123 Distributor vacuum advance set up and curve, Advise on seting up the vacuum advance curve on 123 distributor Options

[Clydeskeeper]

I have searched the forum and watched too many YouTube videos. I am either missing the answer or just don't quite understand.
I am replacing my distributor with a Bluetooth 123. I am a little confused on setting up the vacuum advance curve and maybe even the mechanical curve. On a basic level, I understand that it needs to go from a static of 10 degree at idle up to 27 or even a little more at 3,500 rpm's. Of the videos I have watched, seems like most are not even using the vacuum advance part and just using the mechanical to achieve the above curve. Others go into details I just don't understand including using the vacuum to retard the timing at certain rpm's.
Is there a simple answer and old guy like me can understand? I grew up with cars that actually had mechanical distributors with points and carburetors for fuel delivery. So these concepts are not completely foreign to me.

Just for reference, the engine in question is a modified 2 liter that is now 2549cc with dual 48 Webers.

I await your thoughts, should be interesting at always.

Robert!

[emerygt350]

Don't worry about the vacuum advance. Just set the curve to what the engine likes. 10 at idle seems a bit high to me but others with Bluetooth 123s will chime in.

If you like, you can then set a vacuum advance, but you need ported vacuum to do that. If you want you could set it to a 7 degree advance when the 123 sees vacuum on the port. If you have hooked the line to ported vacuum on your webers it will then advance the timing at cruise and improve your mileage and maybe reduce temps. If you are just racing and having fun with it, it may not be worth your time to do anything with the vacuum advance.

Retard was an old thing to reduce emissions at idle. Don't mess with that, it's a mistake in the 123. The original design had an analog response to vacuum but the digital does not and it can end up retarding your timing at cruise. A bad idea

[wonkipop]

I have searched the forum and watched too many YouTube videos. I am either missing the answer or just don't quite understand.
I am replacing my distributor with a Bluetooth 123. I am a little confused on setting up the vacuum advance curve and maybe even the mechanical curve. On a basic level, I understand that it needs to go from a static of 10 degree at idle up to 27 or even a little more at 3,500 rpm's. Of the videos I have watched, seems like most are not even using the vacuum advance part and just using the mechanical to achieve the above curve. Others go into details I just don't understand including using the vacuum to retard the timing at certain rpm's.
Is there a simple answer and old guy like me can understand? I grew up with cars that actually had mechanical distributors with points and carburetors for fuel delivery. So these concepts are not completely foreign to me.

Just for reference, the engine in question is a modified 2 liter that is now 2549cc with dual 48 Webers.

I await your thoughts, should be interesting at always.

Robert!

whats vacuum advance do beyond mechanical advance you ask?

vac advance was something all air cooled vws had back in the 60s and 70s.
the world over. (Not sure date it came in VWs).
its pretty simple. kicks in at steady revs (ie cruise). advances the timing even further than the mech (centrifigal) advance took it. did this for a couple of reasons.
fuel economy. and as emergygt350 notes also made for cooler running/lower head temos. the vac line for vac advance in a vw at least came off a port above the throttle body so it only ever operated at steady state cruise. as soon as you gassed it at cruise it came straight off so your engine responded to the throttle. and your timing fell back to advance position of the mechanical part of the distributor. you had power.
its not an emissions device - rather it was a fuel economy device in the main part and enabled greater efficiency and smooth/cooler running at varying cruise speed.
side effect was greater emissions of NOX.

it started to be discontinued due to emissions standards in the usa.
for instance even though the distributor had an advance can function it was disconnected in the 74 L jet cars in california and disconnected across the board in the 75 L Jet cars.

as to retard. dual can distributors with a retard function were strictly limited to the usa market back in the 1970s. did just what it says. retarded the engine at stand still idle.
again for emissions. except that made your engine idle hotter. the port was below the throttle plate. as soon as you gassed it to take off from standstill the retard snapped off as the engine vacuum dropped. otherwise your engine would just cough and hesitate at the retarded ignition position.

as emergy says you don't really need the retard set up. that was there purely for emissions. it reduced NOX at idle.

i dont know anything much about 123 ignition systems. others will. but there will be an advance curve that is ideal for most situations. all you lose with the old vac advance function was efficiency at cruise.

[rjames]

Retard was an old thing to reduce emissions at idle. Don't mess with that, it's a mistake in the 123. The original design had an analog response to vacuum but the digital does not and it can end up retarding your timing at cruise. A bad idea

Tell me more about this. I've got a non-bluetooth 123 distributor in my '75. It's been a while since I installed it, but I'm pretty sure I've got it set to a setting that was supposed to mimic the stock dizzy's retard function I think.

The two options as a replacement for my stock dizzy according to the 123's documentation was setting 2 or setting B.
I assumed using setting #2 would result in a high idle, but maybe not? Am I leaving performance on the table by using setting B? Both have a max advance at 2700rpm but it shows differences as to when advance starts and ends. (IMG:style_emoticons/default/confused24.gif)

[emerygt350]

I use setting 1, seems to do well for my engine. I have ported vacuum and use the vacuum advance.

The problem with the retard is the original design was supposed to fight the advance, then in late 74 or something they dumped the advance and that was lost. Then to compound that the 123 retard is on or off and sensitive to the slightest vacuum (I think I measured it turning on the retard with as little as 3 inhg. Probably less. Your retard port on the Tb can see that at cruise and even when you start cracking the throttle. I found my car was retarding the timing at all the wrong moments. The original wouldn't have reacted or at least reacted much to such a small signal.

It will reduce your idle of course but my car is at 8 degrees at idle with my leaky idle screw all the way in and idles at 900. I could go lower if I didn't have a leaking idle screw.

[rjames]

I use setting 1, seems to do well for my engine. I have ported vacuum and use the vacuum advance.

The problem with the retard is the original design was supposed to fight the advance, then in late 74 or something they dumped the advance and that was lost. Then to compound that the 123 retard is on or off and sensitive to the slightest vacuum (I think I measured it turning on the retard with as little as 3 inhg. Probably less. Your retard port on the Tb can see that at cruise and even when you start cracking the throttle. I found my car was retarding the timing at all the wrong moments. The original wouldn't have reacted or at least reacted much to such a small signal.

It will reduce your idle of course but my car is at 8 degrees at idle with my leaky idle screw all the way in and idles at 900. I could go lower if I didn't have a leaking idle screw.

Thanks for the response. I may have to try setting '2' and see if I notice a difference.

[Clydeskeeper]

Thank you all for you knowledge! I think I now know more! (IMG:style_emoticons/default/smile.gif)

I think I will just set it up with the mechanical advance curve and disable the vacuum advance curve. Seems to me, because of the advanced modern features, I can get all the engine needs with the mechanical only.

Question for the engine masters? I am inclined to mimic the stock advance curve, 7 - 10 degrees at idle up to 27-30 or even 35 degrees at 3,500 rpm's.

Given that my engine is so much larger than stock, 2549cc, any considerations for the increased displacement?

Thanks for your input, I am going to tackle this install this weekend and see if I can get more of the bugs out of my 914.

[emerygt350]

Thank you all for you knowledge! I think I now know more! (IMG:style_emoticons/default/smile.gif)

I think I will just set it up with the mechanical advance curve and disable the vacuum advance curve. Seems to me, because of the advanced modern features, I can get all the engine needs with the mechanical only.

Question for the engine masters? I am inclined to mimic the stock advance curve, 7 - 10 degrees at idle up to 27-30 or even 35 degrees at 3,500 rpm's.

Given that my engine is so much larger than stock, 2549cc, any considerations for the increased displacement?

Thanks for your input, I am going to tackle this install this weekend and see if I can get more of the bugs out of my 914.

If you can get yourself on a chassis dyno, I would figure it out there. Depending on your quench and compression and all that change in volume, I wouldn't assume 7-27 is right or good for your motor. I tuned mine originally on a dyno and then over time by my butt and the feel and the head temps and the MPG. I have found a sweet spot at 8-28ish. Any more advanced and the idle is high and the temps (both oil and CHT) go up. Any lower and the engine is lame and the temps also go up. They will also be able to tell if your mixture is looking good at cruise and WOT. Even if you don't pick up more HP I guarantee you will get more area under the curve by going to a dyno. I went from a peak at 4k to a flat line from 3k to almost 6k by playing with the mixture and the timing at the dyno. Dyno for the shape of that curve for sure.

[Clydeskeeper]

Mr emery.GT350,

You bring up a good point and a direction I wish to go after I get some more of the bugs figured out. I would love to have the care dyno tuned in order to set up all things including the timing curve and most importantly the carburetors.

Bay Area people!! Suggestions on a place that can dyno tune a car with Weber carbs on it??

[wonkipop]

I use setting 1, seems to do well for my engine. I have ported vacuum and use the vacuum advance.

The problem with the retard is the original design was supposed to fight the advance, then in late 74 or something they dumped the advance and that was lost. Then to compound that the 123 retard is on or off and sensitive to the slightest vacuum (I think I measured it turning on the retard with as little as 3 inhg. Probably less. Your retard port on the Tb can see that at cruise and even when you start cracking the throttle. I found my car was retarding the timing at all the wrong moments. The original wouldn't have reacted or at least reacted much to such a small signal.

It will reduce your idle of course but my car is at 8 degrees at idle with my leaky idle screw all the way in and idles at 900. I could go lower if I didn't have a leaking idle screw.

Thanks for the response. I may have to try setting '2' and see if I notice a difference.

i'm taking an educated guess here re those two advance curves.
what i think it will be is the EC-A versus EC-B thing of the 74 L Jets.

EC-B engines for the 49 states used the vac port above the throttle plate and the hose was hooked up to the advance side of the dual action vac can on the distributor.
the vac port below the throttle plate was hooked up the retard side of the dual action can (green hose originally).

the EC-B (for california) had the advance hose disconnected from the throttle body and the hose was tucked under the plenum. the port on the throttle body was capped.

same distributor, same ECU, same AFM on both the EC-A and EC-B.


in 75 neither the 49 state 1.8 or the california 1.8 connected the advance can on the distributor to anything. the californian cars had the vac port above the throttle plate connected to an EGR. so 75 1.8 same as 74 1.8 california. no vac advance.
same distributor, same ECU, same AFM.

the way it worked is:
EC-B.
retarded timing at idle - purely through action of retard side of can.
advanced timing at cruise - through action of vac advance - vac retard = true vac advance. the port above the throttle plate influenced the advance side of can.
but at the same time the port below the t plate influenced the negative side of can.
net result was the desired vac advance at cruise.

EC-A
retarded timing at idle.
retarded timing at cruise.

the 49 state car was required to reduced NOX emissions at stand still idle.
the californian car was required to reduced NOX emissions at standstill idle and also at freeway/highway cruise. the retarded timing did that.

power output is not really affected in either instance. there is no vacuum acting on the timing under throttle. purely mech advance.

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i am not sure if the 75 ECU settings are suited to "restoring" the lack of vac advance originally.
but certainly the 74 1.8s can be run either way. simply a matter of connecting the hose or disconnecting it.
the car runs better with the hose and vac advance connected when at highway cruise.
for a 74 you would definitely choose the first of the advance curves.
i believe there is good chance the second of those settings mimics the 74 california and the 75 49states/california stock settings.

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