Hi all,
As promised, here is the timing curve Performance Distributors put on my distributor.
I figure this will be helpful since, even though I've done a few performance upgrades to my engine, it is still relatively stock. If your specs are similar to mine (which I imagine most are), this is the timing curve DUI would send your way.

Also, these are the ONLY things they take into consideration. If you have oversized
valves, different gearing, different tires, etc. etc. it doesn't seem to matter since they don't even take it into account.

These are the questions they asked me and this is what I put down:

Year, Make, Model: 1981 Ford Bronco
Weight of Vehicle: 4500
Towing? No
Engine Make/size: Ford 300
Compression Ratio: 8.5 (stock)
Carburetion: 4bbl
CFM: 465

These are the stock cam specs, which I still have in my engine:

Cam Duration @ 0.050" 192
Valve Lift: .395"
Transmission: manual
Max RPM: 4500
Fuel Type?: Regular
Additive? No



Timing Curve:
Base 12*

<b>Mechanical Advance</b>
*Note that these all include the base 12* timing.
<table border="1">
<tr><td>RPM</td><td>Timing</td><td>Total</td></tr><tr><td>500</td><td>0</td><td>12</td></tr><tr><td>750</td><td>2</td><td>14</td></tr><tr><td>1000</td><td>6</td><td>18</td></tr><tr><td>1250</td><td>10</td><td>22</td></tr><tr><td>1500</td><td>13</td><td>25</td></tr><tr><td>1750</td><td>15</td><td>27</td></tr><tr><td>2000</td><td>17</td><td>29</td></tr><tr><td>2250</td><td>18</td><td>30</td></tr><tr><td>2500</td><td>20</td><td>32</td></tr><tr><td>2750</td><td>22</td><td>34</td></tr><tr><td>3000+</td><td>22</td><td>34</td></tr>
</table>

<b>Vacuum Advance</b>
<table border="1">
<tr><td>Vacuum</td><td>Extra Timing</td></tr><tr><td>0</td><td>0</td></tr><tr><td>1</td><td>0</td></tr><tr><td>2</td><td>0</td></tr><tr><td>3</td><td>0</td></tr><tr><td>4</td><td>0</td></tr><tr><td>5</td><td>0</td></tr><tr><td>6</td><td>0</td></tr><tr><td>7</td><td>0</td></tr><tr><td>8</td><td>0</td></tr><tr><td>9</td><td>1</td></tr><tr><td>10</td><td>5</td></tr><tr><td>11</td><td>7</td></tr><tr><td>12</td><td>11</td></tr><tr><td>13+</td><td>14</td></tr>
</table>


So, when I'm driving down the interstate at 65mph, my RPMs are 2150. I'm usually pulling around 10hg of vacuum. 2150 = 30* and 10hg = 5* for 35* of total timing.

 

So I assume the mechanical advance table also includes the 12* initial advance, and the 10 hg. signal you are measuring is the distributor hose vacuum, be it ported signal or direct manifold vacuum signal.

Is 'valve lift' lobe lift?

I would be curious to know if the secondaries on your 4V have started to open at 65 mph Road Load? With 10" vacuum I'm guessing no.

 

Yes on the mechanical advance including base timing (and I added a note).


Hrmm...
Yes, that's the number I gave them for valve lift, since that's what I saw when I looked up the specs. Lobe lift isn't the same as valve lift though, is it? If the lobe is 0.249" and the rockers are a 1.6 ratio, that'd put the valves at .398" (.249 * 1.6).
Yikes, I'll write them and ask them how much difference that would make.

 

Okay, so I heard back from Performance Distributors. Fortunately, they figured I gave them the wrong number and that the rocker ratio wasn't taken into account. As such, he looked up the stock specs and curved it for 0.395" valve lift. I updated my original post.

 

The Performance Distributors Duraspark unit I bought from Summit came calibrated for 22° advance at 3,000 rpm, so that must be their default for the Ford 300. Makes sense since a 300 will almost surely be in a truck vs. a SBC which could be in anything from a Corvette to a Suburban.

 

That's gotta be an 11 slot right? Distributor degrees are half of crank timing degrees.

 

Not sure on the slot. I haven't opened up the distributor. I should, and see what's in there.

Baron, how do you know how it was calibrated? Was it marked/written somewhere? I received very little to no information with my distributor aside from installation instructions.

 

It had an ID number and the calibration specs written at the top of the installation instructions. I haven't verified, just checked the static timing at idle.

 

Its probably a good time for somebody to point out that if a head from an EFI engine is used then a lot less spark advance is required.

 

I wonder if that would have normally been taken into account if you filled in your specs while ordering one and put "EFI" instead of "4BBL".

 

Maybe if you said carb they assumed you had a carbed head.
If you said EFI they may have assumed you were using the EFI head.

We hope.

 

Heh, I would definitely hope so.

I was more so meaning, I wonder if they take into account carbureted vs. EFI when designing their timing curves.

On that matter, I wonder why the ask 1, 2, or 4bbl. Why would the number of barrels matter when designing a timing curve?

 

EFI distributors don't use mechanical or vacuum advance, the timing is controlled by the EEC/TFI module.

 

Doesn't mean you couldn't swap it out for a DUI if you were so inclined.

The dropdown menu does say "Fuel Injection". I know I've read builds where people use the MegaSquirt for the fuel injection but still have a vacuum controlled distributor.

Either way, my only point was if one did have the EFI head and wanted to take it into account, that was about the only thing in their questionnaire that remotely had to do with it. Otherwise, there wasn't anything that would be answered differently.

 

Is there a place on the application for 'Additional Comments'? If so, there is the place to do it. If not, one can call ahead of time and 'cuss and discuss it with them...