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Old 10-16-2020, 08:04 PM
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Default Optimum timing curves

Okay guys, I know this is a loaded question and subject to interpretation. But how do we obtain the "optimum" timing curve for all RPM and load conditions?

I have converted to MegaSquirt, current using an HEI allowing the springs, weights and vacuum advance to do their thing. But, I am going to swap to LS truck coils, so I will be able to dial in the spark curve any way I want it.

I would think a load dyno sweeping through from closed to WOT at a braked RPM would be the most efficient. So you can see power changes based on individual cells within an RPM range at at a sweep in vacuum. However, this isn't practical. So, Other than starting with a working dizzy setup, in my case 14 initial, 20 mechanical by 3500 with another 8 (16 crank degrees) from vacuum, how do we make it better?

My load dyno at work won't work for chassis use. So that's out.

Any bright ideas? Not a track car, definitely a driver. Not chasing every last drop of power, but want the low hanging fruit. The car could use a little more vacuum advance. And the fuel curve will be changing a little as I am going sequential. So, I'll be pulling some fuel off the bottom.

455
9.7:1
6X-8 heads. crossovers filled, 1.77 exhaust, just port matched and cleaned up.
284/292, 236/244@ .050", .510"/.505" @ 1.5 112CL

I can add a knock sensor, but I have not spent the time to figure out the proper frequencies and may just be a bigger bag of cats.

Other than listen for knock, read my plugs, ect. Any tips?

Thanks!

Dave

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Old 10-16-2020, 08:21 PM
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Data logging, engine RPM vs driveshaft RPM. Then spend many hours over the data and fine tuning.

If you have a few thousand play money - tfxengine.com
I don't know if MegaSquirt allows you to control spark timing for every cylinder. Different cylinders will prefer different timing.
The resolution of TFX will tell you if a cylinder is getting into detonation.

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Old 10-16-2020, 11:22 PM
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Data logging is easy.

But I am not too concerned about individual cylinder trims for timing. It would be possible to run 8 get probes. But again, overkill for my application

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Old 10-18-2020, 04:36 AM
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Not sure this would work for you ,but the MSD 6AL-2 programmable box is all controlled digitally for a timing curve. Has a few trigger options. It has provisions for a Map sensor. You lock out your distributor and plot a timing and rpm curve in the software and send to the box.

Charles

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Old 10-18-2020, 08:51 AM
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Here's a "bookend" approach;

Pick the Total ADV (say 34* at 3000 for iron heads), no Vac hose.
Pick the IDLE ADV (say 15* at 1000), no vac hose.

Fine tune carb at idle, in gear, for peak Vacuum. Richen mix,then drop plates: pick your taste.

Experimenting with different timing change rates with coarse, medium, fine spring for strong conviction for coarse spring).

Rest assured that Total ADV is tuned underload at the track for best MPH. Set it and forget it, and focus on mixture.

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Old 10-18-2020, 02:21 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
Here's a "bookend" approach;

Pick the Total ADV (say 34* at 3000 for iron heads), no Vac hose.
Pick the IDLE ADV (say 15* at 1000), no vac hose.

Fine tune carb at idle, in gear, for peak Vacuum. Richen mix,then drop plates: pick your taste.

Experimenting with different timing change rates with coarse, medium, fine spring for strong conviction for coarse spring).

Rest assured that Total ADV is tuned underload at the track for best MPH. Set it and forget it, and focus on mixture.
That’s kind of where I am currently at. I have heard that I should get all the timing in by peak torque. However, I don’t know where that’s at as I never dyno’d the engine before installation. My all in timing is at 3200 currently.

Although I know many prefer to use ported vacuum, in my setup, I had to use manifold. This gave crisp starts and allowed for enough idle timing to significantly cool the water temp. This also allowed for more swing in the mechanical timing curve which worked better for the factory weights and springs I had available.

Now all that said, it’s a pretty easy job to move all the current dizzy timing to my tables. Mechanical advance is pretty simple. It’s the vacuum advance at various points of load I struggle with. Does anyone know what the “correct” vacuum advance values should even be for a mild combo like mine? My current vac can is what was on the HEI and I can’t help thinking it’s better suited to a smog era 70’s car than slightly stronger pre emissions vehicle.

In the end, it will take some testing. I know that. Just trying to get as close as possible out of the gate and try to overcome any perceived mechanical limitations of the distributor. I’ll have full control over sequential spark timing soon enough.

Dave

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Old 10-18-2020, 02:53 PM
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I would (and did) start out where I was with a distributor. Add the low load advance a little at a time trial and error. I don't think without a chassis dyno you can avoid the trial and error part if you're looking for absolute optimum.
The main "distributor deficiency" you can see some benefit from is idle. You can play with idle advance watching load and temperature and if its beneficial run more advance at idle with much more consistency than a vacuum advance set up.

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Old 10-18-2020, 08:43 PM
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Quote:
Originally Posted by Scott65 View Post
I would (and did) start out where I was with a distributor. Add the low load advance a little at a time trial and error. I don't think without a chassis dyno you can avoid the trial and error part if you're looking for absolute optimum.
The main "distributor deficiency" you can see some benefit from is idle. You can play with idle advance watching load and temperature and if its beneficial run more advance at idle with much more consistency than a vacuum advance set up.
Something else for discussion you can add that we did quite a bit during the LS tuning days with timing tables.

We would generally pull 1 or 2 degrees out just around the peak torque areas at WOT to avoid detonation on pump gas during peak efficiency, then ramp the total timing that made best power back in. Also some engines responded on the dyno with a couple extra degrees of timing added at the higher rpm ranges, say 5,000 up where the combustion cycle is happening much faster. Really need a dyno though, or a lot of track time, to dial that in.

Things you can't do with a regular distributor really makes the EFI stuff intriguing

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Old 10-19-2020, 11:04 AM
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I appreciate the feedback.

I'll try eh dizzy baseline and try to tune it as close as I can and see if I can get it on a dyno from there.

I have done another application in a boat and we used some timing trick around idle to help stabilize low rpm operation. So, I have a good understanding of what does what, but I do agree, without a way to load test and accurately record that data, it is tough to get a good result. If I had the ability to use a knock sensor, I would just let the ecu retard the timing and dial ion that way. Get a good map and allow for the knock sensor to do it's thing on those occasions of bad fuel;, altitude, load changes, ect.

Dave

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Old 10-19-2020, 01:44 PM
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EFI timing curve is different than a non-EFI curve for a couple reasons.

But, in general, you start with something close to the existing curve of a non-controlled ignition and go from there.

Most idle numbers are more than what a non-controlled ignition are higher, for example, 16, 18, or even as high as 24-26 degrees.

A lot of times the 'curve' is not linear. Like it might increase by 2 degrees for every 500 rpm until say 2000 or 2500 RPM, and then start advancing by 4 or more degrees for every additional 500 RPM.

As a rough example, here is a curve I started with on my 535, and began tuning from there. The only way to really 'do it' is to test test test.


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Old 10-19-2020, 01:57 PM
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Here is about my 18th revision, after tuning. I have a slight amount of det around the 1600-2000 RPM range, when at very light throttle. But I'm getting much closer. This is after about 800 miles of tuning.

I started with a smaller table then went to a larger table for more granularity. I have about 11.25" of vacuum at idle (kPa @ 62).

I also changed the kPa scale to provide more granularity in the idle/light throttle ranges.


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Old 10-19-2020, 02:00 PM
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This is my feeing as well, the curve is not really linear. I appreciate the map and the response! Nice to see what is working for someone else. Although I know it won't be the same for me.

Obviously, the timing numbers are not like most would think where we have a base curve with a vacuum advance. But rather it's all rolled into one value for a given RPM and MAP value.

I may have to spend some time with a few knock sensors and see if I can find or tune one that will work well with our engines. Being HFT, I should not have tons of valve train noise. I am sure a hyd roller would be better though.

I'll talk to the engineers here and see if anyone has any experience with these sensors.

Dave

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Old 10-19-2020, 02:08 PM
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I've never seen anyone successfully retro a knock sensor to an older engine, and even the best attempts I've seen, the results were not favorable.

Shoot, even the OE knock sensor setups are not favorable, and many disable or greatly reduce their' abilities.

This setup is a solid roller, the Olds is a HYD roller. The approach is the same.

Listen for det, read plugs, and go slowly and gradually with changes. Always work on light throttle first.

On the one base settings, I started with no vacuum advance, did straight up mechanical, then added vacuum advance. It took a long time, but it's safe that way. Once you get a hang of it, it gets easier.

Also note that if you make target AFR changes, it impacts your 'curve'. Same with TPS or other enrichments.


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Old 10-19-2020, 02:11 PM
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Here is a MAP kPa - inhg - psig chart, it might help you. Just copy and save for reference:

105 kPa = +1.48 inHg = +0.72 psig
104 kPa = +1.18 inHg = +0.58 psig
103 kPa = +0.89 inHg = +0.43 psig
102 kPa = +0.59 inHg = +0.29 psig
101 kPa = +0.30 inHg = +0.14 psig
100 kPa = -0.0 inHg = -0.00 psig
99 kPa = -0.30 inHg = -0.14 psig
98 kPa = -0.59 inHg = -0.29 psig
97 kPa = -0.89 inHg = -0.43 psig
96 kPa = -1.18 inHg = -0.58 psig
95 kPa = -1.48 inHg = -0.72 psig
94 kPa = -1.78 inHg = -0.87 psig
93 kPa = -2.07 inHg = -1.01 psig
92 kPa = -2.37 inHg = -1.16 psig
91 kPa = -2.66 inHg = -1.30 psig
90 kPa = -2.96 inHg = -1.45 psig
89 kPa = -3.26 inHg = -1.59 psig
88 kPa = -3.55 inHg = -1.74 psig
87 kPa = -3.85 inHg = -1.88 psig
86 kPa = -4.14 inHg = -2.03 psig
85 kPa = -4.44 inHg = -2.17 psig
84 kPa = -4.73 inHg = -2.32 psig
83 kPa = -5.03 inHg = -2.46 psig
82 kPa = -5.33 inHg = -2.61 psig
81 kPa = -5.62 inHg = -2.75 psig
80 kPa = -5.92 inHg = -2.90 psig
79 kPa = -6.22 inHg = -3.04 psig
78 kPa = -6.51 inHg = -3.19 psig
77 kPa = -6.81 inHg = -3.33 psig
76 kPa = -7.11 inHg = -3.48 psig
75 kPa = -7.40 inHg = -3.62 psig
74 kPa = -7.70 inHg = -3.77 psig
73 kPa = -7.99 inHg = -3.91 psig
72 kPa = -8.29 inHg = -4.06 psig
71 kPa = -8.59 inHg = -4.20 psig
70 kPa = -8.88 inHg = -4.35 psig
69 kPa = -9.18 inHg = -4.49 psig
68 kPa = -9.47 inHg = -4.64 psig
67 kPa = -9.77 inHg = -4.78 psig
66 kPa = -10.07 inHg = -4.93 psig
65 kPa = -10.36 inHg = -5.07 psig
64 kPa = -10.66 inHg = -5.22 psig
63 kPa = -10.96 inHg = -5.36 psig
62 kPa = -11.25 inHg = -5.51 psig
61 kPa = -11.55 inHg = -5.65 psig
60 kPa = -11.84 inHg = -5.80 psig
59 kPa = -12.14 inHg = -5.94 psig
58 kPa = -12.44 inHg = -6.09 psig
57 kPa = -12.73 inHg = -6.23 psig
56 kPa = -13.03 inHg = -6.38 psig
55 kPa = -13.32 inHg = -6.52 psig
54 kPa = -13.62 inHg = -6.67 psig
53 kPa = -13.92 inHg = -6.81 psig
52 kPa = -14.21 inHg = -6.96 psig
51 kPa = -14.51 inHg = -7.10 psig
50 kPa = -14.80 inHg = -7.25 psig
49 kPa = -15.10 inHg = -7.39 psig
48 kPa = -15.40 inHg = -7.54 psig
47 kPa = -15.70 inHg = -7.68 psig
46 kPa = -15.99 inHg = -7.83 psig
45 kPa = -16.28 inHg = -7.97 psig
44 kPa = -16.58 inHg = -8.12 psig
43 kPa = -16.88 inHg = -8.26 psig
42 kPa = -17.17 inHg = -8.41 psig
41 kPa = -17.47 inHg = -8.55 psig
40 kPa = -17.77 inHg = -8.70 psig
39 kPa = -18.06 inHg = -8.84 psig
38 kPa = -18.36 inHg = -8.99 psig
37 kPa = -18.65 inHg = -9.13 psig
36 kPa = -18.95 inHg = -9.28 psig
35 kPa = -19.25 inHg = -9.42 psig
34 kPa = -19.54 inHg = -9.57 psig
33 kPa = -19.84 inHg = -9.71 psig
32 kPa = -20.13 inHg = -9.86 psig
31 kPa = -20.43 inHg = -10.00 psig
30 kPa = -20.73 inHg = -10.15 psig
29 kPa = -21.02 inHg = -10.29 psig
28 kPa = -21.32 inHg = -10.44 psig
27 kPa = -21.61 inHg = -10.58 psig
26 kPa = -21.91 inHg = -10.73 psig
25 kPa = -22.21 inHg = -10.87 psig
24 kPa = -22.50 inHg = -11.02 psig
23 kPa = -22.80 inHg = -11.16 psig
22 kPa = -23.09 inHg = -11.31 psig
21 kPa = -23.39 inHg = -11.45 psig
20 kPa = -23.69 inHg = -11.60 psig
19 kPa = -23.98 inHg = -11.74 psig
18 kPa = -24.28 inHg = -11.89 psig
17 kPa = -24.58 inHg = -12.03 psig
16 kPa = -24.87 inHg = -12.18 psig
15 kPa = -25.17 inHg = -12.32 psig
14 kPa = -25.46 inHg = -12.47 psig
13 kPa = -25.76 inHg = -12.61 psig
12 kPa = -26.06 inHg = -12.76 psig
11 kPa = -26.35 inHg = -12.90 psig
10 kPa = -26.65 inHg = -13.05 psig
9 kPa = -26.94 inHg = -13.19 psig
8 kPa = -27.24 inHg = -13.34 psig
7 kPa = -27.54 inHg = -13.48 psig
6 kPa = -27.83 inHg = -13.63 psig
5 kPa = -28.13 inHg = -13.77 psig
4 kPa = -28.42 inHg = -13.92 psig
3 kPa = -28.72 inHg = -14.06 psig
2 kPa = -29.02 inHg = -14.21 psig
1 kPa = -29.31 inHg = -14.35 psig
0 kPa = -29.61 inHg = -14.50 psig



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Old 10-19-2020, 03:00 PM
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What system are you using?

My buddy just went with Holley and it was fairly intuitive.

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Old 10-19-2020, 04:48 PM
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Using a Dominator ECU, the software those screen shots came from is the Holley v5 software.


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https://forums.maxperformanceinc.com...ght=procharger
Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be
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Old 10-19-2020, 05:41 PM
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Hard to tell on my little phone screen.



Dave

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Old 11-25-2020, 01:51 PM
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I recently purchased and installed the Progression Ignition HEI and am new to the whole spark advance table scene. The app software for they’re digital distributors will generate a table based on basic parameters you fill in ie. idle speed, all in rpm and timing, max. vac. adv. timing, etc.. and I’m sure it works fine but can edit the any cell in the table as you see fit.

Like yourself I want to learn and optimize the entire table and know it will take a lot of testing to get there but acquiring good information on has become somewhat challenging.

Came across this on another forum and setup a new SA table based on the math provided but have not yet road tested due to poor weather conditions, hopefully it helps you:

“Re: Spark Advance table example needed
Quote:
Trying to understand the sa tables vs actual engine excelleration vs mph at the foot pedal. Found this graph
from older thread here and compared it to my bin which is a lot different. Can there be a good/simple
reason?
Good reason, yes. Simple, no. Many variations.

Have intended to post this for a while, so your question is timely. I struggled for a long time to get a timing table that worked at all RPMs and MAP. Nothing worked well. Then a racing friend provided a tip that solved everything. It worked for me; it may not for you but will share it here. However, a warning that we'll be in the weeds because there's a lot of detail, but it's worth it and Excel makes it very easy to do. This procedure provided maximum accel at low RPMs, maximum pull to red-line, and best of all -- no knocks! But the graph of the resulting spark table is so far from the factory spark table structure it's hard to believe. All references here are to TDC advance in the spark tables.

Summary:
Determine maximum advance and all-in RPM
In 100 kPa column from upper idle RPM to all-in RPM, enter desired advance -- ramping up to the maximum advance at the all-in RPM. The difference between maximum advance and advance at idle is the "Advance Range".
In each RPM row above idle, increase advance at a linear rate in all kPa columns below 100 kPa
Determine kPa above which advance is not to exceed the maximum advance, and force to maximum advance

Details
Having determined maximum advance and all-in RPM, next determine how advance at 100 kPa is to ramp up from upper in-gear idle RPM to the all-in RPM. It can be an equal # of degrees of the Advance Range for each RPM row, x% of the Advance Range at various RPMs, etc. As an example, assume the following:

Upper in-gear idle RPM: 800
Advance at idle: 21.09*
All-in advance: 32.0*
Advance Range (idle to all-in): 10.91* (32.0* - 21.09*)
All-in RPM: 3200
Ramp of advance from upper in-gear idle RPM to all-in RPM:

800 RPM = Upper Idle
1000 RPM = 10% (1.09* of 10.91* range = 22.18* advance)
1600 RPM = 40% (4.36* of 10.91* range = 26.54* advance)
2400 RPM = 30% (3.27* of 10.91* range = 29.81* advance)
3200 RPM = 20% (2.18* of 10.91* range = 31.99* advance) [.01* rounding difference]
Evenly space advance in the intervening RPM rows.

Next at 100kPa, decrease advance x* in the RPM rows beyond the all-in RPM. Example using 2* reduction at 100kPa:

3200 32* (all-in)
3600 30*
4000 28*
4400 26*
4800 24*
WOT advance is now set.

Next, need to determine how much you want spark to increase at kPa's below 100. For example, assume you want advance to increase 0.1* per 1 kPa decrease. This is a good starting point, but can be 0.1 to 0.3 depending upon how much advance your engine can handle at the lower RPMs. Using the 22.18* advance above at 100 kPa and 1000 RPM, spark at 95kPa would be 22.68*:

100kPa - 95kPa = 5kPa
5kPa * 0.1 degree advance per kPa decrease = 0.5* advance increase
22.18* advance at 100kPa + 0.5* = 22.68* at 95kPa
Continue this process down to 20kPa for each RPM row.

Next, choose a kPa above which you don't want advance to exceed the maximum advance. This is important because can be in a RPM/kPa area before WOT that may cause knocks if advance is > maximum desired. Say that's 80 kPa. Just limit advance above 80 kPa to the maximum advance of 32* in the above example.

Change the entire Upper spark table to match the advance in the 4800 RPM row.

Now that your eyes are glazed over, the attached spreadsheet makes this easy. When completed, copy the computed advances to your spark table. As always, just have to find the maximum advance and all-in RPM the engine requires for best performance without knocks. Everything else is automatically computed providing the proper spark curve.

Here is the table in the above example and a graph. Use at your own risk!”

https://www.thirdgen.org/forums/atta...nce-table.xlsx


As mentioned use at own risk.

  #19  
Old 11-25-2020, 02:35 PM
Fishin2Deep4U's Avatar
Fishin2Deep4U Fishin2Deep4U is offline
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That looks to be a good resource.

Thank you.

Dave

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