When you set base timing to 10 degrees and timing table is set to 34 degrees max do you have 34 degrees total or 44 degrees or what? I have 2 different mefi 4 ecu's,one is set up for N/A,one is set up for a blower. The one set up for a blower needs base timing set to 6 degrees to have the right amount of total timing when ran. Is there a std base amount they should always be set to to make the timing table amount correct? Is there a way to set the amount of total timing that the tables give it that account for the base amount?
Smitty

No, this depends on what is programmed in the PCM. Normally, the base timing in the computer is set to 8deg's. Therefore, if you mechanically set the base timing to 6 (and ecm is programmed for 8), you would take 2 deg's from the entire system, 10 would add 2 degree's.

Chances are, if you set base timing to 10deg's, then you would probably have 36. But if the programmer put 10deg in the base timing table setpoint, then you would have 34degs when you set base timing to 10degs.

One thing to note is that the scanner will only show whats commanded and not actual timing. So if you set base timing to 20, you would actually have 44deg's but scanner will only show 34.

Dustin

Thanks for your reply,thats the way I understand it to be,you confirmed it. My next question then is where in the timing tables or setpoints do you program the pcm for the amount of base timing? On my N/A ecu it was initially tuned on the dyno to run with 10 degrees of base and 34 in the table but I don't know what or where in the pcm to find what the base timing to verify if it was programmed for 8 or 10 degrees of base timing. I run the blower ecu at 6 degrees of base,when I reprogrammed the N/A ecu recently I added 4 degrees of timing to the spark tables from idle to wot so that I don't have to re-time motors base from 6 degrees to 10 degrees when I take the blower belt off to run N/A. This put my max timing in the table at 38 degrees vs 34 but when I used to bump the base timing from 6 degrees to 10 degrees it did the same thing its just now I don't have to pizz around with a timing light to do it but I want to see how much timing it really has at wot without power timing the motor at 5600,Smitty

I just looked thru the whole pcm program and the only thing I found was "Idle spark stabilizer limit" which is set to 12 degrees. If this is what I was looking for would that mean w/6 degrees of base timing and 38 degrees max in the table I would have 32 degrees of total ACTUAL timing (38-12=26+6 degrees of base=32 actual)? Smitty

Smitty,
The why I understand it from Dustin's post is basically the program table is setup for the timing you want the engine to run at. For example, if you look at the table and the total is 34 deg and it is in at 2800rpm then you want 34 deg total. In this example, run the engine to 2800rpm (3000rpm to be sure) and check your timing with a light. It should be 34 deg. That is the timing the program wants the engine running at that rpm. If the light shows something else adjust distributor until light matches table. This seems to me that this will calibrate the actual timing to the program.

Rick

In the proper software, its the very last table. Base timing and rpm for base timing. I normally have this at 8deg and 1500rpm. 8deg is what Mercury Marine ran since 93, GM ran it for awhile on the cars, etc. so it was what I considered an industry standard. Mercury Racing cheated this number on the 500HP EFI motors. They call out for 8deg base in all manuals, computer is programmed for 8deg base, but they all came from factory with 10deg, therefore, they had 2 deg more throughout the curve and 2 more than the scanner would show. This is until someone retimes them to 8 via the manual.

Spark idle stabilization is the amount of spark it can vary at idle from the base table. If you have 10, it can go to -2 or 22 max. I normally put this number much higher, really helps shifting rpm drop. Should be around 24-30deg but you sometimes have to bring down the flare time so it doesn't sound funny.

Why wouldn't you just have the same timing table, then remove timing via the boost/spark compensation table? Then, in a NA form, it would only go to 100kpa and use that table, in boost, you can take whatever timing out of it every 5kpa.

You need to first find the table or find what the original programmer actually set in the ECM for base timing. Could've been 8, then you set base mechanically at 10, then you have 36. Its best to use the boost tables for spark retard and run the same timing at 100kpa and below (as na).

Several settings fall into play. If ANY of these settings are incorrect, actual timing seen with a timing light at different rpm/load will not match what you are commanding in the main spark tables.

To name a few:
Field service mode is where you set the base timing value and rpm, (make sure the rpm value used is less than 1600 rpm).
Engine position sensor configuration
Spark delivery configuration
Spark delivery lag configuration

Another tip, a MSD GM EFI distributor will produce different timing than commanded vs using an ACTUAL GM EFI distributor

It would be hard to accurately "powertime" a mefi controlled motor in the typical way you normally would as you describe,the reason why is first off the timing isn't advanced to maximum until 5200 in my tables and even then the total timing at 100 map is less then at it is at 90,80 or 70 so motor load would have to be monitered to see what actual map pressure is free revving to see what table you are in. The only way to have a consistant timing base is to put engine in timing mode and set it there then possibly verify it at a high rpm. In your example at 3000 rpm's timing would be at:
32 at 100 kpa
32.3 at 90 kpa
33.8 at 80 kpa
36.2 at 70 kpa
36.9 at 60 kpa
38 at 50 kpa
so if it was revved to 3000 motor would be bouncing somewhere between 60 to 80 kpa so it would be hard to accurately time the motor as timing could vary by 3-4 degrees,Smitty

Come on, ya gotta be brave, I've put my head back there while we've run it WOT, while someone watched the timing on the laptop. Also have done it on the dyno, much easier to hold load. RC is 100% correct, ANY other distributor besides GM/Mercury will give you a different total timing output. Typically less, but some are very inconsistent, so you can't count on that.

If you want to check the tables at the upper rpm, but all tables at same spark, say 34deg then it's very easy to check when running at higher rpm.

I spoke with the provider of my mefi tuning program today and found out it does not support or show base timing/rpm setting so there is the reason why I cannot find it. I sent him a copy of the bin file as he was willing to look at it and tell me what my base timing/rpm setting is. I plan on setting a timing table to a set amount thru all kpa settings and running it up to verify how much timing the motor is actually getting as I do have a msd distributer,thanks for your help and advice,Smitty