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Variable ignition timing

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Blairsville Ed
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Variable ignition timing

Post #1 by Blairsville Ed » Tue Jan 29, 2019 9:04 am

I had an idea.
It appears that it is possible to attach a rod to the distributor and to have the rod pass through the firewall and into the cab. The purpose would be to set the cruising timing to the best power while driving the truck.
If I did this, what would be the best test speed or conditions to adjust timing. Also, is this a bad idea?

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THE FRENCHTOWN FLYER
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Re: Variable ignition timing

Post #2 by THE FRENCHTOWN FLYER » Tue Jan 29, 2019 9:16 am

That's pretty much how most of the Brass Era autos varied spark advance. The most logical test point(s) would be at the speeds/loads you drive.
To do it precisely you would need a flow meter capable of measuring instantaneous fuel flow. That is how engineers do it on test tracks. You will also need to monitor wind and weather (barometer / moisture content, etc). You are looking for small incremental gains that could be masked if conditions are not monitored closely. Some modern vehicles have an on-board capability to measure fuel flow and display it on the instrument panel screen in terms of instantaneous fuel economy. If you have one in your vehicle you are miles ahead in terms of instrumentation and data gathering. They are usually very accurate.
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sdiesel
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Re: Variable ignition timing

Post #3 by sdiesel » Tue Jan 29, 2019 11:57 am

will a wide spectrum A/F meter accomplish nearly the same thing?
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

sdiesel
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Re: Variable ignition timing

Post #4 by sdiesel » Tue Jan 29, 2019 12:16 pm

and since im thinking about this....
timing retard using an un board MS or mega jolt.
is there any way to reliably sense knock in our engines so we can ramp up maximum advance?

knock sensor parameters are complex to understand.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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MechRick
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Re: Variable ignition timing

Post #5 by MechRick » Tue Jan 29, 2019 4:16 pm

I've done something similar with a megasquirt while pulling a long, 6% grade. What I found is it's almost impossible to feel a seat of the pants difference when changing the timing tables. Advancing too much causes an audible ping, but no noticeable power change.

I know the power output is changing, but my uncalibrated seat can't feel it.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
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http://fordsix.com/forum/viewtopic.php?f=2&t=73244
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Blairsville Ed
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Re: Variable ignition timing

Post #6 by Blairsville Ed » Wed Jan 30, 2019 7:11 am

1968 F100. 240. 3 on the tree. 3.70 gear. Holley 5200 carb

Is it correct to advance timing until the motor begins to ping then back off a little?
Does that equal maximum cylinder pressure at the correct crank angle?

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THE FRENCHTOWN FLYER
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Re: Variable ignition timing

Post #7 by THE FRENCHTOWN FLYER » Wed Jan 30, 2019 7:48 am

Blairsville Ed wrote:1968 F100. 240. 3 on the tree. 3.70 gear. Holley 5200 carb

Is it correct to advance timing until the motor begins to ping then back off a little?
Does that equal maximum cylinder pressure at the correct crank angle?

A few additional degrees of advance generally will help. Don't over do it.
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Blairsville Ed
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Re: Variable ignition timing

Post #8 by Blairsville Ed » Wed Jan 30, 2019 11:30 am

I have been amazed as to how much timing advance this 240 can take without pinging.
Idle timing with no vacuum is 25 degrees btdc
Full vacuum advance plus mechanical advance is 55 degrees btdc
And this is with a fairly lean mixture.
What I’m wondering........even though there’s no pinging,could I still be to far advanced?

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THE FRENCHTOWN FLYER
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Re: Variable ignition timing

Post #9 by THE FRENCHTOWN FLYER » Wed Jan 30, 2019 3:18 pm

Yes

Engines are generally calibrated for the minimum best spark advance, known as MBT for "minimum spark for best torque" at wide open throttle (WOT) or MSV for "minimum spark advance for specified vacuum" at part throttle conditions - using high octane no-knock fuel in lab conditions. Then another series of performance curves are run using the specified grade of pump fuel. If knock is encountered using the pump fuel the curve(s) are adjusted downward to avoid knocking conditions. Then these curves are put in a fleet and tested under all weather and geographic conditions. That's how it was done when I was a pup. Nowdays it is mostly done in labs where conditions can be dictated and knock sensors record the onset of knock.

There is something called "incipient knock" which essentially is inaudible knock - you can't hear it but some spontaneous explosion of the end gasses is occurring and it does have the potential to cause engine damage even though you can't hear it.

It is a common misconception to think that the more spark advance you can put into the engine the better it will run. Maybe for your locale and weather conditions you can add a little spark advance to edge closer to the optimum MBT and MSV values but it is just as easy to over do it and reduce the engine's efficiency and do potential harm. [I better watch myself - I'm tipping my hand as to the other thread I started - "Re-curved distributors on "modified engines" What do you mean???"] After all, the factory calibration has to be able to work everywhere. Knock detectors have been a godsend in that respect, allowing the factory tune to be closer to optimum.
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Blairsville Ed
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Re: Variable ignition timing

Post #10 by Blairsville Ed » Wed Jan 30, 2019 4:47 pm

Nice detailed answer!

Now I understand the need for a precise method of measuring the results from live timing adjustments.
Would incipient knock show up as erosion of the piston crown or the bowl edges?

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THE FRENCHTOWN FLYER
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Re: Variable ignition timing

Post #11 by THE FRENCHTOWN FLYER » Wed Jan 30, 2019 6:10 pm

Yes, it could show up as a corroded surface of the piston, or speckles on your spark plug insulators. It might even start ring land failures.
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Re: Variable ignition timing

Post #12 by sdiesel » Wed Jan 30, 2019 11:43 pm

Yes to Knock. the damage occurs b4 you hear it, assuming your hearing is 100 percent .
the damage done is early and can be severe. especially if you are merrily rolling along assuming that because you cant hear it it aint there.

So, i am still looking for knock sensors that work in the range of our engines,
i ve tried numerous times to get this subject aloft with not much luck. that mean s there is not much people are doing about knock with these engines.
i believe there is lost power in not sensing the knock properly.
rolling timing up against knock might help in a lot of circumstances not so in others , but where to start?

im tempted to assume the GM sensor for the later inline six is the ticket, but who knows??
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

Blairsville Ed
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Re: Variable ignition timing

Post #13 by Blairsville Ed » Thu Jan 31, 2019 8:37 am

A knock sensor?
Perhaps connected to a dash light or gauge?
It would be a great tuning help.

Which cylinder might show knock first?
Cylinder 1 or 6?
I’m referring to the cylinder that might have the hottest temperature.

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THE FRENCHTOWN FLYER
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Re: Variable ignition timing

Post #14 by THE FRENCHTOWN FLYER » Thu Jan 31, 2019 12:26 pm

I'm sure the technology has improved since I was involved but the biggest hurdle to overcome with knock sensors was correct placement on the engine block. It had to be placed where it can sense knock on any of the cylinders yet not be affected by extraneous noise from other engine components such as timing gears and valve train. Finding the optimum spot with the highest signal-to-noise ratio was a challenge. I do not think I would have a lot of confidence in an add-on knock sensor glued, screwed, or clamped on.
Last edited by THE FRENCHTOWN FLYER on Thu Jan 31, 2019 6:53 pm, edited 1 time in total.
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Blairsville Ed
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Re: Variable ignition timing

Post #15 by Blairsville Ed » Thu Jan 31, 2019 5:26 pm

For a visual inspection, which cylinder would show knock first?

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