Vacuum source for 123 ignition on a tii

[AlfaBMWGuy]

Hello,

 

I have been trying different advance curves for a 123 on my stock '74 U.S. spec tii.  I am currently using this combination of centrifugal and vacuum curves and loving the performance while also getting good idle and off throttle characteristics:

 

Redline 6000

500    0

1000  0

1400  12

1600  16

2400  24

3500 35

8000 30

 

MAP Start   0

0    10

60  10

87   0

100 0

200 0

 

I found this in multiple other FAQ threads and it was referred to as a reference standard that reproduced one of the hardware curves in the older "switched" 123 and was very appropriate for a tii and created by someone referred to as Mr. 123.  The problem is that with this loaded I'm seeing up to 40 degrees of advance in the 123 app "dashboard" gauge just at steady throttle at 50mph around 3K rpms in 4th gear.  While I'm not experiencing any pinging that I can detect, I know I shouldn't be running this much advance as damage can be done.

 

I think I know what's happening based on the MAP gauge readings also in the 123 app dashboard.  I am getting much lower vacuum/MAP readings with that gauge than I was thinking I should be seeing based on the vacuum curve above.  For idle, I see -0.6 Bar.  For that steady state 50mph, I see -0.3 Bar.  For WOT, I don't think I get more than 0.0.  So what I think is happening from those values is that the 10 degrees of vacuum advance only specified for 60 kPa and less is instead being applied 100% of the time on top of the centrifugal advance curve values (since I never see anything approaching 60 kPa).  At idle I do see 10 degrees of advance, meaning nothing added to that vacuum curve value of 10, which is consistent with the centrifugal curve, but also seeming to confirm that anything less than 0 kPA also gets the 10 degrees of advance (my idle would correspond to -60 kPa if I have the Bar to kPa conversion factor of 100 correct).

 

So the clear indication is that I must be taking the source for the 123 vacuum port from an incorrect location to be getting pressures that far off expected.  Below are two pics showing how it's setup now.  That blue hose (yes, I know an incorrect color choice and it will be changed out for black one way or another) is the one going to the 123 vacuum port.  You can see how a tee was added to the line from the intake manifold to the '74 tii specific bit of Bosch emissions equipment on top of the air box--decel valve or whatever it is.

 

So is my solution to instead run this line from somewhere else?  If so, from where?  Or, would it be feasible, if a bit kludgy, to just create a new 123 vacuum curve that offset the pressures values with what I'm seeing?  Since idle at 1000 rpm should be 40 kPa (from what I've been told) where I'm seeing -60 kPa, would it be legitimate to just subtract 100 kPa from the values in the curve above, meaning -40 and lower would get 10 degrees, but at -13 kPa (87 - 100) it turns to 0 degrees?  Does it even work for the 123 with negative pressures specified in the curves?  My concern with just hacking the curves is that if my source for the vacuum line is wrong, it's then not giving me expected/consistent pressures in all conditions (partial throttle, decel in gear, WOT) to simply do that offset by 100 kPa.  Therefore, the hack might work for idle, but not consistently across the board in other conditions as is the whole reason for wanting to add in the vacuum curve at all.

 

Thanks,

Gary

 

 

[Mark92131]

2 hours ago, AlfaBMWGuy said:

it's then not giving me expected/consistent pressures in all conditions (partial throttle, decel in gear, WOT)

 

Gary, I feel your pain!  I spent countless hours trying to solve this riddle with my Bluetooth 123 Distributor on my Cab.  I could never get consistent kPa readings that I could equate to a repeatable condition (cruise in 5th gear) that wasn't also found in other engine conditions (decel in gear).  This led to extra advance in conditions that did not necessarily warrant extra advance.  It didn't seem to matter if I was using manifold vacuum or under the throttle plate, the readings were all over the place.

 

Your static advance map settings seem high for a 1974 Tii (US Version), even without the additional advance.  Blue Book values would suggest the following ignition map.

 

500    0

1000  2

1500  12

2000  18

2400  25

2700  25

 

You can try finding a condition that warrants more advance, like cruising on the freeway, to see if you can get a consistent kPa value, and then live with the fact that you might have other conditions that trigger more advance when you aren't expecting it.  I finally gave up and ran a static map for my setup.

 

Mark92131

[AlfaBMWGuy]

Thanks Mark.  The curve I gave was definitely more of a performance oriented one, but apparently was created to mimic Curve 4 (0 231 151 008) for the switched 123 distributor for BMW 4-cylinders.  Mr. 123, who created it, is a Frank Botenbal and this curve was in that 26 page FAQ thread for the 123 going back many years and covering a variety of 123 issues.  I do greatly appreciate the performance bump it offers over a more standard curve like you provided.  That extra advance bump at 3500 is right where you want it in a tii since mid-rpms are where they are lacking something esp. compared to a dual carb '02.

 

Throughout the FAQ threads that talk about 123 curves there are disclaimers about the need to customize to your engine, modifications, and preferences.  I just was figuring it wouldn't be something this drastic in terms of me seeing kPa values 100 less than expected.  I will do some more experimenting with what the MAP gauge in the 123 app is giving me in different conditions since really I just have those two reference points now, idle and steady state at 50mph in 4th gear.

 

-Gary

[dlacey]

4 hours ago, AlfaBMWGuy said:

Or, would it be feasible, if a bit kludgy, to just create a new 123 vacuum curve that offset the pressures values with what I'm seeing?

I don't think that's a kludge... It's an alignment of the signal with the required setting.

This vacuum is just a signal for the 123 to recognise different engine demand. So if you can see that idle is consistently 60kPa, cruise 80kPa and full throttle is 100kPa in your situation/plumbing then it's fine to program your 123 to add your idle and cruise advance at those pressures.

I also agree that adding vacuum advance makes a tii more responsive and lively in normal part-throttle conditions. Why didn't BMW do that back in 1972? Different fuel? Cost pressure (expensive injection)?? Focus on peak performance only???

[AlfaBMWGuy]

Since I was still confused, but neither Mark nor Dave indicated I was doing anything too crazy, I decided to take a more detailed look at the help provided on the 123 USA website.  There I discovered in one of their YouTube videos something I hadn't seen documented on the FAQ, although it probably is and I just overlooked it because I wasn't trying to solve my current problem when I saw it.  I also found it discussed here on the 123 website: https://123ignition.com/support/create-curve-tutorial/

 

The magic is that the values in the MAP curve you create must be offset by atmospheric pressure, which at sea level is 100 kPa.  This offset converts from relative pressure (as shown on the app dashboard gauge) to absolute pressures that are independent of elevation (and thus allows uploaded 123 vacuum curves to still be good as you change elevation).  Therefore when I see -0.6 bar on the app dashboard gauge at 1000 rpm idling, that really corresponds to a data point in the MAP curve of 100 - 0.6*100 = 40 kPa!  That's assuming I'm at sea level, which is not quite the case, but not too far off.  I did find that trying to upload a curve file with negative kPa values gave me an error so that's not even feasible in terms of directly inputting the app dashboard MAP curve values into a 123 vacuum curve.  But, the offset for atmospheric pressure means it all makes sense and 0 kPa in a MAP curve corresponds to -1.0 Bar on the 123 app dashboard gauge.

 

With that revelation, for me at least, I was able to tweak my curves with confidence and get the total advance down lower than the 40 or so degrees I was seeing before.  One other issue with that reference curve (which is also uploaded on the 123 USA website as a tii curve, not just in other FAQ threads) is that with only vacuum advance at low rpms, starting is much more difficult.  Need to add in some centrifugal advance to help with that.  I'm still trying to pick the curve I'm going to run with so I won't provide one now, but maybe my trials and tribulations along with starting to come out the other end into the light will help someone else out.

 

-Gary

 

Edited May 26, 2022 by AlfaBMWGuy

[AlfaBMWGuy]

Also to answer my own question in my original post, that source for the vacuum line to the 123 vacuum port is a decent one.  I just need to swap out the blue silicone line for something appropriate under the hood of a classic BMW.

[jimk]

No math needed if absolute pressure is used and when manifold pressure is used for load.

[cda951]

On 5/25/2022 at 12:43 PM, AlfaBMWGuy said:

 

The problem is that with this loaded I'm seeing up to 40 degrees of advance in the 123 app "dashboard" gauge just at steady throttle at 50mph around 3K rpms in 4th gear.  While I'm not experiencing any pinging that I can detect, I know I shouldn't be running this much advance as damage can be done.

 

Hi Gary,

 

An important point to make is that detonation/pinging will only occur if the engine is under heavy load. While you may need to tweak your vacuum curve, the 40 degrees of advance during light-throttle cruising is perfectly acceptable, and is in fact one of the main benefits of vacuum advance. The engine is not achieving good volumetric efficiency in this state, and the sparsely distributed air/fuel mixture needs a lot of time to burn, which is facilitated by the extra spark advance. This improves engine efficiency and fuel economy while cruising. Any factory EFI system with 3D ignition timing control will be using close to 40 degrees advance during light-load cruising, if not more.

 

Now, of course you need to ensure that as soon as you open the throttle (which decreases manifold vacuum), the timing curve should fall back to what is allowed by the centrifugal advance, and this needs to be dialed in based upon your engine configuration, compression ratio, and the octane rating of the fuel you are using.

 

Another point to make is that most factory installations of vacuum advance distributors use a pre-throttle, ported vacuum source for the vacuum advance. There is much debate on Internet forums about the ported vs manifold vacuum advance argument, but the fact is that ported and manifold vacuum tend to equalize once the throttle plate is open, and the main difference is that at idle, manifold vacuum will be much greater than ported vacuum. Ported vacuum advance allows a "shot" of timing advance off the line when the throttle is first opened, which increases responsiveness of the lower compression, emissions-controlled engines such distributors were often installed on.

 

The neat thing about the 123 ignition is it doesn't really matter if the vacuum source is manifold or ported---you can program the RPM at which the vacuum advance is enabled, which means you won't have vacuum advance at idle if using a manifold vacuum source. I intend to play around with this on my own '73 2002tii, but it rips using a centrifugal-only curve that is only slightly more aggressive than the factory curve, so I have left it alone thus far  .

 

 

 

[AlfaBMWGuy]

That advice is greatly appreciated cda! I was backing off my vacuum advance to 6 degrees max because of the concern on the total advance with more being around 40. Now I can still get some extra vacuum advance while having the bit more aggressive centrifugal curve where the tii really performs, as you stated.