SOHC.co.uk Forums > CB500/550
Electronic ignition
K2-K6:
--- Quote from: Sesman on January 17, 2022, 06:09:11 PM ---I’ve just seen a squirrel…..
Seriously though. I transistorised switch has got to be a better solution to achieve a superior Ldi/dt HT performance and reducing stored energy across the points Cdv/dt?
I’m betting that if CDI or and EI was available to Mr Honda back in the 70s he would have used it in preference to a mechanical system.
Just wondering….
--- End quote ---
Interesting point, there's more to the fundamental part and characteristics of this ignition type than first appearance.
Undoubtedly Honda would have known then the variance in options available to them, with some more suitable than others. The general view given out over many years by popular opinions that the bigger the spark the better. In essence, that the flash-bang-wallop and lightning-level-blow-your-trousers-off provision of sparks is going to out perform anything else couldn't be more inaccurate.
CDI for example could be viewed as mostly unsuitable for these four stroke combustion designs from this time. Two stroke, yes, as they have a fundamentally different requirement in their combustion chamber. More related to diesels in reality, the central (usually) mounted plug with almost perfectly sized initial burn chamber in a cone geometry, is perfect for high energy short spark duration output of CDI systems. It gets the mixture going locally to the plug which effectively ignites the rest of the chamber as it comes up to squish (and why tuners often concentrate on their favourite swish geometry) to efficiently light the remaining charge as it comes to full compression.
The honda four stroke strategy is completely different (as are most compared to 2T ) in that the spark duration is lengthened to work with the engine to burn effectively. Of the ignition system modifers/suppliers only Hondaman talks about this element, and mimics the Honda stategy in switch time to deploy the coil output in extending the spark.
In essence, the Honda design (I'd consider them absolute masters of this capability) get the complete four stroke cycle to optimum such that it's easy to ignite the chamber, it really doesn't need anything with increased energy to fit the strategy they've created. You can throw as much flash-bang at it as you wish, it won't make a blind bit of difference (compared to properly performing original) as you aren't changing combustion conditions by doing so.
In reality, if you shorten the spark too far the risk of uncontrolled detonation travels closer to the ideal combustion, eating safety margin as it does so.
The only thing supplimentary systems do is to take switch load from breakers and make them last longer.
AshimotoK0:
Mr Honda did use CDi extensively in the very late 70's into the 80's and beyond on both the CX500, Superdream , CBX etc. made by Hitachi and it wasn't multi-spark AFAIK.
Back in your naughty corner Ash :-X :-X
K2-K6:
Oh, definitely but a fundamental change in combustion chamber as the four valve at narrow angle design moves in geometry toward that discussed in the 2T part. And one of the reasons for designing in that way.
You'll see a much reduced overall combustion time for that type of head which is why high revving faster engines use the layout as it has a much higher ceiling in combustion terms.
You can broadly separate them by looking at total ignition advance. The lower that is the faster the chamber is burning, and by default doesn't need the same lead time from ignition to get the burn coinciding with the piston being just past TDC.
K2-K6:
Here's the "missing link" Ash with CDI type
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The Honda RCB endurance racer of 1970s. The bottom end is straight 750 SOHC, note ignition removed, twin cam 4 valve head, ignition I think is picture central (see the two opposed pickup) running on the rear of alternator spindle that's geared/chain driven to left of crankshaft.
They also went further on later modification of this engine by converting it to gear primary drive.
deltarider:
AFIK, we have not seen verifiable signs of a created longer burn time by adding resistance, let alone that we have seen testimonies about a benificial effect, with the exception maybe of one by a gentleman on an elevated mountain road in Colorado.
Could it happen? In theory yes. After all, I vaguely remember something about Rc time from school. It's my view, it will be hard to tell, if there's a significant and benificial effect. The first can be realised by applying test equipment I cannot afford. The latter will be harder to tell. How can you tell what the burn time attributed over the flame front's performance? With a stock ignition or with a transistorized one there will be ample burn time during enough degrees crank rotation. With discharging capacitors this might be different however. As I understand it, there's no reserve and a CDI may not be able to 'try again' like the pic below shows.
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