Timing regarding cetane number

[dripley]

That assortment will come in handy down the road.

[Southpole560]

I have a viton o-ring assortment that hopefully will work. The adapter said it came with a crush washer though. Should I just use that o-ring then instead?

[Gregturley]

I'd usee the o ring. 

[Southpole560]

If I get the timing right, should I see a low engine load, low oil temp, and low egts? I'm trying the winter economy tune with a 2° cruise timing advance instead of 1° but it seems like my egts have gone up as opposed to higher timing with lower egts. Can good mpgs be had with a slight increase in egts regarding the lower timing?

[Mopar1973Man]

When you advancing timing typically EGTs will go down, unless your still too retarded. I can bump 23 degrees at 2k RPM and EGTs are about 100 degrees lower.

[Southpole560]

49 minutes ago, Mopar1973Man said:

When you advancing timing typically EGTs will go down, unless your still too retarded. I can bump 23 degrees at 2k RPM and EGTs are about 100 degrees lower.

I'm at 700-750 now with the lower timing instead of around 650 with timing advanced around 18-19. Do you know what your winter cetane number is over there in Idaho?

[Mopar1973Man]

Last time I checked it was like 48 to 53 in the dead of winter.

 

I've not been driving my truck much lately. Waiting on my transmission to come back.

[Southpole560]

5 minutes ago, Mopar1973Man said:

Last time I checked it was like 48 to 53 in the dead of winter.

 

I've not been driving my truck much lately. Waiting on my transmission to come back.

Do you know if it drops down to 42 in summer? I probably shouldn't be using a cetane booster with the B20 over here. I'm starting to think that it makes my fuel economy worse.

[dripley]

Can you two really compare timing numbers with the large difference in tire size? Just curious. 

[Southpole560]

1 hour ago, dripley said:

Can you two really compare timing numbers with the large difference in tire size? Just curious. 

I've wondered the same thing since I have 35's. After I installed the 7x.010 injectors, my load has gone down about 5-8% and I noticed a slight drop in egts but that could have been from a tail wind. I think the percentage drop may be from the pop pressure being set at 320 bar though. My best mileage so far has been 18.9 tank average with 18.5° timing @ 1650 rpm going 65 mph. I'm starting to experiment now with the lower timing values but my egts have gone up a little which is making me think that this tank average will be a bit lower but I guess I'll see.

 

Here's a really good article I found. It doesn't pertain to the Cummins engine but it does have a lot of good information on timing, cetane, etc that I believe we can put to use.

http://www.maxxtorque.com/2009/03/diesel-timing.html?m=1

 

Edited March 8, 2020 by Southpole560

[Mopar1973Man]

11 hours ago, Southpole560 said:

My best mileage so far has been 18.9 tank average with 18.5° timing @ 1650 rpm going 65 mph.

 

RPM too low and timing too high. Cruise at 65 MPH needs to be closer to 2,000 RPM. Then your timing should be close to 18 to 19 degrees at 2,000 RPM's not at 1650 RPM. Should be much lower. Again this is tire issue impacting you. 

 

11 hours ago, Southpole560 said:

Here's a really good article I found. It doesn't pertain to the Cummins engine but it does have a lot of good information on timing, cetane, etc that I believe we can put to use.

 

The problem with our truck between the injection pump to pump the line up, inject fuel, cetane ratings, pop pressure of the injector, nozzle size, etc. All these variables will change what timing you use.

 

Then in your case 35 inch tires that now change your final ratio to 3.2x:1 roughly compared to some like myself with 3.69:1 ratio to the ground. Tires and gearing will impact you timing figures because of the required retard to launch then cruising RPM is too low.

[Southpole560]

Once my 35s wear out, I'll be going to either a 32 or 33. Might even change the gearing if I have to.

 

There have been some articles that I've read where people say they have gotten around the 20-22mpg mark with 35 inch tires and same gearing but I just don't see how it's possible especially going faster.

 

If I kept my rpms around 1800-2000 going a bit faster, would I just be using more fuel with those 35s and having a drop in mpgs? That's what I've always thought. I just don't really drive 75-80 that often.

[Mopar1973Man]

Not possible... all these people do not have a corrected odometer to track distance accurately.

 

Everyone I told to use a GPS to track distance told me the MPG was much worse.

 

Cummins engine isn't designed for 35s with 3.55 gears. When working with tires you need to aim for 3.55 to 3.73 to the ground after calculating tires.

 

At 3.69:1 to the ground at 80 MPH I'm twisting 2,500 RPMs and hit 20 MPG everytime. Even a few times hit 21 MPG. Corrected odometer exactly on the money with GPS.

 

I made my gains in dropping 31 inch tires and switching to 30 inch 245/75 R16.

Edited March 8, 2020 by Mopar1973Man

[Southpole560]

That's pretty dang good fuel economy! You can't even get anywhere near that in a new truck. One of the reasons why I'm gonna stick with my 2nd gen. Apparently those 245s came stock on my truck according to the door sticker. Why didn't the last owner just keep those on? Would have saved me the trouble 

[dripley]

2 hours ago, Southpole560 said:

That's pretty dang good fuel economy! You can't even get anywhere near that in a new truck. One of the reasons why I'm gonna stick with my 2nd gen. Apparently those 245s came stock on my truck according to the door sticker. Why didn't the last owner just keep those on? Would have saved me the trouble 

They also came with 265's as option. Thats what l have run on mine ts entire life. 70 at 2000 rpm. I usually run about 75 and get right at 19.5 and thats with the Comp.

Edited March 8, 2020 by dripley

[Mopar1973Man]

245s and 265s were stock sizes. If you want larger tires you need 4.10 gears.

[Southpole560]

4 hours ago, dripley said:

They also came with 265's as option. Thats what l have run on mine ts entire life. 70 at 2000 rpm. I usually run about 75 and get right at 19.5 and thats with the Comp.

That's what I'm gonna get here soon once my tires are worn out. Well if it can fit on the rim. If not, I gotta go with 33's. It would be pretty nice to get 19.5 at those higher speeds. Does it go up for you if you drive a bit slower?

[LorenS]

If you don't like the idea of jumping all the way from 3.55 to 4.10, I have found 3.73 gears for Dana 70U axles. I believe it's Yukon Gear but wouldn't swear to it.

[Southpole560]

4 hours ago, LorenS said:

If you don't like the idea of jumping all the way from 3.55 to 4.10, I have found 3.73 gears for Dana 70U axles. I believe it's Yukon Gear but wouldn't swear to it.

I've looked into regearing before but it just seems pricey to do on both diffs right now. I'd have to get the Dana 80 ring and pinion since mines the 80/70 hybrid.

 

It's looking like I'm gonna have to go with a 285/65r17 tire. That's the smallest one that will fit my rim (17x10). I have three options to choose from; Mickey Thompson Deegan 38, Cooper Discoverer AT3, or Yokohama Geolander G015. These are all all-terrain tires but the Yokohama ones have the least amount of tread according to the specs. Kind of leaning towards the Mickey Thompson's but not sure. Any opinions?

[dripley]

8 hours ago, Southpole560 said:

That's what I'm gonna get here soon once my tires are worn out. Well if it can fit on the rim. If not, I gotta go with 33's. It would be pretty nice to get 19.5 at those higher speeds. Does it go up for you if you drive a bit slower?

I would not know. My work takes me away from home and l am only there for the weekends. Time there is much more peecious than squeezing out a bit more mileage. 19.5 mipg out of a truck that weighs 7500 # is fine by me. I am not hyper miler. If l only 17.5 at that speed I would not slow down. My 96 had a V10 in it. Try 12 mpg empty goung downhill wit a tailwind.

2 hours ago, Southpole560 said:

I've looked into regearing before but it just seems pricey to do on both diffs right now. I'd have to get the Dana 80 ring and pinion since mines the 80/70 hybrid.

 

It's looking like I'm gonna have to go with a 285/65r17 tire. That's the smallest one that will fit my rim (17x10). I have three options to choose from; Mickey Thompson Deegan 38, Cooper Discoverer AT3, or Yokohama Geolander G015. These are all all-terrain tires but the Yokohama ones have the least amount of tread according to the specs. Kind of leaning towards the Mickey Thompson's but not sure. Any opinions?

I am on my 5th set of Cooper ATP's. They have been very good tires fo me. 

Edited March 9, 2020 by dripley