spark plugs

Q&A regarding engines, turbos, and intercoolers and power upgrades

Postby pg » Fri Sep 28, 2007 7:28 pm

CDN-GT4 wrote:It should be fine. 0.31~0.32 won't make a noticeable difference if you're on stock boost levels.


What if I'm running 14 psi, how do i know what gap/sparkplug to use?
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Postby tw2 » Sat Sep 29, 2007 3:06 am

Someone posted up a short guide ages ago with boost level to show which range to get and always gap them at 0.31" or whatever is stock. I think it was something like- you want to use stock up to 14psi, go a step colder up to 22psi and something special over that.

I have NGK 7's at the moment on 13psi and I am pretty sure they are causing some hesitation down low especially when cold but I am waiting on new ignition leads to make sure. I will swap 6's back in to see what happens. I imagine since most people who run low to moderate boost still spend almost all their time off boost anyway 6's would be the way to go.

Are there any merits to going 0.28 instead of 0.31?
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Postby tw2 » Sun Sep 30, 2007 3:11 am

I swapped 6's at 0.032" back in today and it idles a lot better without the very occasional miss. The 7's were very black with the tips a dark to medium grey so I am guessing I do not spend enough time in high boost to warrant them.
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Postby WarTowels » Tue Oct 02, 2007 6:22 am

I'm on NGK 7's right now. Running stock boost on a ^HIGH^ mileage stock engine. Seems to run and idle just fine. Purs like a kitten for me.

:shrug:

I'm using the BGB measurement of .08 metric.



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Postby furpo » Tue Oct 02, 2007 9:08 pm

tw2 wrote:Someone posted up a short guide ages ago with boost level to show which range to get and always gap them at 0.31" or whatever is stock. I think it was something like- you want to use stock up to 14psi, go a step colder up to 22psi and something special over that.

I have NGK 7's at the moment on 13psi and I am pretty sure they are causing some hesitation down low especially when cold but I am waiting on new ignition leads to make sure. I will swap 6's back in to see what happens. I imagine since most people who run low to moderate boost still spend almost all their time off boost anyway 6's would be the way to go.

Are there any merits to going 0.28 instead of 0.31?


This shows a miss understanding of how the plug works. The spark energy remains the same as the coil remains the same. A hotter plug will not 'boost the spark'. The plug heat range is a measure of the plugs ability to move heat energy away from the electrode. A hotter plug will have a hotter electrode. The electrode must be above a given temperature to burn the combustion deposit off so not to foul.

You only need to go down in plug temperature if the eletrode shows signs of over heating. This is influanced by the temperature of combustion and not the boost level.

A wider plug gap gives a greater surface area for which to ignite the charge. The down side it is harder to fire electrons over a greater gap especially when the charge is more dense. A reduced plug gap will reduce peak VE miss fires.

The stock plug is BKR6EP8. i.e. 14mm thread, 5/8 hex, projected tip, resistor type, NGK heat range 6, Platnuim plug gaped to 0.8mm.

If you run a non presious metal plug you will have to run a smaller gap.

The BGB has both metric and imperial gaps. Not that it makes any difference.

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Postby tw2 » Wed Oct 03, 2007 6:01 am

furpo wrote:The electrode must be above a given temperature to burn the combustion deposit off so not to foul.

This is why I changed back to 6's since I believed that the 7's were fouling up more than they should. It idled and ran fine but it ran better after I changed them (after 5000km) which I don't know- might? be due to carbon build up?
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Postby 86turboswap » Sun Oct 21, 2007 2:14 am

Corey Darling wrote:any ideas on why NGk has different lead sets for the 90-91 and 92-93? on 935motorsports, the 90-91 is more expensive too :shrug:


The 90-91 3S-GTE used 7-8mm plug wires in 92 they changed to the current toyota scheme of 5mm wires with clips that hold them into the cap. If you have a 92-93 you can switch to the 90-91 wires you just have to buy a new 90-91 cap.

I prefer the 8mm wires!
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Postby Corey » Sun Oct 21, 2007 3:13 am

Gotcha, thank you :)
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Postby BriinumsBo » Fri Feb 01, 2008 1:08 pm

Im running NGK iridium grade 8 on stock boost, the only mod is de-cat downpipe. would some OEM type grade 6 be better than grade 8 Iridiums? what can go wrong with grade 8 ?
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Postby Corey » Fri Feb 01, 2008 3:48 pm

grade 8 is pretty cold isnt it, especially for stock boost? stock grade is 6.
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Postby BriinumsBo » Fri Feb 01, 2008 4:46 pm

im just not sure about the technology / physics - what can go wrong, etc.. can you guide me to some explanation?
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Postby Corey » Fri Feb 01, 2008 6:06 pm

From what i under stand:

The colder the plug, the better able it is to disipate heat away from the tip of the plug.

This is good if you are running higher boost settings, because it will help stop detonation.

But if you arnt, then the colder plug wont be able to burn off the carbon deposits, causing it to foul up.

So, Stock range for the NGK is 6, most people with higher than stock boost seem to run 7. I think thats when they run 12-14 psi.

I dont hear of many people running more than 7 heat range.
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Postby tw2 » Fri Feb 01, 2008 7:41 pm

I have never heard of anyone running more than 7 although I don't doubt that many do. 6 is good up to around 14. 7 to about 22 any then its anyones guess as to what works best.
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Postby BriinumsBo » Tue Feb 05, 2008 7:17 pm

what do you mean by "foul up"? my english knowledge is beyond this one :D is it bad for spark plugs or for engine? or for both? does it make engine like this? :)
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Postby Corey » Tue Feb 05, 2008 8:04 pm

I think most engines will look like that at their age, but thats kinda what a fouled plug will look like - carbon deposits.

Here's a good site that describes different plug conditions

http://www.centuryperformance.com/spark2.asp
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