The Dynamic Advance thread...

[Alleslowbuged]

Here is diagramm whichs shows stock fuel cutting at vw injection pumps:



Uploaded with ImageShack.us

Best Regards

[Alleslowbuged]

yes, eventually, as you spin more and more RPMs, the flame speed of diesel is exceeded by the speed of the engine.. read as: diesel is still burning as it is exhausted from the engine.. a bigger plunger may help to get the fuel in there quicker, but idk if that bigger plunger is going to help any with an engine that is exceeding the burn speed of diesel..

Hi again,

from my point of view, you can delete the "may" regarding the biger plunger. With the stock camplate and the stock plunger you can not effect the massflow (fuel) vs. time fictures. When the stock internals are good for 75 hp at 4500 rpm, is getting worse in the moment when you increasing the overall fuel amount, which is necessary if you want to make more power. In fact what happends is, that even if the dynamic timing is working properly (stock pump does this up to ~4500 rpm) the time for full injection mass is getting longer and longer, which getting more important as higher yoe revs, as you still inject, even when the piston is nearly at the botton dead center. Besides burning this "late" fuel does not make any power, you also massive increase you egts and grill your turbo.

If you want to make good power, go ahead with 12 mm plunger and stock camplate or 9 mm plunger and DI camplate and you will see, that you can get max. power at less than 3500 rpm, as the efficiency with higher fuel massflow is that much improved, that you running into stock flow capacity limittations of the cylinder head (and also for stock turbos). If you wand to make good power at high rpms, you have to improve, flow capacity of the turbo and the cylinderhead first and also have to do some work on the advance timing figure of the injection pump.

Please read "you have" and "if you wand" not personal, it is due to my limited english that it sound a bit harsh.

Best Regards
Alleslowbuged   

[carrizog60]

i agree on the timing being one limiting factor.
yes,diesel burns slow but if we could advance the timing we could have extra time to burn it completely.
advance piston shaving and better springs will alow that,could we shave the pump body to allow for more travel?
i dont know for how much degrees could we gain doing that mods to the pump any degree up top is good.
how much does a tdi pump advance?isnt it similar in body to the mech ones?
one could mesure the insides and go from there...

[Alleslowbuged]

Hi,

i have done all that allready (teyt is in german):

http://www.golf1.info/forum/index.php?page=Thread&threadID=61668&pageNo=1

but from my actual point of view, the hardcore mod (like enlarge casing channel)
is not necessary.

The stock timing has a stroke of 8,9 mm, which is limited due to the front cover plate.
This means 10,4 ° rotation angle (injection pump) or 20,8° rotating angle (crank shaft).
By using constant 0,001s for ignition lag, this means advance timing up to ~4500 rpm.

My stock spring has had a free length of 35,2 mm and a solid length of 21,0 mm.
My pre-stressing was 2,2 mm together with 3,2 mm shims (all together), so the max.
timing stroke, limited due to the solid length of the spring would has been 12 mm.

In my first attempt, i have shorten the timing piston on both ends, have move the
static position 3,0 mm in direction of the choke lever and used the front cover cap
and spring of a VP37 pump, which has given a stroke of 12,7 mm (up to 5900 rpm).

But if you shorten the timing piston on both sides this will massive increase leakage, so
that the inner pump pressure is high depending on the position of the piston and thereby
not stable, which will bring serious timing (running) issues.

So at least i have just shorten the choke lever side of the timing piston, as leakage to
that side will not have any impact. By doing this, you change the static position of the
timing piston and directly increase the stroke posibilities, what you have to do further is
to readjust the spring pre-stressing to stock level. You can find something around 3 mm
of extra stroke and this is enough for everthing this side of super crazy short stroke high
reving 1,5 super turbodiesel.

So as summary from my side, increase stroke due to shorten the piston from the choke side,
readjust the spring pre-stress and everything is fine.

Best Regards

[RabbitJockey]

Very informative and very interesting

A few thoughts I have had is that it makes sense that a lower compression ratio will help with higher rpm power because it will allow more timing advance with out pinging

Also on Dave's build he dynoed with Mercedes nozzles and made less power I am curious if this is due to the difference in the prechamber design or if it is because the Mercedes nozzle needs a larger plunger to match its increased flow. Or if he lost power because the Mercedes nozzle injected the fuel more quickly and earlier because of a higher flow rate thus causing advanced timing

Also something I thought id mention on top of diesel burning more slowly it also must mix with air and combust all in one process where gasoline has already been mixed with the air long before tdc

[RabbitJockey]

Ahh good point Trev, very good point. Just because the pump is capable of pushing fuel to 6500 doesn't mean the engine is capable of burning fuel at 6500.. I wonder if a slightly lighter more volatile fuel would make a difference? With lubricity taken in to account as well.

i think you and i are on the same track of thought here buddy!

Haven't u been on that track with your abf haha

[Alleslowbuged]

Hi again,

i also think, that the rev limit for diesel are more due to that direct injection fact, as due to the lower burning speed of diesel, even
if i have to say that i have never made the math for that. Did someone know what the redline of actual direct injection gasser is?

I have also thought that lower compression will allow more advance timing or better say higher boost pressure, as i have always read
this everywhere regarding turbo engines. But i came to the point, that i start to think how pinging should happend in our direct injection
engines (either DI or IDI), as we just inject the fuel in the moment we wand it to burn.
As i mention, from my actual knowing (experience) even if you enable massive advance timing, you will not get high power with useable
efficiency at high revs. The only way to get that, is to also highly decrease injection time by simultaneous increase injection flow.

But this is just my point of view and i do not insist to be right.

Best Regards
       

[R.O.R-2.0]

Ahh good point Trev, very good point. Just because the pump is capable of pushing fuel to 6500 doesn't mean the engine is capable of burning fuel at 6500.. I wonder if a slightly lighter more volatile fuel would make a difference? With lubricity taken in to account as well.

i think you and i are on the same track of thought here buddy!

Haven't u been on that track with your abf haha

ABF got put on the back burner again. my diesel is blown up, and i only got 1/3 of the money i was supposed to be getting..

every time i get close to making my jetta driveable again, something ALWAYS goes wrong.. ive been trying to get my jetta back on the road for almost 4 years now. im about ready to just give up on it since i can never spend any time or money on it..

and how do you get a diesel to ping? ive always been under the impression that you couldnt get a diesel to ping, because it is basically pinging the whole time its running. pinging is just detonation, and diesels run off detonation. its there only form of ignition..

[RabbitJockey]

Pinging as in overly advanced timing my dad once ran too much kerosene to aid cold starting. And while were on a trip to Philly if he tried to accelerate it would act and sound like a pinging gas engine. Or an overly advanced diesel. But what I meant was that with less compression the air won't get as hot as soon so that will open the window for more time for fuel to be injected. But like was said really increased fuel flow is needed but even that may not help cause the fuel still needs time to mix and burn. What happened to your rabbit?

[jimfoo]

ABF got put on the back burner again. my diesel is blown up, and i only got 1/3 of the money i was supposed to be getting..

every time i get close to making my jetta driveable again, something ALWAYS goes wrong.. ive been trying to get my jetta back on the road for almost 4 years now. im about ready to just give up on it since i can never spend any time or money on it..

and how do you get a diesel to ping? ive always been under the impression that you couldnt get a diesel to ping, because it is basically pinging the whole time its running. pinging is just detonation, and diesels run off detonation. its there only form of ignition..

Sounds like you have my luck. I don't think I have driven mine an entire year yet since I got it, always something, and always something different.

Alleslowbuged, in your chart, are we looking at the entire mit LDA curve? Meaning at 3000 RPM is where fueling starts to be cut?

[carrizog60]

i put the left cover(from land rover pump)to allow more travel.
ith this cover the spring would be loose,i put a schim so the spring would make contact to the cover.
what did you do?
left it loose?

another thing regarding injection more fuel on less time:bigger plunger.

but wont bigger plunger also limit rpm?

[RabbitJockey]

I have read of bigger plungers limiting rpm because they break but I recall a discussion from tdi club where they said the problem had more to do with too low of flow injectors being used with the larger plunger. How true any of that is I don't know

[R.O.R-2.0]

Pinging as in overly advanced timing my dad once ran too much kerosene to aid cold starting. And while were on a trip to Philly if he tried to accelerate it would act and sound like a pinging gas engine. Or an overly advanced diesel. But what I meant was that with less compression the air won't get as hot as soon so that will open the window for more time for fuel to be injected. But like was said really increased fuel flow is needed but even that may not help cause the fuel still needs time to mix and burn. What happened to your rabbit?

head crash. timing belt broke. yadda yadda. fun stuff..

was only blown up for 12 hours.. figured out i have a 12mm block in the car, so it has a TD head on it now..

[Mark(The Miser)UK]

An interesting read Alleslowbuged...
I've not played with the pumps at all. It's so easy to loose driving licence over here
With regards to that diagram, it looks like a cleaned up version of the SAE #820441 paper, which is an average of 23 TD pumps. Can you explain the meaning of the coloured points on the graphs which all lie on the outer limits of the range of pump results. Is the pump named on this diagram the one you are using?
If so I notice your physical measurements of the range of dynamic advance seem to correspond nicely with the range stated on that pump, namely VE4/9F2250R...

"The stock timing has a stroke of 8,9 mm, which is limited due to the front cover plate.
This means 10,4 ° rotation angle (injection pump) or 20,8° rotating angle (crank shaft).
By using constant 0,001s for ignition lag, this means advance timing up to ~4500 rpm."

As there are many  VW pumps out there that are rated to 2500,[5000 crank] from 107's to AAZ ones, your research makes me think that they  will have more dynamic advance  to start with. Is this not true? If so why did you not use one of them?

Your reference to the pre-ignition of 1ms  is interesting. Is that at the desired rated rpms?
From what I've read this pre-ignition phase is independant of the main burn, but actually shortens slightly under faster injection and higher combustion air pressures, probably due to increased temperatures. Does this make lowering general compression ratios counterproductive for top end speeds?

The main burn is almost purely linked to swirl rate, and so conveniently speeds up with rpm.
From what I've read, tapered needle injector nozzles add faster increasing volumes of fuel to the pre-injection  compared with parallel needle types. AAZ adjustable pre-injections may be useful here, although I guess main burn wants to follow pre-ig ASAP...

Could   a finer wire 'weaker' spring be used in the advance mechanism, but with a few coils cut off to strengthen and the whole spring stretched to the desired length not help with the range?

[R.O.R-2.0]

oh yea, another thing.. i DEFINITELY had the rollers skipping in my pump yesterday, no questions.