Rail Pressure for mileage

AH64ID

AH64ID

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Has anyone played with dropping the rail pressure on a 5.9, similar to a 6.7?

What did it do while cruising, or for turbo spool?

It looks like it will really increase the duration, so is that longer duration better for economy or worse?

What about injector life, think that 5-8K psi less at cruise would prolong life any?
 
That is a good question. I don't see it hurting the longevity of the injector's though.

I could see the mileage staying similar to current. Less pressure, more duration flows x amount of fuel, where as more pressure, less duration flows similar unit to x amount of fuel.

Subbed in for this one.
 
Right, so the question is does one make the power required to cruise more efficiently?
 
Stock rail pressure is all over the map, I am not convinced it was setup with economy in mind.

Why does the 6.7 have such a different map? They get great mileage once deleted.
 
I played with that when I first got U.D.C. Lowering the cruising rail pressure made more smoke and laggy. Going from a 17K cruise rail pressure to a 15K, didn't seem to matter much, but going lower things went down hill fast. What seem to work the best on my truck (far from stock), is to to move the existing "trough" in the rail map, to where the pickup cruises. I suspect that on a stock truck, the trough is at cruise, but when you put larger injectors, etc. the trough is no longer in the right spot. Adjusting where the trough is (load, rpm is unchanged at cruise), and adjusting the rate of rail increase, and the amount of increase, makes the truck much more responsive when accelerating from cruise. Increase it to fast or to high, and you will get a rattle. Not fast enough, or high enough, and you get excessive smoke.

Oh, and the timing needs to go the opposite way. High timing at cruise and less with increased load.

Marco must have spent a lot of time working on those maps trying to get them to work for all the trucks...

Paul
 
More responsive and less smoke at cruising rpm's, is my guess. Could be wrong, only timing I have done is 12v timing.
 
I figure you would want more responsiveness and less smoke under increased load, so it should be a continuous increase in time the higher the load, not too far, but increased. Maybe a 'flat' at the top of the map from mid load %age to increased Load %age.
 
Those peaks are there for light load advance. A stock calibration will have "bump" of advance when your operating points suggest your cruising at light load for the best economy. Throw a trailer on and you will be out of that "bump" and timing more reflective of the load.

IMO the rail pressure would normally need to be higher for a 04.5 piston due to the non re-entrant bowl compared to the 6.7 re-entrant.
 
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Joe, why does the piston design require more pressure?

Paul, did you just adjust rail pressure, or did you redo the timing to account for the rail pressure decrease? In order keep the BTDC/ATDC ratio the same at 2000 rpms and 20% load the timing would need to be advanced 3.3° with a rail pressure from from 116 MPa to 64 MPa. If just the pressure was dropped and the timing not advanced I could see it smoking.

LAMiller, you want to advance timing in the cruise region to get more cylinder pressure per mm3 of fuel, but that also creates a high piston temp per mm3, so as you increase fueling you need to decrease the relative timing (not actual degrees, just the BTDC/ATDC ratio) to keep the cylinder pressure and piston temp under control. So cruise timing may be 4° at a given mm3, and WOT is 20° at the same rpm, but at the lower mm3/cruise there is more fuel being injected BTDC, even thou is has 16° less advance.
 
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Both the 03 and 6.7's use a bowl more likely classed as a re-entrant bowl that induces a greater swirl during the compression and mixing stage as compared to the non re-entrant bowl 04.5+. To make up for this it is likely they use a greater injection pressure.

Off the cuff, if I was shooting for mileage, its going to be hard to beat the stock calibration. But I might try some more timing, pressure similar. The stock calibration would be limited by timing due to NOx formation from hot combustion.
 
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So would that effect low fuel flow? They certainly need pressure as load increases, but at low load I wonder if it would work... I guess there is 1 way to find out...
 
Joesixpack said:
Off the cuff, if I was shooting for mileage, its going to be hard to beat the stock calibration. But I might try some more timing, pressure similar. The stock calibration would be limited by timing due to NOx formation from hot combustion.
Click to expand...

Stock timing is really whacked, which I have already messed with and found what my truck seems to like. I am going to start messing with rail pressure, and would like to run lower pressure while cruising, but not at the cost of mileage.

I think stock can easily be beat, just because economy was not the main goal of the tuning, emissions was.
 
Here's a smarty comparison timing table just for kicks. Watching load % on my scanner with my cruise set at 73mph i varied from 16-22% load at 2100rpm. Based on that the spot I marked on the map should be cruise zone and should have the most effect on fuel mileage on the interstate.
timingtable.jpg
 
That's how I have mine with EFI Live.

I've been netting around 17-18 MPG.

EFILivescreen.jpg
 
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LAmiller said:
Here's a smarty comparison timing table just for kicks. Watching load % on my scanner with my cruise set at 73mph i varied from 16-22% load at 2100rpm. Based on that the spot I marked on the map should be cruise zone and should have the most effect on fuel mileage on the interstate.
timingtable.jpg
Click to expand...

That region looks like stock, or did you extend that island? The stock timing goes from very advanced to very retarded at about 2000 rpms under cruise loads. Infact the low load and 1200-1800 rpms is the only place the stock timing is very advanced, relatively.

I carry my cruise timing out to 2400, which keeps me in that "island" at 80 mph.

holsky said:
That's how I have mine with EFI Live.

I've been netting around 17-18 MPG.

EFILivescreen.jpg
Click to expand...

I was running about that much and my economy wasn't as high as I thought it should be, I cut it in roughly in half and it seemed to have gone up a little. All of the fuel is being injected well before TDC, and a pilot, so IMHO the ignition is most certainly happening before TDC, creating too much "negative pressure". Mine is timed to stop injecting at TDC, and I am hoping that I have reduced negative pressure and increased positive pressure. My load is down, but it's too hard to tell on mileage since I don't get to do any driving that is mileage worthy too often.


What's VERY important to both of those is how much rail pressure you are running down there. Even 1000 psi different makes a world of difference in relative timing.
 
AH64ID said:
What's VERY important to both of those is how much rail pressure you are running down there. Even 1000 psi different makes a world of difference in relative timing.
Click to expand...

I don't have my laptop with me but I'll have to look and see what they are and try to post it up sometime.
 
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