Correct, completely stock distributors, you'll both get to the same place. The 69 Distributor will be at 19-23* @ 1800 RPM, and so will the Stage1 distributor, 10* initial + 9-13* mechanical. Then, 30-34* @ 4600 RPM.
I looked around before I'm asking this question and could not find the answer- What should the initial timing be on a 70 350 ?
Unless I am doing something wrong; using a digital timing light it is 25* with the vacuum hose plugged. It is a unknown HEI .
Impossible to answer that in 2024. Why? Because the car you are asking about is now 54 years old, and the specs below only apply if it has the factory installed distributors, #1111986, or 1112006. What are the chances of that? Unless you have owned the car from new, and know for sure, chances are the distributor and other engine components have been changed. Different distributor? The specs below go right out the window. Same answer, unknown HEI, unknown specs unless you can get a part number and look it up in a Buick Chassis Manual. It could have still been modified in the past. HEI's typically had too much mechanical advance built in, and they didn't allow maximum advance until at least 4000 RPM. You may not be revving it high enough to see all the mechanical advance. Changing the springs to the lightest available springs will let you see all the mechanical advance at low RPM.
Thank you for your help. I will order some lighter springs. I am going to reread your tuning thread - do you suggest an adjustable vacuum advance as well? The on the the distributor looks very old; since I have it apart....
You'll only need an adjustable vacuum advance if you intend to bring the mechanical advance in much earlier. You can modify a stock vacuum advance if you like. Everything is in that first post of the thread.
If I understand correctly , the purpose of lighter springs is to bring the advance in earlier. Does the vaccum advance aid in increasing the advance rate ?
Vacuum advance operates on engine vacuum. At light throttle/load, engine vacuum is high. At high load, vacuum is low, and at wide open throttle (WOT), vacuum is at or near zero. The vacuum advance canister has a spring that opposes vacuum pull. To advance the timing, engine vacuum must overcome spring pressure. The vacuum advance is a load compensating device. At light loads/cruise, the engine can tolerate more ignition advance, and that results in better fuel economy. At high load/WOT, vacuum drops and the canister spring wins out pulling out any advance that the canister generated. The mechanical and vacuum advance operate independent of one another. All of this is in the very first post of the Power Timing thread.
Larry, in this post you mentioned initial timing tells you nothing only when sitting at a traffic light at idle. Today i set my initial to 10 btdc to see what the difference is over 2 btdc. At part throttle it felt somewhat smoother and my very small exhaust manifold leak seemed less noticable at light load/part throttle. So setting a more advanced initial will make a difference at part throttle right? So there is more to it than just at idle? Thanks
You're missing my point entirely. When asked what their timing is, a lot of guys will tell you the initial timing, and nothing else. That tells me nothing but the initial timing. It doesn't tell me anything about the distributor being used, the amount of mechanical advance in that distributor, and at what RPM it is all in. If you ask them that, they don't know. In that case, initial timing really is meaningless without the rest of that information. The only time the engine runs at initial timing is when you are sitting at a traffic light stopped. As soon as you open the throttle, ignition timing changes.
I understand. I was referring to my own stock timing set up of which i changed to 10 btdc and adjusted air/fuel setting on the carb to feel what the difference is.
10deg initial (w/o vac advance) on a 69 430 is way too much unless total advance has been limited. It may feel better at low speeds and part throttle but it will likely have a death rattle at full throttle from too much timing.
Exactly. I did not go full throttle though. Also i wondered if it could hurt the engine cruising at highway speeds? I adjusted it back to 4 btdc instead of 2 btdc which i was running. Also why is initial a factory spec at 0 TDC? I mean 2 or 4 btdc feels better
The factory wasn't tuning engines for max performance. A Riviera was a luxury car. Buick tuned it for fuel mileage and smoothness. You want to know if your tune is good- look at the plugs. The spark plugs will tell you all you need to know about it. If your engine is running good, there's no detonation and the plugs have good color, then your fine Give the engine what it wants
The 67-69 430 relied on manifold vacuum advance at idle making timing close to 20deg at idle. That's why spec is 0-2.5 deg. With vacuum advance at idle they idled better than 70-72 455s that ran no vac adv at idle for only 8-10deg at idle.
If your on the highway and the engine isn't surging or running lean, your good. I would highly recommend seeing what the air fuel ratio is at idle and cruise.
It runs both good at 0 TDC or 2 BTDC but you feel it can do better (with just a bit of part throttle you notice that). Now at 4 BTDC it is just great. It is even smoother and with just a little bit of part throttle you notice the engine is more alive but quieter. I have a very slight passenger side exhaust leak which i can now accelerate with (part throttle) without hearing it because it is smoother.
