Ignition Timing Changes - Affects of
What about part throttle power - like driving around town or exiting a 2nd or 3rd gear corners.
At part throttle, the trapped compression is obviously less than it is when at full throttle (otherwise you'd make the same power at part throttle as full throttle). The pressures and temperatures inside the combustion chamber are lower and cause the trapped air and fuel to burn slower than when at the higher pressures and temperatures as under full throttle conditions.
For best power, the peak cylinder pressure must occur at a crank location that is very, very slightly before TDC.
To reach peak cylinder pressure at the proper location for maximum power, you should "light off" the mixture sooner so that it can reach peak cylinder pressure at the proper crank location, not later - perhaps after TDC!
Retracted gap, surface gap, projected tip
If I change the type (i.e. geometry of spark plug, does that change the timing?
Well, that's an interesting question to answer.
Changing the spark plug shape doesn't actually change the timing. BUT!
The MBT (Makes Best Torque - optimum) ignition timing for the style of each spark plug IS different.
If you were to to test spark plugs, using the geometry as the variable, and matching ignition timing for each geometry type, you will probably find that, as we did with the 4 Gas EGA EC997 dyno, that:
Spark plugs with "retracted and
surface gap" style as compared to "extended tip" styles, require
more ignition lead / advance to make best power.
Spark plugs with "projected / extended tip" electrodes require less ignition lead to make best power.
In other words - if you place the spark closer to the middle of the combustion chamber with a "projected tip" spark plug you will need less time (ignition advance) to reach peak cylinder pressure. That's a good thing.
With an "extended tip" style plug, as the piston is rising on the compression stroke, you will generally find that you will start the "burn" later for MBT setting - decreasing the amount of time that you are burning, heating and expanding the trapped air and fuel as the piston is still going up. Any pressure that is created as the piston is coming up to Top Dead Center tries to push the piston back down - subtracting power from the total amount of power produced on the following power stroke. This is IMPORTANT!
Soooo...... in general:
You want to build / tune an engine to have
the quickest burning, most efficient combustion chamber.
Use a spark plug that requires the least amount of ignition lead for best power.
Use a fuel that has the quickest possible burn rate, without detonating, so that you end up using the least amount of ignition lead / advance for best power.
That will produce best power.
In reference to the above ignition timing comments:
Should I use more or less ignition advance to make best power?
You missed the point!
You have an engine, you have a spark plug, you have a fuel.
With YOUR engine package, you need to find
the BEST ignition timing setting for IT.
Too much advance or too little advance will decrease power.
The goal is to put together a package that requires the least amount of ignition lead / advance to best power. That will better power than a combination that required more ignition lead / advance.
How do you test for best ignition advance settings?
The ONLY correct way to test for best ignition settings is under full load of a dedicated load dyno with a 4 Gas EGA - NOT under a sweep test on an inertia dyno with a bogus A/F Ratio fiasco.
Inertia dynos, like dj dynos, do not recreate correct combustion chamber temperatures as are present in the real world or on the EC997.
Typical temperature difference on a dj dyno vs. EC997 vs. measurements taken by Champion Spark plugs on a gsxr750,, during on road use show that the dj dyno completed the test with combustion chamber temperatures 300f to 400f lower than with normal track or EC997 use.
Since temperature drastically affects the burn rate of the air and fuel mixture, optimum ignition timing settings as shown on a dj dyno are incorrect for best power on the track or road.
Why the 4 Gas EGA EC997 over an A/F ratio generated by an O2 sensor as dj uses?
When combustion is occurring efficiently at
the proper combustion chamber temperature, there is a general optimum ratio
between the residual gases.
For tuning purposes, there is a "general" relationship for CO% of total exhaust and best power. Once you are correct on the best mixture, which delivers best power under actual braking load (not inertia) and CO% is just a clue, there is percentage of CO2 (carbon dioxide) that will be present WHEN THE IGNITION TIMING CORRECT.
Why? When ignition timing is correct for best power, there is enough time and temperature to make a general narrow range of a percentage of CO2.
What's wrong with a "wide range" O2 sensor like dj uses in a sweep test?
It's just wrong, as my friend Patrick says.
An O2 Sensor, wide range or otherwise, only senses leftover O2 / oxygen in the exhaust gas.
Well, there's nothing that an O2 sensor does that helps you find best ignition timing.
The optimum real A/F ratio changes GREATLY with the amount of load applied (part throttle vs. full throttle), compression ratio and ignition timing and fuel used - ranging from 10.5:1 to 13:1. The real A/F ratio can only be derived from measurements of the amount of air and fuel that the engine receives - not from the amount of oxygen left in the exhaust.
What's wrong with measuring residual oxygen and calculating an A/F ratio? "Everybody knows that engines make best power at 14.7:1 (or 11:1 or 12.5:1 or 12:8:1)"....
All that you are measuring is the amount of oxygen left in the exhaust.
In chemistry class, you'd learn that 14.7:1 will provide a proper match of hydrocarbons molecules and oxygen molecules.
In Theory, in a classroom, that works well - assuming perfect efficiency.
In Reality, no combustion chamber is perfect, some are better or worse than others, and there is always some oxygen and some hydrocarbons that just can't find each other at the right temperature and pressure and right location to form that magic, heat producing reaction that expands the air and pushes down on the piston - making more power.
What affects residual oxygen in the exhaust?
Type of fuel.
Efficiency of the combustion chamber.
Temperature of combustion chamber material.
Jet Stagger between cylinders. Jet stagger GREATLY affects residual oxygen - and therefore makes an O2 sensor show a lean A/F Ratio when tuned for best power.
Almost every new FI Suzuki has poor stagger
between cylinders at some rpm's - even the new 1000, especially at low and mid
rpm's. So, if you assumed that you would make best power at 12.8:1 on a Suzuki,
and adjusted fueling to get that, according to your "wide range" O2
sensor that someone sold it to you as an A/F Ratio sensor, instead of tuning for
best power, you will throw power away because you relied on incorrect fuel ratio
data from an incorrect sensor.
Even if you previously actually had measured air and fuel intake properly for a correct A/F ratio, because the stagger was leaving 2 cylinders still too lean as compared to the other 2 cylinders - an O2 sensor WILL NOT read the same ratio as the real measured A/F ratio - because, it's being affected by incorrect fuel rate stagger cylinder to cylinder, and combustion chamber efficiency, etc.... It will read leaner than actual - to some unpredictable amount.
How much really?
As Mike (who has a model 250 something
inertia dyno with an huge eddy current brake hung on the side) said last night
of his dynojet A/F Ratio -
"I don't use it for anything because it doesn't work."
Using an oxygen sensor to display an A/F ratio is incorrect, we would NEVER sell an O2 sensor and claim that it show's A/F Ratio - because it is NOT A/F ratio.
It's a cheap, (but costs a lot) fragile, moisture and lead intolerant sensor that makes a graph and leads tuners off and away from best power and tuning. Witness the Aprilia maps created by dj.
I'm sorry if you paid $2500 for one for
your dyno. I didn't sell it to you and you didn't do enough research before you
Calling an O2 sensor an "EGA" is a new, creative use of "EGA" and real stretch in the industry. To display it's measurements in your software as A/F Ratios in just wrong and misleading and a detriment to the tuning industry in general.
The 4 Gas EGA EC997, as it auto logs gas information at each RPM point, provides residual oxygen readings as a percent of exhaust value. The ONLY things that residual oxygen (O2%) will show, when an engine is already tuned for best power is:
1. Whether the stagger on the jetting is
incorrect or correct.
2. Whether ignition timing is close to optimum or not.
3. When you have tuned for best power, you can look at the relationship of the exhaust gases to get an impression on combustion chamber efficiency.
Will the OEM manufacturers ever get "it" right?
They do "get it right" - under their test parameters, their conditions, their requirements. Your requirements of increased power may, just possibly be primary for you - but only 1 factor of many for the OEM manufacturer.
On the other hand, perhaps there's a guy that mapped out the ignition curve or carburetion and he blew it.
It's always interesting to do testing on a bike that's "wrong" then try to figure out how and under what test conditions that the manufacturers provided ignition timing curve or carburetion actually showed that the delivered settings were optimum.
Sometimes, the high rpm timing and carburetion is off - even to the point of 2%-4% down in power. That's not emissions because some of the worst bikes ended up getting much too rich at redline. Seems consistent sometimes - with one manufacturer's 600, 750 and 900 sportbikes all suffering from the same malady for a couple of years. The bikes remained unchanged until the models were replaced. They fixed the high rpm problems in some of their 98 models. Another manufacturer's 600 and 750 sportbikes had problems leaning out at redline in 93-96. The 600 is fixed, now, but the early 600's, when the 1.7-rk RaceKit was installed, swept the WERA Grand National Finals in Atlanta in 94 - however, the riders struggled with poor power over the whole year up to the Finals, where we installed the 1.7-rk kits. That same manufacturer's 750 had the same problem - and when fixed with the #1.7-RK Factory Pro Kit, won the A Superstock Class (1100cc upper limit).
Maybe in next rewrite, he'll fix the ignition timing and dyno chapters...
Otherwise great book with great starting ideas.
The little blue bible for quick references and little known facts.