The Cal-look Lounge

So. All engines are different, and not all timing numbers work for all engines. How are you guys getting to the right timing numbers, and how do you no it's right. I usually set it by ear and road test plus guess it. . Think I'm gunna try the highest vacuum way using a vacuum gauge. I'm unsure if taking a vac signal off just 1 cylinder is the best way or should the reading be done off the 4 cylinders.

Dizzy or programmable Ignition?

Using a dizzy.
It works fine, just wanna optimise with the parts I have to hand

This is an interesting topic.
Any advice on initial timing and building a curve or map appreciated.

I used to think the set it at 10* was always  the
idle timing  number for all engines, but it's not is it. All engines run different. Due to cam/heads/stroke/exhaust/induction and so on.
Also the max timing of 28~32 doesn't work for all engines, you have find the right timing number for your engine and not use timing figures that the other guy uses.
Ive started advancing the idle timing and readjusting the total.
Using a vac gauge and advancing the timing till you get highest vac reading seams as good way to achieve best idle timing for any engine.

Interesting... I haven't really had any ignition issues with my car, I just set max timing at 33* and then let it settle down to idle at around 1050 rpm, the idle timing is usually around 13-14*. I might give that vacuum method a shot one of these days and see where that lands vs setting it via full advance.

Interesting. Setting the Idle timing would only make sense with an ignition system that lets you control timing at idle and full advance separately. What system do you have?
Full advance timing is critical bc your engine could detonate. Idle timing only affects ease of starting as well as low end response.

Seems like you are starting to answer you own question ;)

Biggest problem I see you have there by setting timing high at idle and limiting max timing by adjusting curve is at low rpm and high load timing will be to high & really good chance of detonation, this is where EFI/programmable ignition is so good, I have run as high as 26degrees idle timing and then mapped it to drop it down for low rpm/high load and back up again as rpm goes up or load drops off which you cannot really do with a dizzy. 
You are right with every engine is different though, I don't think I have used 32degrees max for 15 years or so, most higher compression aircooled VWs don't need or gain anything by running that sort of timing on pump fuel

cheers Richie

I'm running a 009 with a Pertronix kit, so I know I can't separately adjust the two settings, but I'd still like to know if my idle advance is off at all, that way if I go to a programmable system in the future I can have an idea of how to set it up.

Cool. You can adjust the advance curve by playing with the weights in the centrifugal mechanism.
My EFI engine has advance added in a cold idle situation as an extra little boost for idle speed when it’s cold.

If running IDF/IDA/DRLA  style carburetors you really want to set your throttle plate so that the first progression hole is just about starting to get exposed so that as soon as you start to accelerate the engine the progression circuit starts working. Same thinking with the vacuum advance port however the carb manufacturer took that into account.

So now if your throttle plates are fixed the only other way to adjust your idle RPM is with timing, so anywhere between roughly 8 to 15 degrees that makes the engine idle at a speed you like will work. If you have a Mallory, MSD or other distributor that you can easily adjust the total mechanical advance so that you have 28 total or whatever your engine needs. Now just adjust the springs/weights so that the advance starts not long after your idle RPM, all in at 2500 to 2800 for a large duration cam and 3200 to 3500 RPM for a short duration cam. That is sort of the goals and the things that can be done with a distributor, obviously trial and error is the way to approach it. Make a change and note the results however at some point the seat of the pants is not sensitive enough to tell the difference.

I am still thinking about this one, I am not sure this is quite accurate.

Certainly as you adjust your mixture screws and get them just right you know it is right because the idle speed increases, hence the vacuum increases.

I think the vacuum increased because the rpm increases therefore chasing max vacuum will result in a high idle speed.

Idle is the one condition that you do not want to set your timing to MBT because you want to leave some torque in reserve so that when you come off idle you can bring in the extra timing so you can pull away from the stop sign.

Regarding EFI and idle timing, I have read that one of the OEM manufactures does this test. They increase the idle timing until they reach a point that the engine RPM stopped increasing, they then would target half that value as the idle timing setting.

When I did this test on my engine, it stopped increasing RPM at 28-30 degrees.

Jeremy

Here’s my ignition table. Note the bump in idle advance at the middle of the vacuum range.