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Sparkplug heat range

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Does anyone have any opinions on optimum spark plug heat range on an EJ257 running about 200kpa boost pressure?

The standards are a 6 in NGK so I was of the opinion that I should go one colder so I fitted a set of 7's

I fouled that set very quickly.

My AFR is Lambda 1 on idle after warm up. My target AFR goes to 0.78 at 200kpa to help with Detonation.

My coils are brand new and the system ran fine with 6's when I was only running on waste gate pressure around 60kpa.

Should I lean out my AFR to 0.80 or less, or should I just go back to 6's?

Your thinking is sound, a 7 (or even an 8) in the NGK range is probably what I would have selected for your application. My general rule of thumb is that for a mild to moderately modified turbocharged engine I will generally select a spark plug one heat range cooler than stock. If it is seriously modified, running a bucket load of boost or predominantly being used for racing then I would go colder again.

I doubt that the spark plug is the reason you are having trouble with the plugs fouling. I regularly run cars with heat range 8 with no trouble so I believe your problem is elsewhere. There is nothing wrong with a lambda target of 0.78 under full boost, and if you are seeing lambda 1.00 at cruise then I would be looking at what the lambda is doing straight after a cold start. This is often the place you will see trouble with the plugs becoming fouled - particularly if the engine is cold started a number of times without being allowed to come to full operating temperature.

Andre, as a general rule of thumb, what would be your recommendation on a NA engine ?

A little more information is needed to really make a decision. the heat range needs to be selected and matched to the expected combustion chamber temperature that the engine is likely to see. This depends on a number of aspects - Fuel, compression ratio, maximum engine speed, type of engine use and obviously specific power output.

A good guide is to look at the factory recommendation for your particular engine and then base your decision from there - Mildly modified would be ok with stock or one heat range colder. If you are building a high rpm screamer then 2 heat ranges colder would be a good option. An all out race engine running on fuel such as methanol may require colder still.

It's also worth noting that NGK and Champion heat ranges work in opposite ways (ie in the NGK range a higher number is colder while in Champion a lower number is colder).

I'm building (at least trying to) a screamer 4A-GE. Fuel will be 98Ron, 13:1, 9000RPM, and I hope close to 200hp.

The use should be a mix between track (time attack/ drift) and street.

Standard spark plug heat range on this engine is 16 (Denso, 5 for the NGK equivalent) and I know that the later version of this engine who make a little bit more HP and have a higher compression ratio have a heat range of 20 (6).

So I was thinking to go directly to 27 (8) to avoid damaging the engine and work my way up in the heat range if I fouled the plug.

I just try to avoid the trial and error to save time and money.

(Spark plugs are not the most expensive parts but if I can get it right the first time that would be better)

Bikeboysam, what part numbers are you running?

Also which injectors are you running?

What modifications have you done to allow 200kpa boost pressure?

Ludo86, given your application I would expect a 7 or 8 in the NGK range to be a safe place to be. There is no real danger with going colder than required. The only downside is that a colder plug is more prone to fouling. This is made worse if you aren't regularly giving the engine a decent amount of load and getting the plugs hot enough to burn off any contaminants.

If you are using the car for street driving and regularly cold starting it without allowing the engine to completely warm up then you are more likely to have issues with fouling.


I am running a GTX3076r compounded with an SC14 supercharger. Early days yet. Only done a few drives with it plumbed up with some fairly conservative igniton numbers.

Injectors are ID1000 and the spark plugs are BKR6EIX or BKR7EIX or PFR7B.

I just changed out my WB02 sensor as it was a few years old and may be out of range.

Not trying to highjack the post but I my question is ...does fuel type affect the heat range of the plug? for Eg I have heard people say that they run a colder plug for E85 . To me that's a little confusing of what I understand of the combustion process of E85 (cooler intake temp/ cooler egts etc etc ) one would tend to think that a "hotter/same as pump" plug could be used.

Is it because the motor is making more power on E85 that a ppl are using colder plugs? If its even required?

Just drove the car with the new O2 sensor.

I had to pull 30 percent fuel out of the whole map to hit target.

30% is a hell of a lot of fuel ... was your car black smoking before? Does your new O2 sensor require free to air calibration? What wideband are you using?


No smoke that I noticed but mainly only driving at night.

The last sensor had been calibrated in clean air, as was the new one before fitting it into the pipe.

The wideband unit is 2co from TechEdge in Australia. The refresh rate is very quick and I have it connected to my Haltech.

30 percent is a lot. I am still having some issues with my fuelling.

My numbers were all adjusted. I had to put about 10 percent back in after the last post.

I did a couple of runs with the data log and corrected a few lean points.

Took it for another run which was all good until I was heading home and the o2 went full rich.

I doubt it is the wideband as it started to run like a pig.

I checked that there was no corrections in effect in the background.

Pulled out about 20 percent fuel to get it back to Stoich.

Has anyone else ever dealt with this situation?

I have had trouble getting consistent fueling previously. It has always been under 8 percent though.

Previously I had Seimen Deka injectors and I had put it down to those but obviously there is something else going on.

Tomorrow I will close all of the correction tables just in case I am missing something obvious.