I'm picking up just BCPR6ES-11's down the street from my gym. For a set of BCPR7ES-11's, I would have to drive about 30 minutes. ;oops:
I was also going to suggest plugs as one possible maybe. You may want to be careful about changing the heat range of the plug, which is what you'll be doing with the alternative plug you say you'll be using.
If you don't know, the first numeral in the NGK plug identification code denotes the heat range of the plug, with a lower number being a 'hotter' plug and higher being 'colder'. If you use a '6' instead of a '7' then the plug will tend to run hotter and this will increase the chance of pre-ignition (from a glowing spark plug tip) under heavy load.
This isn't to say that you
will get pre-ignition, but the chance at least increases, and my understanding is that supercharged engines tend to be more prone to pre-ignition problems than are naturally aspirated engines.
Please preface the following paragraphs with 'it's my understanding that";
If pre-ignition does occur, then I'm fairly sure this would be detected as a 'knock' and the ignition would retard, but since in this case the (
pre)ignition event is occurring
at the plug before the plug actually fires, retardation of the spark may not help.
I put "at the plug" in italics because spark retardation
would tend to help reduce / eliminate knocking
if the pre-ignition were spontaneously originating from another point in the combustion chamber and thus creating two flame fronts (one originating at the source of pre-ignition and the other from the correctly timed plug firing). In this case the two rapidly expanding flame fronts will collide and cause a possibly severe 'knock' against the rising piston. In this case retarding the spark will retard the point at which the two flame fronts collide, when the piston is higher in the cylinder, lessening the severity of or even eliminating the knock.
But, with a single flame front originating too early (possibly much too early) from an overheated plug (too 'hot' a plug), the flame front will prematurely collide with the rising piston, and cause knock, so in this case retarding the spark (which in this case isn't the source of the single ignition event, as it fires after the horse has bolted) will not retard the point at which the flame front collides with the piston crown, and knocking won't be reduced.
Uncontrolled knock is a bad thing, and not always kept in check by the knock sensor. Knock sensors can only really help with minor knocking events, such as you might get with the wrong grade of fuel (which tends to create pre-ignition originating from some point other than the spark plug, i.e. tends to create two flame fronts, so more amenable to spark retardation).
Some manufacturers recommend more than one heat range plug (for use in different conditions), but it doesn't seem that Saab lists the '6' plug as an alternative to the '7' (at least not in the handbook), so I'd be careful about using it. About the only time you might want to risk a hotter than standard plug would be in an engine that tends to foul the plugs, such as one that burns a fair bit of oil (the hotter plug tip will tend to stay cleaner because the heat helps burn off deposits, helping prevent misfiring).
Regards,
John.