Holley stubstack

I don't have one anymore but when I did, I found that my particular combo needed to be 2 jet numbers richer because it helped airflow enough to lean it out that much. It did help ET a bit but don't recall how much.

Naturally it helps to have your jetting as close to optimized as possible.to begin with. Otherwise, if you're on the rich side, adding a StubStack can lean the engine out a bit and be faster right off the bat. If it's lean to begin with, you could lose ET by putting it on.

I've has an engine lean out a bit just by taking off an air cleaner but retaining the base to keep the airflow consistently smooth. This was with a K&N air filter and it does depend how restrictive the air cleaner is to begin with.

Test, test. test!