Why are there so many injector timing settings?

[Scott Crosby]

Why are there so many different injector timing settings on the 71 series?  Not including different size injectors annd S & A differences, I've seen many different settings for 4 valve head 71 series with the same injector in my book.  Are all the different 70's standards just for emission settings?  In the 70's it seems like they changed it every few years in my book.  How do you know which one to use?  Also differences in highway coach, fire truck, and city coach is that optimization for the power curve or something?  My N60's are at 1.460, should they be at that or is something better or not and why?  Oh and why not 1.46 or 1.460000 for that matter

[luvrbus]

The injector it's self has different calibrations like high,low,medium etc, a good injector shop like the one I use will calibrate a injector for what ever I am planning for the engine fwiw a injector for a 2 stroke can have as much as 25+ variations 

 Me I never A time a 71 series if people want it I do it through the injectors,if you ever get a shot at the Snap/On timing gauge then you can really have some fun without all the different pins 

[Scott Crosby]

Mine is standard timing.  So how does a shop mark how they set up an injector?  If 5 years from now an injector goes bad how does one know how to set up a replacement?  As an outsider it seems N60 should always = N60. If something gets jacked with its no longer a N60. It would need some sort of constant scale or reference available to identify what's been modified.  N60b or N60+.012 or something that standardizes it.  And even that would still require a set standard of injector timing from the rocker.  So what's high and low etc and is there a scale?

Luvrbus also what different setups are you asking for and why?  For example why would you want coach A setup be different than coach B?   Driving conditions, performance for primary uses that might need optimized etc.  Yes I'm still in the two year old "Why" stage of answering every answer with a Why?

[lostagain]

The DD engine service manual has tables that specify what injectors to use for what applications and desired HP and torque outputs.

Or call Don Fairchild (cctskit.com). He can explain it very well.

JC

[Scott Crosby]

I'm not talking about different injectors.   The book shows multiple timing settings for the same injector.  I'm just asking why?  I'm not talking about differences in a or s just standard timing it's one specific injector it showes different timing settings.  I assume for emissions or changes in fuels, or performance for use.  1974 1978 1981 etc I don't know the years specifically but there are different injector timing numbers.  What do the different timing numbers do?  What's the reasoning behind the madness? 

[TomC]

I had Don Fairchild time my engine for optimum operation at 1800rpm. You can see with the exhaust when climbing a hill when I get down to 1600, will start to see smoke. Holding at 1800 in 2nd climbing hills (43mph) won't see any smoke. This is one of the reasons the DDEC engines are more fuel efficient-they are running at optimum injector timing at all rpms.  I'll still take the reliability of mechanical injection. Good Luck, TomC

[luvrbus]

Scott it is all about fuel to air ratio the fuel needs to match the air for a clean burn lots of things come into play like port size, the blower ratio the cams it goes on and on.

We just rebuilt a 8v71 it has S timing with N-70 injectors I changed the blower speed and installed a high capacity blower it has plenty of power with no smoke it does not hurt one to experiment with timing settings the few settings in the manual were for hi way EPA settings 

 I have said over and over DD just gives you enough info for a safe reliable engine but it doesn't hurt to think outside the box buy you handful of timing gauges the N65 injectors can come in all different flavors with a dozen of different setting depends all on what people what 

[Brian Evans]

The injector pushrod rides on the cam lobe all of the time, there is no clearance the way there is with a valve pushrod.  When you set the timing on the injector you are setting the static height of a plunger inside the injector.  The plunger is in a chamber that is full of fuel.  When the cam lobe pushes the plunger down, it covers up a fuel port and now the injector can develop pressure to fire the fuel into the chamber.  When you set the timing height you move the plunger closer or farther from the fuel port, so you are setting how fast the injector begins to develop pressure to fire after the cam lobe starts to move the plunger.  A smaller number on the timing gauge will fire faster than a larger number, in other words it will be more advanced and a larger timing gauge number will be more retarded.  As a point of interest my manual has two different settings for brown tag N65's - 1.484 for advanced timing on the cam gear and 1.460 for standard timing on the cam gear.  As you would expect, with standard timing they add in more injector advance with a tighter static height.

Each type and specification of injector will have different internal gubbins that control fuel volume, where the fuel ports are, the profile of the plunger, the needle valve spring setting, the size of the spray tip.  As the control rod moves it rotates the plunger and changes where the plunger covers the port and so changes the volume of fuel and the timing of when the injector fires.  By changing the static timing height you can change or optimize the injection event for different engine operating conditions.  If you take TomC's case the engine was timed - both static timing and internal injector settings, I have no doubt - so that the engine ran as efficiently as possible at 1800 rpm.  You could have a slightly different setting and get optimum performance at 1300 rpm, or at 2200 rpm, and you would want to change it for turbo pressure, etc.  There are also settings that minimize pollution, soot, smoke, and those would almost certainly be different than settings for maximum power or fuel efficiency.  Advancing or retarding the injection event changes cylinder pressure, heat production, when the fuel burn starts and finishes.  Other changes to the injectors change the volume of fuel and the duration of the injection event - all have different effects.  Setting the cam gears to advanced or standard timing not only changes the base timing of the injector, it also changes the timing of the exhaust valves.  Advancing the exhaust valve timing opens the exhaust valve sooner, possibly robbing the cylinder of some useful pressure to contribute to the crankshaft as power, and closes the exhaust valve sooner, probably raising the dynamic compression ratio and allowing more power to be developed, but again potentially increasing cylinder heat.  It's all a balance and there are many many variables.

The document that I sent to Technomadia and they posted on their site had a very good description and diagrams of how injectors work.

Brian

[luvrbus]

The last 5 years of production for the 71 series there was no such thing as A timing on those engines they were basically the same setup as a 92 series with different cams how many have had a 92 series A timed ? I never saw but one and it was 600 hp 6V92 in a boat with a 3 rotor 6 lobe blower

[Bill Gerrie]

Brian
You say a smaller number fires sooner so I guess that is what my 6V92TA is doing. I told Don that I was timed at 1.540 and he said to change to 1.484. What a difference in the sound. So smooth sounding.
Bill

[luvrbus]

Basically the lower numbers on the timing shortens the stroke, a 1.540 setting would be almost impossible to make a mechanical engine run on that

[Brian Evans]

When the rack moves the control rack of the injector it rotates the plunger, which has a profile built into it so that it can vary the volume of fuel that it moves in each stroke.  It does that by first covering the lower fuel port so pressure can build, then when it covers the upper fuel port it locks the volume of fuel that it has captured and is going to inject.  When the rack is set to no-fuel, it basically leaves the lower port open and so never captures any fuel at all.  When an injector sticks, what usually happens is the plunger sticks so it can't rotate and so will freeze the control rack.  While the static timing height controls the range of timing that the injector can have, the actual timing is set by when the plunger actually closes off both ports and develops the pressure to open the needle valve and actually inject the fuel.  The profile of the plunger can be varies so that as the control rack is moved and the fuel volume changes the injection start time is constant and the stop time varies, the start time varies and the stop time is constant, or both the start and stop times vary.  What you can't have is both the start and stop times constant because then there would be no way to vary the fuel volume.  Unlike a gas engine, which wants an air\fuel ratio to be kept very close to 14:1, a diesel engine can have widely varying air/fuel ratios.  You basically adjust it's power output by varying the amount of fuel injected from very little to a lot, while the air volume stays relatively constant subject to blower and turbo boost changing a bit.  If you get more fuel into the engine than can be burned with the amount of air you get black smoke from unburned fuel.  You then have choices - you can de-fuel a bit to eliminate the smoke, you can advance the injection timing to give the fuel more time to burn at the risk of melting a piston, or you can add more air with a bigger blower, or more turbo boost. 

Brian

[Scott Crosby]

Here are some of the variations I found in my Detroit manual.  All are for the same engine, same injector, but different settings.  Once just city coach 1.470 then all 71N series with N60's 1.470.   There were many other charts that N60 wasn't even listed, but lots of other injector numbers were available.

All settings for N60 6v71N Standard

1982 1.484
1972 1.460     with a footnote about all 2 and 4 valve 8v71N & 6v71N now having a setting of 1.470
1970-71 1.460
Injector Timing Gage Chart
1.460
1.470 city coach

[Brian Evans]

If I had to hazard a guess, I would say that the 1.484 in 1982 was a pollution control setting, 1.460 was a efficient power setting, and 1.470 moved the power band slightly lower and reduced soot a bit.  But I really don't know why the different settings, I am just guessing.  It also points out that the engine will run fine with a variety of different settings, what is more important is to have them all the same, and that since the actual effective timing is highly dependent on the control rack position having all the control racks synchronized ("running the rack") is of significant importance.

BTW the reason the setting is given as 1.460" rather than 1.46 or 1.460000 has to do with precision.  1.460" is precise to 1/1000" while 1.46 is only precise to 1/100".  In other words, 1.46 can be equally accurate at 1.455 or 1.465".  1.460000" would need to be measured with a laser and at a set temperature - varying the temperature a few degrees would change the measurement.  So by saying 1.460" they are telling you that you need to measure with a technique capable of being accurate to one thou, which is quite achievable with a go/no-go gauge like the timing pin.  Quite hard with a dial caliper or a depth micrometer, to be honest.

Brian

[Scott Crosby]

Excellent answers Brian   Thanks

Are there any tricks to setting with the timing pin?   I found that holding it completely perpendicular was a challenge that had to be overcome. I played with it for quite a while just trying to get the feel just right before I ran the rack.