Revised Base Timing Table Generator Tool

[GPatrick]

I was working with 63 Bomb OHC on a Base Timing Table project and was attempting to duplicate the settings from the factory manual. While I could get it close, I found that with some slight modifications it was a little easier for me to use. I take no credit for the calculations performed in the Excel spreadsheet, they work quite well as originally designed.
Revised EFI Timing Table Generator.zip

I changed the following:
Enter the initial timing (equivalent of engine at idle with no vacuum).
Enter the total mechanical advance of the distributor.
A new value of mechanical plus initial is now displayed and is the WOT value.

The vacuum advance portion is unchanged. Note that in the GM manual that we were using, it provided the total vacuum advance and it also provided the start vacuum and the all-in vacuum values. Using the calculator the vacuum advance starts at five inches of vacuum which converts to 84 kPa, for example.

The table axes did not match what we wanted to use for MAP or RPM in the Config File. You can now enter these values to match your Config File. The axes spacing is uniform, but if you manually adjust values after setting the range the calculations will still be correct.

The Excel spreadsheet currently only supports N/A applications. It will add timing for increasing vacuum and has no provision to retard on boost. I believe there are some tools on the web that can do this.

I also added two columns for psi and inHg next to the MAP kPa axis. These are approximate values for relative comparisons. Here are the revised parameter entries:
Initial Timing 10°
Mechanical Advance
Total Mechanical 22°
Mech plus Init 32° (Calculated, do not enter.)
Start RPM 1000
Peak RPM 3000
Vacuum Advance
Total Desired 10°
MAP Start 84
MAP End 52

Vacuum Conversion
Vac inHg 5
MAP kPa 84

Table MAX kPa 105
Table MIN kPa 20

Table MIN RPM 500
Table MAX RPM 5500

To see how the table works, enter zero for the total desired vacuum. You'll see that advance will start at 1000, for example, and it will be all-in at 3000 if you use the values above. Next, enter zero for initial and mechanical and you'll see the vacuum advance contribution. Changing the start and end MAP values will raise, lower, widen, or narrow the vacuum advance range. A wild cam with low idle vacuum may require a higher initial timing value and/or a higher start MAP value, for example.

[63 bomb ohc]

@GPatrick: I'd like to send a huge thank you your way for the changes you made to the Base Timing Table generator. With the additions, it really makes sense to me now coming from a mechanical timing world.

[GPatrick]

You're welcome. You mentioned in the other thread that you had some more timing changes to make. Send me your Config File when you're done so I can see what else you had to do. Now I have to figure out how to make it handle boost.

[Hjackson3149]

Good afternoon all. GPatrick, I was checking this out and have a question, I must be missing something. When I open it the sheet comes up with kPa set to 20 on the bottom and 105 at the top. When I fill it out the base timing, in my case 18°, is at the at 105 kPa, not at the bottom at 20 kPa. It's upside down. What am I missing? Hank

[GPatrick]

Look at the inHg scale instead of the kPa. The base is a 105 kPa because this is the base mechanical timing with no vacuum. The kPa is essentially a pressure scale versus a vacuum scale. The maximum vacuum that the MAP sensor in the Sniper can read is 20 kPa which correlates to 24.7 inHg of vacuum. So if you add a vacuum advance equivalent it would start, for example, at 80 kPa and then perhaps reach its maximum advance at 50 kPa. These would correlate to 5 inches of vacuum to start and reach its maximum at 15.3 inches of vacuum. I had to force myself to think in kPa and when you factor in some applications with boost it started to make more sense to me. If you are at low RPM, for example, and press the accelerator pedal, the vacuum will drop (higher kPa) and the timing will back off from the idle setting. If you look at the 105 kPa row you'll see the base timing and then with basic settings the mechanical advance will kick in at 1000 and reach its peak at 3000 with no advance, the WOT condition.

The lower right quadrant of the Base Timing Table uses the same mechanical advance plus an equivalent in distributor terms of vacuum advance. So, instead of 35° at WOT at 105 kPa, the advance might be 41° at the same RPM in the cruise area. Hope that makes sense.

[Hjackson3149]

Good afternoon all. GPatrick, thank you for that explanation. After reading it a bunch more times the light bulb should come on. Do have somewhat better idea and will give it a try. Should use some suggestions on what settings to start with for a stock low HP GM 6 cylinder. If you have any again, thanks for all you do for the group. Hank

[GPatrick]

Recently I worked with someone with a OHC 6 cylinder to try to mimic the factory timing specs. He was able to go through the service manuals for his engine application and find the distributor timing settings. These are a good starting point. The manuals will provide both the mechanical and vacuum settings. The only potential confusion is that many of the specs are based on distributor angles and speeds and not engine speeds. For example, you may see a spec that shows the mechanical advance starts at 450 RPM and reaches a max at 1800. This translates to a mechanical advance that starts at 900 and ends at 3600 RPM of the engine. Some of the specs also show the vacuum advance in distributor degrees. 5° advance at the distributor again translates to 10° of advance at the engine. Most distributor test machines measure distributor speed hence the related specs. If you can find your factory timing specs post them here and we can help you enter the correct parameters for the spreadsheet.

You should note that the factory specs were pretty conservative to cover a range of fuels, drivers, and altitudes and also were designed to help meet some emissions requirements. You can often improve performance/driveability with more idle timing and a faster mechanical advance. The beauty of computer controlled timing is that you can create five different timing setups, save them uniquely, and test them to see how the engine responds as you load each file.

[Hjackson3149]

Good evening all. GPatrick, see attached and let me know if this is what you're talking about. Hank

[GPatrick]

I'll take a look and give you some parameters to use for the Excel spreadsheet in the AM. What's your redline? I like to set the RPM axis to about 250 to 500 RPM above redline. You'd use the same RPM values for the fuel and timing tables. It sure seems to want a lot of vacuum advance. I'll give you several variations to see how it reacts.

[Hjackson3149]

GPatrick, redline is 4500, so I have it set 5000. The chance of it seeing 5000 is very little to none. Thank you very much for your assistance. Hank

[63 bomb ohc]

I'd try these settings to start with:
Initial Timing 18°
Mechanical Advance
Total Mechanical 16°
Mech plus Init 34°
Start RPM 1000
Peak RPM 3200
Vacuum Advance
Total Desired 23°
MAP Start 77
MAP End 50

Vacuum Conversion
InHg 15
MAP 50

Table MAX kPa 105
Table MIN kPa 20

Table MIN RPM 500
Table MAX RPM 5000

However, this is going to have the engine idling at 41° which it may not like very well. I ended up modifying the setup that GPatrick helped me with, and Advanced ICF Table that knocks out the "Vacuum" advance portion of the table at anything less than 2% throttle. That way it acts more like the original vacuum advance did with the stock distributor. It's much happier with those settings than it was before.

[Danny Cabral]

Just for reference, for those who want to use the full "2D Table" type Base Timing Table (not the "Simple" type with only Idle, Cruise & WOT entries):

Originally Posted by Danny Cabral The Target Air/Fuel Ratio Table & Base Fuel/Timing Table (and MAP kPa & RPM axes/scales) should be configured using the Sniper EFI software: In the Sniper EFI software (LINK), Target Air/Fuel Ratio Table (Fuel ICF) & Base Timing Table (Spark ICF), select "2D Table" Type (not "Simple"). The Target Air/Fuel Ratio Table & Base Timing Table can then be properly configured & tuned for any engine. I always suggest taking notes of your current distributor's ignition timing specs/curves beforehand, and then program the Base Timing Table accordingly. https://www.holley.com/support/resou...Fuel_Injection (Sniper EFI Software & Holley 558-443 CAN/USB Dongle) https://forums.holley.com/showthread...679#post100679 (Sniper EFI Optional Comm/Data Cable Accessories) https://www.efisystempro.com/efi-pro...timing-control (EFISystemPro.com - ECU Timing Control, From Simple To 2D Table)