At the end of the day this true. I believe it's also best to go into any mini-experiment being aware of all relevant facts adn expereince. Common to just about all motor related forums is the desire to improve upon what the OEM did. The difficulty is finding the areas where something 'was left on the table' vs. those where there's nothing to be gained.

 

I agree with that.

 

nothing ventured ... nothing gained.

there is no likelihood of any ill effect from going one heat range colder other
than fouled plugs ... not a big deal for anyone who can manage to do a
sparkplug change in the first place.

all engineering is a set of compromises and assumptions that might not
fit the exact usage of any one particular user.

and not all engineers are infallible else there would be no such thing
as a TSB or recall.

 

This is a situation where nothing can be gained, no matter what is ventured.

The OEM plugs last well beyond their design life by all accounts.

They suffer no ill effects from being either too hot or too cold. Looks like Jag got it right by choosing the third bowl of porridge that's just right.

We have to remember that there's a huge aftermarket out there that likes to cast the element of doubt about OEM equipment with vague promises of something better. The vast amount of this merchandise is aimed at the easiest to replace engine components like filters, plugs, coils, sensors, chips and let's not forget- oil!

There's a difference also with owners that have their eyes wide open and just like to play and those that have no real experience and have been influenced by advertising.

It's hard to tell which is which when questions pop up.

 

I agree, that was certainly advised by Saab whiz-kids for high-boost upgrades. Wuzupez - save up $6-7K for a twin-screw S/C and, at 21 psi the colder plugs will be perfect! Until then, I'm interested to hear how things go.

 

Spark plug update:
My commute to work is 46 miles one way. I reset my mpg and drove to and from work. Cruise set at 78mph both ways. Highway is mostly flat. Averaged 20.7mpg
With new plugs "IFR6D10" and same conditions, cruise at 78mph, to and from work I averaged 21.9mpg.... So far it's only been about 100 miles since plug install but the car runs smooth and is getting 1mpg better!

 

Just an update to anyone interested. Plugs are working great! I have 10k miles on them already with zero problems! Average 22.6 mpg at 85mph on the highway! Pulled a couple plugs and burning perfect! Nice light brown color

 

Wuzupez
Thanks for the update! My question is by what mechanism would your changing the spark plugs cause an increase in mileage? approx 5 percent is a pretty significant increase.

 

Could be a number of things steadicam. Maybe the fact that I change the oil every 3,000 miles? Maybe because I keep my k&n filter clean and rotate with the second one I have every oil change? Maybe because I clean my mass air sensor? Maybe because I cleaned my throttle body? Maybe because of the fuel injector cleaner I run every 10,000 miles? I also check my tire pressures weekly! Could be a number of things or all of them working in conjunction together! Perks of being a Technician I guess! Some say I "over maintain" my vehicles! I like to call it "preventative maintenance"!