Digital ignition curve

[408swinger]

I am at taking the plunge into the world of digital ignition and would like some input on what my curve should look like and where I my initial should be set ?
I will deal with the vacuum advance next.
This will be mostly street driven.

The ignition is a Daytona Sensors CD-2 .

The engine is a 408
Cam = 246/250 -108 - .648 lift solid roller
Heads are W2 Race closed chamber ( Polished and ported) and .036 Quench
Intake is a Victor W2
Carb is a Pro Systems custom 850+ Cfm DP
TTI. ...1 7/8 to full 3 " exhaust

Dart Swinger 4 sp. 3.55s for street...3.91 + for the track.

[andyf]

You'll just have to play with it until you find a map that seems to work best. It depends on a lot of factors so there isn't a universal answer. For that engine I'd start with 20 at idle and maybe 35 at WOT and 40 or more at cruise. Put those three numbers into their areas and then smooth between them and see what it does.

[408swinger]

I wasnt sure if the 4sp made any difference on the curve.

[Caprimaniac]

And up to 50 or more at decel. (Vac advance).

At load, quite steep at 3000- 3500 rpm up to 35 or higher. I'm at 40 max at WOT, With a dip in max torque band, around 5000 rpm (36 degrees?). I have Victor Jr heads w/ flattops for comb Chamber...

a 347 With Lunati cam very similar to Your numbers, N/A. I might post my map for the joy of it, if I can get photobucket to cooperate...

[408swinger]

And up to 50 or more at decel. (Vac advance).

At load, quite steep at 3000- 3500 rpm up to 35 or higher. I'm at 40 max at WOT, With a dip in max torque band, around 5000 rpm (36 degrees?). I have Victor Jr heads w/ flattops for comb Chamber...

a 347 With Lunati cam very similar to Your numbers, N/A. I might post my map for the joy of it, if I can get photobucket to cooperate...

That would be great !
My thinking is that 35 will be the max for mechanical using these heads...
I wanted to use a map sensor and create a 3d curve but was told MAPs dont read vacuum all that accurately.

[FC-Pilot]

I wanted to use a map sensor and create a 3d curve but was told MAPs dont read vacuum all that accurately.

They may not be perfect, but they sure are better than nothing. I would imagine having it on there and using a vacuum advance curve would help keep the part throttle driving cleaner and crisp. ...But I have been wrong before.

Paul

[408swinger]

I wanted to use a map sensor and create a 3d curve but was told MAPs dont read vacuum all that accurately.

They may not be perfect, but they sure are better than nothing. I would imagine having it on there and using a vacuum advance curve would help keep the part throttle driving cleaner and crisp. ...But I have been wrong before.

Paul

I plan on using the vacuum advance . It would just be nice to do it digitally .

[RW TECH]

I wasnt sure if the 4sp made any difference on the curve.

It does.....You need to be careful with how much spark you have in the transitions between light and moderate to heavy loads with a stick shift car.

Automatic with torque converter (especially high-stall) will be much more forgiving,
'

[408swinger]

So should I do a linear curve from off idle to around 4500.
Would there be an advantage to having less timing at idle as far as heat build up etc... ?

[BigBlockMopar]

I have a MegaSquirt 3 in my daily Dodge Dart (360ci / auto), controlling ignition timing, for a number of years now. Spent plenty of time playing with the ignition curve to find out what the engine likes best.
Install the vacuum-source right away. Running digital igntion without vacuum-source is useless.
You'll learn that the 'initial'-value is only used once, and that's during startup. Right after the engine starts it will use other cells in the table and never reach that 'initial'-value anymore.

You'll usually want 'more' timing at idle to keep the engine from running hotter. That's the 'vacuum advance connected at intake manifold'-part.
More idle timing = cooler running engine. Find the cell that your engine idles in and change the number up or down to find out what the engine likes.
I've tuned it for best engine vacuum and steady idle. I have the advantage of also being able to test what the engine liked with the transmission in Drive.
For an even more steady idle, make sure the surrounding cells around the idle-cell are the same, so the engine doesn't get nervous after a small disturbance in idle-speed or vacuum.

As for the curve itself, you'll have to find out what your engine likes best, and 'slowly' creep up to the max. advance limit of the fuel.
As a start you could look at the ignition curves shown at MSD.
A linear curve should work fine as a start, but more power can be found by say doing a 'quick' advance as mentioned earlier.

[408swinger]

I realized I had the timing @ idle vs heat backwards as I hit enter...
I am just looking for some feedback for an intial curve from people who can wrap there heads around the variables better than I can.
Would you disagree with the opinion of MAP sensors not reading vacuum efficiently ? Obviously you run one with a Megasquirt system.
Also.. what about running more timing at idle then dropping it out just off idle upto around 1600 rpms to prevent bucking with the 4sp at very low speeds ?

[FC-Pilot]

Take my words with a grain (or the whole shaker if you prefer) of salt as I am not an engine expert, but my profession is in vehicle testing and instrumentation. As far as a MAP being "off", the bigger question is "from what"? MAP sensors are not as accurate as a high end pressure transducer, but then again the installation (in my opinion) will be the bigger factor than the instrument itself. I can't say there is a perfect position to install either of them, but at least having it gives you something to work with in spite of its imperfections. Having said all that,what ever you use, as you tune it, you are tuning it to your specific instrument as well as your installation. At that point it will be right for your application, regardless of its imperfections or limitations.

Paul

[andyf]

I realized I had the timing @ idle vs heat backwards as I hit enter...
I am just looking for some feedback for an intial curve from people who can wrap there heads around the variables better than I can.
Would you disagree with the opinion of MAP sensors not reading vacuum efficiently ? Obviously you run one with a Megasquirt system.
Also.. what about running more timing at idle then dropping it out just off idle upto around 1600 rpms to prevent bucking with the 4sp at very low speeds ?

Why wouldn't a MAP sensor read vacuum correctly? There are millions of cars on the road with MAP sensors, that is what everything has used for the past 20+ years. The nice thing about a digital curve is that it is easy to change. So just start with a basic curve and then drive the car and see how it works.

[peejay]

MAP sensors are precise enough that any discrepancy gets lost in the noise.

There's no sense being concerned over the sensor reading 56.3kpa when manifold pressure is actually 56.5kpa if the controller has an 8 bit DAC so it can only tell differences of .4kpa anyway... and then we're tuning by-guess-and-by-gosh so there is no sense in having super high precision in the first place.

Plus the manifold pressure itself fluctuates so much, even with a large plenum, that you either need to use signal smoothing, or some sort of mechanical damping to the sensor.

Measure with micrometer, mark with chalk, cut with sledgehammer?

[408swinger]

I realized I had the timing @ idle vs heat backwards as I hit enter...
I am just looking for some feedback for an intial curve from people who can wrap there heads around the variables better than I can.
Would you disagree with the opinion of MAP sensors not reading vacuum efficiently ? Obviously you run one with a Megasquirt system.
Also.. what about running more timing at idle then dropping it out just off idle upto around 1600 rpms to prevent bucking with the 4sp at very low speeds ?

Why wouldn't a MAP sensor read vacuum correctly? There are millions of cars on the road with MAP sensors, that is what everything has used for the past 20+ years. The nice thing about a digital curve is that it is easy to change. So just start with a basic curve and then drive the car and see how it works.

I dont know why a MAP sensor would be less accurate... its just what I was told. 2 guys at ignition companies told me I was better off using the vacuum advance on the distibutor instead of trying to create a 3D curve digitally . As I understood them it had something to do with how fast they react ???

Input on baseline curve is what I am looking for. I will tweek it from there. I have less experience with tuning than most (or all..) of you guys and was hoping for insight into it.
For instance does a curve always have to be linear and upwards ?