Robbie, I really don't know how to explain it any better than I did. Your English seems pretty good, but you are clearly not understanding what I wrote. Not sure how to fix that.
I am only interested in an answer to my question. No extra info needed at this point Larry. Let's say i bought a brand new 69 riv of the showroom floor. I check initial with a timing light and i see it's at 0* TDC. Now: i turn the distributor loose with a wrench and i set initial to 4* BTDC. Would that be just fine for the engine?
I am only interested in an answer to my question. No extra info needed at this point Larry. Let's say i bought a brand new 69 riv of the showroom floor. I check initial with a timing light and i see it's at 0* TDC. Now: i turn the distributor loose with a wrench and i set initial to 4* BTDC. So no total timing check just setting initial to 4* BTDC. Would that be just fine for the engine?
Impossible for me to answer that question. You could theoretically end up with 38* of WOT ignition timing. Would that be OK? Would it be OK if the engine detonated because of that?
I am asking this just to verify that when there is stock 30*-34* in the distributor it seems that the engine might be just fine anywhere between 0* TDC initial to 4* BTDC initial without detonation.
Only thing you can do is try it and see if the engine likes it. If it detonates, adjust it back. There is always trial and error with tuning work. It's not as exact as youd like it to be
Ofcourse. I could do that. I am running manifold vacuum. Stock is connected to ported. So at part throttle i am guessing ported vacuum will start detonation earlier?
Not exactly. When the vacuum advance sees vacuum, it's going to add more advance. Total timing is initial, mechanical and vacuum advance. It's going to depend on how aggressive your mechanical timing curve is and how much advance the can is giving you On my car, I have 10 initial, 22 degrees mechanical and 14 vacuum. I've since flattened the curve a little so the mechanical comes in a little later Detonation isn't just a product of too much timing. Your air fuel ratio comes into play as well. Try adding timing to an engine running very lean. You'll find out what kind of head gaskets you have
On my 455, my air fuel ratio is 12.9-13.0 pretty much across the board- idle, cruise and wide open throttle. My engine likes it like that. If I get close to 14.0 my engine complains and runs poorly. 13.0 is smooth as silk
Make SMALL changes and test. One thing at a time. READ Larry's thread. Power timing is for stock and stock-ish cars also if you want best performance.
It's a great thread. But i do not see any advantage to bring in advance earlier than factory specs. When i drive most of the time i only gently move the accelerator pedal. And at part throttle it has lots of power too. At full throttle it really kicks in hard and a lot of power to topspeed which is far beyond 120 mph at the speedo which to be honest i do not need. Why would i want to mess with factory specs. I am sure it's a good idea for the drag strip.
10 initial/22 mechanical/14 vacuum doesn't seem right to me. Your total seems way too much. Back to factory situation: The manual says 0* TDC so my thoughts were when you adjust the fuel/air ratio too (if necessary) you can play a bit with initial and move it up to 4* BTDC. A while ago i set my points dwell exactly at 30* and i had to adjust initial too ofcourse and i set it at 2 BTDC. Although dwell used to be smaller it felt a tiny bit more agressive at part throttle. Now that dwell is exactly at 30* there is no issue with a spark plug starting to misfire which i had once in a while probably because dwell was off.
69 Buick run late timing. Zero initial. According to the service manual, your distributor has 30-34 mechanical advance. Your vacuum advance adds another 14-18. Thats 40-48 degrees . My 70 455 runs 10 degrees initial. But my distributor only gives me 20-24 degrees mechanical. Plus 14-18 vacuum. That's 40-48 degrees. We both get to the same number just different paths
Not quite. Vacuum advance needs vacuum to operate. On the stock canister, advance needs 6-8" of vacuum to start, and 16" of vacuum to max out at 14-18*. The 1969 430 Distributor may max out mechanical advance at 30-34*, but that is at 4600 RPM, and to get to that RPM most likely means large throttle angles and high load, which lowers vacuum. Additionally, the 430 Distributor has 19-23* of mechanical advance @ 1800 RPM, and that would most likely be at cruise where throttle angles are small and vacuum is high. The Stage1 Distributor gets to the same place advance wise, at the same RPM. At light load, an engine can tolerate a lot more advance for better fuel economy. 40-50* is not out of the question, but if you look at the completely stock distributors, Cruise total advance is around 40*. This is the reason you may need to reduce vacuum advance when you bring in mechanical advance much sooner, at typical cruise RPM.
Right Larry. I realize a vacuum advance needs vacuum. At cruise, your going to pretty much get max vacuum advance correct? At cruise, your also not getting max mechanical advance with a bone stock distributor with the factory weights unless you installed lighter springs. Both our distributors max out at the same rpm
This is all very academic about timing, advance and what not. Just adjust your timing and see what happens. If it detonates with the fuel that's available, just knock it back a little. It took me a while to get the tune just right on my car. Lots of trial and error. Trying this, trying that. You'll likely have to do the same
