comments on my 123 ignition curve? - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 41 (permalink) Old 07-12-2019, 09:18 AM
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I encountered a similar pinging problem with my first 2 liter hot-rod build. In the mid-to-late 80's the best pump gas we could get in Texas was 91 octane. At the time I was running 10.4 Borgos with cams that were similar to what we're talking about here. I was using my trusty, re-curved MarelliPlex that I'm now running on my new motor. Here's a couple of factoids from that period.

First a definition of terms: "Knocking is more commonly known as pinging. But it differs somewhat from detonation. Knocking / pinging is caused by the peak cylinder pressure event coming too early because the flame front from the spark plug initiated too soon." --- from the internet.

Especially in 100 degree Texas summer weather, my high-compression motor would ping under even a light load. At the time, I had recently discovered David Vizard's various books on engine building and was reading everything of his that I could find. In one of this tuning books Vizard mentioned that a common characteristic of Otto cycle engines is a knock/pinging event at about 2400 rpm. With my "all in at 3k" advance curve this is exactly what I was experiencing. I surmised that that I was experiencing the flame front problem described above.

Vizard was also enthusiastic about MSD CD ignitions which, as we know, were designed to have longer firing events at lower speeds. I put two and two together and decided to see if the MSD's multi-firing over about 30 crankshaft degrees design would reduce or eliminate the pinging I was getting. To shorten a long story, the experiment worked. With the MSD installed, my 10.4 (actually about .5 or .6) was completely eliminated. It was really surprising to drive in 100 degree stop and go traffic and not experience pinging. Even with the 91 octane gas, my hot-rod 2 liter was a smooth as could be. So what was the MSD ignition doing? It appears that the multi-firing design was doing a better job of controlling the ignition evet, despite the limitations of the 91 octane fuel.

The culprit, of course, was the crappy 91 octane gas which was all that was available at the time. With my newly built 2 liter and 93 octane gas, I'm comfortable running the same MarelliPlex and no MSD.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #17 of 41 (permalink) Old 07-12-2019, 10:01 AM Thread Starter
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Originally Posted by alfaparticle View Post
Your centrifugal curve is quite steep at idle rpm and you may find that it does not want to settle at 1000 rpm and instead slowly speed up.
I have some concerns there, but so far the idle is fine. I'll see how it drives and starts over the next couple weekends.

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post #18 of 41 (permalink) Old 07-12-2019, 10:17 AM Thread Starter
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Originally Posted by Craig_m67 View Post
It’s the “what” makes the best curve info that I lack.
I find that my car will idle fastest with 15-25deg advance at 800rpm
I suspect this is too much when load is applied to the engine
Setting up for fastest idle when warm may not result in easy starting when cold.
In my opinion, the idea is to retard the ignition for easy starting. We all talk about advancing the ignition... but really it is often helpful to think of things in the reverse. Consider the full advance target to be where you get best power at your mid and high RPM. That is why it is best to tune on the dyno, as over advancing can actual result in the power falling. After you have the mid and high RPM figured out, it is about making the car easy to start when cold and idle and to rev cleanly up the scale.


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I can also run at 45deg advance from 3000rpm.. but will get pinging (if that’s what it is.. I’ve never had it explained to me correctly)
Pinging is a poor and vague term. And it is best to know many misuse the terms, so you often have to deduce what they mean from the context. Best to google: pinging, knock, preignition and detonation. Generally, when I say pinging, I am describing a sound I hear, a bell like rattle.
In my case the pinging comes for too much advance for the relatively low octane fuel. Either reducing the advance or increasing the octane solves it. That likely means that with the excessive advance the fuel burns too early and quickly, while the piston is still rising.

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post #19 of 41 (permalink) Old 07-12-2019, 01:19 PM
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Pinging is detonation if it can be eliminated by less spark advance or higher octane gas. Mild detonation is not always destructive but severe detonation can damage things quickly.

Ed Prytherch
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post #20 of 41 (permalink) Old 07-12-2019, 02:43 PM Thread Starter
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Update.
I had a chance to drive my test loop today that has a couple good hills and on one of the steeps I found the engine pinging between 2500 - 3000 RPM.
I ended up with this new curve, with that area softened. I lowered the advance a bit at 2000 RPM and and pushed full advance out to 3500 RPM. But I need a bunch more testing.
I do like the steep early part of the curve, the car runs very nicely down low. No problems so far without the flat spot for idle. It idles right at 1000 RPM, and I am sure I could adjust the idle speed down at the carbs( as I was idling at 700 RPM with my 8 degree flat spot from my earliest tests).
Oh, and I need to tape up a few things that rattle in my car. When I am listening for pinging, every rattle startles me. My passenger seat belt and seat back, when empty, produce a bunch of rattles that can easily be mistaken for pining if I'm not paying attention!
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post #21 of 41 (permalink) Old 07-26-2019, 02:52 PM Thread Starter
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Well, I was still getting a bit uphill pinging on a hot day between 3000 and 3500 RPM, so I have pushed out full advance to 4000 RPM. If I still have pinging, it is very slight. I need to go to a bigger hill now for fine tuning. Latest curve:
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post #22 of 41 (permalink) Old 07-26-2019, 04:03 PM
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Well, I was still getting a bit uphill pinging on a hot day between 3000 and 3500 RPM, so I have pushed out full advance to 4000 RPM. If I still have pinging, it is very slight. I need to go to a bigger hill now for fine tuning. Latest curve:
Ever thought about using a rolling road dyno? JBA (5675 Kearny Villa Rd -858-495-3395) has one.

Mike
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1966 Super
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post #23 of 41 (permalink) Old 07-26-2019, 04:11 PM Thread Starter
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Ever thought about using a rolling road dyno?
That was my first plan, but the places I called wouldn't do it. JBA said "Only American Cars".

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post #24 of 41 (permalink) Old 07-26-2019, 04:39 PM
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That was my first plan, but the places I called wouldn't do it. JBA said "Only American Cars".
I called and chatted with them and they had no issue with my 69 GTV. I'll have to reach out to them again.

Mike
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post #25 of 41 (permalink) Old 07-30-2019, 12:39 PM
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That was my first plan, but the places I called wouldn't do it. JBA said "Only American Cars".
I just called them and the "American Cars" restriction is only if you want to interface the car ECU computer with their dyno. No problem with an Alfa if you are using the dyno as a simple chassis dyno. Our older Alfas wouldn't interface with their dyno electronics anyway.

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post #26 of 41 (permalink) Old 07-30-2019, 02:23 PM Thread Starter
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Originally Posted by Alfa69GTV1750 View Post
I just called them and the "American Cars" restriction is only if you want to interface the car ECU computer with their dyno. No problem with an Alfa if you are using the dyno as a simple chassis dyno. Our older Alfas wouldn't interface with their dyno electronics anyway.
Well, JBA wasn't very interested when I called. And I did call again after you suggested them again a couple posts earlier. They also did not to have any gizmo to sense detonation. They actually recommended I go to another shop nearby, Cartune. Those guys seemed somewhat interested and use DetCans (headphones with a tube). They wanted $500 for a session.

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post #27 of 41 (permalink) Old 07-30-2019, 03:18 PM
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If you end up going to Cartune and wouldn't mind, please let me know what you think of them. I've been talking to JBA about putting a supercharger on my truck, and they are clearly more focused on the American iron.

Mike
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post #28 of 41 (permalink) Old 07-30-2019, 06:48 PM
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Have you verified the curve with a timing light?

Ed Prytherch
79 Spider
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76 Suzuki GT500
2011 Jaguar XKR

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post #29 of 41 (permalink) Old 07-30-2019, 08:52 PM Thread Starter
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Have you verified the curve with a timing light?
I verified TDC, I have assumed if that is right the gizmo gets the other points correct.
Is there any history of the advance/rpm settings working incorrectly?

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post #30 of 41 (permalink) Old 07-31-2019, 01:33 AM
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Originally Posted by vintageveloce View Post
Well, JBA wasn't very interested when I called. And I did call again after you suggested them again a couple posts earlier. They also did not to have any gizmo to sense detonation. They actually recommended I go to another shop nearby, Cartune. Those guys seemed somewhat interested and use DetCans (headphones with a tube). They wanted $500 for a session.
500 is way cheaper than fixing a engine thats ruined by detonation.
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