Vacuum Advance Curves for FE?

[colnago]

I know this is kind of a long shot, but does anyone have (or know of) any vacuum advance curves for a distributor on an FE engine? I found some for a 302 and a 400, but nothing for a 352/360/390.

Joseph

[Lee]

Hi Joseph,

I don't know the factory advance specs. I do know they were very conservative.

I re-curved my distributor years ago and this is what I learned from hours of researching the net.

From the factory, my 1970 F250 with a 360 had the Initial timing at 8*, the reluctor in the dissy was set on the "13" side (which meant 26* total mechanical advance) and was held with a "heavy" and a "Medium" spring. These springs did not let the full (Initial + mechanical = 34*) advance timing to be all in until well over 4000 rpm.

The goal is to have all of the timing in by 3000 rpm and not going over 36* total timing. I bought a spring set and started changing spring combinations until the mechanical was in by 3000 rpm. I bumped the Initial up to 10* at 650rpm, then with 26* mechanical = 36*. This is checked with the Vacuum advance line to the distributor disconnected and plugged. Here's my curve:

RPM Advance
1 Heavy, 1 light
1000 22*
1500 24*
2000 27*
2200 28*
2500 29*
3000 36*

As you can see I ended up with 1 heavy and 1 light spring. You need a dial back timing light and a helper to perform this but it's not hard. One person operated the gas pedal while watching the Tach and the other operated the timing light. Raise the rpm to 1000 and hold it there, adjust dial on timing light and record valve, repeat at each rpm point and record.

Hope this helps,
Lee

[colnago]

Lee,

Thanks for the info, especially the advance curve. I recurved my mechanical advance a few weeks ago, but I'm not 100% satisfied. Right now, initial is 18, with my reluctor on the 10L slot, giving me 38 degrees total. Since then, I've done a ton of reading on the 'net, so I'm looking at getting pretty radical with the old girl. This is where I'm planning to go:

- 12 degrees initial (to better match the cam)
- Filing the 10L slot to 13L, giving me total (initial plus mechanical) of 38 degrees (my other slot is 15L, which is too big)
- Making a limiter to limit my vacuum advance to 12 degrees
- Adjusting the vacuum can to start advancing at 5"Hg
- Putting the distributor vacuum on manifold vacuum, giving an idle advance of 24 degrees
- Working with the springs to give me total mechanical at 3000RPM
- Initial plus mechanical plus vacuum = 12 + 26 + 12 = 50 degrees (max when cruising on highway)

If it doesn't blow up, it should be fun! And if it doesn't work, I can always go back. The only cost is time.

Joseph

[colnago]

Lee,

I just reviewed your advance curve. I'm surprised that you have 12 degrees of mechanical at 1000RPM. I had thought this was basically where the mechanical advance should start. I think mine starts at 1500RPM. What kind of mileage are you seeing (or do you not monitor mileage)? My advance is fun to drive, but I think I can squeeze more out of her.

Joseph

[Lee]

Hi,

Truthfully, I have never checked the mileage.

I have owned the truck 18 years and in all this time have only put 50,000 miles on it. 16 years ago, I rebuilt the 360 to a 390 and I have added a Ranger Torque Splitter OD unit in front of the NP-425 so now I have 8 forward gears. Swapped the Dana 24 to a rebuilt 205. Lots of other Mods.

90% of the mileage I have put on the truck has been pulling my travel trailer into the mountains. When I first re-curved, I had the all in timing to soon and it pinged under load. A light car can get away with "all in" at 2500 rpm but not my heavy truck pulling a trailer.

I also use manifold vac for the Dissy,.... I hate to even mention the Ported vs full manifold vacuum question as folks are as passionate about it as Ford vs Chevy or Coke vs Pepsi

Lee

[colnago]

I have owned the truck 18 years and in all this time have only put 50,000 miles on it. 16 years ago, I rebuilt the 360 to a 390 and I have added a Ranger Torque Splitter OD unit in 7 of the NP-425 so now I have 8 forward gears. Swapped the Dana 24 to a rebuilt 205. Lots of other Mods.

90% of the mileage I have put on the truck has been pulling my travel trailer into the mountains. When I first re-curved, I had the all in timing to soon and it pinged under load. A light car can get away with "all in" at 2500 rpm but not my heavy truck pulling a trailer.

I also use manifold vac for the Dissy,.... I hate to even mention the Ported vs full manifold vacuum question as folks are as passionate about it as Ford vs Chevy or Coke vs Pepsi

Lee

I'm kind of on the same page as you. Currently, I have mechanical advance all in by 3,500RPM. After all, it's a truck, not a Mustang. I have to remember that when reading things on the 'net, because so much info is geared for these lightweight cars heading to the strip. I've probably read 100 posts suggesting that you don't need vacuum advance (for the strip, you don't; for the street, you do).

I know what you mean about the "ported-vs-manifold" debate. Heck, there are debates on when ported vacuum was even introduced, and why (I don't believe it was for emissions, but I'm not interested in debating it, either). I figured that I would try it, and post my results. As with everything on these trucks, you have to treat them as individuals, and people on this forum can decide for themselves what works for their application.

Keep an open mind, right? I look at your numbers, and freak. But they have served you well for 16+ years, so who am I to argue? More power to you! Just keep her on the road. Thanks for sharing.

Joseph

[Lee]

Thanks Joseph!!