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Thread: Timing the 6.9/7.3 IDI

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    The Grampulator bbjordan's Avatar
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    Default Timing the 6.9/7.3 IDI


    Today seemed like a good day to do documentation, so I did a couple of articles about timing the 6.9/7.3 IDI.

    http://www.blackwire.com/~bjordan/Te....3_IDI_101.pdf

    is about putting the timing straight after messing it up.


    http://www.blackwire.com/~bjordan/Te....3_IDI_201.pdf

    is about fine tuning the timing using Bio-diesel.

    Your question and comments are welcome.

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    Interesting. Back when I got into biodiesel in the early days I was reading on sites like Journey To Forever that you needed to retard your timing 1-2 degrees for biodiesel, now personally I do not adjust timing between the two fuels, in fact I have been saying here that I like more advance with fuels similar to biodiesel because it has fewer BTU/unit than petroleum based diesel and a higher cetane number as you indicated. A well respected member here has made the observation that for same engines, European specs were always slightly more advanced than American specs and that was because they started trying to clean up diesel emissions, use ULSD fuel and Biodiesel blends years or decades earlier than we did here. When the ULSD came out we had a lot of people complain of low power and poor fuel economy. We had been advocating 8.5* BTDC at 2000 with the pulse method and thanks to our fellow OB and his and another members calculations we decided we could make up for some of the lost power with advancing the timing to 9.7 BTDC, those who have tried it seem to think it made a big difference. Now I personally use luminosity timing and of course that measure directly the explosion in the cylinder, so it is ATDC timing. I wanted to put mine right at 1* or maybe even at TDC at 1400, but after finally getting a matched set of injectors and stopping all the leaks 2.5 ATDC already clatters pretty hard, so for the time being I'm leaving it alone. My fuel economy has already improved some. I've been getting 12.7-13.8 mpg in town with mostly stop and go city driving which I'm not real proud of but I think is acceptable for the truck in my sig, bear in mind no OD and an X-cab. My thought is lower cetane/higher BTU=more retarded timing, higher cetane/lower btu=more timing. My understanding was that the suggestion to retard timing with bio was solely to offset the slightly higher NOx emissions which can be observed with using bio, but from a conservation standpoint, fuel economy, CO2 emissions and emissions harmful to human health must be accounted for, and for CO, CO2 and many other pollutants it seems like I've read retarded timing spews more of them out....at least with diesel, I suppose it COULD be different with bio but I don't see why. The NOx makes sense because NOx production is worst with high peak cylinder temps(or is it pressure? or both?) which come from advanced timing. However very good writeup, and you may be 100% right for all I know....would be interested to see what kind of fuel economy in terms of US MPG you get, but the fact that you have OD and probably do less city driving might be confounding variables.
    Truck: 1986 F-250 6.9L ATS Non gated turbo, 3.55s, T-18(that's right the C6 is gone)

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    The Grampulator bbjordan's Avatar
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    question Retarded timing

    Diesel JD, thanks for the reply. There is a lot of good info there.

    There appears to be contradictory information out there. Some of which appears to contradict logic.

    Unfortunately, I do not have a fuel meter on the tank pump, so I have no accurate way to measure the fuel being used other than by the tank full. Maybe your post will convince the wife I need to buy a fuel meter. That said, estimating the mileage by kilometers to the tank full, I guesstimate about 13-14 miles/ US gal. which is pretty close to what you are getting and that was with the 1992 F-250 7.3l E4OD with 4.10 gears. The 1986 F-250 4x4 ZF 5 spd with 4.10 gears has not been optimized yet. I am still retarding the timing on that one. When I got it, it was waaaay too advanced. It rattled like it was going to come apart! The guy I bought it from said it was down on power. No...really?
    Also, I do not have a luminosity probe, or pulse meter. It would be very useful to get actual timing readings. My son-in-law works at a Ford dealership here in Calgary, maybe I can work something out with him.

    I misread the Haynes Diesel Techbook
    Looking at the Haynes Techbook again, I see that following:

    Fuel Cetane Value Calibration
    4-468J ROO 4-68X ROO
    38-42 3.5* ATDC 4.5* ATDC
    43-46 2.5* ATDC 3.5* ATDC
    47 or greater 1.5* ATDC 2.5* ATDC

    That indicates that timing needs to be ADVANCED for higher cetane fuel, which is counter intuitive.
    Is that a typo? Can someone verify that with the Ford Service Manual?

    Higher cetane value fuels burn faster, which require less advance.



    This chart, which I borrowed from Lubrizol, says "Shorter Ignition Delay = Lower Rate of Pressure Rise". However, they provide no explanation of why that is. For a fast burning fuel it would make sense that pressure rise would be quicker/higher rather than lower.



    This is a typical chart of cylinder pressure vs crank angle. Ideally, for maximum efficiency we want the greatest area under the curve after TDC. Its actually a little more complicated than that. ie. the same area under the curve will produce more work if it is moved to the right of the chart. (retarded timing).

    From Journeytoforever.org, "Diesel engines vary widely in their cetane requirements, and there is no commonly recognized way to measure this value. In general, the lower an engine's operating speed, the lower the CN of the fuel it can use. Large marine engines can tolerate fuels with CNs as low as 20, while some manufacturers of high-speed passenger car diesel engines specify 55 CN fuel."

    This would indicate that slow turning engines can use slow burning fuels, and fast turning engines use fast burning fuel. This would make sense.

    Perhaps it comes down to "what do you want?". If you are looking for peak HorsePower, advancing the timing to take advantage of the fast burning properties of bio-diesel at high RPM makes sense. If you are looking for peak torque or peak fuel efficiency, which occur simultaneously, then optimizing the timing for maximum area under the curve to the right is the way to go.
    Peak HP burns all the oxygen/air in the cylinder. Peak fuel efficiency burns all the fuel in the cylinder. Peak torque occurs when peak fuel efficiency matches with the design of the engine: compresssion ratio, bore/stroke ratio, rod ratio, camshaft design etc.

    Has anyone done any dyno runs to find optimal timing for bio-diesel?

    My results are only related to how my timing was set on my vehicles, and is aimed at finding peak fuel efficiency. Perhaps my conclusions are premature?

    Thanks again for making me think.

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    Default More info on Diesel Cetane rating


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    Yeah I have seen that chart before where luminosity timing is based on cetane rating and tends to ask for more timing for higher cetane. As long as we're talking petroleum products what that guy on the Cummins forum was saying makes sense, but we both know that biodiesel is less volatile than diesel while still having the higher cetane content. I'm sure that if we had all parameters that we wanted to consider, including emissions (g CO2/g fuel burned, g/NOx per g fuel burned, PM2/g fuel burned) and performance (maximize HP and Torque) someone mathematically smart could feed these parameters into an optimizer and find the correct timing value. As it is we have a compromise and close to TDC with luminsoity or 9.5-9.7 BTDC with pulse timing tends to be a compromise where these engines will pass easy (specific to making them meet requirements consistent with the years they were produced or slightly better) emissions tests, optimize fuel economy, and make the driver happy. I will actually check mine again soon, as I had planned to go more advanced but it clatters pretty hard at idle. I do know Mel and some of the other timing gurus have said that most IDIs out there are set too far retarded and when you get a fresh fuel system and proper timing you'll scare yourself if you aren't used to it. In my experience with the same dynamic timing settings, biodiesel has less of a "bang" than petroleum diesel, although we know in has actually changed the ignition timing and burn rate relative to diesel fuel. Also the poster, RLDSL that did this research on the Euro diesels has said that in the cases where he tried the Euro specs on American vehicles before the switchover to ULSD, he could not feel comfortable leaving the timing there and had to retard it because they would about shake apart with the old fuel. There remains a lot of work to be done to see what the correct guidlines for B100 fuel are, I don't think anyone here actually has done a dyno run with bio and any setting. I may do one this summer but with school, work and other truck projects there are so many other things. However if I do get any interesting results I will be sure to share.
    Truck: 1986 F-250 6.9L ATS Non gated turbo, 3.55s, T-18(that's right the C6 is gone)

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