Originally Posted by CDW6212R
I was hinting that the gains from any changes to blend the entry will be about the same whether you make a spacer or not. That's why I suggested that first you take the old TB off and see the actual size difference. I think if you just spend five minutes on the plastic intake and keep it clean, the results will be the same.
I received my racing 75mm ported and polished throttle body from Jerry Strannigan (firstname.lastname@example.org) and I'm very pleased. I pulled my stock throttle body off to make some measurements. The air intake plenum has an inlet diameter of 64.7mm. It is composed of two or more pieces that fit together at the inlet. I am not comfortable with modifying (porting) the intake plenum inlet.
The throttle body gasket port diameter is 65.3mm where there are no combs. The combs appear to be shaped in a way to direct airflow toward the plenum chamber splitter in a way to optimize airflow. It would have been much easier and less expensive for Ford to try different comb arrangements than to try different plenum designs. Since the gasket port diameter is larger than the plenum inlet I don't think it is a restriction and therefore will not modify it at this time.
The stock throttle body has an outlet diameter of 65.3mm (same as gasket) and an inlet diameter of 68.7mm.
My racing throttle body has an inlet diameter of 77.0mm, an outlet diameter of 76.2mm and a throttle plate diameter of 74.2mm. There is a mismatch of 10.9mm (76.2-65.3) which may be enough to warrant an adapter (spacer with tapered port).
The large size of the racing throttle body should be enough to determine if there is any real gain in performance or economy by increasing throttle body size. I'm looking forward to some before and after test results.