UK delivered 1975tii no vacuum on distributor?

[wilfredski]

(re-posted here. Accidentally posted in "ti" forum).

 

I’m looking to install a 123 ignition “switch” model distributor to my UK delivered 6/75 2002tii. I’m wondering if I should be connecting the vacuum port on the distributor to the vacuum system and whether it will improve performance.
 

All my searches turn up either US models or different distributor models and setups. I read varying things about whether tii’s had vacuum distributors (advance or retard) but I’m not sure if they only relate to US specific cars. My distributor model is 0 231 151 009 and it does not have vacuum on it. Is it possible my car/kugelfischer is setup so it doesn’t need/want vacuum connected? Or is vacuum always better because the 123 distributor will perform better with it connected even if the car didn’t originally have it? The 123 documentation seems to say it will work better if it is attached. In which case I don’t know where to take the vacuum from. I am trying to keep the car as original as possible, but concede electronic ignition is straying a fair bit! Cheers.

[Son of Marty]

Not a euro specialist  but the 72 and 73 in the US were centrifical dist and the vac dist on the 74 was used to meet smog requirments here I think BMW keep using the non-vac dist in other markets until the end 

.

[rstclark]

By all means go to a 123 tune with vacuum  advance. Unless you are only drag racing with a wide open throttle and no vacuum, there is a place and good reason for vacuum advance The car will be more drivable

A lean mixture (cruise) takes longer to burn so you need to light the match a little earlier. This is where the vacuum advance comes into play. When you do step on it the engine is already ready to respond rather than waiting for rpm and old fashioned mechanical advance to kick in

Tap a vacuum port behind the throttle plate . Do it on the underside of the plenum if you don't want it seen   

[Son of Marty]

So Bmw and their dyno got it wrong?

[visionaut]

Yep, the late Euro E12 head tii continued with a mechanical-only dizzy (Bosch 151 009) whereas the late USA tii went with a vacuum dizzy when it got the E12 cylinder head…

 

The 151 009 curve is very similar to the prior Euro 121 head 151 008 dizzy, and also the “replacement”Euro tii (121 or E12 head) dizzy, the 188 002. I thought 123 had a preset for such.

The late tii vacuum dizzy (180 013) was for USA emissions.

 

 

Edited February 14, 2023 by visionaut

[wilfredski]

Thanks all. Makes more sense now with the slightly different E12 head and distributor setup. My distributor isn’t shown on the 123 preset tunes that I can find. Would the 008 tune (#4) be the closest?

 

Or better to return the 123 “switch” and get the programmable one?

 

@Son of Marty unfortunately my original distributor doesn’t seem to be playing ball, despite many hours of effort from those more knowledgeable than me. I couldn’t find a reliable rebuild option, hence the 123. I chose the 123 with pre-programmed curves because I gather they are an exact copy of the BMW tune.

[dlacey]

Curve 4 or curve 7 should work...fuel has changed a lot in 50 years, so you might want a less agressive full throttle advance than BMW originally intended....

The switchable 123 probably more future proof than the programmable one (who knows what your cellphone looks like in 5-10 years time, will it still interface with old tech??)

 

Why didn't BMW use vac advance?? My personal conspiracy theory is that having spent the whole development budget on the enigmatic kugel, the bean counters wanted savings elsewhere....

[SydneyTii]

My euro 74tii does not have a vacum distributor, yes I’d use the programable 123, also get them to cut the scroll into the shaft to stop any oil issues, have a search and see if it’s still an issue.

[rstclark]

Oh didn't notice you said switchable  Only have familiarity with programable  with which you can put in the Tii curve and add a little vacuum map. Actually  you can program two different curves and control which curve you use by a toggle switch

[John76]

Manifold vacuum advance is used to improve start-up and idle when the engine is cold. This helps reduce high HC (hydrocarbon) in the exhaust...which is frowned upon. Your Tii might have a coolant temperature switch and a Black electro-valve that turns off the vacuum advance once the engine is warmed up to operating temperature (no more cold-start circuit or choke). When this happens, your dizzy works like a non-vac advance (ealier Tii) model.

Vacuum advance is an emission control device only in the sense that it helps the lean burn, low compression engines pollute less in various markets worldwide to meet emission standards.

It can also advance the timing under low load conditions when the manifold vacuum is high (i.e., cruising speed) which actually improves combustion efficiency, drivability and fuel consumption. So, vac advance is actually desirable for a street-driven car.

When you put the "pedal to the metal", the vacuum advance drops out and only the mechanical advance is in play...just like a race car.

What's not to like?

 

[rstclark]

PS  from looking at the table for the switchable curves I'd say none are the best for a Tii with todays fuels.  And the BMW dyno work is now about 50 years old. The electronic ignition of a 123 tune compared to the original Tii mechanical devise makes the 123 tune so superior When you run a timing light the mark is steady and doesn't move around like a mechanical device

[visionaut]

9 hours ago, dlacey said:

Why didn't BMW use vac advance?? My personal conspiracy theory is that having spent the whole development budget on the enigmatic kugel, the bean counters wanted savings elsewhere....

The first tii used the exact same dizzy (129 037) as was used in the last ti that BMW were phasng out ( tii replaced ti).

 

It makes sense to use the mech-only dizzy in a dual sidedraft set-up. Why they stuck with mech-only isn’t clear - but it’s not a cost savings issue.

 

9 hours ago, wilfredski said:

Would the 008 tune (#4) be the closest?

Yes. Curve 4 ( for the 151 008) like Dave mentioned above is closest to your 151 009…

Edited February 14, 2023 by visionaut

[jimk]

10 hours ago, Son of Marty said:

So Bmw and their dyno got it wrong?

No, it was a situation where device technology was not capable of dealing with the vacuum profile of the MFI. 

 

Plot the sensed vacuum of the MFI along side the ported vacuum values of a carburetor fueled engine beginning at light load and increasing to full load.

 

The carb vacuum curve profile will have no vacuum at idle and the MFI will have high vacuum.  At some level of increased load the carb port will begin to see increasing vacuum, while the MFI will have decreasing vacuum.  And at still higher loads, both will have the same (relatively).

 

Try to make a std mechanical distributor with a vacuum pot work for both a carb'd and a MFI fueled engine and you could make a million.  Easier to use a 123 distr with programmable curves.  Both types of fueling will have better low load economy with it.

 

So I think BMW said screw it and did away with any vacuum pot idea, those Tii owners drive at wot all the time anyway

Edited February 14, 2023 by jimk

[rstclark]

"Those Tii owners drive at wot all the time anyway".  

Good point   Makes vacuum advance irrelevant

[wilfredski]

Wow, unbelievable knowledge here. Thank you.

 

Based on the advice (thanks @rstclark @dlacey), I've found the vacuum port under the throttle body.

 

I now realise my 75 2002tii with E12 head and 009 distributor is a slightly uncommon combination so I've swapped out my 123 with pre-programmed curves, to the programmable bluetooth 123.

 

@dlacey I'd love some of the tuning programs you suggested please.

 

What's the best strategy for getting the tune just right? Should I be loading these tunes as a starting point then go to a dyno? Do I just tell the dyno people I'm looking to get the advance curves right?

 

Anyone happen to know a good dyno place in Sydney please?