Safe Ignition Advance

[roydm]

Hi,
I have a new Engine Control Unit for my Moto Guzzi that allows me to alter the spark setting and injector timing at any rev range.
I gather there's a point at which advancing the spark results in little increase in power but higher risk of engine dammage due to higher piston load at TDC

My question is what is the maximum safe advance to use?
Is there a simple formula to calculate advance vs engine speed.
I guess the same goes for injector timing I immagine there's a formula for that also.

I am not seeking super performance just a nice smooth ride with reasonable fuel economy and reliability.

Thanks in advance
Roy

 

[dgallup]

While there are lots of "rules of thumb" for spark timing, there are far too many variations in combustion chamber, inlet, exhaust, plug location, fuel quality, etc. to ever boil it down to a simple equation. There are very complex FEA codes that do a reasonable job of simulation but for practical purposes your best bet is to rent some dyno time with a knowledgeable tuner and develop the best tune for your particular engine.

I assume when you say injector timing, you mean duration. There is not a lot to be gained by changing the timing of the injection but the duration controls the quantity of fuel injected which directly controls the air fuel ratio.

 

[roydm]

Yes, both the spark advance and injector duration are completely adjustable at every throttle setting and engine revs. Like a spreadsheet with throttle on one axis and revs on the other.
Thanks for the response.
Roy

 

[Tmoose]

"just a nice smooth ride with reasonable fuel economy and reliability."

Start with the factory timing curve.

Does the system accept some kind of throttle position or intake vacuum input signal?

 

[evelrod]

To start---Your sitting atop the thing. It's not like it's hidden under a blanket of sound/vibration insulation "under the bonnet". You have decided that this new addition can possibly alter the engines performance in a beneficial manner, at least as your post appears to me. So---The same advice I give to all the kids that come into my shop to "learn the secrets" of my engines performance......

Take it out. Ride it long enough to get a "base line". Now, TINKER with it. If you go too far, your gonna be the first to know it...Those two big cylinders hanging out the side will let you know, for sure. So long as you do not over do your changes, so long as you do not press the issue, so long as you use a little common sense...you may be able to improve your ride beyond any percieved "factory compromised performance".

Remember the "truism"...Free advice is often only worth it's cost!!!

Rod

 

[roydm]

Thanks for all the responses, I have a few maps that show a maximum spark advance of 42°, that seemed like an awfull lot to me hense my original question.
The stock ECU on the bike had a few issues, cutting out etc.
For about 1/2 the cost of a new Black Box I purchased a kitset that allows me to freely set the advance and injector duration.
Yes, it has throttle position, atmospheric pressure, oil & air temperature along with provision for a lambda sensor for closed loop operation.
The bike naturaly goes like a rocket so I am not seeking any more power I would rather go for reliability and better fuel economy.
Regards
Roy

 

[Tmoose]

Full throttle with 4 inch pistons and crummy low turbulence combustion chamber might need 40 plus degrees of advance. (Or bores as small as 3 inch with really convoluted combustion spaces created by "high compression pistons"

http://www.dumbassbiker.com/PhotoID5463.jpg

)

An extra 10-15 degrees of "vacuum advance" might be correct for part throttle economy

 

[roydm]

The Engine Control Unit is a Jefferies MyECU out of Australia. It allows you to set the advance and injector open time at any combination of throttle position and engine speed (over 200 points on the map) I think the Guzzi must have one of those combustion spaces Tmoose mentions, I know one upgrade is to add a second plug