LT SERIES GEN II SMALL BLOCK CHEVROLET INFORMATION
The LT1 series Gen II small block Chevrolet is very similar to the standard small block.  They use similar internals, exhaust manifolds and oil pans.  The main difference in the LT1 is the reverse cooling design, which cools the cylinder heads first, then the block.  Because of this, there is no water that passes through the intake manifold.  Coolant is transferred from head to head by a steam line on the back of heads.  The thermostat is located on the water pump.  Also, the water pump is cam-driven, rather than belt driven.  In 1996, an LT4 was available in the Corvette.  The LT4 had the same features as the LT1, but had larger valves, larger intake ports that were located higher, and an intake to match.  The LT4 also came with a more aggressive cam to enhance the better heads. The most common technical questions we receive is about balancer/hubs, timing covers and timing sets, and it can get confusing.
  BLOCK CASTING #'S HEAD CASTING #'S INTAKE MANIFOLDS
OPTISPARKS WATER PUMPS FUEL RAILS FRONT DRIVES/HUBS

 

 

LT SERIES GEN II SMALL BLOCK CHEVROLET CASTING #'S

CASTING # YEAR CID MAINS NOTE
10125327 92-97 350 2 OR 4 LT1 Camaro/Firebird/Corvette/Impala, LT4 Corvette
10168588 94-96 265 2 L99 4.3L, B-Body
There are only 2 castings for an LT1 block. Corvettes come with 4-bolt mains, Camaro/Firebird/Impala come with 2-bolt mains.

LT1 GEN II SMALL BLOCK CHEVY CYLINDER HEAD CASTING #'S

CASTING # YEAR CID NOTES
10125320 94-96 350 LT1, Cast Iron, B-Body
10128374 92-97 350 LT1, Aluminum, 175/68cc ports, 53cc chamber
10205245 93 350 LT1, Aluminum 175/68cc ports
10207643 94-96 350 LT1, Aluminum, 175/68 cc ports
10208890 94-96 265 L99, Cast Iron
10239902 96 350 LT4, Aluminum, 195cc ports, 54.4cc chamber
12529742 95-96 265 L99, Cast Iron
12551561 96 350 LT1, aluminum
12554290 94-96 350 LT1, Cast Iron, B-Body
12554291 95-96 265 L99, Cast Iron
12555690 96 350 LT4, aluminum
12551561 96 350 LT1, aluminum
12554290 94-96 350 LT1, Cast Iron, B-Body
14088526 92-97 350 LT1, Aluminum
LT1 cylinder heads share the same head to block bolt pattern as the standard small block Chevrolet.  The exhaust ports and holes are also in the same location.  All LT1 heads use self-aligning rocker arms.  The intake manifold is proprietary to the LT1, however, a standard small block Chevy intake can be modified to work.  There are no coolant crossovers on the intake, coolant is routed through the back of the cylinder heads through a crossover tube.  All LT1 engines use center bolt valve covers.

 

LT SERIES GEN II INTAKE MANIFOLDS
There are 3 different basic LT1 intake manifolds, 92-93 LT1, 94-97 LT1 and 96 LT4.  There are several casting #'s between 94-97 LT1. The 94-97 LT1 and LT4 intake manifolds appear the same from above, all LT4 intakes are powder coated red from factory, but the difference is in the intake ports. LT4 intake ports are raised, and use different cylinder heads, rocker arms, and intake port gaskets.  The 92-93 intake manifolds do not have the fuel rail crossover in the front like the 94-97 intakes, however the 94-97 intakes can use the 92-93 fuel rails.

 

LT SERIES GEN II FUEL RAILS
     
 

   There are 4 factory LT1 fuel rails. There are 2 fuel rails for the early (92-93) LT1 intakes, and 2 for the late (94-96) LT1 intakes. Corvette fuel rails have the inlet/outlet on the passenger side, Camaro/Firebird/Impala have the inlet/outlet on the driver's side. If swapping an LT1, you can use any fuel rail that fits the intake and side you need the lines on. If you plan on installing the plastic engine covers, modifications to the engine covers will be required when using Camaro/Firebird/Impala fuel rails since the covers are cast to fit a Corvette fuel rail.

 

LT SERIES GEN II FRONT DRIVE CONFIGURATIONS
     There were basically 3 different front drive setups for the LT1 engines : Corvette, Camaro/Firebird and Impala.  The Camaro/Firebird and Impala are very similar to each other.  They are basically the same other than the main accessory bracket and power steering pump.  The rest of the components are compatible with each other.   Both of those setups had the accessories located on the passenger side.  The Corvette had the accessories on the driver's side.  The accessories and components are not interchangeable between Corvette and Camaro/Firebird/Impala. 
There are 4 different LT1 hubs.  Basically, there are 2 hubs for each style balancer : Corvette & Camaro/Firebird/Impala.  Then there are 2 hubs, depending whether the car is OBD I or OBD II.  The OBD II hubs are .100" shorter than the OBD I hubs, since there is a sensor ring (crank position sensor) sandwiched between the hub and the crankshaft timing gear, and the shorter hub is to keep proper belt alignment on cars with that ring.  All OE hubs are neutral balanced and can be installed in any clock position.  None of the factory LT1 hubs are keyed, we do offer keyed hubs. There are only 2 style LT1 balancers, Corvette and Camaro/Firebird/Impala. The balancer must match the front drive configuration.

PLEASE NOTE : if you are converting a front drive from OBD I to OBD II or vice-versa (example : adding or removing the crankshaft sensor pickup ring), you MUST use the corresponding timing gear woodruff key with the matching hub, as they are different lengths.  The OBD II keyway is longer, so it requires the longer key to hold the crankshaft sensor pickup ring in place, and then a shorter hub to keep proper belt alignment.

 

 

APPLICATION OBD OVERALL LENGTH
92-95 Corvette, 93-95 Camaro/Firebird OBD 1 3.519"
96 Corvette, 96-97 Camaro/Firebird OBD 2 3.419"
94-95 Impala/Roadmaster/Caprice OBD 1 4.09"
96 Impala/Roadmaster/Caprice OBD 2 3.99"  
 

 

LT SERIES GEN II OPTISPARK DIFFERENCES
Optispark differences Cam gear differences
Cam differences

     The LT1 Optisparks are very similar between years, but there are only 2 styles : vented and non-vented. Non-vented Optisparks have no ventilation used by the engine, whereas vented Optispark have 2 vacuum lines that attach to the engine to ventilate the distributor. Non-vented Optisparks are spline drive, which is a splines shaft that slips into the center of the cam gear, which drives the Optispark. Both the cam gear and Optispark shaft are keyed, so it only fits one-way and no timing adjustments are required by the installer. Vented Optisparks are pin drive, which an extended pin (dowel) protruding from the cam drives the optispark. There is a dimpled hole which controls the timing of the Optispark. Also, the vented Optisparks have a longer centering shaft, which protrudes further into the camshaft vs. non-vented units. Because the vented Optispark uses a larger diameter shaft vs the non-vented Opti, the chances of an oil leak are less. Also, the electrical connectors on the Optisparks are physically different. The vented Optispark uses a longer connector vs the non-vented Opti. The electrical wiring is the same. No tuning is necessary when converting the Optisparks.

So, the big question we get? "How do I convert to a vented Optispark?" There are a few methods, 2 are listed below:
  • Purchase the MSD replacement Optispark. This is a direct swap, and includes the necessary vacuum lines to complete the conversion. The MSD Optispark uses the splined shaft, so it installs like factory. It includes the electrical extension harness, so no electrical changes are necessary. The cap uses an additional clamp to increase rigidity and reduce leakage from water entering the distributor.
  • Purchase the factory style components. This is the most difficult method, but will allow you to run the large seal. All of the following components are required:
    • 95 or 96-97 LT1 timing cover
 
    • 95-97 LT1 cam gear or complete timing set
    • 95-97 LT1 camshaft or drilling the center of the cam deeper to accomodate the longer drive
    • 95-97 LT1 vacuum harness (the harnesses are vehicle specific, Corvette uses it's own, Camaro/Firebird uses it's own)
    • 95-97 LT1 electrical extension harness
    • 92 Corvette note : 92 Corvettes used a 6-cavity connector on the engine harness (Optispark is still a 4-wire connector). When switching to a vented Optispark, whether factory or MSD, you will need to swap the connector to a 6-pin, or purchase our conversion harness to complete the installation.
 


LT1 FRONT TIMING COVERS
  
There are 3 LT1 timing covers. 92-94 is for factory non-vented Optisparks. 95 is for factory vented Optisparks that are OBD 1. 96-97 are for factory vented Optisparks that are OBD 2. The OBD 2 cover (96-97) has a provision for the crankshaft sensor, none of the other covers work with the crank sensor. The exception is the 94 Caprice/Roadmaster/Impala, which uses the 95 timing cover and optispark.
     Some advantages of the vented Optispark are (1) the ventilation system allows for a longer life span and less misfires, (2) the bearing and drive method allow for longer bearing life, and (3) the larger diameter front seal reduces the change of oil leakage through the cover and into the Optispark.  You can convert from a non-vented Optispark to a vented Optispark by changing the Optispark unit, the front timing cover to a 95-97 model, camshaft timing gear to a 95-97 model, adding the vacuum lines, and changing the Optispark extension harness to the later model.  The camshaft does not necessarily need to be changed, but you will need to drill the cam centering hole deeper for the Optispark unit to slide in all of the way.  MSD now offers a hybrid vented optispark for 92-94 LT1 engines, which uses the small seal and spline drive, but the housing and cap are vented, and no changes are necessary to the timing set, cam or cover.

 

LT1 GEN II WATER PUMPS

     There were 3 different water pump designs, based on the front drive setup : Corvette (2 variations), Camaro/Firebird, and Impala.  The water pumps are specific to the front drive solely for the purpose of heater hose clearance, but the pumps can be swapped from platform to platform, pending you have adequate clearance for the outlets.  The Corvette setup has the least amount of heater bosses.  If you are converting to an electric water pump, we now have blank housings with the internals pressed out, so your ready to install the bolt-on electric motor.