Setting timing on a Vacuum advance distributor

kenfyoozed

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Plan on replacing my distributor today and want to make sure I have the proper parameters to set the timing.. '67 300 440...
Disconnect vacuum hose and plug....
1. Initial timing at 750 rpm idle = 11*
2. FSM timing at 2400rpm = 16*
I searched a post where the timing at 3500rpm should be 36*...where does this come from?

Once this is set, I reconnect the vacuum hose and check total timing again. If its above X @ 3500rpm then I should adjust the diaphragm allen screw to match the proper total timing at 3500....

Is this basically correct? If not please advise. I hope to start work on the car in a few hours. Trying to get all my ducks in a row and only one trip to the parts store....like that ever happens to me.
 

Trace 300 Hurst

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No....no.
Ignore #2. From the FSM, that's DISTRIBUTOR degrees, and will only confuse you.

Here, do this.

Set timing at idle to 10*, vac hose unplugged.
Go drive car.
Does it ping? (listen closely!)
Yes? Set initial to 5* and try again. Maybe you'll end up at 7.5*.
No? Try initial at 12*, then 14*. I'll bet it'll ping there.

You see....there's 20-24* of mechanical advance in the distributor, in crankshaft degrees, depending on the dizzy, year, engine, etc. If you set initial at 10*, the mechanical advance will gradually but fully come in at about 2500/2800 rpm and then the timing will be at 34*. 10+24. That's where the 34-36 comes from.
 

CBODY67

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Unless you have altered the engine from stock, use the FSM hot base idle speed, optimized for idle mixture and such. Do plug the ported vacuum port on the carb, where the vac advance should be hooked to, per FSM.

Adjust the hot base initial timing to FSM spec. That's ALL that is needed to do.

The 3000rpm total timing is for reference, IF you have a dial-back timing light. BUT setting timing THERE can affect the base initial timing. More of a "hot rod" thing, rather than a "stock" thing.

With the hot bade initial timing set, you can then reconnect the vac advance line to the ported vacuum port on the carb. DONE. As long as the vac advance works. If it doesn't, you'll need a new vac advance can.

It seems you are confusing several different methods of timing an engine. EACH has their purpose, but for a stock engine, use the FSM specs and directions.

If you desire to check the advance curve in the distributor, at particular engine rpms, you'll need a dial-back timing light. Which is much easier to do that to remove the distributor and put it on a distributor test machine.

BEFORE doing any base timing settings, MAKE SURE where the point dwell reading is, as changing that after the base timing is set WILL affect the base timing. IF it's still a points distributor.

Look at the FSM distributor advance specs. Then add the base timing to that number. You'll probably find that the total advance at 4000+ engine rpm is pretty close to the desired 38 degrees total (vac advance unplugged). Some like to see that come in sooner, though.

Enjoy!
CBODY67
 

kenfyoozed

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Thanks. Should I still test the total advance timing with the vacuum attached and adjust it to be no more than 36 total?

Im replacing the electronic ignition as a kit, the one thats on it i think hs issues and i know the vacuum can does not work.
 

CBODY67

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Forget adjusting the vac advance (which is an internal adjustment). It is NOT a part of the initial setting or ANY setting.

The vac advance + mechanical advance at about 2500rpm should be about 50 degrees or so. Reason? It's at part-throttle, rather than WOT. That's normal for best fuel economy. At WOT or heavy throttle, NO or little vacuum advance as the vac level at the ported vacuum port is similarly decreased.

It usually takes about 10" Hg vacuum to start a factory-spec vac advance to work. That's normal, too. Just as the factory centrifugal advance usually starts at approx. 1000 engine rpm.

Just worry about getting the hot base idle timing setting done. As mentioned above, if it doesn't ping/trace rattle at part-throttle/WOI accel, you might add a 2 more degrees to the base setting and recheck. You want no ping, but a trace amount won't hurt anything, typically. Best to use the FSM settings for your baseline and tweak from there.

CBODY67
 

CBODY67

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The 38 degrees total advance is the approx. optimum advance for best WOT power output. For Chrysler B/RB engines and also some other brands. At WOT, the air/fuel mixture is "thicker" and easier to ignite. At part-throttle, higher vacuum levels, it's a "thinner" mixture, which is a bit harder to ignite, because it's not as rich.

The 38 degrees relates to the time, in crankshaft degrees, from the time that the mixture is initi9ally ignited until it is fully ignited/"boomed" at TDC. Too much lead, it ignites before TDC (works against the piston's movement). To little lead, it ignites after TDC (lost power). Usually, you can go a few degrees more, up to about 40 degrees BTDC on a wedge-combustion chamber Chrysler B/RB engine. Some fuels are more ignitable than others, by observation. Which is NOT related to Research Octane Number, per se. Although RON needs are related to compression ratio.

On our '66 Newport 383 2bbl, when it was "a used car", I had the FSM and read through it extensively. I noted that when set to its FSM specs, the total timing was spec'd at 36 degrees BTDC total. I smiled as that was pretty close to what was said to be optimum. On THAT set-up, initial timing was 12.5 degrees BTDC. I later tried it at 15 degrees initial, with no problems. On THAT engine with the "closed chamber" heads, moving the timing up to 15 would increase the idle speed a bit, but not too much to need a readjustment, unless I wanted to.

By comparison, on my '70 Monaco 383 "N", which set at 5 degrees initial, but still hit the 36 degrees total, due to different springs in the distributor, when I added another 2.5 degrees, it didn't affect idle speed at all. Difference in the close chamber and 906 open chamber heads, best I could tell.

The '70 engine had the first signs of emission controls, which included less initial base timing, but at WOT, the total was still about 36 degrees total.

As your car is a 10.0CR engine, which spec'd for "premium fuel" back then, you'll probably need to keep "super unleaded 92 Pump Octane Number" fuel in it. "Mid-Grade" will probably make it ping under throttle, but if you can set the timing back 2 degrees and that works, you might save a little bit on fuel costs. ANY power loss at WOT might not be noticed at part-throttle, though. YOUR judgment call on that. Otherwise, feed it well and keep it happy, octane-wise.

Enjoy!
CBODY67
 

70bigblockdodge

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36° total is rule of thumb best power at WOT this is in a RPM normally above highway cruise RPM and of course way above idle.
The reason for a mechanical advance curve is most cars with 36° advance will kick back against the starter or not start at all. Also provides a nice smooth idle.
Vacuum advance is there for part throttle, high vacuum, cruise operation for efficiency, less cylinder pressure you need to light the fire earlier.
The factory specs are normally conservative on timing better to give up a few horsepower than have a customer bitching.
If this is okay in your book, set it to factory specs with vacuum advance disconnected and leave it.
If you would like a little more, maybe, you may not get there without detonation. Trial and error. The best way to quickly tune for efficiency is use a vacuum guage to set the best idle mixture and initial timing. You want the highest vacuum reading possible.
 

Trace 300 Hurst

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The advice from CBODY67 is better than mine. I was advising on how to get optimum timing without ping, but he is "more correct" for what you're doing at this point. Set that initial timing at the OEM/FSM number to get yourself started, then you can begin to bone-up on timing and tuning. After your new systems is working nicely, you can experiment with a few degrees more advance to see if it rattles, etc. But this isn't really necessary if you're simply wanting your boulevard cruiser to start and run properly.

Just as a reference, my engine will only take 32* total before it rattles at WOT, so my initial is 10* (10+22 mechanical advance = 32). But it's 11:1 compression ratio, weighs a million pounds, has a 3:23 gear...and simply doesn't like the 34-36* optimum unless I LOAD it with octane booster. And why bother with that to make just a bit more power? It's just fine at 32*.

So yeah, listen to CBODY, not me! :thumbsup:
 

The Goose

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The advice from CBODY67 is better than mine. I was advising on how to get optimum timing without ping, but he is "more correct" for what you're doing at this point. Set that initial timing at the OEM/FSM number to get yourself started, then you can begin to bone-up on timing and tuning. After your new systems is working nicely, you can experiment with a few degrees more advance to see if it rattles, etc. But this isn't really necessary if you're simply wanting your boulevard cruiser to start and run properly.

Just as a reference, my engine will only take 32* total before it rattles at WOT, so my initial is 10* (10+22 mechanical advance = 32). But it's 11:1 compression ratio, weighs a million pounds, has a 3:23 gear...and simply doesn't like the 34-36* optimum unless I LOAD it with octane booster. And why bother with that to make just a bit more power? It's just fine at 32*.

So yeah, listen to CBODY, not me! :thumbsup:
Your advice reminds me of how we used to do premium gas station max timing when we’d go camaro hunting in the 80’s. Gas was so crummy and varied wildly from store to store (most real stations were killed off by then...) that we’d bump test for pinging find the max point and then go hunting. You’re 100% correct, it works, but mr goodwrench would probably frown upon this method. And thanks for the trip down memory lane! Those were great days to be alive even when we got busted...
 

kenfyoozed

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Followed the instructions I was given and all went as it should. Got back home with the other parts I needed at 1pm and by 4pm we had swapped all new ignition ECM, Ballast, VR, Dizzy, Plugs, Plug wires and even a new fuel pump and filter. Set initial timing at 10* and she was happy so I left it there. Took her for a ride and all seemed good. No more pinging or rattle when i opened her up. I think the rattle i was having was because th #8 cyclades was not getting proper fire. All the other spark wires made a distinct "pop" when they came off, but #8 did not. It almost seemed to just fall off. Also saw my kick down tranny arm was disconnected so i reattached that as well. And be cause of the new fuel pump I not have at least 3 leaks in my fuel line from the tank. Off to start a thread on how to fix that now.... But a big thanks to all you guys. With your advice it all went quicker than expected so thanks again!:thankyou::thumbsup::thankyou:
 

Trace 300 Hurst

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Set initial timing at 10* and she was happy so I left it there. Took her for a ride and all seemed good. But a big thanks to all you guys. With your advice it all went quicker than expected so thanks again!

Good on ya for stepping outside your comfort zone and learning/doing something new. Successfully! :thumbsup:
 

Gerald Morris

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The 38 degrees total advance is the approx. optimum advance for best WOT power output. For Chrysler B/RB engines and also some other brands. At WOT, the air/fuel mixture is "thicker" and easier to ignite. At part-throttle, higher vacuum levels, it's a "thinner" mixture, which is a bit harder to ignite, because it's not as rich.

....
On our '66 Newport 383 2bbl, when it was "a used car", I had the FSM and read through it extensively. I noted that when set to its FSM specs, the total timing was spec'd at 36 degrees BTDC total. I smiled as that was pretty close to what was said to be optimum. On THAT set-up, initial timing was 12.5 degrees BTDC. I later tried it at 15 degrees initial, with no problems. On THAT engine with the "closed chamber" heads, moving the timing up to 15 would increase the idle speed a bit, but not too much to need a readjustment, unless I wanted to.

....

As your car is a 10.0CR engine, which spec'd for "premium fuel" back then, you'll probably need to keep "super unleaded 92 Pump Octane Number" fuel in it. "Mid-Grade" will probably make it ping under throttle, but if you can set the timing back 2 degrees and that works, you might save a little bit on fuel costs. ANY power loss at WOT might not be noticed at part-throttle, though. YOUR judgment call on that. Otherwise, feed it well and keep it happy, octane-wise.

Enjoy!
CBODY67

Gotta LOVE those 516 heads w a 2-barrel 383! 10 degree initial timing works nicely with 91 octane out here. Even 9.2 CR pretty well dictates using nothing but 91 or 92 octane juice. I too have tried running the timing as far as 15 degrees, which did fine during the winter a couple yrs back, but come Spring, I got too much pre-ignition ping. I probably will bump mine, currently set to FSM 12.5, back to 10 for the summer AND flush the cooling jacket thoroughly in the next week or so. The ping increases exponentially with temperature over 200F, which I why I so strenuously work to keep Mathilda purring at 195 F max. Cooling impacts timing in a big way when asphalt gets hot enough to cook on......
 
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