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Ignition curve discussion

General engine tech -- Drag Racing to Circle Track

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GRTfast
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Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 11:42 am

I have the programmable ignition from Progression Ignitions in my big block now (along with a new cam from Mike Jones), and it has never run better. With this new cam and my big intake ports, the engine likes a lot of advance, as my compression is probably a full point lower than what it could be for street driving (9.5:1 vs 10.5:1). I have it setup "all in" by 2600 RPM. 30 degrees at idle, 40 all in, linear in the transition. Runs fantastic. I also have 8 degrees of vacuum advance gently coming in starting around 1800 in the high vacuum cruising RPM part of the map.

This got me thinking though, what are the chances that the correct advance for max power is the same at 2600 RPM as it is at 6600 RPM (talking about wide open pulls through the entire power band)?

It seems that it's likely for every cell in the map to have a different optimal value. Do any of you with programmable ignitions every experiment with finding the optimal advance at every point in the table? It's hard to imaging this thing running any better, and at this point I would need a dyno to dial it in further. Is it the case that the engine would like more and more advance as the revs build, and the reason for not adding more advance after 3000 rpm or so is because you just run up against detonation? Just curious what you all think.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by PackardV8 » Sun Jun 21, 2020 12:24 pm

Image

Yes.

The OEMs spend thousands of hours on chassis dynos, on the highways in all possible weather, temperature and altitude combinations to dial in the ignition advance curve.

They're optimizing power from a smaller, often turbocharged engine, fuel economy, emissions, driveability and cost. You've got fewer points to hit and plenty of horsepower to cover up the tradeoffs.
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Re: Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 12:54 pm

PackardV8 wrote:
Sun Jun 21, 2020 12:24 pm
Image

Yes.

The OEMs spend thousands of hours on chassis dynos, on the highways in all possible weather, temperature and altitude combinations to dial in the ignition advance curve.

They're optimizing power from a smaller, often turbocharged engine, fuel economy, emissions, driveability and cost. You've got fewer points to hit and plenty of horsepower to cover up the tradeoffs.
I figured there is a lot of r&d going on at the oem level, as the cars these days run so perfect in basically every condition, and modern valve/ignition timing and fuel injection systems give superb control of all parameters. I’m really more curious about what the race engine builders on here are doing. Are they pretty much just doing a initial value with linear increase to some all in value, then keeping it there? Or are they going to the lengths of the oems to make fully optimized maps that consider every input parameter?
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by hoffman900 » Sun Jun 21, 2020 1:04 pm

Really sophisticated professional level teams use pressure sensors to optimize the ignition curve on each cylinder. They get into it here:

98% of the builders out there are likely running the same ignition timing across the board and tune it via dyno testing.
-Bob

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Re: Ignition curve discussion

Post by Schurkey » Sun Jun 21, 2020 1:50 pm

GRTfast wrote:
Sun Jun 21, 2020 11:42 am
Is it the case that the engine would like more and more advance as the revs build, and the reason for not adding more advance after 3000 rpm or so is because you just run up against detonation? Just curious what you all think.
My understanding--from listening to other folks, not from my own independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need a few degrees of "high-speed ignition retard" because the in-cylinder turbulence becomes so much greater as the RPM builds. The turbulence speeds combustion.
Last edited by Schurkey on Sun Jun 21, 2020 1:57 pm, edited 1 time in total.

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Re: Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 1:51 pm

hoffman900 wrote:
Sun Jun 21, 2020 1:04 pm
Really sophisticated professional level teams use pressure sensors to optimize the ignition curve on each cylinder. They get into it here:

98% of the builders out there are likely running the same ignition timing across the board and tune it via dyno testing.
Awesome video, thanks for sharing. The super slow mo of the valve spring at 9500 RPM is amazing!
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 1:52 pm

Schurkey wrote:
Sun Jun 21, 2020 1:50 pm
GRTfast wrote:
Sun Jun 21, 2020 11:42 am
Is it the case that the engine would like more and more advance as the revs build, and the reason for not adding more advance after 3000 rpm or so is because you just run up against detonation? Just curious what you all think.
My understanding--from listening to other folks, not independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need some "high-speed retard" because the in-cylinder turbulence becomes so much greater as the RPM builds.
In our two stroke shifterkart engines, the curve for best wide open power was very advanced down low and got progressively more retarded through the rev range. Probably due to some form of the same phenomenon.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by BobbyB » Sun Jun 21, 2020 4:22 pm

Did you look into a dragy?

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Re: Ignition curve discussion

Post by Truckedup » Sun Jun 21, 2020 4:52 pm

GRTfast wrote:
Sun Jun 21, 2020 1:52 pm
Schurkey wrote:
Sun Jun 21, 2020 1:50 pm
GRTfast wrote:
Sun Jun 21, 2020 11:42 am
Is it the case that the engine would like more and more advance as the revs build, and the reason for not adding more advance after 3000 rpm or so is because you just run up against detonation? Just curious what you all think.
My understanding--from listening to other folks, not independent research--is that there's no need for additional advance after a certain RPM. In fact, high-RPM use may need some "high-speed retard" because the in-cylinder turbulence becomes so much greater as the RPM builds.
In our two stroke shifterkart engines, the curve for best wide open power was very advanced down low and got progressively more retarded through the rev range. Probably due to some form of the same phenomenon.
Same for vintage 4 stroke flat track bike. Generally fixed timing, more advance for midrange on a shorter track. And less for top end power or on a greasy surface...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 5:04 pm

BobbyB wrote:
Sun Jun 21, 2020 4:22 pm
Did you look into a dragy?
Yeah I’m gonna get one.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by BobbyB » Sun Jun 21, 2020 5:40 pm

GRTfast wrote:
Sun Jun 21, 2020 5:04 pm
BobbyB wrote:
Sun Jun 21, 2020 4:22 pm
Did you look into a dragy?
Yeah I’m gonna get one.
Good. I really look forward to knowing what your final timing curve is. Hopefully the dragy will prove worthwhile for you.

If you end up much different than what most expect, I might consider an ignition like yours.

The only problem with this phone app stuff is will we eventually have to have our phone to even drive our hot rods!

How is your rear suspension set up? Can you get decent traction?

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Re: Ignition curve discussion

Post by GRTfast » Sun Jun 21, 2020 6:09 pm

BobbyB wrote:
Sun Jun 21, 2020 5:40 pm
GRTfast wrote:
Sun Jun 21, 2020 5:04 pm
BobbyB wrote:
Sun Jun 21, 2020 4:22 pm
Did you look into a dragy?
Yeah I’m gonna get one.
Good. I really look forward to knowing what your final timing curve is. Hopefully the dragy will prove worthwhile for you.

If you end up much different than what most expect, I might consider an ignition like yours.

The only problem with this phone app stuff is will we eventually have to have our phone to even drive our hot rods!

How is your rear suspension set up? Can you get decent traction?
Never had any really sticky tires on it. It's a triangulated 4 link with pretty short arms (a compromise to make the car look a certain way). The instant center is somewhere around the bell housing. The car is 58% rear biased (the body is pretty heavy and the engine is a good bit behind the front axles). I had an app on my phone for a while that used the accelerometers on the phone to give me 1/4 mile statistics. I was getting 60 foot times on the street in the 2.2s range. The tires are just some 12 inch wide hoosier pro street tires, not a race compound at all.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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Re: Ignition curve discussion

Post by BobbyB » Mon Jun 22, 2020 3:18 pm

GRTfast wrote:
Sun Jun 21, 2020 6:09 pm
BobbyB wrote:
Sun Jun 21, 2020 5:40 pm
GRTfast wrote:
Sun Jun 21, 2020 5:04 pm


Yeah I’m gonna get one.
Good. I really look forward to knowing what your final timing curve is. Hopefully the dragy will prove worthwhile for you.

If you end up much different than what most expect, I might consider an ignition like yours.

The only problem with this phone app stuff is will we eventually have to have our phone to even drive our hot rods!

How is your rear suspension set up? Can you get decent traction?
Never had any really sticky tires on it. It's a triangulated 4 link with pretty short arms (a compromise to make the car look a certain way). The instant center is somewhere around the bell housing. The car is 58% rear biased (the body is pretty heavy and the engine is a good bit behind the front axles). I had an app on my phone for a while that used the accelerometers on the phone to give me 1/4 mile statistics. I was getting 60 foot times on the street in the 2.2s range. The tires are just some 12 inch wide hoosier pro street tires, not a race compound at all.
What does the total car weigh?
With the dragy you can look at 0 to 60 times broken down in 10 mph increments, which might help you with your timing curve. You can also do custom setting from say 5mph to 25 mph if you want to. Or you can record based on distance.

One day I would love to build something similar to yours... Im getting old fast though.

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Re: Ignition curve discussion

Post by PackardV8 » Mon Jun 22, 2020 5:17 pm

How did we get ten posts in without someone saying, "Just lock 'er in at 34 degrees and forget about all that initial and advance stuff."
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Re: Ignition curve discussion

Post by GRTfast » Mon Jun 22, 2020 6:12 pm

BobbyB wrote:
Mon Jun 22, 2020 3:18 pm
GRTfast wrote:
Sun Jun 21, 2020 6:09 pm
BobbyB wrote:
Sun Jun 21, 2020 5:40 pm


Good. I really look forward to knowing what your final timing curve is. Hopefully the dragy will prove worthwhile for you.

If you end up much different than what most expect, I might consider an ignition like yours.

The only problem with this phone app stuff is will we eventually have to have our phone to even drive our hot rods!

How is your rear suspension set up? Can you get decent traction?
Never had any really sticky tires on it. It's a triangulated 4 link with pretty short arms (a compromise to make the car look a certain way). The instant center is somewhere around the bell housing. The car is 58% rear biased (the body is pretty heavy and the engine is a good bit behind the front axles). I had an app on my phone for a while that used the accelerometers on the phone to give me 1/4 mile statistics. I was getting 60 foot times on the street in the 2.2s range. The tires are just some 12 inch wide hoosier pro street tires, not a race compound at all.
What does the total car weigh?
With the dragy you can look at 0 to 60 times broken down in 10 mph increments, which might help you with your timing curve. You can also do custom setting from say 5mph to 25 mph if you want to. Or you can record based on distance.

One day I would love to build something similar to yours... Im getting old fast though.
2800 ish with me in it.

That app was showing me getting 100 mph in about 8 seconds or so, 12.0 ish 1/4 at 122 mph.

I think if I had some sticky tire and could launch it hard it has low 11's in it. The final drive gear and tranny are not optimized for 1/4 mile at all, this is not a drag car by any means. It goes 108 mph in 3rd gear at 6000 rpm, so the last part of the 1/4 mile is in 4th gear pulling from 4100-4500 rpm or something like... and the car is a brick aerodynamically. With a glide, slicks, and the right rear gear it is probably a high 10 second car.

I'm pretty sure I will only get one run at the test and tune night though. I think it needs a cage if I go in the 11's.
Last edited by GRTfast on Mon Jun 22, 2020 6:18 pm, edited 2 times in total.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. -Hitchens

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