in the right lane. We go down the road at 60 with 10-15 lbs boost and get 10-14 mpg. The recent thread on "565 hp with smoke control" ( https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=29453 ) leads to the website http://www.dieseldynamics.com/ . This website shows dyno 24 valve runs with stock cam and a modified cam. The dyno run shows a modest increase in HP, 10-15% . Also on the website is a claim that the cam also increases milage by 3. 8 mpg. At first I took the milage gain to be snake oil. Then I was mulling why a HP increase when the 24 valve engine computer would not have increased fueling? I finally recalled from college days 40 years ago that diesel engine efficiency increases as the compression ratio increases. Since there are always some losses and pressure drop in filling and emptying the cylinders, any way of getting more air into the cylinder will effectively increase the apparent compression ratio and will increase the efficiency of converting the fuel heat into power. This was seen on the dyno runs with an approximately 30 HP increase (10-15 % over 2100 to 2400 rpm range) and I assume no increase in fuel use. The other side of the coin is higher efficiency with the same HP production will result in a milage increase. Therefore, there could be some increase in milage at low power outputs as claimed. In addition, air flow improvements will reduce exhaust gas temperatures with the same fuel usage.



If this is so, then other air flow enhancements like mufflers and air filter changes might give some efficiency improvements to the other Cummins owners operating at less radical conditions (not full throttle drag racing, sled pulling, or dyno runs). I checked out some of the older posts and supplier web sites and found claims for milage increases with exhaust and air intake system changes.



I assume that efficiency and milage increases due to cam changes and different turbos might not be cost effective. Changes to the muffler and a BHAF might be paid for by the savings in fuel. One other benefit would be the reduction in exhaust gas temperatures when pulling that long 8 or 9 percent grade. The higher the altitude and/or the higher the outside temperature the more you have to back off to keep temperatures in check.



I am speculating that the maximum efficiency of the 12 valve at 1600-1800 rpm and maximum for the 24 valve at 2000-2200 rpm is due to the most efficient range of filling the cylinders with air. The 4 valve head will flow more air at higher rpms. If so, the efficiency improvements of cams, exhaust systems, and air filters might have move impact on 12 valve engines than 24 valve engines. I know I pull my fifth wheel in drive (no OD) at 2150 -2300 rpm which is considerably above the most fuel efficient rpm for the 12 valve.



If any of you kept good records of milage towing and solo before and after any exhaust and/or BHAF changes, tell us what, if any, milage increase you have seen. A 1 mpg increase whould be great to us who are getting 11 or 12 mpg towing an 11,000 lb, 12 ft tall porta-potty.

 

[Bill Lins]

I put the K&N RE-0880 (with the Psychotty hole in the firewall and a Hitco exhaust blanket from Geno's) and the 3" Walker muffler on my truck and got about a 1mpg increase.



I then had Dr. Joe install a #12 plate and AFC spring kit and change the timing from 13 to 15. 5 degrees and picked up another 1. 5mpg.

 

[illflem]

I installed a Banks Stinger Plus system on my 3500 in stages starting with the K&N and larger exhaust, free flowing muffler, it was good for 1 mpg over stock towing 26k. Stock was 12 mpg. After installing the rest of the kit, the plate and turbo, gained 2. 5 mpg more, mainly because of fewer downshifts due to high EGTs. All mpgs were checked on the same 44 mile roundtrip, same 26k load, eight times a day for four months, same fuel from my own tank. Results should be very accurate. Also cut around 12 minutes on each round trip, which resulted in a $22 a day less I paid my driver. This with the saved 6 gals of fuel per day paid for the Banks in two months. Adding the Physcotty air unit a couple of years latter lowered the mpgs by . 6 and cut another 4 minutes off the round trip time also due to lower EGTs, BHAF should do about the same. Mpgs are now 15. 6. This is with a 12 valve, 24 is a different animal.

 

[SlyBones]

Well this is overall mileage and not broken down by towing or anything. Funny you ask, I just figured this out this afternoon.



I write down all my fuel expenses in a book. I have marked down when certain events happen. In this case I will use BP and AP ( before Piers and after Piers ).



BP = 15,297 mi / 959. 0 gal = 15. 95 mpg

AP = 8,740 mi / 514. 3 gal = 16. 99 mpg

 

[Boldt's Wagon]

It looks that replacing the muffler and air filter with more free flowing units will give you 1 to 1. 5 mpg.



Does Walker or other manufacturer make a 4" x 3" replacement muffler? Or do you use a 3" or 4" muffler with a reducer fitting?



Has anyone used the Fleetguard AH1141 filter for their BHAF?



The AH1141 is 8. 5 inch diameter by 12. 38 inch long. The AH19037 is 10. 5 inch diameter by 11. 88 inch long. Both filters have a 4. 0 inch ID connector. The slightly smaller AH1141 would be easier to shoehorn into the space with shields and less rubbing potential.

 

[SlyBones]

Boldt's Wagon,



You and I are same equipment, maybe less the PDR turbo and housing. Just a question, what are your EGT's like?



If you are trying to be budget concious, or are not going to BOMB too much more, then get a 3" in/out walker muffler. Get about a 32" piece of 3" pipe to replace the cat. Go with 3" flow thru system.



I found removing the cat was a nice EGT reduction. And the sound improved a lot. The muffler with cat was barely louder than stock, and no noticable EGT drop. My system is 4" from the ex-cat on back. Still has 3" downpipe.



If BOMBing at lot more, then go for the 4" turbo-to-tail. You can see from the other thread going, that there is much debate over the need for a 4". I dont know about power, or spoolup, but from a EGT/Mileage/Sound point of view, nuking the cat and getting a flow thru muffler will go a long way and be very cost effective.

 

[Boldt's Wagon]

I have a post-turbo thermocouple. With the cat I saw 900 F. With the cat test pipe I have seen 850 at higher elevations. The combination of cat test pipe and 235/85 tires to lower the rpm 100 I saw a 0. 25 mpg increase this year over last year (4000 mile trips with the fifth wheel).



I am not looking for more power. I want more milage, don't want excessive exhaust noise, want low cost paid for by milage savings. Any exhaust gas temp reduction, less smoke at 8,000 ft altitude, and faster spool up would be nice fringe benefits.

 

[Bill Lins]

Originally posted by Boldt's Wagon

Does Walker or other manufacturer make a 4" x 3" replacement muffler? Or do you use a 3" or 4" muffler with a reducer fitting?

I used the 3" Walker with a 4" X 3" adapter- both from NAPA.

 

[illflem]

One thing I didn't add in my post above was removing the cat, it was a mod done before anything else. I saw no increase in mpgs nor decreased egts, did sound a little different though. The truck only had a few thousand miles on it when I removed the cat so it probably wasn't clogged at all, it probably would be by now and would have made a difference removing it.