Early (92-94) LT1 motors have a non-vented Optispark distributer. Given the climate under the water pump, some owners find it advantageous to upgrade a failed optispark for a later vented model. Given the number of design changes in the six years of LT1 production, this is a non-trivial swap.
To swap, the later distributor, vacuum harness, distributor harness, and timing cover must be used. A camshaft with a longer dowel pin and a hole in the center is required, along with a modified cam gear or 95 or later timing set or the LT4 or LT4 extreme duty timing set. The best time to do this is when you're doing a rebuild or cam swap anyways, because you will be removing and reinstalling a cam for this job.
The rest of this page shows the parts list and compares all the parts swapped during this job. I didn't bother to disect the Optispark, because Mike Chaney already has a good Optispark Disection Page
Here's everything but the water pump gaskets and timing set. The standard LT4 timing set is an 8mm roller set for under $200.
|95 GM Optispark||1104032|
|95 Opti elec harness||12130319|
|Opti vacuum harness||12555323|
|Opti vacuum fitting||14082470|
|95 Timing cover (incl all 3 seals)||12552426|
|GM timing cover gasket||10128293|
|95 Cam Timing Gear*||10206039|
|Stock replacement timing chain*||10128485|
|Intake Manifold Gaskets||.|
|Water Pump Gaskets (2 required)||10128343|
*Stock replacement parts. You may want to upgrade to the 8mm single roller LT4 set or the extreme duty set (12370835).
In these years, three timing covers were used, one compatible with the non-vented opti, and two compatible with the vented opti.
Here's the cover used
in 92 to 94.
Here's the cover used in
95. The hole in the center changed to accomodate the new optispark
Here's the cover used
in 96 and 97 for OBD II motors with crank position sensors. In the
bottom of the cover is the four tooth reluctor for the crank position
sensor that sits on the crank. You can see the sensor in the lower
Here's the 93
non-vented optispark and related components. Note the splined shaft in
the cam gear that drives the optispark, and the short connector to the
optispark on the harness
Here's the new 95
vented optispark. It is now driven directly off the cam pin, and the
long shaft on the back of the optispark with the two o-rings traverses
the cam gear and seats in the camshaft. The vent draws air from the
intake tract and exhausts it in the intake manifold.
Here is a closeup of
the early cam gear with the drive pin installed. The pin is splined and
keyed, only allowing the optispark to be installed one way.
Here's the 97 cam
gear. Note the hole in the center the optispark shaft passes through.
The LT4 and LT4 Extreme Duty timing sets are also set up in this
manner, making them incompatible with 92-94 LT1 motors without updated
Here's the shaft that
drives the non-vented optispark.
Here's a 97 camshaft on
the left with the longer cam pin and the hole in the center to receive
the optispark. An early cam can be machined to match this, but free
stock LT1 cams seem to be readily available from fellow f-body list
members. The cam on the right is a 93 cam without the center hole and
with the shorter drive pin. A late cam is compatible with an early
optispark as long as the cam pin is installed at the correct height.
More of a side profile
of the same two cams.
A closeup of the 93
optispark. The splined drive pin connects the optispark to the cam.
A closeup of the 95
vented optispark. The shaft fits in the cam, and the larger surface has
three slots, only one of which is large enough for the cam dowel pin.