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Old 04-30-2020, 09:52 AM   #1
Ken Henry
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Default Optimal ignition timing curve?

I've adapted an electronic fuel injection and ignition system to the stock 8ba in my 51 tudor, which now gives me the ability to set the timing to whatever I want at any vacuum level and rpm. I've read on here that timing should increase from 4* BTDC at idle speed to 20-22 at 2000 rpm and above, and that I should have ~8* of vacuum advance at cruise. How much vacuum advance should there be at idle? I had 8* entered in my table which gave an idle advance of 12*, but when I open the throttle and vacuum drops, the advance decreases to 4. Is this what I want or should there timing not depend on load at low rpm (as with a ported vacuum source)? Thanks for any input on this!


The throttle bodies of from a Ducati motorcycle and have 1 330cc/min fuel injector each below the throttle plate, controlled by a MegaSquirt system. The injectors are a little undersized so I'm in the process of upgrading to 500cc units. The ignition is a Ford distributorless (EDIS) system and works great. It runs pretty well but is bogging off idle, which got me thinking about what the timing should be doing at those speeds. Need to tune in the acceleration enrichment as well. Click one of the links below to see more photos.. Ken


51BC364D-8513-49D4-97FD-F12B13EBA294 by kenhenry_06268, on Flickr
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Old 04-30-2020, 12:14 PM   #2
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Default Re: Optimal ignition timing curve?

Pretty ingenious. I have nothing to offer but, I'm going to follow along and see how it all turns out. Good luck.
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Old 04-30-2020, 12:47 PM   #3
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Default Re: Optimal ignition timing curve?

It looks like a clever, well thought out setup. I will be waiting to see if you can get the bog out of it.
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Old 04-30-2020, 12:50 PM   #4
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Default Re: Optimal ignition timing curve?

Generally, I thought that the advance was controlled from idle to appox. 2000 RPM by mechanical means. Then the vacuum came into play.
Would be interesting to see how the system reads RPM to mimic the distributor.
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Old 04-30-2020, 03:51 PM   #5
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Default Re: Optimal ignition timing curve?

Maybe this is just an over simplification but: "Bogging off idle" on the original system was usually cured by moving the linkage to increase the amount of fuel into the carb. You mentioned: "The injectors are a little undersized so I'm in the process of upgrading to 500cc units." It would be interesting to know, once you upgrade to the 500cc units if this issue is resolved, with the additional fuel.

When you accelerate at speed, what is the response?

Last edited by Merc Cruzer; 05-01-2020 at 07:48 PM.
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Old 04-30-2020, 04:00 PM   #6
Ken Henry
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Default Re: Optimal ignition timing curve?

Thanks everyone for your encouragement! For input to the EDIS distributorless ignition system, I brazed a 36-1 toothed wheel to the crankshaft pulley and mounted a VR sensor on the timing cover. It's a 'wasted spark' system so it fires each plug once at ~TDC and after the exhaust stroke. The Megasquirt system sends a signal to the EDIS that controls the ignition timing based on load and RPM, but it's up to me what that table should look like! Ken


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Old 04-30-2020, 04:02 PM   #7
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Default Re: Optimal ignition timing curve?

Right, the bogging off idle might be more of a fuel issue. There are settings for acceleration enrichment but I just need to figure out what they should be...
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Old 04-30-2020, 04:50 PM   #8
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Default Re: Optimal ignition timing curve?

Ken,nice work! I'd give it less advance at idle...say 6-8 degrees at 550-600 rpm. Then program it to begin advancing steadily as soon as you touch the throttle...maybe 1 degree per 100 rpm increase for a starting point. It may even like it to advance a bit quicker than that at the initial hit.

Accel enrichment is absolutely needed of course,and if the above advance still results in a bog I'd richen it up on the accel setting off idle.
I'm a carb guy...but that's what I've seen that they like....


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Old 04-30-2020, 04:52 PM   #9
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Default Re: Optimal ignition timing curve?

I think your timing curves are almost spot on. Consider haw the engine runs when your driving it. At idle you have max vac adv and minimum mech adv OR 3/4 M and 8V this is giving you 12 degs adv. Whicjjis about right for idle. Now the minit you spep on the throttle you loose the vac, which is normal in a standar system. but you do not have a accelorator pump it inrichen the mixture off idle. However as the rpm increases to 2000 rpm your ignition also advances to the max 18/20. I've been dreaming of a system like this for years ans have a megsquirt system for a GM throttle body a unit I built back in the 80;s but never got to work with the original computer.
Can you read your AF as this operate??

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Old 04-30-2020, 07:25 PM   #10
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Default Re: Optimal ignition timing curve?

OK, good to know the I’m in the right timing ballpark before I work more on fuel. I have an Innovate WB O2 sensor to help me get it dialed in. I guess it makes sense that not as much advance would be needed as the mixture richens up when I first open the throttle and vacuum drops. Greater advance being needed for lean mixtures (I’m tying to idle at 14:1 AFR
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Old 04-30-2020, 07:48 PM   #11
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Default Re: Optimal ignition timing curve?

I have run our 33 with an innovate o2 sensor on. and it would never idle at that figure.it was always way too rich at the idle, even though it idled nice, eng is 260 ci with stock new 97 carb and stock 33 inlet manifold and sign system,
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Old 04-30-2020, 08:06 PM   #12
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Default Re: Optimal ignition timing curve?

I put the sensor in before the FI system and as I recall, it wanted to idle at ~13 with the original carb. It wouldn’t run well if I tried to increase AFR at idle. Might need to stick with a richer idle...
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Old 04-30-2020, 09:34 PM   #13
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Default Re: Optimal ignition timing curve?

I have an O2 sensor on my test stand, and have always seen that when I got the engine running the way I liked it, the O2 sensor was in the 10-11 range at idle. (These were not stock engines , however.)
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Old 05-01-2020, 12:00 AM   #14
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Default Re: Optimal ignition timing curve?

The AF and timing is not important at idle. Tune for cruse first, then power, and let the idle take care of it's self
Having a sysstem like this will alow you to experiment with the cruise performance,. Richard was getting well over 15 AF but had to run the advance to far ahead. With the computer you can just pick a number and see how it runs. JWL made a set of heads with a relocated spark plug to place the plug in the center of the transfer arel. This allowed for a power timplug and a much shorter flame front. You should also consider milling the heads for .045/050 Piston to head clearance. THis created a Quench around the piston which creates a turbulent combustion chamber. WE do that to all our engines. I envy you, wwish I had mine working????
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Old 05-01-2020, 02:42 AM   #15
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Default Re: Optimal ignition timing curve?

Quote:
Originally Posted by Ken Henry View Post
How much vacuum advance should there be at idle? I had 8* entered in my table which gave an idle advance of 12*, but when I open the throttle and vacuum drops, the advance decreases to 4. Is this what I want or should there timing not depend on load at low rpm (as with a ported vacuum source)? Thanks for any input on this!


51BC364D-8513-49D4-97FD-F12B13EBA294 by kenhenry_06268, on Flickr
I've built my own system for giggles, that sounds about right, but at below 100 RPM i didn't have any vacuum to retard the spark as i figured i wouldn't need any, not like i lug it that low often... (Pulls from 80 RPM though!)
I've never used the system you've got so i'm not sure if you can change it, or just live with it.
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Old 05-01-2020, 11:41 AM   #16
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Default Re: Optimal ignition timing curve?

Ditto the comments on idle below 13:1, but that is also with a carb, where the idle system is in play for a good bit above idle.

I'm running an MSD ready-to-run distributor with manifold vacuum to the advance, using a specific GM advance unit that limits vac advance to ~8 deg. Very hard to get a smooth idle with that much advance and lean idle mix.

I would point out that the Innovate O2's are not super accurate, in my experience. I've had two of them and the latest one reads almost a point (1.0) lower (richer) than the other one did, with no other changes.
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Old 05-01-2020, 06:48 PM   #17
Ol' Ron
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Default Re: Optimal ignition timing curve?

When the Vac goes to zero the AF should go to max and come off as the Vac goes up. Remember this system has no accelerator pump Yes, I'd first set it up to run in the hi14's in cruse, then work on power.
I draged my Megasquirt out of the mess in here but can't find the directions. Have to go on the internet and see if they offer any tune uo ideas. It should work OK all the new cars have them.
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