LT4 in B-body Wagon / Chevy High Performance link

LT4 Swap - Old Rob Cheek Page

LT1 vs LT4 Specifications

LT4 Hot Cam Specifications

LT4 Crate Engine
By Scott Mueller.

There are now two LT4 crate engines, but one will soon be gone forever. They can be summarized as follows:

LT4 '96 Corvette Production Engine - p/n 12551183, $5,950 list, $4,462.50 dealer cost. This is a complete '96 Corvette engine which includes everything from the oil pan to intake manifold with throttle body, fuel rail, fuel injectors, opti-spark distributor, ignition module and coil, spark plugs, and even wires. It also includes 'vette exhaust manifolds, water pump, harmonic balancer, accessory bracket, all engine sensors such as knock sensors, temperature sensors, oil psi and temperature sensors, and the throttle position sensor. It even includes $1,800 worth of (unnecessary) 'vette flywheel, magnesium bellhousing and clutch.

When installing this engine in an Impala, you will be removing the following parts and replacing them with the equivalent parts from the LT1 in the Impala or discarding them completely.

-Flywheel, Bellhousing and Clutch
-Oil pan and pump pickup
-Fuel rail and injectors
-Throttle body
-Exhaust manifolds
-Accessory bracket
-Water pump

These are all NEW parts that come on the production LT4, and will be left over after the swap is complete. The magnesium bellhousing and clutch alone sell for $1,800 new, the injectors are over $600, throttle body is $450, exhaust manifolds are $275, and the water pump is $70. I am trying to find a buyer for these items as well as the original LT1 from my Impala.

You also get many other notable items with the production engine including a new $450 distributor, $200 worth of red LT4 sparkplug wires, a $25 '96 higher energy ignition coil, new updated double platinum '96 sparkplugs, various new engine sensors, and even 6 qts of Mobil-1 oil and a PF-52 filter already installed.

Unfortunately the complete production engine will not be available much longer. There were only 300 extra LT4 engines left over after the '96 production run, and SLP took over 100 of them for the 100 '97 Camaro SSes they will be building with LT4 engines. The rest are the only ones left over for warranty and service exchange as well as over the counter sales.

To fill the gap once this engine is gone, GM Performance Parts has introduced a new LT4 Engine Kit, p/n 12371172. This is a 3/4 LT4 engine which is commonly referred to as a long block. This engine includes everything up to the heads, but is not a fully dressed production engine. It does not come with an intake manifold, fuel rail, injectors, throttle body, engine sensors, wiring, spark plugs, distributor, or exhaust manifolds. It does include a separate kit of parts with a 4bbl carbureted intake manifold, HEI distributor, Corvette water pump and harmonic balancer. Unfortunately all of these extra parts except the balancer are not needed in an LT1 swap situation and they will be left over. These parts are also not installed on the engine and do not include attaching hardware or gaskets.

The following parts will be left over from the LT4 Engine (3/4 engine) Kit:

-4bbl intake manifold
-HEI distributor
-Corvette water pump

The following items would need to be purchased separately to complete the swap:

-LT4 intake manifold

Most everything else that is needed would be swapped over from the LT1 engine including the following items:

-Oil pan and pump pickup
-Fuel rail and injectors
-Throttle body
-Exhaust manifolds
-Accessory bracket
-Water pump
-Distributor
-Ignition coil and module
-Spark plugs and wires
-Engine sensors

Note that the LT4 Engine Kit is ideal for an LT1 swap since most of the missing parts you would need come off of the existing LT1 anyway. The only difference between using the Production LT4 vs. the LT4 Engine Kit is that you will have many more parts left over to sell if you start with the production engine compared to the engine kit version.

Theoretically the LT4 Engine Kit should be much more economical than the production engine due to less leftover parts, however if you can sell those leftover parts, it may shift the economy over to the production engine. I calculate roughly $3,200 worth of NEW parts will be leftover after the swap using the production engine, assuming you can get half price for them, that would mean a $1,600 rebate on the deal. Not to mention if you sell your original engine for $2,000 then the total cost of the LT4 swap is now only about $1,000 using the production engine!

The LT4 production engine is the one I have, as the LT4 Engine Kit is not available yet, although I was told it should be available in January. Pricing has not been set to my knowledge. For somebody doing an engine swap in an Impala, the LT5 Engine Kit would be perfect. All of the missing parts would be simply swapped from the existing LT1 engine. With the production engine such as I have, many of the parts will have to be removed and sold as they are not usable in the Impala application. This includes the 'vette exhaust manifolds, water pump, oil pan, accessory bracket, clutch and bellhousing, etc.

LT1 vs LT4 ... What are the Differences? from the Gransport Registry Website at:  http://www.grandsportregistry.com/lt1vslt4.htm While sharing the same bore and stroke, there is a LOT more to the 1996 LT4 engine than just a red intake manifold! What follows is a detailed listing explaining the technical differences between these two Corvette powerplants. What cannot be shown here is the "seat-of-the-pants" difference only a drive in an LT4 equipped Corvette can provide. The LT4's horsepower increase and reliability at higher RPM's (compared to a standard LT1) is largely achieved through the following differences: New camshaft design Larger valves Roller rocker arms Revised Head design Head Gaskets Revised Piston Design Positive-twist top piston rings Fuel System Intake Manifold Roller timing chain Specially machined crankshaft Dual-mass front torsional damper Nodular iron main bearing caps Teflon rear crank seal     LT1 Engine LT4 Engine BASIC LT1 and LT4 SPECIFICATIONS Specification LT1 LT4 Block, construction Cast Iron Cast Iron Bore, inches 4.00 4.00 Compression ratio 10.4:1 10.8:1 Connecting Rods Powdered metal Powdered metal Crankshaft Cast iron Cast iron with undercut and rolled fillets Cylinder Heads Cast Aluminum, 2 valves/cylinder Cast Aluminum, 2 valves/cylinder Displacement 350ci (5733cc) 350ci (5733cc) Fuel system Fuel Injection, Electronic sequential port Fuel Injection, Electronic sequential port Horsepower, factory rating 300 @ 5000 RPM 330 @ 5800 RPM Main Bearings 4-bolt centers, 2-bolt ends 4-bolt centers, 2-bolt ends Pistons Eutectic aluminum/silicon alloy Eutectic aluminum/silicon alloy Redline, factory rating 5700 RPM 6300 RPM Rocker Arms Conventional, stamped steel, 1.5:1 ratio Roller, forged aluminum, 1.6:1 ratio Stroke, inches 3.48 3.48 Timing Chain Link chain, powdered-metal sprockets Roller chain, steel sprockets Torque, factory rating 340 @ 4000 RPM 340 @ 4500 RPM Torsional Damper Single mass Dual mass Valve Diameter, inches 1.94 intake, 1.50 exhaust 2.00 intake, 1.55 exhaust Valve Duration 279 intake, 276 exhaust 282 intake, 277 exhaust Valve Lift, degrees .447 intake, .459 exhaust .476 intake, .479 exhaust Valve Overlap, degrees 41 46 Valve Springs Round Section Oval section, higher closing force LT1 and LT4 COMPONENTS & PART NUMBERS Parts: LT1 Description Part # LT4 Description Part # Camshaft See specs below 12551705 See specs below 12551142 Cap, (Retainer) valve spring   10212802   10212808 Connecting rods Powdered Metal 10108688 Powdered Metal 10108688 Chain, Timing Powdered metal butt link 10128485 Single Roller (made for GM by Cloyes) Steel 12555887 Crankshaft   12556307 Nodular Iron (Additional Machining) 12551485 EGR   ? Overlap leaves EGR redundant ? Gasket, Head   10168457 Composite w/ steel rings 12551488 Gasket, Intake   12524653 for higher ports 12528884 Head (L/R Same) 212 CFM flow 10168448 240 CFM flow Higher ports 12555332 Injectors 3.0gps 24lbs/hr 17124248 3.5gps 28lbs/hr 17124251 Intake Manifold   12552137 Higher ports 0.10" (2.5mm) than LT1 12550630 Knock Module   16177700 Less Sensitive to engine noise 16214681 Knock Sensor   10456287   10456287 Pistons   10159437 Shallower valve pockets than LT1 12551526 Rings, Piston     Positive twist 12528817 Rocker arms 1.5:1 Ratio Stamped steel 10089648 1.6:1 Ratio Aluminum Roller 12557779 Shim/spacer under spring       10212809 Seal, Crankshaft   10206040 Teflon 10206040 Spring, Valve 85 lbs. (38.6 kg.) Seated 10206040 100 lbs. (45.4 kg.) Seated -260 lbs. (117.9 kg.) open 12551483 Sprocket, Cam Webbed 10206039 Solid (Add Mass) 12555885 Sprocket, Crank   10128346   12555886 Throttle Body Twin port, 48mm ? Twin port, 48mm ? Valve, Exhaust 1.50" (38.1mm) Solid stem Weight:95 grams, 3.35 ounces 12550909 1.55" (39.4mm) Sodium filled stem Weight:75 grams, 2.65 ounces 12551313 Valve, Intake 1.94" (49.3mm) Solid stem Weight:110 grams, 3.88 ounces 10241743 2.00" (50.8mm) Hollow stem Weight:85 grams, 3.00 ounces 12555331   NEW CAMSHAFT DESIGN... The LT4's more aggressive camshaft profile compliments all the valvetrain upgrades. The cam has more lift, duration and valve overlap. Exhaust valve lift is .479" (12.17mm) (net is less .006" inch (0.15mm) lash), @ .050 (1.27mm) Lift, up from .459" (11.66mm) for the LT1, and the intake is .476" (12.09mm) (net is less .004 (0.10mm) inch lash), up from the LT1's .447" (11.35mm). Duration is also increased slightly on both exhaust and intake... 203 deg. Intake and 210 deg. Exhaust with 115 deg. lobe separation and 1 degree of retard. By increasing overlap significantly, it eliminated the need for an external exhaust gas recirculation (EGR) device. CAMSHAFT SPECIFICATIONS ('96 model year) (LT1 w/1.5:1 Ratio rockers and LT4 w/1.6:1 ratio rockers) Engine Valve Lift @ .050"(1.3mm) Specification Engine Lobe Lift @ .050"(1.3mm) Specification LT1 Intake .447"(11.35mm) LT1 Intake .298"(7.57mm) Exhaust .459"(11.66mm)   Exhaust .306"(7.77mm) LT4 Intake .476"(12.09mm) LT4 Intake .298"(7.57mm) Exhaust .479"(12.17mm)   Exhaust .299"(7.60mm) Engine Duration @ .050"(1.27mm) Specification Engine Lobe Separation Specification LT1 Intake 205 deg. LT1   117 deg. Exhaust 207 deg. LT4   115 deg. LT4 Intake 203 deg.       Exhaust 210 deg.       LARGER VALVES... LT4 valves are 2.00-inch (50.8mm) Intake and 1.55-inch (39.4mm) Exhaust valves (as opposed to the 1.94 (49.3mm)/1.50-inch (38.1mm) combination used in the LT1) were made lighter to reduce inertial stress, both intake and exhaust valves are hollow and the latter sodium & potasium filled to improve heat transfer. Valve springs are stronger, with a higher installed seat pressure (100 lbs.in. for the LT4 vs. 85 lbs. for the LT1) and wide open pressure (260 lbs. on the LT4) to keep the valves following the camshaft's contours. Special valve springs, eliptical shaped instead of circular in cross-section (Larger horizontal cross section than vertical), allow a spring with a higher free height to be compressed more for higher operating pressures. LT4 Intake valves weight 85 grams. LT1 Intake valves weight 110 grams. LT4 Exhaust valves weight 75 grams. LT1 Exhaust valves weight 95 grams. ROLLER ROCKER ARMS The LT1's stamped steel rocker arms exhibited ball galling at 6400 rpm, so modified Crane roller rockers were substituted in the LT4 with lock nut and set screws to replace the conventional ball and friction nuts. Shims were added to maintain the valve stem accurately and the stud slot widened. The roller axle reduces friction measurably, the 2 lbs-ft reduction increasing economy and responsiveness. The rocker arms also have a roller tip. The LT4 has 1.6:1 and LT1 has 1.5:1 Rocker Ratio. The LT4's new valve springs are made from egg shaped wire for higher seat pressure and improved valve dynamics at higher RPM. REVISED HEAD DESIGN The big difference in the heads is the intake and exhaust ports. Both are larger with bigger radius bends. The "short side" radius of the LT4's exhaust port in particular has been increased to reduce back pressure at higher RPM,s. A throat cut just past the exhaust valve seat also opens up the exhaust port. (Unshrouding valve). The Intake port volume has increasd by 25cc. Increased from 170cc on the LT1 to 195cc for the LT4. The flow through the heads have been increased from 212CFM (Cubic feet per minute) @ 28" (711mm) (LT1) to 240CFM (LT4). The roof was slightly lowered and the walls were moved back slightly from the valves for better breathing, undercutting next to the exhaust valve thereby "unshrouding the valves." Revised port contours enhance air flow into and out of the engine resulting in increased fuel burning efficiency. Combustion chambers are almost identical with a negligible .4cc increase in volume for the LT4 Combustion chambers at 54.4cc's. Both the LT1 and the LT4 Heads accomodate 7/16" studs but the LT4 has larger 7/16 rocker studs. There are some reports of early LT4's with 10mm top threads. The LT1 studs are 3/8" on top and 7/16" bottom. GM part numbers are #3921912 for 7/16" LT4 and #1255216 for 3/8" LT1. Shown below is a cross section comparison of the LT1 (photo A) and the LT4 (photo B) heads. The LT4 Intake port is 25cc larger than the LT1. The revised rocker cover rail is due to the taller intake port opening. Intake valve sizes are 1.94" on the LT1 and 2.00" on the LT4. In the photo below, note the differences in the exhaust ports on the LT1 (photo A) and the LT4 (photo B). The short side-radius offer much smoother flow and the throat cut is slightly different. Exhaust valve sizes are 1.50" (38.1mm) on the LT1 and 1.55" (39.4mm) on the LT4. Also notice the LT4's 7/16" top thread on studs vs. the 3/8" on the LT1. HEAD GASKETS The LT4 also features new composite head gaskets necessitated by higher compression ratio. Rather than the "impregnated surface" of the LT1's gaskets, the LT4's are "graphoil" with stainless steel fire rings. REVISED PISTON DESIGN A gain in compression ratio, from 10.4:1 to 10.8:1, comes from machining the valve pockets in the pistons shallower than the LT1's. POSITIVE-TWIST TOP PISTON RINGS A new top compression ring. High-speed durability tests of the engine revealed that ring flutter became a serious problem above 5,500 rpm, and the result was excessive blow-by. To cure this, something called a positive twist compression ring was specified. A chamfer cut into this type of ring's inside edge causes it to flex down in response to the introduction of cylinder gas pressure, leading to better sealing at higher rpm. "If you look closely at the inside edge of the ring, you can see that there's a chamfer cut on it, and by changing the cross-sectional area on that inside-and the properties associated with it was the end gap of the ring comes together, the ring actually takes on a slight positive twist. It is no longer perpendicular to the bore." But when cylinder gas pressure is introduced, the ring flexes down and seals better against the bore. "If you start with a ring that's flat, when you flex, you end up with a line seal, This way you end up sealing across a broader area." FUEL SYSTEM The engine's higher rpm also exceeded the LT1's fuel injector's ability to keep up, so the LT4 got larger fuel injectors rated at 3.5 grams per second (28lbs/hr), replacing the 3.0 gram (24lbs/hr) injectors of the LT1. The larger injectors were designed to keep pace with the better breathing, higher revving engine. The 48mm throttle body remained unchanged from the LT1, however all LT4 equipped Corvettes (not just Z16 Grand Sports) featured a throttle body top cover plate with the words "Grand Sport" in red letters. INTAKE MANIFOLD A specific intake manifold was cast for use with LT4 heads. Although the manifold and head intake ports do not precisely match, the manifold was cast with additional material to allow safe machining of the ports to more closely match the LT4's higher head ports. LT4 intakes were powder coated red to differentiate them from the standard LT1 manifold. ROLLER TIMING CHAIN Stock LT1 has powdered metal butt link chain drive for the camshaft and water Pump. LT4 has smaller but stronger steel roller chain. Although it seems that the new chain and sprockets would reduce mass, The cam sprocket was left solid, rather than webbed, specifically for additional mass. Increased inertia in the system reduces the tendency for cam torsion. SPECIALLY MACHINED CRANKSHAFT The crank itself was improved via something called undercutting and rolling. Undercutting is the machining of a groove into the corner of a journal. Though this would seem to weaken the crank at that point, it actually makes it stronger where tensile stress is most likely to cause sudden failure. Rolling the undercut introduces compressive stress to the area. This makes it more durable, because potentially catastrophic tensile stress generated during high RPM operation must first overcome the compressive stress before that area of the crank is subjected to tension. Undercutting, a groove cut into the corner of a journal, looks counterintuitive, but makes a crankshaft stronger where tensile stress is most likely to cause failure. By undercutting and then rolling it, compressive stress is introduced. Tensile stress during high-speed operation first has to overcome the compressive stress before there's any tension on the joint. And as tensile stress is what breaks crankshafts, undercutting and rolling make the crankshaft stronger. DUAL-MASS FRONT TORSIONAL DAMPER Tuned for high engine speed, also helps reduce stress on the crankshaft. LT1 pt.# 10128489 and LT4 pt.# 12551486 NODULAR IRON MAIN BEARING CAPS These LT4 components are considerably stronger than their LT1 counterparts and resist failure at higher RPM's. TEFLON REAR CRANK SEAL Offers improved durability over the standard LT1 crank seal. References: GM Assembly Manual (LT4) Chevy High Performance magazine March '99 Chevy High Performance magazine October '95 Vette magazine October '95 Corvette Fever magazine November '95 Corvette Fever magazine October '96 Corvette Fever magazine March '99 The information presented here is believed to be accurate but the authors and the Grand Sport Registry assume no responsibility for errors. If you have evidence to the contrary on any of the above, or have worthwhile additions to increase the value of this information, please submit to info@grandsportregistry.com. Many thanks to "Steve" as the original compiler of much of the above information.