3rd party Proof that retarding a diesel leads to cooler engine/higher boost

[Mark(The Miser)UK]

Some may remember my proclamation a month back or so when I said that my engine was happy running @0.5 to 0.6mm, and got good turbo response, and fuel economy.

Then, yesterday I said reducing the timing from 0.95 to 0.8 should reduce engine temperature. In an act of good will, to prevent those who despise me making foolish comments, here is an extract from a write up that I haven't seen for 10 years from the Dodge-Ram-diesel-Cummings site....

 Well, well it still exists!


> "What changes in measurable parameters such as EGT, power, noise, smoke, fuel
> consumption, etc. will I find as timing is varied?  I'm not looking for
> numbers, just relative changes?"

      " Here is a general overview of what happens when you change timing on Cummins' B- and C-series engines. I would imagine that this holds true for any engine that uses a pump-line-nozzle type fuel system; results may be different for larger engines that use unit injectors (on-highway truck engines, for example):
 

Engine parameter:   
TIMING is:
                                                        RETARDED ( - )   ADVANCED ( + )
                         EXHAUST TEMP            increases           decreases
                CYLINDER PRESSURE             decreases   increases
INTAKE MANIFOLD PRESSURE 
  (BELOW P-TORQUE) WASTEGATED      increases           decreases
BSFC (brake specific fuel consumption)  increases   decreases
NOX (oxides of nitrogen)                     decreases   increases
HEAT REJECTION                              increases   decreases
HYDROCARBONS (HC)                       increases   decreases
BLACK SMOKE:  1000RPM                      increases   decreases
BLACK SMOKE:  PEAK TORQUE             decreases   increases
BLACK SMOKE:  RATED                      increases   decreases
WHITE SMOKE:  < 1000RPM              increases   decreases
WHITE SMOKE:  > 1000RPM              increases   decreases
 
        For Cummins' B & C-Series engines, the timing is part of the CPL (Control Parts List), which is basically the emissions "recipe" that we use when certify the engine with the EPA. There is a tolerance band around that timing, and setting the timing out of the tolerance band around the specified timing is technically illegal."

       " The VE pump used on Cummins engines in '89-'93 Dodges is a rotary style pump with an engine-speed dependent timing advance mechanism: as engine speed increases, the timing advances. The P7100 pump used on Cummins engines in '94-'98 Dodges is an inline style pump with no dynamic timing adjustment capability (technically, you can get dynamic advance by using a really complicated fuel pump gear, but we chose not to do that). The VP44 pump used on Cummins engines in '98.5-later Dodges is an electronically controlled rotary pump. It uses a timing advance mechanism that is similar to that of the VE pump, but it's controlled by a solenoid. This gives us the capability of varying timing throughout the engine operating speed range (roughly 700-3600 RPM in a Dodge)."

     

[745 turbogreasel]

Extracting less heat from your  exhaust  just means you are blowing it out the tailpipe.  I have never heard anyone advocate  retarding the timing on a Cummins  On mine the coolant temps get more rise from thermostat cycling than  running wide open uphill (something to be said for a 7 gallon cooling system).  BSFC and EGT both go up  with retard.  boost goes up because you are burning fuel in the turbo instead of the engine.

Mine being a 94 motor is  timed to the most retarded spec, and what to you know, power isn't  that good, and it gets  under 20 MPG

[Mark(The Miser)UK]

LOL I wouldn't know a Cummins from a Caterpillar.

I'm not advocating everyone retards their engine by vast amounts, if at all, despite my weird engine, but my point was that Rising EGT due to changes in timing like from a perfectly feasible 0.95 to 0.8, are not linked to rises in cylinder temperature, unlike rises in EGT due to putting one's foot down.Thus a slight improvement may be welcome when running near the engines limits.

EGT is a crude, but convenient measure. Advantage of a timing based rise in EGT will give you a quicker rise in boost pressure.Coupled with the lower peak pressure in the cylinder, which presumably allows those who wish to add more fuel, with a goal of  speed increase, rather than economy... After all this is the GTD site, despite my owning a GTD; I'm in search of Spock, oops, reasonable fuel economy, with or without a power increase.

[TylerDurden]

I don't have my pyrometer installed yet, but can attest to a bit more power in the lower rpms after retarding my timing a bit.

[dieseljunkie69]

Well shyoot TD, I never thought of it that way.. I must just need to retard a little bit.. The 1.6TD is so sluggish off the line.

[TylerDurden]

I have a pyro and boost gauge waiting for install, so I'm flying blind... and not advocating much adjustment without gauges.

YMMV

[745 turbogreasel]

What would I know, I don't drive my IDI at low RPMs, it's happiest at 2700 RPM Torque peak.

The Cummins formula is advance timing 3-5 degrees  for a few HP and +3 to 5 MPG, or 6+ degree if you are ready to break off some driveline parts.
While the more boost might sound appealing, 90% of the time unless you have a Banks 6.2 or first gen Dodge, the wastegate will be the limiting factor anyway.

[dieseljunkie69]

I have a pyro and boost gauge waiting for install, so I'm flying blind... and not advocating much adjustment without gauges.

YMMV

Very true, I understand. I am not by any means "new" to this .

[Gizmoman]

Interesting topic for sure. I don't know enough to jump in, but it's good reading.

[libbydiesel]

It was/is understood that retarded timing increases EGTs but does not increase cylinder temps.  It will decrease cylinder temps by sending the still burning fuel out the exhaust pipe instead of turning it into useful work.  I don't see why anyone would want any of the effects of retarded timing listed above except the reduction of NOx and the increase in manifold pressure.  Both of those 'benefits' come at the cost of reduced engine efficiency, reduced power and increases of all the other emissions.  

[Mark(The Miser)UK]

Retarding timing reduces cylinder pressures, because the chamber at peak burn is larger. It is larger because the piston has moved further down the chamber.
Further down the chamber naturally means the peak is peaking on say 15 degrees ATDC, which means more energy goes into the torque, contrast with the extreme  of peaking @ TDC for instance, with higher pressure less extractable torque, greater heatloss to the engine.

What I strove for years ago, was to try and flatten out the combustion pressure, my main method being to extend injection period by lowering break pressures. Down to 125bar for instance.

Was I successful? Well I don't know, but my car beats official handbook economies. This was at 0.57, 46mpg [imp] round town and 62+mpg  on a flat run. So despite low value timing it clearly doesn't all go out of the exhaust.

I would like to spend more time researching. Obviously too retarded and the potential gain in torque is exceeded by excess energy out of the exhaust.

If I had a machine to measure area and angle under the pressure curve, it would help...

[dieseljunkie69]

What I strove for years ago, was to try and flatten out the combustion pressure, my main method being to extend injection period by lowering break pressures. Down to 125bar for instance.

Was I successful? Well I don't know, but my car beats official handbook economies. This was at 0.57, 46mpg [imp] round town and 62+mpg  on a flat run. So despite low value timing it clearly doesn't all go out of the exhaust.

Huh, that is quite interesting. 0.57mm... How did it start when cold out? I have never even dabbled with the lower end of injection timing because I have always been told that the "advanced" side of the Bentley specs was where you wanted to be regardless..

This is very intriguing. 38mpg -city and 52mpg -hwy US MPG? That's surely not wasting fuel.

[libbydiesel]

Take it with a grain of salt.  Giving a 'timing setting' in mm of plunger lift with non-stock injectors or non-spec pop pressures is very misleading.  I believe that Mark has significantly lowered injector breaking pressure and so the actual timing of the start of injection or more importantly start of combustion is very likely similar to spec or more importantly completely unknown.

[theman53]

Take it with a grain of salt.  Giving a 'timing setting' in mm of plunger lift with non-stock injectors or non-spec pop pressures is very misleading.  I believe that Mark has significantly lowered injector breaking pressure and so the actual timing of the start of injection or more importantly start of combustion is very likely similar to spec or more importantly completely unknown.

I would guess this is accurate. I would think any gains in mpg would be because of the pump not having to work as hard to open the 155 turbo spec or whatever n/a spec is.

[Gizmoman]

Take it with a grain of salt.  Giving a 'timing setting' in mm of plunger lift with non-stock injectors or non-spec pop pressures is very misleading.  I believe that Mark has significantly lowered injector breaking pressure and so the actual timing of the start of injection or more importantly start of combustion is very likely similar to spec or more importantly completely unknown.

I would guess this is accurate. I would think any gains in mpg would be because of the pump not having to work as hard to open the 155 turbo spec or whatever n/a spec is.

Makes sense to me as well, and an interesting perspective. The piston in the pump, moving non-compressible fluid into a high pressure chamber. The only variable in that equation is the spring in the injector.