Indeed if you are using a 'head temperature' gauge with the sensor at the union between the head and plug you are just reading that one location. If it is digital then there is always a sampling delay and you have to actually read the display.
Old school you would use a Exhause Temperature Gauge with the tip of the probe mounted so it is mid stream of the exhause near to where the divergent (diffuser) cone attaches to the header. Running the setup like that you can get the temperature of the medium inside the exhause expansion chamber. You want to tune to have this at around 1150-1250°F at wide open throttle and on the pipe. So you do not have to read the gauge you rotate it so that 1200°F is pointed straight up (actually all analog gauges should be rotated so optimum is straight up so you dont have to read them all)
You can get good self powered EGT gauges from ultralight folk or even eBay knock offs for 60$.
> Mikey Antonakakis Wrote:
> Per your links, spark plug heat ranges are about pulling heat out of the
> plug tip (heat that came from combustion) to avoid preignition. That bit
> about one step in heat range changing temp by 70-100deg is referring to
> plug nose/tip temp - not cylinder head temp.
> Spark plugs are relatively small, have lower conductivity than aluminum,
> and are hotter than the surrounding cylinder head, so although they
> absorb heat from combustion, they don't pull heat out of the head. In
> fact, it's the head that pulls heat out of the plug... as shown in the
> picture in the second link:
> So, if you're measuring with a ring under the plug, sure, a colder plug
> should give a lower temperature reading - but that doesn't necessarily
> mean less heat is going into the head. It gives that lower reading
> because the colder plug conducts the combustion heat into the head more
> effectively (and absorbs less heat from combustion due to its smaller
> exposed surface area). Yes, the plug ends up cooler, so you're safer
> from detonation, but that heat went right into the head.
> So if you're timed too aggressively, a colder plug will help avoid deto,
> but it won't prevent overheating the head or piston, and it might hide
> the fact that you're doing that when you read head temp at the spark
> In any case, for OP: if you're going to claim this BU8H plug is superior
> for your application than conventional plugs, you have gotta do
> back-to-back testing. Put a B8HS in there (or whatever is the identical
> conventional plug) without changing anything else and see what happens.