Electronic Ignition advance variations

My old Boyer went south a while ago and I went shopping for a new unit. I thought about purchasing another Boyer, but decided to look at more contemporary designs. I really liked the idea of having rev limiter included and the Multi-spark units seemed like they might have some advantage without any perceived disadvantages. After doing some research I purchased a Power Arc unit. However, after reviewing the advance curve I was surprised it had so much advance and so early. I made inquiries I found that there was an enormous variation in total advance between (and opinions on) currently offered systems. I cannot recall another engine with this large disagreement on such a fundamental and potentially damaging setting.

The factory setting for points is 28 degrees (at 5000 rpm as I recall). According to Brian Slark the mechanical points had a scatter as much as 7 degrees.

The Boyer recommendation was 31-32 degrees (also at 5000 rpm I think) and that is what I have run over the years.

Matt at CNW said that the Tri-Spark unit is programmed for 28 degrees.

The Power Arc ignition offered by Old Britts is set at 36 degrees and it reaches this advance at 3000 rpm.

I have read generally positive reviews on all of these units here and elsewhere on the web and Fred and Matt are both reputable guys, but an 8 degree variation in advance setting is a darned wide spread. Kenny Cummings races using one and seems to be doing fine. But having said that I cannot imagine that Matt is going to offer $1500 flatside carbs and leave a bunch of performance on the table if there was an reasonable risk/reward ratio for running simply greater advance.

Can anybody offer a logical explanation/opinion?

We had a similar 'advance curve' discussion, recently:
advance-retard-electronic-ignition-t19917.html

austinnorton said:

The factory setting for points is 28 degrees (at 5000 rpm as I recall).

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(Points: 28 degrees at 3,000 RPM)

http://www.classicbike.biz/Norton/Repai ... mmando.pdf

Austinnorton,

I am not running 36 degrees. Tried it once a few years ago, but have since gone back to 28 degrees for my racer.

Old thinking on getting Max power from gnition timing- - advance until pinging can be detected then back timing up a little.
New thinking on getting Max power AND safety with igntion timing- retard until power loss is detected then advance only enough to have full power return.
It helps to have a dyno, but a big steep hill with a constant grade and good speedo also works.

Glen

Holmeslice said:

Austinnorton,

I am not running 36 degrees. Tried it once a few years ago, but have since gone back to 28 degrees for my racer.

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Thanks Kenny. I assume your curves from Old Bitts reflect this. Dave

Typically 28 degrees at full advance is close to the optimum advance for normal Commando engine. Might go as low as 26 degrees for really high compression ratio engines, or as high as 31 for low compression engines. Also depends on other tuning factors (cam, pipes, etc.), but not much. Unless you've got something weird, like reshaped combustion chamber or seriously altered porting, or running on alcohol, that's pretty much the range. But that's only for full advance. The real arguments about the advance curve are over the shape of it before it reaches full advance, particularly at starting and idle rpms. I don't have anything to add there, but there are plenty of opinions to keep you confused in the posts referenced above. My experience has been with race engines, many of which were fixed advance, so all I've ever really looked at is maximum horsepower at high rpm. YMMV.

Ken

austinnorton said:

The Power Arc ignition offered by Old Britts is set at 36 degrees and it reaches this advance at 3000 rpm.

Can anybody offer a logical explanation/opinion?

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Just to be clear, Old Britts offers 2 PowerArc units, the C1 and the C2.

The C2 has the ability to change wires for different advance curves. One such curve is in fact the 36 degree option. This is the high end of the options and is regard as a racing curve and more applicable to Triumphs.

The owner/designer advertiser of PowerArch says he's worked with Norton drag racers for years past and reason he says Nortons can use 36' full advance, which flys in face of all experienced Norton hot rodders. The main reason to get a PA ignition is to program your own curve to suit your own set up, which of course takes more time to have others do it or costs more money to get the interface to brew your own. In very hi rpm engines its common to advance spark to give time to start combustion before TDC but not sure if any but maybe Sir Eddies 500 land speed wonder can endure spun fast enough to benefit. Fast advance if engine can take it w/o detonation is the standard way to get good response faster.

Drag race engines can run 36 degrees advance simply because they are raced starting with a cool engine. 1/4 mile is not enough to bring the engine up to full operating temperature. When the engine is cool then the mixture in the chamber is cool so it burns more slowly and requires more advance. The cool mixture is more dense so it makes more power.

When an engine is up to full temperature then the mixture in the chamber is also hotter and burns faster so less advance is used. If you use 36 degrees advance on a street motor the result will be shortened engine life on a low compression motor and detonation and destruction on a high compression motor.

The way to more power on anything but a drag racer is burning the mixture fast with high compression, a turbulent mixture and a good squish band. This lets you run less advance which means there will be less pressure before TDC . Pressure before TDC is lost power and more engine heat and wear.

The Power Arc ignition is still the least powerful ignition per spark of any ignition system I have tested -including stock points. That is why they specify a very small plug gap. Jim

Thank you JIm for filling us in on exceptions to the rule on Norton timing tolerance. i've seen non cycle racers pack heads and fuel tanks in water or dry ice, which is not very practical after a few minutes in public use. I've got most the exceptions to the Powerarc faults solutions on hand so will try to make it work on Peel but in back of mind hope to talk you out of your now excess single injector-ignition system and dyno dialing in to survival level. The Commando distractions form our real life is priceless time waster.

Pazon Altair curve:

http://www.pazon.com/files/AL2-advance.jpg

When you are tuning a bike for maximum performance you are balancing three things - mixture, ignition timing, and compression ratio. Best power comes from a situation just prior to self-destruct. The combustion event takes a fixed time to occur so as the revs rise, it is normal to advance the ignition timing so the completion of that even always occurs just after TDC. If you are getting max power and slightly advance the timing or lean if the mixture, or raise the compression ratio, you should at least get detonation if not destruction. The specified advance for a command on petrol is 28 degrees and with specified jetting, you should not have problems. In my own case I use methanol fuel, so you can immediately add about 4 degrees to the ignition advance because of it's superior antiknock properties. However in other ways it is similar to petrol except that it's high latent heat of vaporisation cools the incoming charge, so the jetting has to flow about twice as much. Because I am using standard compression as for petrol, my jets are much leaner than what would be used in high comp. engines. I've been using a Boyer ignition with 32 degrees advance along with vey lean mixture, and the results are superb on short race circuits. However I suspect that on a big circuit I would certainly experience detonation. You find the situation where the motor is running at high revs with the throttle wide open, and lose vacuum so the mixture leans off. In the 70s two strokes they used power jet carbs to solve this problem. My answer is to find an ignition system which retards slightly over 6000 RPM. I've been looking at the reasonably priced Dynatek 2000 systems which are used on Harleys (bite my tongue). They have 8 advance curves available with a vacuum operated switch which changes the advance curve to one with a bit of retard when it senses loss of vacuum. I use Mk2 Amal carbs with Mikuni petrol needles, with the methanol fuel so there is plenty of opportunity to trim the mixture to suit the advance curve. I think the curve I will try first will be 32 degrees advance at idle, moving up to 38 degrees at 6,000 RPM (methanol fuel, so subtract 4 degrees if you are using petrol). I would expect a slight improvement in midrange to top end torque, i.e. 3/4s of the way down the straights on race circuits.

Most engines require different advance curves, so why do all motorcycles have to put up with only I advance curve to fit all. Even in the days of points, there were different springs, weights and max advance stops.
Why can't these ignition systems be made engine specific, by simply using a different chip for each engine.
I make the point that if some out there are prepared to pay $5,000.00 for an engine rebuild, then to pay $300.00 for one of these units instead of $200.00 that they cost now, would be chicken feed.
I realise these manufactures have to make things fool proof, so a programmable ignition might not be such a good idea, otherwise some fool would do the wrong thing and stuff his engine.
I would be keen to have input from Pazon or Boyer.
The only trouble I had with my Boyer was the wires breaking at the sensor and probably because they were not crimped properly. I have foam rubber cushioning the wires as well.
Dereck

"Why can't these ignition systems be made engine specific, by simply using a different chip for each engine."

Because, unless the engine is being RACED, there is a usual safety margin for street driven engines and the wide variety of variables... altitude, terrain, gearing, fuel quality, compression ratio, operator skill/error, load (single jockey size person or 2 fatties and camping gear). The good news is, being one full step away from the ragged edge of disaster is usually not forfeiting a large amount of power. The whole point of diminishing returns thing.

There has always been a contingent of people who want to run race equipment on the road... they must be keenly aware of all that's at play and adapt for it. To them it's a fulfilling endeavor.

Then there's the guy that wants someone to build a hot race engine for him, and expect it to be Camry reliable under all conditions with no adjustments. Those are available, called modern sport bikes.

Or you have your cake and eat it too.

is that a knock sensor.

comnoz said:

Or you have your cake and eat it too.

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A marvel of engineering! Using modern day tools to solve age old problems. :idea:

Loved it when my 800 PTek Rotax came with a knock sensor. Saved countless 2-stroke lives! :lol:

kerinorton said:

Most engines require different advance curves, so why do all motorcycles have to put up with only I advance curve to fit all. Even in the days of points, there were different springs, weights and max advance stops.
Why can't these ignition systems be made engine specific, by simply using a different chip for each engine.
I make the point that if some out there are prepared to pay $5,000.00 for an engine rebuild, then to pay $300.00 for one of these units instead of $200.00 that they cost now, would be chicken feed.
I realise these manufactures have to make things fool proof, so a programmable ignition might not be such a good idea, otherwise some fool would do the wrong thing and stuff his engine.
I would be keen to have input from Pazon or Boyer.
The only trouble I had with my Boyer was the wires breaking at the sensor and probably because they were not crimped properly. I have foam rubber cushioning the wires as well.
Dereck

Click to expand...

The difference in strokes and rod lengths of various engines means that the deceleration rate of the piston is different as it approaches TDC. If the combustion event takes a certain fixed time at the optimum mixture, then rate of change o timing of the start of the event with revs, must change for various engines. It is probably possible to calculate the profile of the optimum curve from the stroke and rod length, up to near max revs. Then there would only remain the mixture and the static advance to consider, as with fixed timing. I suspect that the shape of the taper on Mikuni carb needles for various engines reflects similar considerations.
There is one aspect which it would really be worth talking to Boyer about and that is the dwell time of their programmable ignitions which use hall effect sensors. Might be a problem depending on the rev range and comp. ratio you intend to use.
Derek, you won't stuff your engine if you use a timing light or engine analyser to check what the ignition system is doing, and take a bit of care with carburation - you will be doing that anyway. Two things - if the motor coughs while it is metering on the needle - too lean. And always do a plug chop using one range hotter plug than normal to check the main jets.

kerinorton said:

is that a knock sensor.

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Yes,
I have a 144 entry timing lookup table that uses map over rpm. It is loaded with an aggressive advance curve.

When the motor is started it uses the advance curve as it is loaded in the table. If the knock sensor hears a ping it will retard the timing at that load/rpm point 1 degree at a time until the ping goes away. Then it uses that "learned" timing figure from then till the engine is shut off. It does this for each of the 144 table entries.
When the motor is shut off it looses the memory and learns all over again the next time it is started. The sensor is sensitive enough to pick up very light ping so it will retard the timing before you even hear the ping when riding.

This is a new addition and so far it is working very well. I tried using it once before but had trouble with normal engine noises triggering retard but I found a tunable module to filter the engine noise so all it can hear is the ping frequency. Jim

FWIW-I have a Power Arc on my 71 roadster. Engine is stock with fairly low compression judging by the effort it takes to start it. In two years of normal (sane?...sometimes not) riding I've never heard a ping or rattle out of it. Never any overheating or plug fouling as well. Not real sure what the actual number are on the advance, but it has an extra wire from the unit that the instructions say to power up for more "aggressive " riding. I've never tried it.