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I ordered new spark plugs before I decided to purchase headers and am now realizing the the factory replacement plugs were probably not what I needed. The car goes in later this coming week, so what plugs should I order and where is the quickest place to get them from? Is there just a one step colder ngk plug that is a safe bet? Also, will the plugs come gapped to what I need or is there a spec I should have them gapped to?
No benefit. I pulled my OE plugs to take a look after quite a few k miles and they were a perfect color. I mean perfect.
Does climate and/or driving style play a part? I have no problem selling the ones I've bought and buying other ones if there is any positive, otherwise I'll stick to your guys' suggestion. The car will end up in lots of stop and go traffic being in Vancouver, and also weather similar to Seattle.
You only want to go colder if you are detonating or at risk of detonating. Otherwise you'll get a better burn with a hotter plug. You can experiment with gap if you've got the time. I run them at .040 but if you can get away with widening it and not get a misfire/blow out, you'll get a more complete burn.
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
^ This
My car runs at high rpm and high load for most of its life. I like the colder plug for this reason. It is 100% unnecessary for a primarily street-driven car because it won’t burn hot enough to get rid of deposits. Especially in stop-and-go traffic it will perform worse.
Does climate and/or driving style play a part? I have no problem selling the ones I've bought and buying other ones if there is any positive, otherwise I'll stick to your guys' suggestion. The car will end up in lots of stop and go traffic being in Vancouver, and also weather similar to Seattle.
My car sees avg temps in the 60-80º F range at night and 75-95º F during the day. Strictly warm/hot weather. Last week I saw 134º F on the cluster indicator (ambient coming off pavement) although normal summertime cluster temps on sunny days are in the 11xº F range.
You only want to go colder if you are detonating or at risk of detonating. Otherwise you'll get a better burn with a hotter plug. You can experiment with gap if you've got the time. I run them at .040 but if you can get away with widening it and not get a misfire/blow out, you'll get a more complete burn.
this is where it gets tricky and part of what makes me worry about the tune, I'm in canada and our gas isn't as good as yours. Our best gas is seems to be shell 91. We have chevron 94 (only place with 94) but apparently it's a lower ron rating/aki than our shell 91 and our shell 91 isn't as good as the 91 in the states. I would assume this could make me susceptible to detonation but that all comes down to the tune that eurocharged uses for the canada cars. Is this something that would make me want to use a colder plug or still no?
I guess it doesn't hurt to run the new oem plugs I bought from RM and go colder if I have to, it's not exactly the hugest expense to swap.
this is where it gets tricky and part of what makes me worry about the tune, I'm in canada and our gas isn't as good as yours. Our best gas is seems to be shell 91. We have chevron 94 (only place with 94) but apparently it's a lower ron rating/aki than our shell 91 and our shell 91 isn't as good as the 91 in the states. I would assume this could make me susceptible to detonation but that all comes down to the tune that eurocharged uses for the canada cars. Is this something that would make me want to use a colder plug or still no?
I guess it doesn't hurt to run the new oem plugs I bought from RM and go colder if I have to, it's not exactly the hugest expense to swap.
Huh? Not sure what you're talking about and where this is coming from. I use Chevron or Petro Canada 94 octane when I'm up there. My M5 tuned for 94 octane averaged 18 RWHP higher on Chevron 94 octane vs the 91 octane version of the same tune over three runs, same dyno same ambient. Chevron 94 octane IS NOT lower octane than Shell 91 octane. Who told you that?
Huh? Not sure what you're talking about and where this is coming from. I use Chevron or Petro Canada 94 octane when I'm up there. My M5 tuned for 94 octane averaged 18 RWHP higher on Chevron 94 octane vs the 91 octane version of the same tune over three runs, same dyno same ambient. Chevron 94 octane IS NOT lower octane than Shell 91 octane. Who told you that?
Well, to start, I'm going to assume you don't even live in western canada as we don't have petro 94. It's fairly common knowledge in BC that our shell 91 is our best bet, especially with a FI car. This comes from countless friends, forums, tuners, people who own dynos, etc, it's just known around here for the most part. About 15 years back husky had just a few stations around with a true 94 in the lower mainland that everyone tuned on, but they're all long gone . If you simply google shell 91 vs chevron 94 I bet you'll come across a page or two of results from random BC car enthusiast forums that are having the discussion and 9/10 the consensus is shell 91. Also, not that it matters as it sounds like you're not in BC, so it's not the same, but running chevron 94 here would obviously make more power than the chevron 91, but shell 91 will usually make more power than both.
All that aside, my point was that my best local gas is going to be vpower 91 and it's not as good as the 91 in the USA, and 94 octane isn't even an option here. I can't technically run a "94 octane tune" on the chevron 94.
It is possible to answer this question factually.
In the aeronautic field, they monitor not only the EGT, but also the CHT.
The CHT is the cylinder head temperature.
For my Subaru, I bought a 4 channel CHT rig for around $200.
It includes a very nice gauge and 4 thermocouples.
I was trying to use the rig to change settings in the tune, to change per cylinder fueling, to make it more evenly loaded. One cylinder was constantly colder... i deviate
Anyway, the way the rig is mounted is you use silver solder to solder the thermocouple tip to the spark plug washer (back side). Then you route the thermocouple wire out of the well, sneak it past the rubber boot of the coil pack and past the coil pack, then bring it to the gauge.
You get very accurate readings of temperatures by the spark plug and NGK has a diagram with coefficients that allow you to infer the temperature by the tip.
Then you could look that up in different tables and factually know if you need colder plugs......
I didn't think to look into changing the plugs on the Subaru, was only worried about fueling.
this is where it gets tricky and part of what makes me worry about the tune, I'm in canada and our gas isn't as good as yours. Our best gas is seems to be shell 91. We have chevron 94 (only place with 94) but apparently it's a lower ron rating/aki than our shell 91 and our shell 91 isn't as good as the 91 in the states. I would assume this could make me susceptible to detonation but that all comes down to the tune that eurocharged uses for the canada cars. Is this something that would make me want to use a colder plug or still no?
I guess it doesn't hurt to run the new oem plugs I bought from RM and go colder if I have to, it's not exactly the hugest expense to swap.
Do some data logging and you'll get a good idea of what's going on. Like blkrkt said though, you're worrying about nothing. Even running nos (where manufacturer recommends a step down in plug temp) I've had zero issues with factory heat range. Put the OE's in, make a few hard pulls, then pull them out and read them. It'll tell you more than any of us can.
06-30-2018, 07:09 AM
