water injection and spark plugs

[cmj]

What temp plugs should be used when implementing water injection hotter or colder then stock? What should the plugs look like after being used with water injection?

[rxstephen]

Hi,

Thinking about this one way, if you have not modified your car because of WI then you should run hotter plugs because the combustion temps are less. However in practice, you will have modified your engine to take advantage of the WI and will be running more advanced spark, higher compression or higher boost. In which case you run either standard heat range, or more likely a colder heat range.

I have a turbo charged rotary. Rotaries are notoriously harsh on spark plugs because they fire twice as often as a 4 stroke piston engine, and also have no intake stroke that flows cool air past the plugs. However I have been running WI for 2 years now, and have significantly increased the life of my plugs. Generally they stay cleaner, otherwise you wouldn't notice any difference when running WI. This may also be thanks to the leaner mixture I can ran.

The only gottcha with WI and plugs, is that there is a higher chance the flame can blow out, I have had to change to a different style plug and run a smaller gap to prevent missfires. Also it helps to have a mapped WI that delivers the right amount of water across the rev range.

HTH
Cheers
Stephen

[atl93fd]

rxstephen,

take a look at my thread in the gasoline forced induction forum re: rotary engines and WI. I'd love to hear your input if you have been running it for 2 years.

[Roger G.]

On the Mitsubishi 3000GT the ignition system is known to be weak. When we increase boost to 14 psi we often suffer from spark blow-out. For this the gap of 0.044 is gapped down to 0.032 and even more to 0.028. This solves the blow out but idle and milage get worse. With WI the spark may need more power to ignite the new mixture in the chamber. I noticed this when I installed the ERL System 2s and had always to use 0.028 gapped platiunums. With coppers I was able to run a larger gap though. Now I use Denso Iridiums 1 range colder than usual. They are pregapped at 0.035 and I do have no problems with either spark blowout or bad idle.