Timing adjustments.

Craig

Craig

Active member
I can adjust my timing via the dissy:out: duh.

But there are several tables in the ECM that can be adjusted too.

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Once my fuel looks good and I what to make timming adjustments, do I leave the ECM timing settings alone and just turn the dissy until I see my knock count go up?
I know thats one way, but what is the correct way.
 
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Cut and paste.

If, however, you have a chamber design that burns very slowly, like a mid-60s engine, you need to advance the spark and fire at 38 degrees btdc. Because the optimum 14 degrees after top dead center (lpp) hasn't changed the chamber has far more opportunity to detonate as it is being acted upon by heat and pressure. If we have a fast burn chamber, with 15 degrees of spark advance, we've reduced our window for detonation to occur considerably. It's a mechanical phenomenon. That's one of the goals of having a fast burn chamber because it is resistant to detonation.

from here

Does anybody know the size of a 345 cylinder head?

All this is from read a billion pages here
timing table tips? - diy prom - third generation f-body message boards

I guess I trying to understand what people change when they say they bump the timing 3 deg.

Also trying to understand adjusting the main spark table. Maybe I need to see a before and after
 
Cut and paste

you want the timing that yields the least amount of tps and map for a given rpm.
 
The stock combustion chambers for a 345 head are 75-80cc.
But what is that going to tell you? How is it going to help?

You went thru tunercat and pulled out several tables that say timing, but what are they for?
Did you check the help file in tunercat to see if there was a definition?
Not to mention just the basic title.
Are you running highway mode? What is it. How can it be used?
The table is 0 so what will it affect?

Egr...are you running one? Is it active?

When "they" say to add 3° of timing. There are a couple ways to do it.
You can simply turn the distr to a base timing of 3 or add 3 to the entire main spark table.

Now if you are looking for some definative answer on how to tweak the timing...you won't get it.

I only give the basics. It would take some serious time and equipment to do it.
You have to achieve max cylinder pressure under each rpm and load condition.
You can get close by monitoring the vacuum or map at a specific speed as you drive.

The less map or higher the vacuum reading you can achieve for a given speed the closer the timing to optimum.
This means you are producing more power each time the cylinder fires.

Using the knock sensor is just a way to identify the max timing you can run without having spark knock. This May or maynot be the point of max cylinder pressure.

Then we get into accelleration and max timing setting during wot.
These can be determined by accelleration runs...1/4 mile.

Of course several hours on a dyno would help this tuning process also.

So what do you think?

See distributors are just a happy medium for timing.
That's why a recurved distr makes more power on a carb'd engine.
 
Do you have a before and after spark table pic? Just looking for where you started to make changes first. I can do runs and log data and tweak the table, just trying to make sure I start out right. Some basic guidance, like bump this range of cells or what not.

Grumpy posted different timing based on cly head size, med or large.

The egr is disable, so that spark table won't make a hill of beans difference. Not sure if you adjust the others, or just the main spark table. So when they say they bump timing, they could be adjusting the dissy, or ECM constants or bump every cell in the spark table. You mention there are a lot of thing you could change, just trying know which ones I should be working on.
I started a tuning 401 doc, but have not posted it as there is a lot of gray areas, just trying to take it to the next step. The 3rg gen site is good, but they use a lot of different ECM, I'm just trying to get a handle on the 7747 first.

Thanks

Craig
 
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The initial fuel and timing set up is in this Thread.
I show how to do the initial smoothing of the timing and fuel tables.
From there you start with where the engine operates and where you are looking to make gains.

When you save the blm table you also have the counts table.
The higher the counts indicate where the engine operates the most.
So you start with those areas.

Iirc I also discuss some of the tweaking in the step by step thread on the bb. Bottom of first page.
 
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I figured out that you need to have the numbers open for the main spark table, not the graph to select all so you can make a bump to all the cells using the add feature.
 
I've made and lot of changes to the timing. For a while I was just bumping it to get the knock counts to show up. Now that I got there I've been lowering areas that show a few hits.
A lot of changes and testing is needed to get this adjusted. ( newbie) I've been driving the Scout to work all week which has a nice big hill to get the map up there and the rpm's steady. I been doing tunning at lunch too. I find it's hard to do the map/rpm/tps type testing when driving. I need to figure out some excel compares to look at that data. Been played around with the excel and graphing as you can rotate main spark table to see it from other angles.
 
A pilot comes in handy so you can sit in the copilot seat and tweak.

Are the changes helping?

You May need to lower more in the summer.
 
Good tip on summer heat and timing. I assume you just can just drop the whole table a degree or two. It's easy and faster then adjusting the dissy.

Never thought of "being" the copilot. Might work, as my wife has drove the Scout a bit.
I have some smaller tires (32") I'm going to put on to see how it drives with them. The current ones are 38" which works good on the freeway. The last changes are working out good. I still need to work the fuel as each timing change moves that around a bit.
 
Cold weather to hot weather then take into consideration humidity and it's more like 5 degrees retard to get out of the knock sensor or hearing the pinging.
 
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