Increased efficiency for my 92

[SRT-6]

I am debating on which turbo housing would be the most fuel effecient for mostly in town driving empty. It still has the 21 on it and it has to go. I am currently getting 13 mpg empty. The engine is all stock with 155k. Any suggestions?

 

[AlK]

I am no expert on this, but I don't think that a change in turbo size will affect the mileage very much either way. Personally, my thinking is if you go with a smaller housing (such as a 16,14 or 12) what will likely happen is that because the cummins will be more responsive, the right foot becomes a bit heavier, hence the mileage may drop a little.

---

Al

 

[Midnite]

This is something I've been thinking a great deal about as well recently. Now that I have my boost gauge installed, I can see that most of my in town driving uses only 1 or 2 pounds of boost. This is with a 21. 5 cm2 housing.



Going with a smaller housing means that boost will come on earlier. Because increased boost at a given rpm means an increase in the effective compression ratio, we get more a more efficient burn assuming that fueling stays the same.



Now, it goes without saying that most "city" driving tends to be relatively low throttle (especially unloaded, which is the case with both 6BT's truck and mine). Because boost should come on much earlier with the 16 cm2 (or smaller), milage should increase. For example, with the stock housing, when I accelerate from 0 to 45 MPH, I typically see 3 or 4 pounds of boost with my 21. 5 cm2 housing. However, if that were changed to a smaller housing, I might see 6 - 10 pounds of boost given the same throttle level (or 3-4 psi boost with less throttle). Granted, I'm guessing on some of those numbers, but I hope you see my point -- more boost = higher relative compression = greater efficiency.



Mike

 

[R.E. Miller]

FWIW,

I just bought two 12cm^2 housings, yeah the little guys and I am going to install them on both my Dad's truck and mine. My Dad's truck has the 16cm^2 and a little pump tweaking and it scoots good My truck has pump tweaking but the 21cm^2 housing



When I am finished I will report all of the findings here.



Russell

 

[NOMOFO]

Today I just put on a 12cm non wastegated on my otherwise ( as far as performance goes ) stock truck. I normally get 13 to 15 around town depending on foot. Iwouldn't know about fuel mileage improvement yet but think AlK probably has it right!

I still have a bit of lag right off the line but once it starts boosting it's much quicker. It used to see 15psi absolute max and I would have to push the pedal through the floor going straight up the steepest hill to get that. In similar condition today I saw 19 top. Normally would see 10 or 11 while working pretty hard. Seems to run at about 5psi higher and get there way quicker across the board except after about 2000 rpm it drops off to 15 max. I'm sure I will make more accurate observations as time passes. Oddly the exhaust temps at the top were cooler. It would come up to 700 to 800 much faster but could not get it over 950 where I used to see near 1100. ????????????????

This is all with about 1000 to 1200 lbs. of my everyday stuff in the truck.

I'm disappointed about the lag off the line. I thought this would totally eliminate that.

Maybe it's starved for fuel now. Maybe pump or timing is not quite right. Am a little chicken to tweak the pump yet. Will have to get those Lucas' in I guess but want to size up/clean up exhaust first.

I finally just had to say phuque work and do something to this thing. Please don't tell my wife, daughter, customers, or others I've made excessive commitments to! I have been sitting on all this great stuff for way to long while you guys are having all the fun!

 

[NOMOFO]

Hey Dan I already have them and embarrased to admit how long they have been sitting on the shelf! Have been thinking about ways to come up with time to mess with truck. One thought was to only defecate every 2nd or 3rd day but then I would probably only prove my wife right! Oh, I'll figure it out.

Are these the only things you have done, the 16cm, Lucas, and DTT stuff?

What about exhaust? Did you tweak the fuel pump? Did you buy a new trans before the DTT mods?

I have revived jones to get on this thing so I'll be asking questions and reviewing old posts.

Thanks for listenin'

 

[Tim1]

lucas injectors

Hey Dan, did you have your pump turned up when you installed the lucas injectors? Did you leave it up? I was wondering if if is a good idea to turn the pump back down when installing the lucas injectors. I'm concerned about overtaxing the pump however it runs real good now. Thanks Tim

 

[BushWakr - RIP]

13 MPG around town in a '92' ????

Thats kinda low IMO. You can see what i've done to my '93' and i get 18. 5 - 19. 5 MPG around town, and thats with an occasional 'spasm' of the right foot to boot.

On the highway I'm getting about 21 - 22 MPG at 65 MPH (all empty) Thats all honest measured and checked mileage too.

IMO the 14cm will give you what you want for response and boost. Temps come down because you moving more air, faster which helps burn your available fuel more efficiently/fully. In my case the mileage I'm quoting here is including some dark grey/light black smoke at low boost WOT as well. I wish I had gone to the 14cm when I changed mine from the 18. 5cm.



FWIW.



Regards, Bob

 

[Matt S]

Tim1,

I didn't tweak my pump until after I installed the Lucas injectors. It all depends on what your pyro tells you what you can handle.

 

[AlK]

The first modification to my truck was changing from the 21 cm to the 16cm. I noticed a definite reduction in the amount of time that it took to spool up the turbo. The real difference came when I put in the "PW" injectors. Then last summer I had Piers set the timing to 1. 4 and increase the rpm up to 2900, and again a very noticeable difference. Other than smoke adjustment and the rpm the pump is at stock. She is even more responsive now and sure goes. . In retro-spect I wonder what 14cm and the "Prince of Darkness" injectors would have done?

---

Al

 

[barkerdl]

I installed the 16 cm housing and a Diesel Dynamics Stage One pump kit at the same time. The mileage did not change, either around town or while towing the fifth wheel. What I did notice was a much faster power rise on launch - especially when towing. I'm one of the lucky ones who get 17-18 empty in the city, 20-22 empty on the highway, and about 12 while towing. The gentlemen at DD told me the increase was due to the combination of smaller exhaust housing and increasing the fuel flow at low boost. The dyno runs before and after were the physical proof. My truck showed a 47 HP and 98 Ft/lbs gain. The real difference is in driveability, especially while towing.



I'd recommend this solution.



Dennis