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Nissan vk56 v8
N/A carby, running e85, 450hp highly worked
This is a common problem with the engine these plugs will get 2-3 races and will come out looking like this, when they go black its causing the
engine to miss due to spark tracking down the black part.
spark plugs are ILFR7H Iridium plugs.
The colour is only ever on 1 side of the plug.
My thoughts are the plugs should be an 8-9 heat range and the porcelain is getting to hot and something in the fuel or maybe leaky valve seals are leaking and coming into contact with that part of the face (facing the inlet) and its causing it so stick to the plug.
All 8 cylinders are doing it.
Usually I'd also be thinking oil from the intake guides being pulled through and being deposited on the valve - more likely if the deposit is in line with one or both - because I've seen it quite often. Or that's the side opposite the intakes and the incoming fuel was cleaning the side facing the intakes.
However, there seems to be some erosion of the 'plug body on the same side, something I don't recall seeing before?
Is it all the spark plugs or just one or two?
Usually I'd just be looking at going one grade harder for petrol, but you're using E85 which 'should' be cooler running and the OEM grade (which I think those are) should work - deposits are normally because the spark plug tip isn't getting hot enough to burn it off, but one has to be careful one doesn't go too hot and cause a "glow plug" affect.
If this is for a stock car class, with restrictions on the breathing, that would also be expected to keep tip temp's down and may be another nod towards stock heat range spark plugs?
I would be hisitant on blaming any misfire on the deposit and possible tracking - remember, not only would it have to track, but the gap from the deposit to the body is still several times the electrode gap - it's possible but I'd start looking elsewhere first.
All the plugs come out looking like this. engine has a clear miss change plugs and its fine again for a period of time.
my understanding of e85 is yes it burns cooler then petrol but thats on the basis if you were using the same anount. You use more e85 then petrol which in turn creates a bit more heat. I was thinking more power has to = more heat. Ie 200hp on petrol vs 450hp on e85, the 450hp has to be running hotter cylinder temps.
the base of the plugs are fine it just looks that way in photo.
I can't specifically say what's causing the localised discolouration on your plugs however that is not normal for dedicated E85 - Typically the plugs should come out looking very clean. I'd be picking that you potentially are slightly on the rich side with the tune up and over time you're fouling the plugs which is leading to your misfire situation. Do you happen to know what the AFR/lambda is?
E85 does run cooler than gasoline despite the fact it makes more power. If you ever compare EGT between gasoline and e85 you'll generally find that E85 will be perhaps 100-150 C cooler than pump gas. While this isn't a direct measurement of combustion temperature, there's a correlation. Despite this, I would generally still step 1-2 heat ranges colder for a dedicated race engine due to the fact that irrespective of combustion temps, you're going to be using a lot more sustained wide open throttle so the plug tends to be exposed to more heat on average than a road going application.
The general guide on heat range is to monitor the point where the ground strap discolours. In your case this is quite close to the body of the plug which suggests the plug is slightly too hot. You want to be aiming for this discolouration to occur about halfway along the ground strap. I'd personally try running an 8 and check that your mixture isn't too rich. This will give you a good comparison on the ground strap discolouration which will help guide you as to whether you need to drop another heat range again. The downside is that a colder plug will be less able to burn off deposits so if you're too rich then the colder plug will actually make the situation you're experiencing worse.
Its coming in later in the week for a dyno session, this was a problem I happened to walk into while at the track. Just found it being so localised on the plug strange.
I have talked to a guy who said this was common with leaded petrol and 2 strokes.
he said the plugs used to get to hot and the fuel mixture would burn and stick to the plug, he said it was like having a red hot pan and throwing something on it, it instantly bakes to it. (its a theory anyway) is it possible that its really rich and its fouling that one side as its directly pointing to the intake? The other side is staying hot enough to burn it off?
if its that rich with those temps maybe a colder plug is definitely worth a try.
interestingly though they have said its using far more fuel then it used to, and some1 mentioned they swapped the fuel system around to a non return style.
Yes, the discoloration is near the body of the spark plug, but above this line, the ground electrode is black. It is my understanding that the ground electrode would be lighter in color above, not darker... If the heat range was indeed to hot.
Perhaps, overly rich mixture masks this in this case?
It would seem the interim move would be to go a range harder on the spark plugs, even two, and see what that does? At least you'll confirm or refute the heat range not being cold enough.
OP, what spark plug gap are you using? Try reducing it by 5 and then 10 thou' to see what affect that has.
Also, next time the heads are pulled, check the guide clearances and condition/fit of the stem seals, the primary problem may lie there.