Spark plug/tuning question
 

'83 SC w/ 930-10 row 204 hp w/SSI's dansk rsr 2/2 muffler ( so 220?). Otherwise stock but car is lightened up by about 300 lbs.
I was running NGK BPR7ES plugs...factory calls for BPR9ES so I just put in a set only one grade hotter the 7's...the 8's.
I do run the CO fat and idle at an afr of 13.
The car ran great with the 7's but thought I'd err on the side of caution with the 9.8 to 1 comp. and AZ heat.
I swear I can feel a loss of crispness with the one level cooler plug.
Is this my imagination or can that happen?

I notice a slight change in mileage and performance when refineries switch to "winter blend" fuel. I'm in ohio so not sure if that's even a factor in az, but if it is, that could explain it more than plugs if its a recent observation.

Good point but it's the same tank of gas with both plugs..just changed them today at home and went to my 'test strip' when full warm for some runs.
Good smooth acceleration but yesterday (old plugs) there was a noticeable jerk/push into your seat at the 'on the pipe' rpm level that seems gone with the new plugs.
This is also making me think an increased spark upgrade (MSD unit) is in my future.