Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by itchyfeet »

Funnily enough I was going to do the same.

Also going to plumb the DJ dizzy into the DG when time permits with advance to 2nd throttle vac and retard below throttle, see what the curve looks like.

I have an old Aircooled dizzy too and this has twin vac, I find it hard to believe its just emissions.

None of tbis tells us how it responds when driving though, can they give a plot of ignition advance on the rolling road?
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by itchyfeet »

looking at Andrews picture in inches hg?
5-10 power
10-18 Driving
18-22 idle
22-30 coasting

full advance is about 10 inch hg ( 250mmhg)
advance starts about 4 inch hg (100mmhg)
these are published in the VW manual


my gauge to about 750mmhg or 30 inches

..Image
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by itchyfeet »

Must be much lower when driving than when stationary.

PS I tried a multimeter on frequency and found it inaccurate

PPS the 2nd throttle opens with a tiny amount of vacuum, it won't even register on my vac gauge so probably a few mmhg

ImageVacuum by Paul_Barr, on Flickr


ImageTim Vacuum by Paul_Barr, on Flickr
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

itchyfeet wrote:Must be much lower when driving than when stationary.

PS I tried a multimeter on frequency and found it inaccurate

PPS the 2nd throttle opens with a tiny amount of vacuum, it won't even register on my vac gauge so probably a few mmhg

I've just been out doing the same thing, with very similar results. Essentially we get 'idle' levels of manifold vacuum, even at fairly high engine speeds. I didn't measure rpm, or record any numbers, but I did turn the throttle quite a long way I thought, and the vacuum didn't really start to drop off. It's enough to make me question the explanation that a wide open throttle causes atmospheric pressure to fill the vacuum. I didn't go to full WOT, because with no load the engine revs rise too far for comfort when I'm leaning over the engine, so maybe it's literally only at WOT that the vacuum disappears. I did notice that when I released the throttle quickly the vacuum rose to maybe 600 mmHg briefly and then dropped back to idle levels.

Re your PS - is that a multimeter with a dedicated rpm setting?

Re your PPS - I couldn't get any vacuum to register either, so I was wondering if something was wrong, but of course your explanation that it takes only a tiny vacuum to open the vac unit makes sense. My spare unit is the same. Of course, this raises the question as to why we can't get the second throttle to open when testing stationary. As long as the throttle is opened far enough to release the interlock, the vacuum ought to be always sufficient to open the second throttle.
Last edited by CJH on 02 Oct 2017, 18:20, edited 1 time in total.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

Had a discussion with the rolling road owner. He's happy to help me set up a few distributors, as well as the two carbs. I didn't ask about whether the system measured timing in real time. He said that vacuum advance on the 123 unit couldn't be set up on the rolling road, and is something he would suggest doing by 'feel' on the road, and interestingly he said that would be done for best economy. Need to look into that to see what that's all about. He said with the 123 unit he can get the mechanical advance so precise that there's no need for vacuum advance. Again, I'm not sure I follow.

Regarding the dual vac distributor, he said he'd set it up with the retard disconnected, as it can cause problems - poor performance if it doesn't disappear quickly enough. I don't know enough about why vacuum retard is used, other than one piece that I read that said it was for emissions only. But given that my engine seems fine on some advance even at idle, and given that even vacuum advance seems optional and aimed at best economy, I'm starting to wonder how critical any of this is!

Anyway - I think it could be worth taking both the 123 unit and the dual vac DJ unit to the session, so I'll talk to Andrew and Paul offline about maybe borrowing their units.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by itchyfeet »

Don't forget you do need to pass an MOT :rofl
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by bigherb »

CJH wrote:it doesn't disappear quickly enough. I don't know enough about why vacuum retard is used, other than one piece that I read that said it was for emissions only. But given that my engine seems fine on some advance even at idle, and given that even vacuum advance seems optional and aimed at best economy, I'm starting to wonder how critical any of this is!
The retard is used with certain carbs/throttle bodies where the idle/overrun mixture is very weak, retarding the timing helps with complete combustion.
I would check out the maximum centrifugal advance of the DJ distributor before you go too far.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

bigherb wrote: The retard is used with certain carbs/throttle bodies where the idle/overrun mixture is very weak, retarding the timing helps with complete combustion.
I would check out the maximum centrifugal advance of the DJ distributor before you go too far.

Ah, ok. Is that weak mixture issue something that affects both carbs and injection systems? Could it be part of the reason that the DJ setup uses vacuum retard? Incomplete combustion sounds like an emissions issue though, regardless of the fuelling system - does it cause other problems?

What's your thinking with the maximum centrifugal advance issue? Is it possible the maximum advance on the DJ is greater than the DG, e.g. to avoid pinking, so that using the DG distributor could damage the DJ engine?
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by bigherb »

CJH wrote: What's your thinking with the maximum centrifugal advance issue? Is it possible the maximum advance on the DJ is greater than the DG, e.g. to avoid pinking, so that using the DG distributor could damage the DJ engine?
No the other way.
See how low it is compared to a carbatoot engine.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

bigherb wrote: No the other way.
See how low it is compared to a carbatoot engine.
Image

Ok, yes, it maxes out at 2400rpm, so that explains why the chart in the wiki stops at that point. The DG chart continues to 4200 rpm. But I've also seen the DG maximum mechanical advance quoted as 12-16 degrees I think, yet the wiki graph shows it going up past 30 degrees. Do you have the same sort of information for the DG?

As you can probably tell, I don't really understand any of this very well. There's a quote in the piece I linked to above, which says:

The specific fuel consumption of a SI engine improves out to about 50 degrees BTDC, but the mechanical advance curve is limited to much less advance because of the possibility of knock under WOT.

Is 'knock' the same as pinking? So, assuming the higher compression of the DJ makes it more prone to pinking, then it needs to have less total advance than the DG. Is that right? If so then there's a danger in using the DG distributor with the DJ engine, as I'm doing at the moment. I wonder if pinking/knocking would be audible in my engine going full tilt at the back of my noisy van. I can't say I've noticed it, even with it set inadvertently to 12 degrees at idle.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by bigherb »

CJH wrote:
bigherb wrote: Ah, ok. Is that weak mixture issue something that affects both carbs and injection systems? Could it be part of the reason that the DJ setup uses vacuum retard? Incomplete combustion sounds like an emissions issue though, regardless of the fuelling system - does it cause other problems?
No but it means it will actually reliably idle.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by itchyfeet »

It seems quite a few are using DJ distributor with just the advance conneted and 2e3 on a DJ base engine so it must work.

I think we have learned a thing or two Chris by playing but ultimately your rolling road chap is going to be the one to advise which is best between DG and DJ distributor, he may even conclude it makes no difference at all.

Interesting to find out because DJ distributors are hens teeth and if a DG is as good or better this will be good knoledge.

I hope they do exhaust gas analysis as you need to pass the emissions test :D

Pm me your address again and when the rolling road session is and I will lend you my spare DJ dizzy, I know you will look after it :D
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by bigherb »

CJH wrote: Do you have the same sort of information for the DG?
Of course.
Image

CJH wrote: Is 'knock' the same as pinking?
Not quite but assume it is for this purpose. Knock is really detonation, pinking is pre ignition.

CJH wrote: So, assuming the higher compression of the DJ makes it more prone to pinking, then it needs to have less total advance than the DG. Is that right? If so then there's a danger in using the DG distributor with the DJ engine, as I'm doing at the moment. I wonder if pinking/knocking would be audible in my engine going full tilt at the back of my noisy van. I can't say I've noticed it, even with it set inadvertently to 12 degrees at idle.
Yep your on the right track. But bear in mind injection can have more optimal fueling through the rev range.
Ideally the advance would be set 4 deg before pinking occurs through the rev range, hence the different amount and strength of springs on the balance weights for different engines. It's usually not as close for stock engines to be safe, due to other factors due to different ambient temperatures etc.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

itchyfeet wrote:
I think we have learned a thing or two Chris by playing but ultimately your rolling road chap is going to be the one to advise which is best between DG and DJ distributor, he may even conclude it makes no difference at all.

Interesting to find out because DJ distributors are hens teeth and if a DG is as good or better this will be good knoledge.

I hope they do exhaust gas analysis as you need to pass the emissions test :D

From what I can tell, the re-jetting process is all about analysing exhaust gasses across the whole rev range, to ensure that the correct stoichiometric ratio is maintained. So they definitely have the kit to do it, and I'm hoping they'll take the idle emissions into account when setting up the distributors.

I guess Bigherb's point about the total mechanical advance on the DG distributor is an important one. I don't know what they'll be able to tell me about pinking/knocking from their kit. At least standing close to the engine, with the engine cover off, while they run it through its paces I might stand a better chance of hearing any such effects. It's one of the things I'll try and discuss with them anyway.
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Re: Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

Post by CJH »

bigherb wrote:
CJH wrote: Do you have the same sort of information for the DG?
Of course.
Image

Thank you. Interesting that the DF has some retardation as well. And the two different sets of DG specs are interesting too. With the 'Q' variant the advance comes in a lot sooner than the C and J variants, and looks like it might be more like the DJ curve. I guess the plot in the wiki came from a C or J variant. I haven't checked my own one, but I guess I have a C or J variant on my DJ, since the advance didn't pick up until about 1500rpm. I do have a spare Q variant which I could try.

It'll be interesting to see what the rolling road tells us about the effect of the higher maximum centrifugal advance (if anything), since if we're trying to find out if a DG distributor can replace a DJ version then that earlier advance of the Q variant could be useful.

By the way, my memory failed me in the earlier post - I'd remembered the specs for the maximum *vacuum* advance (12-16 degrees), which is common to the DG and DJ, but had attributed them to the mechanical advance.
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