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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old September 1st, 2010, 11:12   #1
Aspergers
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Default Effects of diesel timing

I'm trying to learn more about diesel combustion theory to help me get the best tune out of my Bosch VE IP. A friend has promised to lend me a good book on the subject but I want to cut right to the heart of the matter - timing. Specifically the effects of too much advance (or retard) on an IDI engine.

This specific query is born out of a post I read on this forum suggesting the application of 12v to the timing solenoid for more power (which is ECU controlled) but I think it might have been tongue in cheek as I suspect that too much advance at lower RPMs would be unwise and detrimental to the health of my engine? Perhaps a load/rpm based switch would work?

If someone could point me towards some (free) good reading or even describe the effects of diesel timing in this thread, I would be most grateful.
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Old September 1st, 2010, 13:31   #2
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So you IDI volkswagen has an ecu?
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Old September 1st, 2010, 13:47   #3
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Late model IDI engines (like VW's AAZ) have an ECM... Engine Control Module... an analog control system that like the TDI's ECU makes some timing decisions, including when to apply power to the timing advance defeat solenoid bolted to the front of pumps on these engines.



OP, in terms of reading... your best bet is to hunt down the Bosch Yellow Jacket for distributor-type injection pumps... it is pretty inexpensive and probably have the most through "real" info on how Bosch designed these pumps, timing, etc:

http://www.bentleypublishers.com/bos...-fuel-inj.html
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Old September 2nd, 2010, 05:56   #4
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Hello good souls and thanks for your replies,

I have a PSA XUD9T engine, it uses the Bosch AS3 to completely control the timing while the rest of the fuelling is mechanical.

The combustion theory I'm looking for is cause and effect of timing on a diesel engine. I have read the Bosch book on VE pumps and it has no information on diesel timing events, just how the pump works.

I want to understand the combustion process itself - perhaps there is a "...for Dummies" copy that would suit me?
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Old September 4th, 2010, 13:03   #5
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I guess I'm asking too much, I apologise.
Perhaps if I could break it down and ask, for instance, what are the effects of too much advance on an IDI diesel engine using SVO on otherwise stock TD pump/injectors?
Ditto for too much retard.
And if it's not too much to ask, how can I determine the best timing for power? I guess a dyno would be invaluable but cannot afford that at this time.
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Old September 8th, 2010, 09:47   #6
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No-one knows or wants to tell me?
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Old September 8th, 2010, 10:30   #7
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While I don't profess to be a diesel injection timing wizard I'd recommend you think of injection timing somewhat like spark timing/advance on a gas engine. If the event happens too early (advance) the piston is still travelling up in the bore and the flame front will meet piston crown on the up stroke fighting the inertia of the reciprocating mass. Too late (retard) and the combustion energy is chasing a piston crown that is already moving away from it.

As rpms rise so does piston speed and more advance is required to time the flame front to provide the optimal push as the piston travels down in it's stroke. There are additional factors (temperature, load, fuel quality, etc) but that's the general concept of internal combustion engines. John
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Old September 9th, 2010, 05:05   #8
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Thanks for your input John. That analogy I understand. I'm more interested in tuning for best power and how to recognise too much advance/retard - ie how the engine behaves and how I can "read" the signs.
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Old September 9th, 2010, 20:51   #9
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I think one person said to do a 60-80 run in 3rd gear, change timing and do it again, see if time gets better or not. Or, if you have access to a dyno, do the runs, changing the timing. If you find an ideal max timing at xxxx rpm, please do let us know!
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Old September 10th, 2010, 08:00   #10
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Hi Rob, I've got a plan to work out best acceleration, thanks but that won't help me understand the effects of timing in general.
For instance, while I'm wanting best power, I'd also like to know why, at part-load, my engine knocks - is it too too retarded or advanced? - while full load she's sweet sounding. I'd even like to know best timing for cold idle, fast idle etc.
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Old September 11th, 2010, 05:41   #11
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In general less advance (retarded timing) favors low speed operation while more advance favors higher engine speeds; think piston speed relative to injection event. The manufacturers recommendated timing is a compromise on both based on intended engine operating speeds. If you intend to run your engine mostly outside their parameters adjust accordingly.

It soounds like you timing is advanced if knocking at low speeds and running well at higher speeds. I'd recommend you set timing stock, try it for a week or two (maybe more ~500 miles), then try the same with a slight advance, then slight retard. Try to keep all other parameters the same during these trial periods. You should feel the performance and mileage differences and then can "tune" to your liking. John
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Old September 11th, 2010, 07:12   #12
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Ive never enjoyed factory timing, as apposed to advanced.Advanced timing will gain mpg's,power,probably smooth out a tired injection pump and injectors.
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Old September 11th, 2010, 07:33   #13
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Quote:
Originally Posted by Aspergers View Post
Hi Rob, I've got a plan to work out best acceleration, thanks but that won't help me understand the effects of timing in general.
For instance, while I'm wanting best power, I'd also like to know why, at part-load, my engine knocks - is it too too retarded or advanced? - while full load she's sweet sounding. I'd even like to know best timing for cold idle, fast idle etc.
Diesel engines are supposed to "knock". They are knocking whenever they are running.

Perhaps you are thinking this sound is bad because of gasoline engines where this knocking sound indicates that the fuel has been combusted (too early) by too much compression. In a diesel engine, the fuel ignites purely from the heat the engine generates from compression.

Personally, I prefer the 'ping' or 'knock' sound that a diesel engine will make when timing is mechanically advanced a little bit.
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Old September 11th, 2010, 07:46   #14
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You have to make a compromise when you choose timing. Too far advanced, and some might say that the increase in cylinder pressure right after ignition might cause damage. However, increasing the start of combustion gives the fuel more time to burn. This can make the car more efficient- 2-3mpg better. (So far, those testing advanced timing on ALH engines have had little trouble, however attempt at your own risk...)

There will be a "sweet spot" where your timing and injection quantity will match the maximum amount of boost your car is tuned for and burn the fuel most efficiently to produce the most power possible. I would guess that this spot will be only slightly advanced from the 'center of the graph' in vag-com.

I am not a tuner and I don't know enough about the subject to tell you that anything here is actually factual, I am merely passing on the unverified information I believe that I remember reading here on tdiclub various places. It is easy to get in trouble repeating information only to find out that it was incorrect in the first place, so take my words with a grain of salt.

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Old September 11th, 2010, 07:56   #15
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I don't know about your specific VE pump, but on the ALH our injectors actually have three separate pulses of fuel. First, a small pre-ignition fuel pulse is injected into a small piston bowl where it has a chance to start a good little fire. Once that fire is going, the injector spits out a bigger shot of diesel, which really gets the fire roaring. At this point the piston is really starting to move- but there is a little more oxygen left in there and things are really hot, so the injector spits a little more fuel, and viola, good power and economy!

The newest "CR" engines have 5-pulse injectors!
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