Finding ideal timing curve

[Rustang Racer]

Can anyone help me with some procedures for determining the best timing curve for my engine?

I'm not looking for instructions on how to change the curve but rather how to determine the specs I should change it to. I'm also not looking for what settings worked for other people. I want to know how to figure it out myself, for my particular engine.

Here are the different specs I want to find and my guesses so far for how to figure them out. Please fill in the blanks and correct mistakes if you have some answers:

Total Advance: So far I think this is found by advancing timing until you get pinging and then backing off until you don't. But do you do the checking for pinging with vacuum advance disconnected and maybe a quarter mile pass?

RPM of Total Advance: No idea on this one. Maybe a percent of peak RPM? Or is it just a fixed RPM for each family of engines (Mine is a 250)

Initial Advance: Just use the factory spec or is there a way to find ideal? Possibly set for maximum manifold vacuum at idle?

Vacuum Advance: Set total and initial first, then adjust by listening for pinging on hills or when lugging engine?


I've found lots of posts on how to recurve but very little on how to figure out what you should recurve to other than the generic statement of "It depends on compression, cam, etc." I think an explanation on how to determine the ideal curve might help a lot of people, especially me.

 

[Rustang Racer]

After a little more searching, I found a link someone here posted that answered most of these questions. I'll post it again since I think this string has a more search friendly title.

http://www.carbdford.com/viewtopic.php?t=5543

 

[wsa111]

John, that link is very informative on advance curves.

However, what is your compression ratio & what octane fuel are you using??

Both will have to be factored into the equation.

Having a T-5 trans will make it easier since your curb idle will not change.

Don't be afraid to ask, many of us have done recurving for years.

The ideal tool is the use of a Sun distributor machine. Bill

 

[Harte3]

It appears that you are looking for a final, irrevocable rule or definitive formula to determine the timing for your vehicle. I don't think it can be found by discarding the "It depends..." factor. It does depend on a number of variable factors that are generally unique to your vehicle, it's usage, and your manner of driving. Experimentation and tinkering will most likely be required.

 

[BIGREDRASA]

We've gone around and around before. On MPG:
http://fordsix.com/forum/viewtopic.php?t=52002&highlight=
http://fordsix.com/forum/viewtopic.php?t=30894&highlight=

Make sure you take good plug readings while you play. That means finding a place where you can pop the engine out of gear and shut it off, coasting to a stop. Best not done in heavy traffic.

 

[wsa111]

Tony, the only way you are going to check A/F at idle, WOT & cruise is with a wideband tester like the Innovate.
Once you get the mixture correct then you can go after the correct heat range spark plug.
Otherwise you are just guessing. Bill

 

[Rustang Racer]

I understand that compression, cam, octane and all that stuff matters. For the record I have about 8:1, 264 duration, 87 octane, and mostly street driving. I'm not after a formula though. What I'm after is a list of real world tests for finding each of these timing settings. This is what I'm thinking so far:

RPM of total advance: No guesses on how to find this and I've seen a lot of different numbers. I'm gonna go with 2800 unless there is a consensus on something else or some sugesstion for finding it. I'll set this first by adjusting and changing springs.

Total advance: Disconnect vacuum advance. Find RPM where total advance come in. Make several WOT passes listening for pinging from that RPM on up and finding the maximum advance that doesn't cause pinging.

Initial advance: Vacuum advance still disconnected. Set advance for maximum manifold vacuum.

Subtract initial from total, divide by 2. This is the number of the avance slot I need. After installing this new advance slot I may have to go back and readjust RPM of total advance.

Vacuum advance: after the other avances have been set, and if the vacuum canister is adjustable, floor the car while bogged down a little and listen for pinging. Adjust until it barely doesn't ping.

How does this sound?

 

[JackFish]

I'll suggest hooking up a vacuum gauge between the manifold and the dizzy and go for a drive with a buddy taking notes at various rpms and load situations. This will give you some baselines with regard to vacuum.
Have you got a timing light with an advance feature?

 

[Stubby]

The Innovate LM1 has the capabilities of data logging and realtime readout. This will be wideband O2 and optional rpms.

If you add the LM3A aux box you can monitor O2 plus five more inputs. The other inputs can be just about anything you want.

I am currently reading O2, rpm, map, and 2 axis G's. I have learned that channel 3 can be setup for measuring ignition advance. 8) If I add a sensor for crank position, it will measure the offset between tdc and the ignition event and give me the ignition advance. I plan to add this feature and try to hunt the optimum curve.

The optimum timing event will give peak cylinder pressure around fifteen degrees ATDC. I don't know what the indicators for optimum timing will be, but I bet I have enough things that I can monitor to allow me to figure it out.

I haven't answered your question. I can only share the method that I will be using on my quest for the curve.
You already know how to check, measure and change all of the timing events. You know of the variables. I think it will require some method of measurement of power/efficiency and data aquisition is the best I can come up with.

Good luck and if we come up with enough answers to your question, we will make it a sticky.