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LT SERIES GEN II SMALL BLOCK CHEVROLET INFORMATION

LT1 Gen II Small Block Engine
     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.

 

LT SERIES GEN II SMALL BLOCK CHEVROLET CASTING #'S


CASTING # YEAR CID MAINS NOTE
10125327 92-97 350 2 OR 4 LT1/LT4, Corvette blocks normally 4-bolt main
10168588 94-96 265 2 L99 4.3L, B-Body

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 aluminum cylinder head 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

92-93 LT1 intake manifolds do not use the fuel rail with the crossover, so the intake isn't nocthed in the front 94-97 LT1 and 96 LT4 intake manifolds use the fuel rail with the crossover in the front.  These intakes can use the 92-93 fuel rails as well. LT4 Intake Manifolds are all powdercoated red from factory
There are 3 different LT1 intake manifolds, 92-93 LT1, 94-97 LT1 and 96 LT4.  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 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

94-97 LT1 Camaro/Firebird/Impala fuel rails all exit on the driver's side rear All LT1 Corvette fuel rails exit on the passenger side rear
93 LT1 Camaro/Firebird fuel rail has entry/exits on the driver's side valve cover over cylinder #3

    There are a total of 4 factory fuel rails for the LT series engines : 2 different Corvette rails, and 2 different Camaro/Firebird rails.  All of the Corvette rails have the feed/return lines on the passenger side, while the Camaro/Firebird/Impala all have the feed/return lines on the driver's side.  92-93 fuel rails do not use the fuel crossover in the front.  94-97 fuel rails use the fuel crossover in the front.  You can use the 92-93 fuel rails on all of the intakes, but you can only use the 94-97 fuel rails on the later model intakes.

 

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 LT1 hubs are keyed. 

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.
LT1 Hub APPLICATION OVERALL LENGTH
92-95 Corvette, 93-95 Camaro/Firebird 3.519"
96 Corvette, 96-97 Camaro/Firebird 3.419"
94-95 Impala/Roadmaster/Caprice 4.09"
96 Impala/Roadmaster/Caprice 3.99"
 

LT SERIES GEN II OPTISPARK DIFFERENCES

Vented Optispark backside (left in photo), non-vented Optispark backside (right in photo)

     The LT1 Optisparks are very similar between years, but there are only 2 styles : 1992-1994 and 1995-1997.  The 2 cannot be interchanged without front cover and camshaft modifications.  There are 3 main differences in the units : drive method, ventilation system, and electrical connection.

OPTISPARK DRIVE METHODS

Vented Optisparks use a larger bearing and seal, as well as a pin drive slot and longer shaft Non-vented Optisparks use a splined driveshaft that slides into the timing gear.
Vented optisparks have a deep centering hole in the camshaft and a longer dowel pin (left photo) Non-vented Optisparks use a splined timing gear, vented gears are hollow in the center

     The Optisparks use 2 different drive methods : Spline drive and Pin drive.  On spline drive system (92-94), the Optispark has a splined shaft that mates to the camshaft timing gear.  The gear is clocked so the shaft only goes in 1-way for precise timing.  On the pin drive system (95-97), a pin extended from the camshaft runs through the timing gear and into a slot on the Optispark, and the shaft from the Optispark runs through the camshaft center for better bearing support. 


OPTISPARK VENTILATION AND CONNECTORS
 
Vented Optisparks have a vacuum line on the housing and distributor cover for ventilation Non-vented Optispark has 3 small holes (in some models) that allow for pressure ventilation LT1 Optispark connectors, vented shown at top of photo

     Vented Optisparks have 2 small vacuum line attachments (left photo).  These attachments allow for engine vacuum to remove moisture from the Optispark unit.  Non-vented Optisparks have no vacuum line attachments (right photo).  Instead, 3 small holes are located at the bottom of the unit to allow for ventilation.  This causes failure when driving in rainy weather or through a puddle.

 


LT1 FRONT TIMING COVERS

92-94 LT1 timing cover pictured 95 LT1 timing cover pictured   96-97 LT1 Timing Cover, has boss on bottom for crank sensor

CONVERTING FROM NON-VENTED TO VENTED 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.  We have a convenient kit available for those who wish to upgrade to the vented Optispark.

 

 

LT1 GEN II WATER PUMPS

92 LT1 Corvette water pump (93-96 similar), heater oulet on passenger's side 93-97 LT1 Camaro/Firebird water pump, heater outlets on both sides 94-96 LT1 Impala water pump, heater outlets on passenger side
     There were 3 different water pump designs, based on the front drive setup : Corvette, 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. 


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