Spark Plug Problem In Rb25

[manuel]

Hope you guys can help me.

I have a 1994 r33 gtst rb25 with a full 3inch exhaust, greddy profec2 boost controler and K and N filter running 100 octane fuel with stock smic. I have bosch 040 fuel pump. On 10 or 12psi the car ran well but over a period of 2 weeks it began to misfire and develop flat spots.

I have recently replaced the platinum plugs 1.1m with a set of NGK bcr6es coppers gapped at 0.8. I have also siliconed up my coil packs as well.

The car runs really smooth all the way to redline with out misfires or flat spots, even at 12psi. The problem is that the car feels alot less responsive in power delivery, smoother but slower in acceleration. Could the problem be the gap on the plugs or the fact that they are cheap coppers. Im thinking that the spark in the chamber is alot smaller causing less of an ignition and thus killing some power. What do the experts think.

Ideally i want it running as hard as before with the smoothness and lack of misfire it has at present.

[shyr33]

Hey manuel im no expert unfortunately..... Um so even with the less responsive power delivery do you think you have actually lost maximum power in the car or....?

Um I think that gapping your plugs to 0.8mm should give you a faster ignition so the only thing I could think of is that the timing is slightly out. Maybe its firing slightly earlier and not at its best position. But I knew someone who gapped it to around 0.8mm aswell and he thought he had a slight increase in power with similar mods to yours. Like I said I no expert I'm just throwing up some ideas.

"waits for someone to correct me"

[Humbla]

Maybe the 6 is to hot a plug,i use a 7,seems pretty good no prob.

[blind_elk]

"6" heat range should be fine, considering the factory spec is a "5".

The gap has no effect on the "speed" of ignition, so the timing will not be affected to any significant degree. The type of plug is pretty much irrelevant. Pt plugs are used standard because they require less maintenance and a longer replacement interval than Cu plugs. In all other respects, they are the same - they simply provide a facility to ignite the fuel / air mixture inside the combustion chamber.

Try opening the gap out to, say, 1mm. This should provide a stronger spark, and therefore a better burn of the fuel/air mixture.

Or maybe you are just used to the power delivery, and there is no problem at all.

[shyr33]

Sorry 'blind elk' I think my term of faster was a little misleading. I was told by a 'performance' mechanic that when increasing the boost in the car and making more power you should decrease the gap of the plugs to give you a more reliable spark especially at higher RPM? So I was thinking that with a larger gap the plug had the tendency to possible 'miss' or be delayed slightly due to the speed of everything at higher RPM's and thinking logically, smaller distance = quicker time to get there. As I said im no expert just throwing an idea. After all this forum is a place to learn something for us noob's haha

After doing a little reading I do agree with your point of getting a stronger spark and better burn at a larger gap.

[mad082]

you are correct in what you say about the smaller gap giving a more reliable spark. a bigger gap at higher boost can result in the spark being blown out, so to speak.

blind elk is correct though about a bigger gap being better. the bigger gap means there is a bigger.... lets go with fire front. the spark has a bigger surface area when arcing across so is able to ignite more fuel in it's duration. will it result in more power though? not enough to notice unless you were running seriously rich, but that would also make the bigger spark less reliable.

as for the feeling of a loss in power, has the weather been hotter when you are feeling the loss of power? that will make a big difference in power, especially with a SMIC. in summer the stock cooler will suffer from heat soak extremely quickly at 12psi, resulting in a loss of power. you could probably drop the boost to 10psi and not lose much power on a hot day.