[Tinker51]

Not sure if this is applicable since you are running a big block but this was my experience. A friend had a pretty hot 289 built using a Holly 650 that was running around 370 hp on the dyno with no air filter. The motor was for a Sunbeam Tiger and we were curious what would happen to HP when we put the air cleaner on. A Tiger air cleaner is smaller but essentially the same as the oval Cobra cleaner. We put it on with a K&N element and ran it again on the dyno. No difference in HP. Go figure.