In the next month or so I will be installing my 9.8:1 engine into the car. A couple of questions regarding the ignition timing.
1. Will I need to retard the timing any in order to avoid detonation? I plan on running at least 92-93 Octance.
2. Does anyone have any ignition maps for a programmable ignition on a 2.0L? This is another option I have that I am still undecided on.
Thanks
Ignition Timing for HC 2 liter
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vcg
9.8 is not that high of compression. In fact it is the standard compression of the 1969-1975 Euro 1600 & 1800 124 Spiders.
Regarding timing Euro specs suggest not more than 38 degrees total advance and 10 degrees static.
My personal advice is go for 38 total if you use high octane fuel, or keep around 35-36 with standard fuel.
Regarding timing Euro specs suggest not more than 38 degrees total advance and 10 degrees static.
My personal advice is go for 38 total if you use high octane fuel, or keep around 35-36 with standard fuel.
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YeLLoWBoAt
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So Cal Mark
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vcg
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emlo
This is a pretty tricky matter, and basically there are no quick and dirty fixes that will give you maximum mileage and performance as long as you are using a distributor. Car manufacturers all use some sort of programmable ignition today, and before then they spent lots of time optimizing distributor advance curves (for performance/fuel economy and not to forget EMISSIONS) for each type of engine. They also have to take in account the fact that the buyer may try to run the car on poor gas or in Arizona or other hot places (high intake temp affects knock very heavily!).
As soon as you start altering your engine any way the ignition requirements change and your OE distributor will be less than optimal.
I would find it interesting to discuss the matter more in-depth with the other members here. To begin with, here are my general thoughts and opinions based on what I've read and some personal experience.
If you are using a OE distributor and are not intending to modify the ignition advance curve, I would look at the maximum advance (>5000rpm or so) only, and probably set it at approx. 35 +/- 3 deg. (if you are using high octane fuel). Vassilis mentions 38 degrees but I personally have not been able to go higher than 35 without detonation problems, and have the dizzy set at 33 for day-to-day use (2L with 10.8:1 compr ratio). Naturally this is a matter of what fuel, air/fuel ratio, compression ratio, exact layout of the engine/intake/exhaust etc. etc., but since you are only running 9.8:1 CR 38 deg would probably be about right.
Keep in mind however that the smog engines from late 70s had a distributors with total advance of 38-40 degrees(!) and a really funky advance curve (for emissions reasons) which would give you pretty crappy low end performance and fuel economy with 35 degree ignition at maximum advance. If this is what you have I would consider letting a shop rebuild it for you or simply replacing the unit.
When running at full load pretty much all relatively high performance engines are knock limited, that is, you will find maximum performance on the "border" of detonation/knock. Setting up you maximum ignition with a slight margin in order not to run into problems on a particularly hot day or with a bad tank of gas may be a good idea. Low compression engines like the circa 1979 FIAT 2L will, in my experience, normally not run into detonation at all, but obviously torque will go down if maximum advance is exceeded.
Retarding ignition slightly into a safer region (away from the knock limit) will give you slightly less power AND slightly decreased fuel economy as efficiency will go down with retarded ignition. Nobody really cares too much about full load fuel economy so that is no big deal. However, at low or part load ignition advance requirements are higher than at full load and a retarded ignition (optimized for full load, which is what you 'll get if you don't have vacuum advance) will give you a certain in fuel economy. On the other hand, if you have a distributor with vacuum advance it will compensate for most of this reduction. A vacuum advance unit may even over advance ignition at low/medium load if you have a an engine with large advance requirements at full load, which naturally also reduces fuel economy.
As if this isn't enough there are a bunch of other aspects to take in account, for instance the possibility of advancing ignition in a certain rpm range because of good scavenging due to optimized intake or exhaust header etc., which obviously only can be done with a programmable ignition system, and lots of dyno time..
I would be interested in hearing from other readers what distributors you have found out to function well, and if there are any good combinations of springs/weights/max advance plates that have given good performance.
Good luck!!
Emil
As soon as you start altering your engine any way the ignition requirements change and your OE distributor will be less than optimal.
I would find it interesting to discuss the matter more in-depth with the other members here. To begin with, here are my general thoughts and opinions based on what I've read and some personal experience.
If you are using a OE distributor and are not intending to modify the ignition advance curve, I would look at the maximum advance (>5000rpm or so) only, and probably set it at approx. 35 +/- 3 deg. (if you are using high octane fuel). Vassilis mentions 38 degrees but I personally have not been able to go higher than 35 without detonation problems, and have the dizzy set at 33 for day-to-day use (2L with 10.8:1 compr ratio). Naturally this is a matter of what fuel, air/fuel ratio, compression ratio, exact layout of the engine/intake/exhaust etc. etc., but since you are only running 9.8:1 CR 38 deg would probably be about right.
Keep in mind however that the smog engines from late 70s had a distributors with total advance of 38-40 degrees(!) and a really funky advance curve (for emissions reasons) which would give you pretty crappy low end performance and fuel economy with 35 degree ignition at maximum advance. If this is what you have I would consider letting a shop rebuild it for you or simply replacing the unit.
When running at full load pretty much all relatively high performance engines are knock limited, that is, you will find maximum performance on the "border" of detonation/knock. Setting up you maximum ignition with a slight margin in order not to run into problems on a particularly hot day or with a bad tank of gas may be a good idea. Low compression engines like the circa 1979 FIAT 2L will, in my experience, normally not run into detonation at all, but obviously torque will go down if maximum advance is exceeded.
Retarding ignition slightly into a safer region (away from the knock limit) will give you slightly less power AND slightly decreased fuel economy as efficiency will go down with retarded ignition. Nobody really cares too much about full load fuel economy so that is no big deal. However, at low or part load ignition advance requirements are higher than at full load and a retarded ignition (optimized for full load, which is what you 'll get if you don't have vacuum advance) will give you a certain in fuel economy. On the other hand, if you have a distributor with vacuum advance it will compensate for most of this reduction. A vacuum advance unit may even over advance ignition at low/medium load if you have a an engine with large advance requirements at full load, which naturally also reduces fuel economy.
As if this isn't enough there are a bunch of other aspects to take in account, for instance the possibility of advancing ignition in a certain rpm range because of good scavenging due to optimized intake or exhaust header etc., which obviously only can be done with a programmable ignition system, and lots of dyno time..
I would be interested in hearing from other readers what distributors you have found out to function well, and if there are any good combinations of springs/weights/max advance plates that have given good performance.
Good luck!!
Emil