rsilver

Sorry about this, I did a search and thought I knew but now I am confused. I am running an 8746 ecm . If I have 6 degrees advance at the distributor and at 3600rpm @50kpa I have a value of 25 in the main spark table, does that mean I have total timing (spark advance) of 31 degrees at this load and rpm?

Is the above the correct way to calculate total timing?

Thanks for the help. I have been looking at fuel so long that I am just now getting serious about timing tables.

thanks very much...............bob

BronYrAur

iTrader: (1)

You should have whatever timing in the main spark table 25* plus the timing at the distributor 6* minus the main spark bias in the chip, that's your total timing.

BronYrAur

iTrader: (1)

Why do you have such a low value of 25* in that cell? Was that changed or is that a stock cal? I just looked at a stock AXKW bin (TBI 5-speed) and at 50kpa and 3600rpm it has a value of 49.92 minus a main spark bias of 20.04 gives 29.88* of total advance.

JokerRS

Just to muddy the water a bit, it may depend on how you are examining your bin file. I am using tunner cat, and I have read in a post that tunner cat combines the main spark bias with the main table and shows you the actual value in your main table. I havent varified this. Maybe I'll try changing the spark bias in a bin and see if it changes the value in the main table.

BronYrAur, your answer is correct. We just aren't all on the same page. I'm using tunner cat, some are into sorce code. I don't know what rsilver is using to look at his bin.

JokerRS

I gave it a try and thats what tunner cat does. I took the 20* spark bias out of the ECM constants and then checked the main spark table. It was greater acrost the board by 20*.

rsilver

Bron and joker. I am glad you guys cleared that up cause thats why I was getting confused. I am using tuner cat so I didn't know what to do with spark bias. So, in my example @3600rpm@50 kpa i have 25 +6 for a total spark advance of 31degrees .

I started out with the cop chip and started playing with that but I always did better with less timing in the table. After reading jokers other post I thought I would start over again with the stock 305 bin and go from there. The value I mentioned above comes from the AXKU bin which I thought was a 5-speed bin but I wasn't sure if it was TBI or TPI. I will check out the AXKW bin and see what it looks like.

I am still having trouble with WOT timing over 3600rpm.
I know the ecm uses the values in the 3600 row above 3600 rpm so what range of timing are you guys using for TBI engines for WOT timing?

Thanks again!!! You all ROCK..............bob

JokerRS

At WOT the ECM adds PE spark to the main table also. All togather I would think you could run 32*- 34* total (main table + PE spark+ enitial timing)in the 3600 block at WOT. However, as Grumpy says, run as little timing as possible and still run strong. I have my enitial timing set at O* and have added timing to the table only. I have a total of 31* at WOT at 3600 and above, and I may take some out.

Also, it depends on your AFR how much timing you can run. The two go hand in hand.

Brent

iTrader: (1)

I didn't see anyone mention the "slope" timing adder. I am tired though and might have missed it.

This adds x degrees of timing per 1000rpm starting aroung 3600rpm and ending at 4000rpm or whatever the particular aplication calls for. Thus giving you more advance than is show in the table.

Read this for more

The bottom line is, the specific advance numbers aren't *that* important. I must be a fool right?

Well maybe, but we don't know that the guy who runs really fast with 38 degrees of timing has a slipped harmonic balancer. Or that another fast guy's dialback timing light is off by 3 degrees. Or that his prom has x degrees +/- hidden somewhere he didn't know to look.

The only thing that is important is testing and finding what number your car runs fastest at.

rsilver

these comments are a big help guys. I know the specific numbers do not mean that much but all of this gets me in the ball park.
I totally missed the the idea ofPE spark adder and the "slope timing adder in calculating total timing.

At 100kpa@3600 rpm I have 15* in the table, +6* initial plus 4* in the PE spark adder
for a total of 25*. If that is my total timing then I probably have some room to advance it. But, How does the extended spark rpm slope affect this?

I have 3.5* in the constants section. does that mean it adds 3.5* for each 1000 rpm? If that is the case then I would have 42* timing at 5000rpm so maybe I have too much spark!

I have done a search on the spark slope issue but haven't found anything to clear this up.

What do most people use for a spark adder number?
the 3.5* is the stock cop chip number and I never changed it.

Your comments are appreciated..........thanks bob

JPrevost

SA isn't all that easy to calculate. There are many tables that change the final SA.
Here's how to calculate final SA;
Actual dizzy advance + Main SA table + CTS SA table + TCC SA table - Initial SA - Main SA bias - CTS SA bias - TCC SA bias = Actual SA that the engine will see.
There are other tables/conditions that add or subtract SA. Some of those tables are Highway mode, PE mode, EGR, Choke, and Idle mode. Looking at the disassembly will give you a better idea of what the ecm is doing to calculate final SA.
Now if you want to datalog final SA (not including the dizzy physical advance) then you should change the ALDL data stream and patch in a ram location in place of the Eprom ID. Then when you datalog with whatever software you're using, the Eprom ID will be final SA instead of Eprom ID. Final SA is then calculated by taking that byte then * 90/256 to get degrees.
I'll be uploading an ecu file patch to Craig Moates file upload so get it and read the included txt document to get a better understanding of what I'm talking about.

Ronny

iTrader: (1)

this SA stuff is confusing. i have distributor set to 10 deg advanced. in tunercat i have the constants set to 10 deg initial advance. what i see in my TC main spark table is the advance my engine sees. this is was led to believe, told by TC. i could set the initial advance at dist to 0 and likewise initial adv in TC to 0 and command any SA in table i wished. in this case engine will still see what ever TC shows in main spark table. PE and the like will add to the main spark table. i could also 0 out the pe and add that back in main spak table at appropriate map/rpm . i just needed to add this to see if i am understanding all this. that is comforting. also what is spark bias? please define why used/whrere used? (used to create a pos timing or no advance?)when does that occur in normal running? i see above in post a 20 ded bias and subtracted from main value to give net adv of 29?. why do that? sorry if this is redundant.

JPrevost

Bias is used to you can get a negative value from a table lookup. Example; CTS vs Vacuum SA table. There is a bias value of 20 so everything in that table is going to be "around" 20 plus or minus some degrees. This is so at low temps there can be more timing added to the Final SA and at higher temps there can be timing removed from the Final SA. CTS table lookup = 18 and bias is 20, Main SA lookup is 55 and bias is 20; result is Final SA = 55+18-20-20 = 33 . Does that help clearify? Obviously that is just a simple example of how SA is calculated, like I said before, there are more tables and more bias values that need to be looked at to calculate Final SA.
To answer one of your other questions, TunerCat does include the bias values in most of his tables. This is confusing because his software will take a table, subtract out the bias and display it. You need to close the active table before you change the bias value in the constants or it won't display correctly. I find it useful but some don't. I also find it useful turning the bias values to 0 and setting up the tables so as if the engine temp was really high. Then I use the CTS vs Vac table to add a couple degrees for when it's really cold. Remember that if you turn the bias values to zero you WILL need to adjust the tables. So if you set the main SA bias to zero and then opened the Main SA table you'll notice very high values. You'll need to subtract the old bias value from that table to get back to where you were before you changed the bias.
Good luck. Also you might want to modify the ALDL datastream to display final SA if it doesn't already.