I have an EST ignition in my 73' 140HP Mercruiser and found something weird while looking at Mercruiser's distributor advance curve charts. The old points distributors have a total timing of around 33* while the EST only has a total timing of around 23*, (this includes initial timing). Several places that sell the EST say it's compatible with the 2.5L/3.0L (120/140HP) engines from 1967-2011, bit I'm thinking this has to be hurting the performance of older "points" engines as there is a LOT less total timing with the EST. Modern GM 4cyl engines have higher 9.25-1 compression, "vortec" head and probably other things to boost performance, so I'm guessing they can't handle the higher total timing of the older 8.5-1 low compression engines. But, what happens when the EST is used on the older engines that Mercruiser spec'd out with more total timing....
I was thinking of adding more initial timing to my EST to get the total timing closer to the points distributors, but the EST bumps timing to 12* at idle when taken out of base timing mode. I don't think I can set the EST's initial timing higher as it might have too much timing in the lower RPM's, and cause problems.
So what's your take on the timing difference between the 2 different ignitions? Do you think the EST is killing performance of my older 140HP Mercruiser? (Modern 87 octant fuel can't be so bad that Mercruiser had to retard total timing 10*.)
Points ignition
6* initial timing
25-29* distributor advance
31-35* total advance by 2000-2200RPM
EST ignition
1* initial timing (in base timing mode)
12-14* at idle (out of base timing mode)
another 10* distributor advance by 2800RPM
22-24* total advance by 2800RPM
(Points advance curve found in manual 2 and 10, EST advance curve from manuals 13 and 26.)
I was thinking of adding more initial timing to my EST to get the total timing closer to the points distributors, but the EST bumps timing to 12* at idle when taken out of base timing mode. I don't think I can set the EST's initial timing higher as it might have too much timing in the lower RPM's, and cause problems.
So what's your take on the timing difference between the 2 different ignitions? Do you think the EST is killing performance of my older 140HP Mercruiser? (Modern 87 octant fuel can't be so bad that Mercruiser had to retard total timing 10*.)
Points ignition
6* initial timing
25-29* distributor advance
31-35* total advance by 2000-2200RPM
EST ignition
1* initial timing (in base timing mode)
12-14* at idle (out of base timing mode)
another 10* distributor advance by 2800RPM
22-24* total advance by 2800RPM
(Points advance curve found in manual 2 and 10, EST advance curve from manuals 13 and 26.)
