Hi all,

I previously posted about performance upgrade priorities, and it was basically concluded I need to get my ignition system in order first. I finally got an adjustable timing light and some time to play around, and I have some questions.

First here is what I have measured (assuming my harmonic balancer's TDC mark is aligned properly with the 0 on the timing tab):

17 degrees advance at idle with vacuum hose connected.

6 degrees advance at idle with vacuum hose DISconnected (and plugged).

25 degrees advance at 2500-3000 rpm with vacuum hose DISconnected... I think the centrifugal timing is all in at that point, but I'll double check.

By my current understanding, it seems like if I add 11 more degrees by rotating the distributor, I should be at the Lars suggested value of 25+11=36 at 2500-3000 rpm, and it would put my centrifugal advance with the vacuum hose DISconnected at idle at 6+11=17, or close to the 18 he suggests at idle. First question: Is that correct?

Second question: how much of a difference do you think this will make? Huge? Noticeable? Somewhat noticeable? Of course I plan on doing it so I will eventually see for myself I guess, but was just curious what your experiences were.

Third question: is it safe to assume the TDC mark has been accurately aligned with the timing tab, or should I for sure check this?

Fourth question: Once the timing is set, does it need to be adjusted periodically, or is it pretty much good to go until you make changes to the ignition system (new cap / rotor etc)?

Thanks for all the help!

 

You forgot about the 6 degrees at idle. If you really are all in at 25 degrees, your initial will have to be 17 degrees. (17 + 19).

As for the difference, it should be between noticeable and substantial.

 

You need to clarify Are you saying you have 31* total? 6* plus the 25* at RPM? If that is the case you need to bump up initial to 10* and you will be good to go. If however you have a total of 6* +19*=25* you will need to recurve the distributor.

 

Sorry. The numbers I listed are exactly what I measure with the adjustable timing light in each of the cases. I recorded the number on the light that showed the TDC mark aligned with the zero on the timing tab.

 

First ... do not assume the mark on your damper is true TDC.

Next ... email Lars (Lars Grimsrud) for his timimg papers (excellent instructions).

 

You may need to factor in the quality of the gasoline that you're able to purchase, in the area that you live, and/or will do the most of your driving. You don't really want to be on the "ragged edge" of drivability, with the total timing advance barely keeping you out of the range of massive "pinging".

 

I think you are on the right track. Disconnect the vacuum advance and plug the hose, rev the engine up until the mechanical advance stops increasing and set the timing to 36 degrees then lock down the adjustment. Double check it, and then reconnect the vacuum hose to the distributor vacuum advance can. You might need to make a carb adjustment or two if the idle speed is way off. See how that works and then plot your next move from there.

 

You want the max mechanical advance at 35 or 36 degrees. This should happen at or before 3000 RPM. If it happens after, you need new dist springs to recurve.

The difference should be very noticeable.

Do you have Lars' papers?

 

1. Initial timing is timing with the vacuum advance disconnected and plugged. Start at 14*, 6* is for emmissions, not performance

Run the car and set your timing light to 36*. Increase your engine rpm until you see the 0 timing mark line up. That is 36* all in. It should get there between 2800 and 3000 rpm. If its there at 2500 rpm it should be fine. If it doesnt get there you need weaker springs. You can buy a distributor spring kit.

Get Lars papers from him on figuring that out or just experiment with the springs. I needed one mid and one weak from my Moroso kit.

Then check add the vacuum advance. You should get an additional 10 to 12. If you get more, then the stock plastic advance limit bushing is gone and you need to replace it with the brass one from the kit.

Lars papers explain all of this and i just did mine. You should definitely ask him for all his papers.

2. yes it'll be a noticable difference in performance

3. yes check it. Theres many ways

4. Once its set it wont change unless something fails like a bushing, vacuum leak, advance cannister, timing chain jumps or stretches after years of use, distributor advance seizes, etc.

 

It sounds like you have a pretty good understanding of what you need to achieve - probably better than I did when I started messing around with MY advance curve. Couple of comments:
First, your numbers sound like what I would expect in a stock setup. Your timing marks are probably OK, but I would confirm them to be sure. There are some good posts on this site and others on how to make and use a piston stop to confirm TDC.
Second, confirm that your centrifugal advance is, in fact, all in at 2500 rpm. You should be able to rev the engine higher without the marks moving any more.
If all this checks out, I would reset your idle setting to 15 degrees. This will give you a total centrifugal advance of 34 degrees. In my experience 36 degrees is a little too close to the edge and risks detonation under some driving conditions, or with less than ideal fuel. It also has a lot to do with the engine you have, its condition, and how it is set up.
This will give you a good starting point, and to answer your question, the difference will be huge.
From there you can start fine tuning. I think you may find you need to slow down the curve to delay full advance until 2800-3000 rpm. 2500 is a bit early. You can also probably tolerate more vacuum advance to get you in the 50-52 degrees total range. There are aftermarket vacuum canisters available that are adjustable.
Once you get comfortable playing with it you can try any number of changes. If it doesn't make things better or if the engine starts pinging, just change it back.
Good luck and have fun.

 

Thats a good point, keep increasing speed past 3000 rpm and or 36* to make sure your not getting too much. I was on my MSD distributor. It was at 36* at 1500rpm and still climbing. It was setup by a 1/4 mile guy previously.

 

one final note keep your total(initial,centrifugal and vacuum) don't exceed 52 degrees.This comes in when you are cruising and engine vacuum is high.You might have to limit your vacuum advance.

 

I checked again and it actually looks like the full centrifugal advance is in already at 2000 rpm. Is that possible or am I mis-measuring?! Basically this is the point where I see the TDC line on the harmonic balancer stop moving counterclockwise as viewed from the front of the car (if that makes sense).

 

If it already had its springs replaced with some weaker ones, yes its possible

 

You can tell if timing pointer is CLOSE by pulling either valve cover. Watch rockers on 6 or 1 as you crank engine. Exh just closing and intake just opening. Timing mark should be at zero at this point. This won't tell you if balancer is 2 or 3 degrees off, but it will tell you if it is more, like a chain off by a tooth for instance.

 

What are the repercussions of the centrifugal timing being all in too early?

 

If the springs are too weak, you'll get mechanical advance at idle, and it will "hunt". You could also get pinging at some conditions. As others have as well, I used one weak and one medium spring to dial my advance in at about 2800 RPM, and a vac advance limited to 12 degrees of advance.

Follow Lars' instructions and do it right the first time. A spring kit is maybe $10-.

 

What is the source of the pinging? Will this be very easy to hear if it happens?

 

wgre3

You might also want to consider changing your vacuum canister, depending on your engine. Mine is a stock 350/300. Lars suggested I switch from a B1 to a B26 and use his limiter plate ($14) to limit vacuum advance to about 12 degrees. The idea here, I believe, is to get all the vacuum advance in at a lower vacuum pressure, while avoiding the 52 degree maximum.
My initial is 12 degrees at idle, plugged vacuum. Total mechanical is 34. ( I use an Innova timing light. Excellent product.)
I found it an absolute MUST to run manifold vacuum, not ported!!
You will find you need to reduce your idle speed once you do these changes. Performance level improvement is substantial!! Way better mileage, runs cooler, starting is easier.

Lots of experts (not me) giving you great advice here.

Let us know how it all works out.

VERYSOON

 

Yes its possible, but it probably means someone has been in there before, or one of your springs is broken. Get a kit with a selection of springs and start experimenting. Set your initial timing at 15 degrees advanced and play with the springs until you get the desired all in by 3000. Come back and tell us how amazing the improvement is. Then you can start playing with the vacuum advance. (As Verysoon pointed out, make sure your vacuum advance is connected to manifold vacuum, not ported.)