What is the most suitable spark plug for Toyota 3A engine in Asia? (NGK/Champion/denso/BOSCH and also copper/platinum or iridium)
Please explain the differences/advantages between them and how it might affect fuel consumption.
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Really what you need to do is learn how to "read" a spark plug. We can tell you what spark plug to use for a stock engine, but once you start modifying the engine, all bets are off. I will explain what reading is and how you, too, can do this at home.
As for the spark plug itself, the base spark plug which Denso says is model W14EX-U11. We can from there look at a cross reference chart and find from any other brand out there from this page:
AC Delco R44XLS Accel 114 Autolite 66 Bosch WR9DC+ Bosch W9DCX Champion RN12YC Champion stk 404 Denso stk 3012 General Motors 5613870 Napa X761 NGK BP4EA11 NGK BP5EA-11 NGK BP4ES-L11 NGK BP4EY11 NGK BP4ES11 NGK GR4 NGK BP5EA11 NGK stk 2635 Valley Forge 34R
You can use this same page to cross reference any type of spark plug you might like to buy. The spark plug I've listed is just the standard case spark plug. You will have to choose which conductor type you'd want from there (copper/platinum/iridium/yttrium). As you go from left to right with the metals, you can expect these spark plugs to last longer, but they will cost more as well. With your car being an 86, which was before the onslaught of distributorless ignition systems, you will probably do just fine with either a standard spark plug or a copper spark plug. I don't think you'll gain much by using the precious metal spark plugs (like platinum/iridium/yttrium). None of these will get you any better mileage or horsepower ... at least using the standard plug.
Like I said previously, you really need to learn how to read a spark plug. What I'm talking about here is the ability to pull out a spark plug and tell how the engine at a specific cylinder is running. You can tell a lot by how it looks and it will want to tell you bunches. Here is a decent chart which shows the different states of the spark plug. I am only going to focus on a few of them, because they are of importance for your application. Please read the rest of them as well, because it is good information.
(NOTE: If you cannot read it, I pulled the image from this URL on the web.)
The first image of note is the upper left hand corner which is entitled Normal Condition. Basically you are looking for the spark plug to be light brown or light gray in color. This tells you the cylinder is burning optimally and your heat range is good.
The next picture to look at the second to the bottom on the left. While this picture on the page is by the heading Dry and Wet Fouling, this is basically what your spark plug will look like if it is too cold of a heat range. You'd need a spark plug which runs hotter (more on hotter and colder plugs later).
The last picture I want to focus on is the one next to Overheating (third from the bottom on the right). This is basically what is going to happen when the heat range of the plug is too hot, which will cause the spark plug to over heat.
When reading plugs, the above chart is a good indicator of the health, but is not an END-ALL-DO-ALL. You really need to get a feel for your vehicle and how it runs. None of the pictures are going to be exactly what you will see when you pull your spark plug out, but are a good indicator.
When you have read your spark plugs, you'll discover one of three things: 1) you have the right spark plug heat range; 2) your spark plug range is too cold; or, 3) your spark plug range is too hot. How do they make spark plugs hotter or colder? Here is a good image example of how they do this:
You'll note how the porcelain insulator is either more exposed (for hotter plugs) or less exposed (for colder plugs). A colder plug allows heat to dissipate into the head easier, while the hotter plug does not. Why is it important? A hotter plug can cause pre-ignition (or pinging). This is very important in your engine, as it probably does not have the electronic means by which to compensate (through retarding the timing). Even if it does have the means to do this, your engine is not running optimally and you will not be getting all of the performance out of the engine, which means worse gas mileage. If your engine is pinging or has "pre-ignition" (actually the same thing), you can cause engine damage if allowed to go on for a long time. On the other hand, a spark plug which is too cold, will tend to not burn all of the air fuel mixture within the cylinder, which also means worse gas mileage and sub-par performance as well. Mind you, there won't be a HUGE difference, but it still will not be optimal. You probably won't see engine damage from this, but you'll get increased carbon deposits in your combustion chamber, which can cause other issues besides just poorer performance.
The different factors which affect the spark plug's heat range are as follows (pulled from this website):
Air/Fuel Mixture: Lean air/fuel ratios raise cylinder-head temperatures, requiring a colder plug. Rich air/fuel ratios require a hotter plug to prevent fouling. Mixtures that cause the plugs to read lean may contribute to preignition or detonation.
Spark Advance: Ignition timing has one of the greatest effects on heat-range selections. Advancing timing raises combustion temperatures, calling for colder plugs.
Compression Ratio: Increasing the mechanical compression ratio raises cylinder pressure, resulting in higher cylinder temperatures. The higher the compression ratio, the colder the spark plug needs to be. According to Champion Spark Plugs, for normally aspirated, gasoline-fueled engines, a good rule of thumb is to go about one heat range colder for each full point in compression ratio increase from 9:1 through about 12.5:1, and two heat ranges colder for each point increase between 12.5:1 and 14.5:1. Beyond 14.5:1, 3–4 heat range reductions per point may be needed.
Gasoline Quality: With leaded fuels, the lead is attracted to the hotter (core-nose) part of the plug, causing glazing; running a slightly colder plug helps prevent this. On today’s cleaner-burning, oxygenated, unleaded gas, an equivalent engine needs to run about 1–2 heat ranges hotter plug than originally specified (many plug makers have revised their catalogs).
Methanol: Alky-fueled engines need a plug at least one step colder than “normal” for an equivalent gas-fueled motor.
Nitrous Oxide: N2O raises cylinder temperatures and may require a plug 1–2 heat ranges colder.
Supercharging/Turbocharging: With increased chamber pressure and temperature, two or more heat ranges colder may be needed. Extreme high-boost, race-only apps may need a surface-gap plug.
Sustained Acceleration: Prolonged acceleration or high-speed driving raises temperatures and calls for colder plugs.
Elevation: Leaning the mixture and advancing the timing partially compensates for lost power and efficiency caused by higher elevation. Spark-plug heat ranges should stay the same as at sea level, unless racing above 3,000 feet, where one step hotter usually suffices.
Also of note is that some engines just like some spark plug brands better than others. What may work in a Chevrolet may not work in your Toyota as well. You will ultimately need to figure out which brand you like and stick to it. I have found good plugs from Bosch, AC Delco, NGK, Denso, Champion, and others. I have personally had bad luck with Autolite. That of course is "my experience" ... yours may differ.
According to the following,the 1986-93 Toyota Conquest 2E can use the following NGK spark plugs:
Spark plugs with a higher number like 6EY refers to a cold range spark plug and spark plugs with a lower number like 5EY refers to a hot range spark plug. The electrode gap is as follow:
If you're going for performance, copper plugs are your best bet. Just know that they don't last nearly as long as platinum or iridium plugs. As far as brand goes, it doesn't REALLY matter, but my personal preference is Bosch simply because Bosch built most of my car's engine management and ignition system anyway. But the other brands you mention are just as good.
Copper plugs are much better at conducting electric current and dissipating heat than other metals, so they'll be better suited to the higher temperatures caused by your performance upgrades. But the effect on fuel consumption is almost zero. It's only if your plugs don't work well when they will affect consumption and even then not by much.
And a small tip on upgrading your performance: for trouble-free performance, you should have a slightly rich-running tune to keep temperatures under control. One of the most common problems tuners face is a melted piston, which is caused by a too lean condition in the combustion chamber. For this, you'll need a better quality fuel pump, bigger injectors and a software update. Your fuel consumption will be slightly worse, but you'll still come out ahead because you won't have to strip and rebuild your engine.