Thanks a bunch for diagram. And I assume timing light is always attached to number one plug?

Well, technically can also connect a timing light to no. 4 cylinder, companion to no. 1. Timing will be the same.

Sherwood

Just to follow up on my original question, I was able to set my idle advance @ 8 BTDC, which is almost where it was when I had a 35 degree dwell with points with the vac line plugged. I then revved the engine and got a final advance right on the mark cut into the pulley so I think I'm there. I also leaned the mix slightly, which gave me a smoother idle.

I'll road test it a few days and check the plugs, but I think I'm going to like it.

This kind of tuning and finessing get's me all tingly in the feel goods!

Hope you are enjoying the process, I know I did :)

Paul,

With the specs you described I would set my timing at 4000 rpm to 28 degrees BTDC and the CO level at 1.5% to 2%.
I believe you will see between 7 and 8 degrees at idle after that and feel all the performance teh car has to give. You could go 30 even 32 but it will not give you anything.

This of course assumes you have a timing light with jog wheel. Or you could put a paintmark on the pulley right of TDC. 1mm is 1 degree for this engine.

Vereeken,

I duplicated the setup I had when there were points in the distributor. I just now measured the marks scribed into the pulley. At idle I'm about 3 or 4 to the right of the 5 BTDC , which translates to 35 or 36 degrees dwell angle. I get full advance right on the far mark, which measures out at 34 mm or 34 BTDC.

I don't know exactly how the modifications made to my engine and distributor affect things but I know that I am now at the same settings that I had when I ran points for the last 31 years. I also found that the engine does not seem to like to be retarded further than 8 or 9 BTDC, with the vac retard removed, which BTW translates to about 0 or 1 ATDC with the vacuum attached.

Now I just need a long overdue valve adjustment to further smooth out the idle.
Thanks for your help.

911SauCy,

Yes, enjoying it, but a little anxious over the changes considering what I didn't know about my particular engine.

Paul, I have the same observation. With the vac plugged the car seems to need th proper advance to get a smooth idle and good cold start.

FYI. Without traditional breaker points, using dwell angle as a reference point isn't needed. Use a timing light to observe the ignition timing, then rotate the distributor housing to adjust the base idle setting. And for good measure, mark the crank at the factory spec, then rev the engine briefly to 5000 rpm to measure/confirm max. ignition advance.

Sherwood

I hear you Sherwood. You are absolutely right under normal circumstances.

I think you may have missed what I did and why, however.

I actually did exactly what you described except, since the engine isn't stock and I knew what settings worked for me for 31 years (and which may or may not have been the stock settings) I first noted what advance numbers I had when the points were newly installed. Then I set the distributor with the ignitor as you described to replicate those numbers. At idle, it is now where it was and at full advance it is now where it was. I didn't want to just rely on the factory spec since the engine and distributor have both been modified and I didn't know if those mods resulted in a different timing spec, but I had the added advantage of knowing what settings were achieved over the past 31 years to give best performance.

If my distributor and engine were stock I would have followed the procedure you described.

Since I'm dealing with mods, I decided to go back to what I knew worked for all that time and see if I could achieve the same results, which I did. Turns out, with the recurved distributor I get more initial advance than stock at idle and get 32 degrees of total sooner, so I'm glad I made note of what I previously had.

Paul,

What Sherwood is referring to, and it’s confused me too, is you keep mentioning the dwell angle and timing together. I set my dwell angle with the distributor out of the car and clamped in my bench vice. Then I reinstall it and set my timing. Once the dwell is set, I don’t worry about it any more.

I want to jump back in since I’m a masochist 🙂

Dwell angle, as it relates to distributor breaker points, is the number of degrees the distributor shaft rotates while the points are closed (related to point gap). And the relationship is that since the distributor rotates at 1/2 the speed of the crankshaft, 1 degree of point dwell change is 2 degrees of crank rotation timing.

If that helps anyone set ignition timing, more power to you. IMHO, it’s much easier to use a timing light with or without points.

OK thanks guys. No problem. LOL.

You are both right of course and I agree with what you are saying. P911's description is correct and Walter's method of setting dwell and timing is what most people do, including me when using points.

What I'm talking about is something different. I'll try to explain. It has to do with switching over from points to ignitor on a modded engine and distributor and not knowing if the mods had an effect on my timing settings. How would I? Why would I just assume the factory specs would be perfect for my engine and distributor? Maybe they were and maybe they weren't.

I think what is confusing to you is that, since I wasn't sure if the mods made to my engine and distributor would affect my timing settings I didn't want to just rely on using the pulley marks and factory specs. So I checked what my timing and advance were when I used to have points and recorded what I got when I had them set at 35 or 36 degrees. This gave me the timing and advance settings that have worked for my engine for the last 31 years with the mods that I have.

I then set the timing with the light in the conventional way to these settings and found that, indeed, they were slightly different from factory.

I'm in no way saying that 36 degrees of dwell directly translates to any particular timing on anyone else's car. I'm simply saying that, since I knew what worked on the engine and distributor I have I wanted to replicate it. And by noting what they were I was able to set things up to match. When I said that 35 or 36 translated to 8 or 9 BTDC I meant that, when using points set at that dwell, that's the initial advance I got as measured.

So that's all. If you read above I think you will see that I'm in full agreement with all your statements. My method proved to be worthwhile to me because, as I said, the idle setting and advance curve did turn out to be slightly different from spec and now I have them set, forever, to what worked best on my engine.

Got it? It all has to do with not knowing if the factory specs would work with the mods I had, or if they could be improved upon, and, as it turns out, the mods did have an effect, which I was able to replicate only by knowing what they were in the first place. It might have been a bit of a belt and suspenders approach but this way I know I have the same settings that worked so well all that time with the points.

I have done some further testing and running.

With my initial timing @ idle set @ 8-9 BTDC without vacuum retard I find I get total advance that matches exactly to a notch filed onto the pulley by someone else, probably either the initial engine builder or the installer. Measuring this out I find that is 29-30 degrees BTDC. I have been using this setting so far this spring and things seem good. Starting, warmup, idle and acceleration are all very good, as are engine temps so I'm going to stay with this setup for now.

BTW when I plugged the vacuum line back into the retard unit as a test, the timing went to 4 ATDC, so that means my vacuum can provides 15 degrees of retardation. This is with a recurved 74-77 distributor and a 1980 engine with 98mm pistons and 10.3:1 CR running on 93 or 94 pump gas.