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Question on the boost/timing relationship
My gut tells me that the presence of boost retards the combustion timing because the engine gets quieter under boost and also, if the injection timing is close enough to the edge of detonation to cause some "pinging", the ping goes away with a little boost.
Anyone have any data to back up this theory? How about a pounds to degrees relationship? Enquiring minds want to know! Thanks!
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
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Cheers! Scott McPhee 1987 300D |
#3
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Makes sense but doesn't fit with what I'm experiencing. Engine seems "happier" and quieter under mild to heavy acceleration. With light loads, low boost, the engine "pings" like a gasser. Now I understand that with my car, some of this is due to a little air in the system but that's not the only factor.
Now regarding the injection timing device, I'm wondering how it adjusts timing with load. I guess the injection pump becomes harder to turn at higher fueling levels and this retards the timing because more force is applied to the timing device?
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#4
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I wish my gut said such sophisticated stuff to me. All I hear from it is, "FEED ME".
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes 1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod 2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die." |
#5
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Be glad it doesn't. Very glad.
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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl. |
#6
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What car are we talking about? I'm pretty sure injection timing on 61X engines is fixed. Not sure about the newer ones.
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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar. 83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles 08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles 88 Jaguar XJS V12 94,xxx miles. Work in progress. |
#7
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In this case, I'm talking about my 606 but all of the engines have a centrifugal timing device integrated into the pump drive sprocket that works the same way by changing the position of the injection pump shaft to the crank shaft as RPM's increase.
There may be a unique example of a Mercedes engine that doesn't have a timing device but I'm not aware of any aside from the modern CDI engines.
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#8
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Evan,
Just a guess, maybe the presence of the extra air is causing the fuel to burn rather than explode. The timing doesnt change under load, just that as you have the stroke on the IP elements increased, it starts injecting sooner & goes on injecting for longer.
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Grumpy Old Diesel Owners Club group I no longer question authority, I annoy authority. More effect, less effort.... 1967 230-6 auto parts car. rust bucket. 1980 300D now parts car 800k miles 1984 300D 500k miles 1987 250td 160k miles English import 2001 jeep turbo diesel 130k miles 1998 jeep tdi ~ followed me home. Needs a turbo. 1968 Ford F750 truck. 6-354 diesel conversion. Other toys ~J.D.,Cat & GM ~ mainly earth moving |
#9
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What is your timing set at? To spec or advanced past spec, which may have an effect on the pinging. If I get ambitious, I may set up my RIV Xenon timing light and diagnostic port digital RPM adapter and do a map of my timing advance curve.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#10
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the bigger amount of fuel takes longer to heat up in the prechamber and reach ignition temperature This ignition delay retards your timing up to several degrees = retarded ignition sounds smoother Gruß Volker |
#11
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I agree it is most likely an air fuel ratio relationship. But a subjective "quietness" doesn't necessarily mean it is doing better. You can look at the "boost" side of the air fuel ratio or the "fuel" side if you wish but it is really a combination of the two that does the job. Here's a standard graphic found in most text books Air And then there's the ALDA section in chapter 07-010 in the (turbo) part of the OM617 FSM that's worth a read. This isn't really delaying the timing (certainly not valve timing!) in terms of the point of combustion it is more like the relationship of how well the rate of burning is achieved. I don't think a comparison of a "crap" burn to a late or too early begin of delivery or point of delivery is really going to be all that meaningful.
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1992 W201 190E 1.8 171,000 km - Daily driver 1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone 1965 Land Rover Series 2a Station Wagon CIS recovery therapy! 1961 Volvo PV544 Bare metal rat rod-ish thing I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior Don't leave that there - I'll take it to bits! |
#12
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From what I found out on My own car at idle speed it will nail if the Injection Pump timing is too advanced and it will also nail if the Injection Pump Timing is too late/retarded.
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84 300D, 82 Volvo 244Gl Diesel |
#13
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The fuel burns rather than actually exploding. This takes time. At higher rpms the piston is moving relatively faster away from it. So the noise of burning may appear less. Advancing the timing does not mitigate this effect. It only allows the burn and its initial expansion to initiate earlier.
In a way fuel milage may be reduced by this effect. Less work might be achieved by the burns attempt to keep up with the pistons speed as well. The rate of the burns expansion remains pretty much a constant I suspect. The load for the burn is diminishing much quicker at high rpms. I also suspect this is why a taller rear end ratio can produce better fuel milage. Last edited by barry12345; 08-08-2014 at 03:34 PM. |
#14
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Just some thoughts that came quickly to mind. Based on the assumption that once compression has dropped off too far the diesel fuel might be somewhat self extinguishing. Just because unburnt fuel comes out the tailpipe does not mean all the unburnt fuel left the combustion chamber. Blower pressure may also help exhaust scavaging leaving less un burnt fuel behind in the combustion chamber. I have no issue with anyone discounting this as I have not really thought it through. Last edited by barry12345; 08-08-2014 at 03:35 PM. |
#15
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That is under heavy pedal the element will load more fuel and reach it's discharge pressure in the injector a little earlier. Plus as mentioned a longer period of injection. |
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