Ignition timing curve

[Mikej26]

In a car with a 3500+ rpm stall converter, is there any need to run a mechanical advance curve?

[induction apprentice]

Smart car?
AMC pacer?
Holdom?
Tesla?

[PackardV8]

Displacement?
Weight?
Gears?
Intended use?

[rfoll]

It could be a challenge for the starter.

[F-BIRD'88]

How tame or how radical the cam is, is a factor.
Starter hot cranking strain can be overcome eith a ignition power interupt switch and/or a cranking retard box.

[Tuner]

You could always rig it with a mechanical spark advance lever at the steering wheel, like Model T and Model A Ford. The irony in this is both my grandmothers, for that matter nearly everybody in the early 20th century era who ever drove a Model T or Model A, had a better understanding of basic engine spark advance requirements than nearly any modern gear head.

OP, if you can't get to a dyno, you could try this: With the engine at WOT against the converter, advance and retard the timing to find whatever timing gives the most RPM. Take care not to get the converter too hot. Then, on the track find whatever amount of advance gives the best trap speed. If the same amount of advance is not optimum for the two conditions, then do what you gotta do.

Keep in mind that if you do this with locked advance, electronic ignition causes the timing to retard as RPM increases, probably about 1 degree per 1000 RPM increase, so when you set or check the timing it will be more at low RPM than at high RPM and you will need to compensate for this retard.

Most engines that are operated thoroughly warmed up (heat soaked, like highway cars or circle track) like more advance at high RPM than at peak torque RPM. Most engines like timing to advance above the torque peak. Drag race engines that are cold on the starting line and warmer at the finish may want the timing to retard as they get warmer, so circumstances alter cases and you will need to compensate to suit your particular situation.

[GARY C]

It seems if you have a fuel curve you would want a timing curve as well, usually peak tq timing is lower than peak hp timing.

[Mikej26]

This was more so just a general inquiry. I have a 360 SBC 11:1 comp, 242/248@.050 ported profiler 195's 2.02/1.60 that likes a lot of initial advance but doesn't require a ton of total advance.

Historically it likes a minimum of 22° initial timing but seems to run the quickest with 28-32° total.

The above was with a crappy beat up set of headers and a stall converter that was too tight 2200 rpm.

I just installed a 3400-3800 rpm stall converter as well as changed the headers. I have not run the car yet with these latest updates so its possible that things will be different once its running.

[David Redszus]

It is interesting to note that computer ignition map curves often resemble the Rocky Mountain range and not smooth curves.

[rfoll]

Run with the curve. 22 initial and 11:1 compression say no need to be locked. If your compression was too low or the cam too big, locked timing would help.

[GRTfast]

It is interesting to note that computer ignition map curves often resemble the Rocky Mountain range and not smooth curves.

Yeah, the custom curves we had for the two stroke 125’s were anything but smooth.

[groberts101]

In a car with a 3500+ rpm stall converter, is there any need to run a mechanical advance curve?

Unless the car is heavy with taller gearing I'd say most likely not. Install a start retard and enjoy fewer variables that can muck things up. 35 degrees is far from being too much idle timing for anything even remotely performance oriented. The motor will make more manifold vacuum and liven the booster up to hit the converter harder too.

[F-BIRD'88]

If you are driving this on the street you'd also want a functional vacuum advance system too.
Typical limited to 10-12-15 degress max at high vacuum.
Rate in-out based on vacuum/throttle load, found by drive testing and adjustment.

[Tuner]

This was more so just a general inquiry. I have a 360 SBC 11:1 comp, 242/248@.050 ported profiler 195's 2.02/1.60 that likes a lot of initial advance but doesn't require a ton of total advance.

Historically it likes a minimum of 22° initial timing but seems to run the quickest with 28-32° total.

The above was with a crappy beat up set of headers and a stall converter that was too tight 2200 rpm.

I just installed a 3400-3800 rpm stall converter as well as changed the headers. I have not run the car yet with these latest updates so its possible that things will be different once its running.

I would say you could safely run up to about 36 degrees max, more if you were real careful...
the issue is making it a 3D curve with the map sensor.
so, lets say 7 degrees at idle

The OP says "run the quickest with 28-32° total" so why would you use 36? Or, are you suggesting to set the timing at low RPM to compensate for the electronic slew retard, 1* per 1000, so 36 at 1000 will be 30 at 7000?

Recently playing on a dyno with a 12.8/1 355 short track engine with the GM large port Bowtie fast burn heads, it was determined this particular engine definitely does not want as much timing at 3-4000 as at 6-7000. It picked up 25 ft.lbs. torque with a timing curve advancing 6 deg. from 3000 to 7000.

[rfoll]

This would be a very tight track to see 3000-4000 rpm except on restarts.