pulsarmad20
Member
Hi all as title says im running standard turbo pressure and 1 bar mod every now and then any advise gd thanks
spark plug gap?
- Thread starter pulsarmad20
- Start date
What are you currently using 0.7mm? You can probably go as high as 0.8mm, but much above that really needs a better ignition system (like an MSD box) to cope with it.
I think Cambellju was all the way out at 1.1mm on his to give him increased fuel economy on the highway.
Don't go any lower than 0.7mm as I put some plugs in at 0.5mm without checking them (rookie mistake), and was loosing power because the spark was blowing out when it came on boost.
I think Cambellju was all the way out at 1.1mm on his to give him increased fuel economy on the highway.
Don't go any lower than 0.7mm as I put some plugs in at 0.5mm without checking them (rookie mistake), and was loosing power because the spark was blowing out when it came on boost.
pulsarmad20
Member
ok thanks pobody i thought the smaller u go the less chance of it blowing out? (as the spark would have less space to travel?) but i will regap them tomos thanks
There's a funny balancing act. - A bigger gap requires a greater potential (i.e. bigger spark) to jump it.
A smaller gap requires less power (smaller spark) to jump the gap.
So you reach a point where the spark is small enough that it easily gets blown-out... or where the gap is so big that the spark can't form (remember that for each +1bar of pressure you've effectively doubled the plug gap because there's twice as much air between the electrodes).
I may have that slightly wrong, but that's how I understood it. - Obviously I'm happy to be corrected.
A smaller gap requires less power (smaller spark) to jump the gap.
So you reach a point where the spark is small enough that it easily gets blown-out... or where the gap is so big that the spark can't form (remember that for each +1bar of pressure you've effectively doubled the plug gap because there's twice as much air between the electrodes).
I may have that slightly wrong, but that's how I understood it. - Obviously I'm happy to be corrected.
Interesting that, I will take that into consideration when I come to map my shed next month!
99% right George. No problem in going lower than 0.7mm but as you say it gives different issues at low load. Standard is okay for 1bar. If your ignition system is healthy then 0.8mm won't hurt much. At 1.2mm I think I was putting too much strain on the iridium plugs, I personally prefer copper now as they don't fail and the extra 0.1mm isn't worth the hassle. I think past 0.9mm I was on diminishing returns.
I went to copper cores after discovering quite how sensitive the iridium tips were to flooding; they're also not prone to loosing the tip.
All I know is that when mine was on the dyno and made low power, the first thing Steve suggested was that I should check the plug gaps. - The power actually drops-off early as the spark blows-out, then starts building again... just in time to hit the limiter.
All I know is that when mine was on the dyno and made low power, the first thing Steve suggested was that I should check the plug gaps. - The power actually drops-off early as the spark blows-out, then starts building again... just in time to hit the limiter.
Sparks blowing out might be giving you the wrong idea of what's happening. The ignition system either discharges or it doesn't, the air/fuel mix ignites but if it doesn't then you get unburnt fuel in the cylinder. Fuel is an insulator so you will make life more difficult for the ignition system if it hangs around your spark plug. As you and many of us have experienced, the design of iridium plugs seem to make them more susceptible to fuel insulating the small tips that the spark discharges from.
To simplify it, the main factors on whether you get a spark is the amount of fuel in the cylinder and the gap the spark needs to bridge. Ignoring the affects of pressure and temp, if you run more boost you will get more air so you need more fuel. You have more insulator so you need more energy to bridge the plug gap. If you reduce the gap, you need less energy. If your ignition system is "energy limited" then reducing the gap will help the spark to bridge the gap.
So why don't we all just run really small gaps or why was I trying to run really large gaps?
To ignite the air/fuel mix needs energy, the amount of energy you need is determined but the amount of fuel (insulator) and the plug gap. If you have a small plug gap and are running at low load you get less energy. Too little energy and too little fuel and you can get lean misfires. This is where ignition doesn't start a because you got poor combustion in the air/fuel mixture.
If you consider a 0.5mm plug gap compared to a 1mm gap, the larger gap is exposing twice as much air/fuel mix to the spark so you have doubled the volume of air/fuel to ignite and to develop a chain reaction. When you consider the larger gap has more spark energy you are also increasing the chance of ignition as you are taking a flamethrower to the fuel rather than a match.
Whether using a match or a flamethrower to start combustion, it is the chain reaction in the air/fuel mix that continues the combustion. This is an exaggeration but the faster combustion from the "flamethower" means you can start the ignition process later to keep the rate of combustion the same. In practice this is very small but it is a consideration when you are pushing gaps, timing and boost to get the most from your car.
So larger plug gaps whether at low load or high load can give you better combustion in the cylinder making for smoother engines. This smoothness is most noticeable at light throttle/low loads. As I was using the R everyday I was spending 99% of my driving time in this area so it was important for me.
If you don't use your car everyday then running smaller gaps doesn't really matter. I think this is why plug gaps causes so much debate.
To simplify it, the main factors on whether you get a spark is the amount of fuel in the cylinder and the gap the spark needs to bridge. Ignoring the affects of pressure and temp, if you run more boost you will get more air so you need more fuel. You have more insulator so you need more energy to bridge the plug gap. If you reduce the gap, you need less energy. If your ignition system is "energy limited" then reducing the gap will help the spark to bridge the gap.
So why don't we all just run really small gaps or why was I trying to run really large gaps?
To ignite the air/fuel mix needs energy, the amount of energy you need is determined but the amount of fuel (insulator) and the plug gap. If you have a small plug gap and are running at low load you get less energy. Too little energy and too little fuel and you can get lean misfires. This is where ignition doesn't start a because you got poor combustion in the air/fuel mixture.
If you consider a 0.5mm plug gap compared to a 1mm gap, the larger gap is exposing twice as much air/fuel mix to the spark so you have doubled the volume of air/fuel to ignite and to develop a chain reaction. When you consider the larger gap has more spark energy you are also increasing the chance of ignition as you are taking a flamethrower to the fuel rather than a match.
Whether using a match or a flamethrower to start combustion, it is the chain reaction in the air/fuel mix that continues the combustion. This is an exaggeration but the faster combustion from the "flamethower" means you can start the ignition process later to keep the rate of combustion the same. In practice this is very small but it is a consideration when you are pushing gaps, timing and boost to get the most from your car.
So larger plug gaps whether at low load or high load can give you better combustion in the cylinder making for smoother engines. This smoothness is most noticeable at light throttle/low loads. As I was using the R everyday I was spending 99% of my driving time in this area so it was important for me.
If you don't use your car everyday then running smaller gaps doesn't really matter. I think this is why plug gaps causes so much debate.