123 ignition timing advance curve

[dpb]

Hello

 

My 4a has an old 123 distributor fitted,   and I thought I would buy a new one as a spare,  as I am off on european holidays later this month.  Reading the instruction for the new one,  it says check which advance curve is required for your engine, then set the microswitch in the 123 accordingly.  I thought I would be clever and just look at the old one, and copy that.   Lo and behold there is no equivalent microswitch in the old one.   Looking in my WSM I cannot reconcile the timing information with the choices given in the 123 instructions.    For example, just for one of the choices it says:

 

....................................advance starts (degr.crankshaft)   1000,   max advance (rpm/degr.crankshaft) 4500/20.0,     remark 2000/8.0

and for another..........advance starts (degr.crankshaft)   1000,   max advance (rpm/degr.crankshaft) 3000/17.0,     remark 2000/8.4

The info in the WSM    says speed 800 rpm,   advance degrees 9-11.    Does anyone know how to reconcile these numbers?

 

Cheers 

Dave 

 

 

Edited June 2, 2022 by dpb

[Lo100469]

Hello,

Are you saying you don't find the switch on the old one?  I may be wrong but i believe the switch on the early ones was accessible from under the unit, and has moved to the side on version 2 (that is the one i have, you just need an alen key to access it).

 

[dpb]

hello

Yep I can't find the switch on the old one.       But if you have version 2,  (which I now have as a spare),   what setting have you used?  

Thanks

Dave

[Z320]

Hi Dave,

the deg. from the WSM are on the distributor,

they are x 2 + static advance on the crankshaft, max. 24 deg. on the crankshaft for the 4 cylinder TRs.

Sorry me for my poor opinion:

all this issue about the correct ignition curve of our iron block engine is needless worry.

I can’t start driving with less than 1,500 revs - and the ignition already on full advance.

Any engine LOVES as much advance as possible on any rev.

The correct curve is digital: 4 deg. start the engine and idle and 24 deg (TR 4 cylinders)  any driving + some deg from the vacuum box.

Ciao, Marco

Edited June 3, 2022 by Z320

[mikej]

When I wrote the article on ignition timing I contacted the very helpful 123 as I did not understand the curves and how the base Advance was set. Early 123s were different and the install instructions reflect that. The curves that are selectable are GENERIC curves for "British Cars" and not TR specific. Must pay attention to Static setting as it is the off-set for any of the curves available. Of course, if you have a non standard cam or CR etc then the curve may be different, this is where the programmable 123 unit is better but... it will involve rolling road dyno costs to set it up. It is not the case that too much advance is a good thing at all engine speeds.