123 and proper vacuum port on Tii

[BCbryan]

I have looked through all the extensive posts here on the 123.  Solid info and learned a lot reading through everything.  Currently my car is running great with a straight mechanical curve.  1974 Tii.  I'm interested in playing around with the MAP settings to take advantage of adding some advance at cruise.  I understand a lot, but wondering about the proper place to connect.  The original retard equipment has all been removed and capped.  I have both a port on the plenam that I could use as well a port that is on the airbox.  What would be the best connection.  Upstream on the throttle body (airbox) or downstream (plenam).  This is probably buried inside one of the 123 threads, but most everything I could find was related to where to tap into carbs.

 

If anyone wants to share 123 advance and MAP curves for a Tii that they have found useful I would also love to compare.  I'm using a pretty stock curve currently.

 

 

Edited June 17, 2020 by BCbryan
spelling

[jimk]

Upstream of the throttle has no reduced pressure.  Take it off the plenum anywhere there is an appropriate nipple.

[BCbryan]

Thank you @jimk  Was assuming that is the case as it is MAP, so manifold pressure not vac technically.  Thanks for your explanations on this.

 

I'm also assuming that most people don't want any additional advance at idle and that is why you would use the RPM setting for when the MAP kicks in.  This way you are getting some extra advance at cruise and very light throttle, but eliminating it at idle and of course at WOT or accel under load.

 

 

[Mark92131]

I struggled with this issue on my Weber DCOE 45 + Lynx Manifold setup.  I tapped the Lynx Manifold for the 123 Distributor and recorded the inHg/KPa readings on the 123 Ignition Application while doing some WOT runs and cruising.  What I found was that the inHg/kPa readings from the Manifold would duplicate (8 inHg to 24 inHg) in different conditions, throttle position, engine load, RPM, Gear selection, etc., preventing me from having an inHg/KPa reading and RPM combination that indicated I was in a cruise state and could benefit from more advance.  Maybe your Tii will be more predictable.

 

Mark92131

[vairter]

Not a tii (mine is a 1975 with Weber 32/36), but I documented a fair amount of experimentation I did with the 123 using either manifold or ported vacuum.  I ended up deciding to go with manifold vacuum because it allowed for a more steady vacuum advance during cruising.