Ignition Mapping - How it works

[boscoe99]

It is so nice to have a computer con*****ed ignition system. No more points to wear (points themselves or the rub block). No more capacitor. No more centrifugal advance. No more vacuum advance. No more distributors. No more high tension leads. No more plugs being worn so quickly.

I love computers.

But then I hate computers.

It is a love/hate relationship.

Now with processors becoming so damn fast and so damn cheap, has there already come a time when look up tables are no longer being used? The processor should be able to take all variables under consideration and make damn near instantaneous calculations as to what the ignition point and fuel delivery schedule should be for any engine at any given point in time. Are there any engine makers using such a processor? Won't be Yamaha for another 5 or more decades given the slowness with which they advance their technology.

[rodbolt17]

exccessive ign timing under a high load leads to "spark knock" otherwise known as detonation.
modern engines combat this with knock sensing capabilities.
be it a sensor or a second firing(V8 Yamaha 1st generation).
as engines got more and more powerful and compression ratios started to rise the early way to prevent knock yet allow light load efficiency was by adding a vacuum advance to the mechanical advance.
as engine speed,distributor speed, rose the centrifical advance would advance ign timing.
at light load the vacuum advance would add a bit more.

however at high loads the intake vacuum drops to near 0"Hg and the vacuum advance would retard.

was a crude method to prevent spark knock.
a few auto actually injected water in the intake as well under sudden high load conditions.

ign timing is a critical part of any internal combustion articulated rod engine.

light it to early and it leads to pre-ignition(detonation again) that can lead to piston damage.
light it to late and the fuel is still burning when the ex valve opens that leads to burned ex valves.
I have seen cast iron manifolds literally glow red.

typically max spark advance has always been in the 22-32* range.
however on certain motors and loads I have seen up to 38*.
the 455 in my 442 had strictly mechanical advance and it was set up for a max of 32* at 3500 RPM.
this was using a fairly aggressive Luanati cam,TRW forged pistons at 11-1 an edlebrok torker intake and an 800 holly spreadbore with mechanical secondaries.
M-22 Muncie and 3.90 gears.

[boscoe99]

exccessive ign timing under a high load leads to "spark knock" otherwise known as detonation.
modern engines combat this with knock sensing capabilities.
be it a sensor or a second firing(V8 Yamaha 1st generation). How well did that work out?


typically max spark advance has always been in the 22-32* range.
however on certain motors and loads I have seen up to 38*.
the 455 in my 442 had strictly mechanical advance and it was set up for a max of 32* at 3500 RPM. I had a 1967 442 but it only came with a 400 ci motor. Wish I still had it. 4.33 gears.
this was using a fairly aggressive Luanati cam,TRW forged pistons at 11-1 an edlebrok torker intake and an 800 holly spreadbore with mechanical secondaries.
M-22 Muncie and 3.90 gears.

What is Yamaha trying to say when they mention 50 degrees BTDC?

[rodbolt17]

the V gen 5 Volvo marine stuff is now all AL variable cam timing and use a direct cyl injection with a mechanical pump that varies between about 500 PSI and 2200 PSI.
with a max RPM of about 6000 ,yep processors are getting quick.

[zenoahphobic]

and I have to vehemently disagree with your assessment of ign timing.
ign timing has EVERYTHING to do with a motors(articulated rod internal combustion) ability to make power.

I am not sure there is a basis for strong disagreement, just a different perspective of looking at it.

That graph shows "arbitrary" points at which the rate of advance (curve) alters. Through out history "arbitrary" points have been selected. The simple argument put, is that ignition advance should increase at the same rate as revolutions increase, because the time available to start the ignition process is reduced at the same rate. But there are other considerations to consider; that have been speculated upon by various people in this thread. I don't know if you disagreed with my proposition that early fiddling with ignition timing was prompted by emission controls and not for horsepower gains.

On the point of HP gains, these tend to be in the realm of 1% to 5% (i.e. small) gains. You reminded me of the past "contraptions" that tend to be forgotten. An outboard example I had was an old in line six Mercury. Off the top of my head, I think max advance should be 21degrees. On checking mine it was 27degrees. Upon correctly adjusting it back that 6 degrees there was no loss or gain in top speed (HP easy to measure as a function of speed); I was curious why there was no change.

Although I realize in the racing world of cars small percentages add up. I remember putting a new distributor (completely different one) in a 351 Cleveland (2V) I had. No idea really where this distributor was supposed to be rotated to, but guessed. I noticed idle speed changes, but set this to not exceed whatever advance was max by manually rotating the sprung innernerds. Took it for a run ran the same (subjective of course). Put it more advanced, same. When I checked the timing light I realized I was reading it wrong and made correct adjustment, I again could not feel a difference. What I am saying is that on this engine a handful of degrees here or there made little difference. But I did not run flatout, foot to the floor WOT.

Add to the argument, diesel engines don't even have a "start ignition" system. Engines with high power to weight ratios running off just glow plugs - no adjustment there. Even altering with colder or hotter plugs don't make a huge difference. I had a motorcycle (trials) that not only had no advance mechanism (set retarded) but at times was happy to run on the overhot spark plug, as I could not kill the engine with the electrical coil to earth stop at times (low revving engine with tons of torque). Yes header pipe glowed in the dark, maybe not to good for the engine I hear people say, but it worked without destruction for decades.

Of course ignition needs to be there for gasoline engines, and timing needs to be within parameters, but maybe not as precise and changing as suggested in medium performing engines for horsepower gains as one might think.

[zenoahphobic]

My guess, and just a guess, would be that it is detonation related. Structural well being of the model as you note.

No knock sensor on this motor. 87 octane gasoline specified. If it makes its rated HP at 5500 RPM then there is no need for any further ignition timing advancement. Reliability trumps more HP.

Or it could simply be that no more air and fuel is able to get in the combustion chamber after 4500 rpm. Meaning that ignition timing is desirable to be linearlarly (?) a function of the air/fuel charge and not a function of the time required to start the burning process?.

[boscoe99]

Or it could simply be that no more air and fuel is able to get in the combustion chamber after 4500 rpm. Meaning that ignition timing is desirable to be linearlarly (?) a function of the air/fuel charge and not a function of the time required to start the burning process?.

I am not understanding how no more air and fuel is able to get in the combustion chamber after 4500 RPM.

Valve(s) open, piston goes down, air gets forced in, fuel has been added based on the amount of air, a power stroke occurs...

More advance timing generally equates to more power. There are companies that remap cdi's and ecu's to make more power. Would be interesting to me to see if the timing on the motor in question was advanced if more power was produced.

[zenoahphobic]

I am not understanding how no more air and fuel is able to get in the combustion chamber after 4500 RPM.

I meant no increase in air/fuel; that it may have reached a plateau due to friction in the air intake system. There is a finite speed at which friction becomes the limiting factor to air flow.

The engine is still able to make power because there still is an increase in power pulses over time. Of course the power output begins to drop after reaching this peak and eventually the friction of all the moving parts becomes so great that it dramatically robs the power produced by the engine.