'73 TR6: Converting dizzy advance/retard values to spark table

[murr32]

Calling all spark table gurus, wizards, and anyone with comments or suggestions.

I need some assistance in converting stock advance and retard values into a starting spark table. This is for a 2.5L straight 6 non-GM engine from the early 70’s. The only aluminum in the engine bay is the cable ties holding the hood release cable :rolleye:.

From the shop manual for the stock dizzy/engine:
Static timing: 12° BTDC (engine not running, crank turned by hand)
At Idle: 4° ATDC (800-850 rpm engine speed, no vacuum retard connected)

Centrifugal Advance:


Crankshaft RPM

Degrees of crankshaft advance





Minimum

Maximum



<400

No Advance to occur



1200

2

6



1800

8

12



2400

12

16



4400

21

25



5600

24

28




Vacuum retard


In. of mercury vacuum

Degrees of crankshaft retard





Minimum

Maximum



<1

No retard to occur



2

0

1



4

0

7



8

8

14



15

12

16




Engine/tranny mods:

1227747 ECM
Compression ratio increased from 7.75 : 1 to 10.5 : 1
Goodparts GP2 cam (specs at: http://www.goodparts.com/shop/index.php?categoryID=9)
Goodparts 1.65 : 1 roller rockers (stock 1.4 : 1)
Upgraded valve springs
Bored 0.040” over
Lightened flywheel ~21lbs down to 17lbs
5 spd Toyota transmission
Electric fan replacing mech fan

Run 92 octane fuel because of the higher compression and no knock sensor.

Car pulls well through 5500 rpm with the current table but I would like to start with something closer to stock and modify myself rather than blindly trust one of two considerably different provided with a mediocre tune via email in 2006.

[RobertISaar]

no vacuum retard listed beyond 15"? that will cover the 50-100kPa columns, but not the 30-45.

[1project2many]

Are you certain that has vacuum retard? The numbers seem reversed! Higher vacuum usually equals higher advance. Less O2 and less air charge density generally requires more advance. Why did they retard spark??? Where is the vacuum retard line connected?

[RobertISaar]

you know, i didn't even look at that...

this is actually fairly quick to do within tunerpro itself thanks to being able to apply a set amount of change per row or column.

[murr32]

Vacuum retard line WAS connected to dizzy, no longer part of the system since the dizzy internals were removed/replaced. I have attached a scan from the service manual page dealing with the distributor advance/retard. In the picture you can see the vacuum retard module on the distributor, but as indicated it no longer is connected internally or externally. Centrifugal advance was also removed.

[murr32]

This was right around the time of stricter emission standards in North America and many things were done to meet those standards including removing the standard injection system in favor of carbs, lowering the compression, de-tuning the engine...

The UK/rest of the world version ran 9.5:1 comp, 150 hp, 16 degrees of advance, no retard.
The NA version 7.75:1, 106 hp., upto 28 degrees of advance, up to 16 degrees of retard.

[delcowizzid]

if the dizzy spins clockwise then thats a stock vac advance setup adds timing at cruise.so the first factory specs with no vac connected is your stock WOT/100kpa timing that 4Atdc is probably a typo and is meant to be 4 degrees before would align with the 6 degrees as the rpm rises.ide use the max figures.the second spec is advance added to the base when cruising and the dizzy has a vac signal.with a cam thats lowering low rpm efficeincy you add timing down lower rpm and keep total the same which by the looks of the maps in the tune table 2 is like that .ide just tweak what you have allready table 2 in the xls didnt look too bad