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#1
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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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'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#2
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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. |
#3
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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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'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#4
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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 |
#5
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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. |
#6
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Quote:
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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'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
The Following User Says Thank You to Fishin2Deep4U For This Useful Post: | ||
#7
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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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'65 Tempest 467 3650# 11.30@120.31 Last edited by Scott65; 10-18-2020 at 03:03 PM. Reason: Addition |
#8
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Quote:
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 |
#9
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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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'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#10
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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. .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#11
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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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. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#12
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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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'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#13
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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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. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#14
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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 .
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#15
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What system are you using?
My buddy just went with Holley and it was fairly intuitive.
__________________
'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#16
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Using a Dominator ECU, the software those screen shots came from is the Holley v5 software.
.
__________________
. 1970 GTO Judge Tribute Pro-Tour Project 535 IA2 http://forums.maxperformanceinc.com/...d.php?t=760624 1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car https://forums.maxperformanceinc.com...ght=procharger Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be |
#17
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Hard to tell on my little phone screen.
Dave
__________________
'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
#18
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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
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That looks to be a good resource.
Thank you. Dave
__________________
'68 Bird Vert, 455 , 6x-8, 1.5 HS, HEI, PPR TC-02-HF, TH400, 2500 Hughes, 2.56 8.2 (getting swapped for second gen with shorter gears) Fishing guide in the Washington state for Salmon, Steelhead and Sturgeon. Fish-On! |
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