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Discussion Starter #1
My recently rebuilt 2 liter Engine (spider 2000, 1976, dual Webbers) has a 10.3:1 CR.

This was not planned. During the rebuild (new cylinders, liners, valves, etc) the block was milled a bit due to some corrosion. My mechanic tried to fabricate some sort of shim made out of a thin aluminum sheet, but it did not work. It leaked under a water test.

So the CR ended up bumped to 10.3:1.

Our normal gasoline is 92 RON (it will be 93 RON in 2022). Sometimes, when starting to accelerate in 2nd gear I can hear some fast cracking noise which I believe is pre detonation. If I press the foot down faster the noise goes away.

So, here’s the question. Would getting one of those electronic distributors (eg 123) would allow me to further adjust the spark timing to eliminate the pinging?

The pinging does not appear very frequently, most of the time only when passing through the 2ng gear in the highway, but at the same time I know it can wreak havoc in the pistons, rings and why not. I’d like the engine to last.

Gui
 

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Oof. You can't get any better gas than 92 RON right now? Even the crap we get in California is 95 RON.

Anyway, a 123 Ignition will allow you to set whatever ignition timing you want and use a more retarded curve, yes. That said, I'm not 100% sure that's going to solve your problem. If your issue is too high compression, what would be happening is the fuel is pre-igniting (before the spark) during compression because of too low octane, so setting the spark later may not help. I could be very wrong, though.

I suppose you could do an experiment and retard your static timing several degrees, see if that improves the situation. It may not idle great but at least you can see if this solves your problem, and then make the call on the 123 Ignition.
 

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10.3:1 isn't all that high. In the mid 80's I was running a modded 2 liter in my old Alfetta with the Borgo 10.5:1 pistons when the 91 or 92 octane was all you could get in Texas. I'd read in one of David Vizard's performance engine books a comment about how the then new MSD multi-firing ignitions could promote cleaner burning. Since pinging is caused by an out-of-control flame front I surmised that the MSD would better margin of control of the ignition event. So I installed an MSD in combination with my new Marelli-Plex ignition and no more pinging even on hot days when stuck in Texas traffic. Would this work on your car? Can't say.

Another solution is to dial back your max advance a few degrees and see if that works. The bigger advantage of the programmable 123 is that you and your mechanic can find an advance curve that doesn't ping, use that until you get higher octane fuel and then program in another more performance oriented advance curve.

Its worth noting that late Alfa spiders with Bosch injection used nominally rated 10.0:1 pistons (closer to 9.7 or so). You can pretty easily lower your compression ratio by fitting a thicker copper faced (said to reduce c/r by .5 or so, but check with the vendor) or solid copper specially made head gasket.

Richard has some pertinent comments about compression and octane on his thread that might be useful to you.

Technical Questions And Rj`s Suggestions
 

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Discussion Starter #4
Oof. You can't get any better gas than 92 RON right now? Even the crap we get in California is 95 RON.

Anyway, a 123 Ignition will allow you to set whatever ignition timing you want and use a more retarded curve, yes. That said, I'm not 100% sure that's going to solve your problem. If your issue is too high compression, what would be happening is the fuel is pre-igniting (before the spark) during compression because of too low octane, so setting the spark later may not help. I could be very wrong, though.

I suppose you could do an experiment and retard your static timing several degrees, see if that improves the situation. It may not idle great but at least you can see if this solves your problem, and then make the call on the 123 Ignition.
We can get 102 RON (premium) which costs about 40% more
 

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Discussion Starter #5
10.3:1 isn't all that high. In the mid 80's I was running a modded 2 liter in my old Alfetta with the Borgo 10.5:1 pistons when the 91 or 92 octane was all you could get in Texas. I'd read in one of David Vizard's performance engine books a comment about how the then new MSD multi-firing ignitions could promote cleaner burning. Since pinging is caused by an out-of-control flame front I surmised that the MSD would better margin of control of the ignition event. So I installed an MSD in combination with my new Marelli-Plex ignition and no more pinging even on hot days when stuck in Texas traffic. Would this work on your car? Can't say.

Another solution is to dial back your max advance a few degrees and see if that works. The bigger advantage of the programmable 123 is that you and your mechanic can find an advance curve that doesn't ping, use that until you get higher octane fuel and then program in another more performance oriented advance curve.

Its worth noting that late Alfa spiders with Bosch injection used nominally rated 10.0:1 pistons (closer to 9.7 or so). You can pretty easily lower your compression ratio by fitting a thicker copper faced (said to reduce c/r by .5 or so, but check with the vendor) or solid copper specially made head gasket.

Richard has some pertinent comments about compression and octane on his thread that might be useful to you.

Technical Questions And Rj`s Suggestions

Great ! Thanks for the info !
 

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In terms of performance the 123 would be the obvious best choice. If you decide to use a more powerful multi-firing CD ignition, then I'd suggest the Pertronix digital HP CD ignition. It's a newer design, substantially smaller, and has lots of tuning options. I'm not sure if it works with the 123 ignition, however.
 
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If I understand you correctly your symptoms are a cracking noise from the engine only when in second gear moderate acceleration. If you ad more gas to accelerate quicker it goes away.
if that’s true it doesn’t match any experiences I have with preignition or pinging. Preignition usually needs something glowing hot as an ignition source, it doesn’t sound like the engine is working hard enough to be in that state. Any pinging I’ve deal with is usually in a higher gear, with an engine trying to make lots of torque. Adding throttle definitely didn’t make it go away. Got worse if anything.
What plug are you using. If ngk, maybe try a heat range 7.
 

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Discussion Starter #9
This would be due to the acceleration pump adding fuel If you are running carbs. It's a sign that you may be running a bit lean so enriching your jetting could help alleviate pinging issues.
That makes sense, as there are a couple of other issues I was going to mention.

My mechanic fuel pump failed recently, and it was replaced, in an emergency situation, by an electric , no-brand, no-name diafragm pump (box shaped). I’ve been running it while a more suitable replacement (Facet) arrives.

So I started noticing some temperature spikes in the highway (not in heavy stop and go traffic, when the car runs steady at 175. On a couple of occasions on the highway it slowly creeped to 212, then it returned to 200, stayed there for several minutes to eventually drop back to 180, where it stays most of the time. This could be symptom of a fuel starved engine running a bit too hot (radiator, hoses and cap are new, so no issues here).

I believe a combination of a weak pump with lean mixture can be aggravating the issue. I’ll change the pump soon and see adjustments in the carbs.
 
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