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Not sure on this: but aluminum was original on the early Autodelta prepped cars though not homologated for 65 - it was FIA homologated December 1966, valid from January 1967 onwards - though definitely used in some cases earlier than that. I have a factory fiberglass box that originally came with the car with what appears to be a metal tag with some letters and the number 68 punched into it - possibly being intended as a homologation tag. The car is a late 1600 with the later GTAjunior style suspension and wheel arches that was homologated for 1/1968.

I have always assumed that the fiberglass box originally went with the later cars - 1600's and particularly juniors - and that 68 may have been the intended homologation date, though I have never seen a homologation document other than one for the original aluminum box - they may have considered the change in material as not necessary to homologate separately after all.

BTW, the box is definitely fiberglass only except for the metal tag. ^^sounds like an early hybrid box w/ aluminum covered by glass.
 

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Also remember that if the box is to original specifications, the commercially available air horns don't fit - you really need to copy a set of the original ones if you don't have them.
 

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The vent is visible on the above pictures at the upper back end of the box - the little bubble. It needs to have a little opening there. Most aftermarket boxes leave that up to the end user who usually doesn't know this bit.
 

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I am also searching for the a proper rubber or silicon sleeve to connect the snout to the airbox.
Depending how much of a perfectionist you are, using sheet rubber cut to the correct size and using rubber cement or whatever else works for vulcanizing/fusing the butt ends will provide a correct looking rubber sleeve with the exception of the seam (can face to the bottom). Another solution is a motorcycle tire tube, though the material is thinner than the original piece.
 

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Most of us have abandoned the curved velocity stacks in favor of the newer "mushroom" horns... flow bench test show these to be better.
see:
Pegasus -Air Horn, 45 & 47mm General Purpose - 40mm Tall
There is no doubt in my mind that the full radius horns without mesh will flow better than the original on the flowbench. Whether the engine will put out more horsepower with them, especially with an original style cold air box remains to be seen.

Replica curved airhorns look like the are likely to flow better than the originals but they won't fit the box w/o modification - a lot of 1600's in European Historic racing are in fact using these with the screens removed w/o airbox.

Generally 105 type engines seems to respond well to a lengthening of the intake tract. Also, the straight horns put the bellmouth very close to the outer wall of the airbox which may interfere w/ flow.

Running short stacks (non-full radius) w/o airbox definitely reduces the torque low down noticeably - didn't drive the car enough with them to ascertain the top powerband. Anyway, I've had good results on the dyno w/ the original curved stacks and airbox on a 1600 twinplug.

Also, I wonder whether slip fit vs. non slip-fit horns give better overall flow. Slip-fit will reduce the barrel diameter of the carb somewhat, but the ridge created by the auxiliary venturi is essentially completely smoothed, thus reducing turbulence in that area of the carb.
 

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Post #55 makes multiple erroneous statements as well as showing pictures that show non-original parts which include but are not limited to the following:

  • First known GTA cold airbox in a race at Targa Florio in 1965 Targa Florio 1965 see post #8
  • airbox and airhorns were not available for 40DCO3 but for 40DCOE
  • 40DCOE was not for GTA which always had 45DCOE14 homologated
  • preso d'aria picture airhorns are aftermarket not Alfa or Autodelta
  • pad 1 picture airhorns aftermarket
  • aluminum box likely had no numbering on box - never seen one with it and I have seen many ...

Original Autodelta airhorns below - 45 DCOE

1629679
 
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