Okay I have been sitting here reading since 6:30 this morning, and my rear hurts. I simply cannot make sense out of all these timing graphs that are posted here.

Why is it that as the rpm is increased the timing seems to be dropping? On my older cars once I have reached a total timing number of say 36 degrees at say 2,600 rpms,,,it stays there all the way to peak rpm,,,but on these timing graphs is goes up and then down again.
And why are the numbers so low? In some areas I see very low numbers, around 20 degrees total advance at higher rpms that would make a very sluggish engine in my experiences. So what gives? Is there another number that is added in somewhere? Could someone please post a timing graph and explain to me how it works exactly and what is added where and why? Larry.

 

In the Prom tuning book up in the stickies, go to the '7747/'8746 section, there is a write up on spark timing. It covers in detail what tables are used and how.

There are several reasons the timing tables are lower then the old school hi-po SBC stuff. One is that stock engines with stock cams build a lot of cylinder pressure at low RPMs. Running 14.7:1 for the CatCon is detonation prone. Engine temperatures are higher (195 stats). Some engines have fast burn chamber designs.

RBob.

 

I read through most all of that but didn't see anything specific on timing tables. Most of it covered Volumetric Efficiency tables. After reading that I do now understand the VE much better and how it is used to trim the fuel curve. Does this work with MAF or is there another process to use for fuel changes?
It seems to talk more about Map readings more than anything, but from what I understand, you take a given rpm and look at the VE, and BLM,,,you divide the BLM by 128 and then multiply the VE for that given spot, then change that number and that ultimately changes the fuel curve for that particular block? Do I have that right? If so thats easy enough but does that work on an MAF car?
I understand fast burn cylinder heads, camshaft overlap and cylinder pressure and how it affects timing etc....but I would like to see a timing graph posted somewhere with an in depth explanation of how the timing tables are calculated etc..much like the VE tables I just read about,,,,very nice explanation for a newbie,,,,thanks for the help so far,,,,Larry.

 

Thread for the spark stuff:

https://www.thirdgen.org/forums/diy-...cs-anyone.html

As for the BLM, it acts directly on the PW. It is a multiplier where the math looks like this:

New_PW = (PW * BLM) / 128

RBob.

 

I read the timing stuff and now my head is spinning, I can't make much sense of it without pictures of the graphs they are referring to. For some reason I feel there is way more info there than I will ever use, it's great that everyone took the time to type it out but too tough for a newbie to understand. It sounds like there are multiple graphs involved to change.
As far as the fuel curve on an MAF car, you said the BLM acts directly on the PW. What is PW? Is this another graph?
If so I assume you take a certain PW reading out of a block in the graph and multiply by the BLM that would be in the same block (in a BLM graph?) and then divide by 128 and this gives you new PW number to put into the PW graph? You then in affect have changed the fuel curve in the engine?
Is that right? Do you have a picture of this graph? Does it extend through the entire RPM range of the engine? Thanks, Larry.

 

PW is the injector pulse width.

May need to give it some time to sink in. It's tough at first, but then all of the sudden things start making sense.

RBob.

 

Thanks Rbob,,,,I was scratching my head for a couple hours thinking of different words for PW, then I got back to this thread and saw Injector Pulse Width Now it makes more sense to me,,,,,damn newbies,,,,lol,,,Larry.