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Diesel Engine Timing
How Important is Correct Engine Timing?

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P7100 Timing vs. Plunger Lift
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Static timing
(degrees BTDC)
49 state
CPL 1863 CPL 1968 CPL 2022
CPL 2175
  (c) (d) (e)
160hp CA auto 160hp 180hp(b) 215hp
9.5 5.15 NA NA NA NA 5.65 5.6 6.05
10.0 5.25 NA NA NA NA 5.75 5.7 6.15
10.5 5.35 NA NA NA NA 5.85 5.8 6.25
11.0 5.45 NA 4.00 4.00 NA 5.95 5.9 6.35
11.5 5.55 4.0 4.05 4.05 4.70 6.05 6.0 6.4
12.0 5.65 4.1 4.15 4.15 4.80 6.15 6.05 6.5
12.5 5.7 4.2 4.20 4.29 4.89 6.25 6.15 6.6
13.0 5.8 4.2 4.28 4.37 4.98 6.35 6.25 6.7
13.5 5.9 4.4 4.36 4.45 5.07 6.45 6.35 6.8
14.0 6.0 4.5 4.44 4.53 5.16 NA NA NA
14.5 6.1 4.6 4.52 4.61 5.25 NA NA NA
15.0 6.2 4.7 4.7 4.70 5.35 NA NA NA
15.5 6.3 4.8 4.8 4.8 5.45 NA NA NA
16.0 6.4 4.9 4.9 4.9 5.6* NA NA NA

* posted by from Piers on the TDR forum

(a) 49 state CPL's include: 1549, 1550, 1815, 1816, 1959 for 175 and 160 hp engines with manual and auto transmissions. Also included in this group are non-Ram CPL's 1551, 1552, 1553, 1839, 1914, 1915, 1916, 1959, 1839

(b) CPL group 2022, 2174, also includes non-Ram CPL's 1968, 2265, 2268, 2308

(c) Non-Ram applications - CPL's  1563, 1566, 1569, 1658, 1812, 1905, 1917, 1918, 1920, 1922, 1923, 1949, 1950, 1972, 2034, 2101, 2103, 2104, 2106, 2107, 2108, 2150

(d) Non-Ram applications - CPL's  1564, 1919, 2011, 2102, 2105, 2158, 2169, 2191

(e) Non-Ram applications - CPL's   987, 1261, 1262, 1263, 1406, 1422, 1582, 1618, 1850, 2118, 2196

CPL 2175, 2023, 2022, 2174,1863: Green box is the recommended setting from TSB 18-11-96

  • CPL 2022 engines should be stamped CPL 2174 and 14.0 deg BTDC
  • CPL 2023 engines should be stamped CPL 2175 and 13.5 deg BTDC
The allowable tolerance range for timing is 0.1 mm.

The engine timing procedure for 12 valve engines is posted in TSB 18-10-94A

Q: How does timing affect engine operation and performance?

Date:       Mon, 6 Apr 1998 16:25:18 -0500
From:      Josh Berman <>
To:          cummins

> My 94 Dodge Cummins with a 5 speed transmission has received
> the TST torque plate and turbine orifice.
> My question is as follows. I also advanced the timing 3 degrees.
> Should I bring it back to stock settings or leave it as is.

I'm not going to recommend one way or another, but here are some things you may want to consider (this is assuming you are starting with a stock engine, which you're not):

Advancing the timing will...

        Decrease exhaust temperature
        Increase cylinder temperatures/pressures
        Increase fuel economy (yes, economy is better)
        Increase your output of NOx (a pollutant)
        Decrease your output of Hydrocarbons (a pollutant)
        Increase the amount of black smoke at peak torque

Raising the cylinder temperatures/pressures after already having increased the fueling (as the TST kit does) pushes the engine that much closer to its design limits, but lowering the exhaust temperature helps balance against the increased heat load from the increased fueling.

-Josh B.

Date:      Mon, 13 Apr 1998 15:30:17 -0500

        Advancing the timing will increase NOx, decrease hydrocarbons, and do various things to black smoke (I don't know how "black smoke" correlates to the PM10 and PM2.5 (10 and 2.5 micron particulate matter) that the EPA and CARB are looking at now). @1000 RPM, black smoke will decrease with advanced timing, at torque peak RPM it will increase, and at rated RPM it will decrease (all compared to the "before advanced" timing.

NOTE:  Engine timing specs are on the diesel specs page accessible from the DIESEL MENU

Subject:    Re: Injection timing?
Date:        Mon, 15 Feb 1999 16:22:04
From:       Josh Berman <>
To:          turbodiesel, cummins

> 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:
EXHAUST TEMP increases decreases
CYLINDER PRESSURE decreases increases
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).

        Timing is one of the many things that the performance engineers consider when they're developing a rating. Putting it simply, they have to balance cylinder pressure limits with emissions and power requirements. It takes many hours in the test cells to select the best combination of timing and fueling for a particular rating. The electronically controlled VP44 makes the process somewhat easier, since changes can be made with a few keystrokes (rather than having to remove and recalibrate the pump, as was required with the VE and P7100), but it's still a time-consuming process.

        I hope this helps to shed some light on your question.


        Josh Berman

From the TDR forum:

Power Wagon
   If you go beyond about 15 degrees, the engine noise rapidly increases, and it tends to smoke more (black, not blue). I don't really think you get much economy increase beyond that unless you're running your engine at rather high rpm during cruise ( 2400+ ), and then you'll never do as well as if you ran it slower. The 12V engine seems to like speeds more in the 1700 to 2000 range for economy, probably for a number of reasons, ranging from timing concerns to breathing abilities. If you advance too far, you'll lose power, as well as dramatically increasing the combustion pressures and peak loads on the piston/pin/rod/bearing/crank area without any significant benefit.

Joe Donnelly:   
  As you raise timing, torque below 1900 decreases and power over 2000 increases, with the former change perhaps more noticeable. So, for an AT with stock rpm range, 14-14.5 is good, one degree more for 5 speeds for power and best economy. Up to 16.5 for modified engines with higher rpm capabilities Piers/BD governor springs).

Ted Jannetty:
   What we are ultimately trying to acheive is for peak cyl. pressure to occur 15 degrees after top dead center on the power stroke, for the best effect on the piston and rod to turn the crank.
   Higher timing really helps the old 160 hp engines, but as these engines create more and more power through higher boost and fueling, they will require less timing, not more. Cummins recommends 14.5 degrees BTDC for most B-Series engines. Our experience has shown 14 to 15.5 seems to work in most applications. More than that can increase smoke, and definitely increases NOX levels.
   For the 24 valve engines of today if all you did was advance the timing map equally across the board, you would see a increase in power and milage, in the range of 5% to 10%. But as you add more and more fuel and boost the timing requirements change, specifically for each combo.

   Each fuel/boost combination needs a specific timing curve. The (ISB) ECM has several timing curves for the various operation conditions.



Last Update: August 20, 2003