Reply to "Header temps"

probably not the air metering carbs I was thinking of but you have 2-stage PV's?

excellent tuning tool but they're discontinued so get what you need ASAP

http://www.mustangsandmore.com...m12/HTML/012338.html

" If I recall correctly, the 4180 used on 1983 to 1985 Mustang 5.0L HO's
were similar to 4160 series Holley but was specially developed by Ford
to meet emissions without any electronic aids. It was rated at 595 CFM
and used annular boosters on all four corners, a dashpot for throttle
control during deceleration, vapor vent equipped fuel bowls, side hung
floats, a specific fuel inlet, two stage power valve, "close limit" main
jets (with tighter tolerances). I believe the metering block is different
as are the emulsion tubes and air bleeds. Also there were no idle mixture
screws in the primary metering block, unlike 4150/4160 the Holley. Instead,
there is an idle mixture screw for each barrel, however they are in the base
plate and are sealed to prevent tampering. You can drill a small hole in
the bottom of the base plate for each mixture screw and pick out the plug to
provides access to the mixture screws with a small Allen key. There is also
no idle speed screw in the base plate. Instead idle speed is set with the
dashpot. I'm told the secondary metering plate is different than a 4160
in shape, so they don`t interchange." ~ Dan Jones