Join Date: Mar 2007
Location: San Antonio, Texas
I have twos sets not mounted on the car and another one mounted that I can't measure. To me it looks like the inside diameter of the tubing is about 38mm. However, there is some crude porting done that is very visible on my NOS set ... and indeed 1 and 2 have the 40mm dimension top to bottom on both sets. the side to side dimension on the used set is consistently 38mm and varies from 37 to 38mm on the other set. My money is that the apparently different size primaries are attributable to the porting of the flanges rather than due to differnt pipe diameters.
I measured the .o.d. of the primaries about 5in down from the curve. I'll be happy to do some more measuring if you want. BTW: I imported these headers about '73 or '74. The guy I bought them from was pretty well connected with Alfa so I think he maybe was buying direct, although at the time Alfa stil had stocking part numbers for the headers along with most other GTA and even TI Super specific stufff that could just be ordered at any dealer.
IMO 38mm works better on the street than 40mm or above and it may significantly lower the rpm when max torque comes in.
Re: some of the comments on drivability ... putting 1600 GTA headers with a 2 1/4" GTA exhaust on an otherwise very stock Giulia Super made a huge difference in bottom-end torque and drivability ... right up there with with close ratio box, lightweight flywheel and good shocks
Coming from someone who won his class in a TI Super against some respectablly fast competition in the '08 Carrera, I'd say this is a pretty solid observation. Your secret sauce works.
Sadly the GTA headers require some modification to fit a 2 liter Alfa motor. Nonetheless, they are such a good design that I've wondered why none of the vendors haven't convinced their supplier to make authentic vintage-style GTA headers that will fit a 2 liter's taller block. I bought the Alfaholics exhaust for my Super because it was stainless and the headers were GTA style and the exhaust dia was 2 1/4" or 2 1/2". I'm very happy with the way it works with my version of John Trevey's "in the style of" version of your Rally motor.
Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
Last edited by 180OUT; 02-25-2019 at 11:24 PM.