Baby High Butterflies
(not for sale)
We recently received a
set of the elusive 2.5 liter ST High Butterfly throttle bodies,
a.k.a. the Baby High Butterflies, that were originally manufactured
for the '72 911 ST. These Baby High Butterflies were the first
castings produced and are different in some ways from the later
2.8/3.0 liter RSR type. Here are some detail photos along with a
description of the difference between the ST and the RSR type High
Butterfly throttle bodies.
The casting number for the
ST is 911.110.107.2R The casting number for the RSR is 911.110.107.5R
The ST has no 6mm threaded
grease fitting hole on the housing for the bellcrank axle, unlike
the RSR.
Return to top
The ST bellcrank lever
(pictured on right) is flat with no strengthening rib. This
particular bellcrank was replaced with an RSR type (left) because of
wear on the axle itself (very heavy usage).
The housing on the left is
the ST housing which shows the holes for the fuel line brackets (on
the lower part of the casting between the barrels). Notice the holes
are located differently on the RSR (empty RSR housing on right).
Return to top
This picture shows the
factory 6mm air screws which are common to both. However the air
screw hole for the ST is 3.3mm vs 3.9mm for the RSR.
The throttle shaft return springs on the ST (left) are made from
thicker wire than on the RSR (right). It is difficult to see in the
picture but the diameter of spring wire is approximately 10%
thicker. On this particular ST housing the two spring retainer
bosses on the throttle lever end were worn down and had to be
replaced. The heavier ST springs likely contributed to the
aggressive
wear and all four return springs were replaced during the rebuild.
Appears from the side to be
very similar to the RSR. Throttle shafts and couplers are the same.
Return to top
Same 50mm top opening on ST
and RSR, shown here with new bushing and the required overbore ( <
1mm in this case). Stud spacing is the same.
This set had the port side enlarged to 42.5mm at some point. The
exact port size on a factory set should be about 41mm but we do not
have an unmodified set to measure. We will post this measurement
when we find one. The port side on an RSR measures a little bigger
than 43mm on the very bottom (about 43.5 or so depending on how it
is measured).
The finished 2.5 ST set,
note the modified throttle arms. This set showed extremely heavy
wear. In addition to the worn spring retainer bosses which were
replaced, this set required six new throttle shafts, one shaft
coupler, the bell crank axle, and the four return springs.
Return to top
|