Yeah, I have 18” collector extensions as well that I can use when going for low et. For car club challenge, mufflers are required so that’s why I have them on the car now. Easy enough to uncork and bolt on the extensions…. lol
I would love to hear the results of an A-B test of open with extensions verses your very good full system. I'd bet on less than a tenth. Maybe two hundredths.
But I'm prejudiced. I think I raced uncorked once in my life, many years ago. (car was going 13.ohs, wanted a 12, bad!....went 12.96)