F-Body Performance Racing

LT1 vs LT4 - By Chase Johnson

Time to take your LT1 to its full patential
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Most people will tell you LS1 is the way to go and to ditch all of your LT1s. In reality this is not so. In fact I would tell you other wise. In the real world the LT4 (LT1 upgrade) will produce the same power and capibility that the LS1 can, PLUS you can upgrade your LT4 to make MORE power than a modified LS1. Check these numbers below in a chart from LT1 to LT4 comparison, then scroll to the bottom and see the LS1 numbers. You will see that in reality the LT1 can become superior to the godly LS1 with a LT4 conversion. The UNconverted LT4 was ONLY available on the 1996 Chevrolet Corvette, the 1997 Chevrolet Camaro SS and the 1997 Pontiac Firehawk. Not to put down the LS1 however there is hope for LT1 owners and not just allowing all the late model F-bodies to have all the fun...THERE IS HOPE thanks to the GM Generation II small-block LT4.

The history of the LT4 is that it was the prize for the last year of the C4 corvette. There were only 1000 C4 Corvette Grand Sports made in 1996 which were the Collectors Editions of the last model of C4 corvettes. The LT4 came standard on all 6-speed manual transmissions (unlimited number). However the grand sports actually generated about 25% of all the corvettes that year. The LT4 is extremely rare and since GM has stopped production on the LT4 Intake Manifolds its almost impossible to come by. You can tell the difference in a stock LT1 intake to a LT4 why its bright red paint. However it seems a lot of people are fooling buyers by painting their LT1s red and calling it LT4. The only way to make sure the engine is a true LT4 would be by the VIN number if it came stock or by the engine code. Nowadays a person wanted a LT4 would have to port out their own LT1 intake manifold and paint it red if they wanted a LT4. You can still find LT4 intake manifolds for sale however it will cost you a pretty penny. See below for all the LT4 parts needed for the LT1 to LT4 engine conversion.

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

LT4 Engine (1996 C4 Corvette)

LS1

General Specifications

Displacement 5.7L (5665cc, 346ci) Gross Horsepower 310 @ 5200 RPM
320 @ 5800 RPM

Bore/Stroke 3.90/3.62 Gross Torque 340 @ 4000 RPM
330 @ 4400 RPM

Compression Ratio
10.1:1 Maximum RPM
6200

Firing Order
1-8-7-2-6-5-4-3 Out of crate weight.
Approximately 390 lbs.

Spark Plug
ACDelco 12
ACDelco 41-985 Spark Plug Gap
.060”, 1.524 mm

Block Specifications

Block Material
319-T5 Aluminum Block Description
90 V, Deep skirt with cast-in iron sleeves.

Bore Spacing
4.40” Deck Height
9.24”

Main Bearings
5 Thurst Bearing
Center Bulkhead

Bearing Caps
4 vertical bolts, 2 cross bolts

Cylinder Head Specifications

Material
356-T6 Aluminum Description
Cross flow, wedge combustion chamber.

Ports
Symmetrical, intake and exhaust Chamber Volume
67.3 cc

Head Gasket
0.052” compressed

Crankshaft Specifications

Material
Cast Nodular Iron Features
Undercut and rolled fillets.

Crank Pin Diameter
2.10” Main Bearing Diameter
2.56”

Piston Specifications

Material
Cast Aluminum Description
Strutless, flat top.

Compression Ht.
1.34” Weight
15.5 oz.

Induction System

Manifold
One-piece composite. Throttle Body
75.0 mm bore dia.

LT1 to LT4 Conversion
The following parts are needed to do a true LT1 to LT4 conversion.

[PLEASE NOTE SOME PARTS FROM GM HAVE BEEN DISCONTINUED]

A bolt on LT4 performance upgrade for your LT1. The LT4 conversion kit includes parts needed to change the top end of the LT1 to LT4 specs.

Conversion kit includes:
2 Cylinder Heads P/N 12363287

1 Intake Manifold P/N 12550630

1 GM Performance Parts LT4 Hot Cam P/N 24502586

1 1.6:1 Aluminum Roller Rocker Arm kit P/N 12370839

2 Head Gaskets P/N 12551488

2 Intake Gaskets P/N 12367777

1 Front Timing Cover Gasket P/N 10128293

1 Water Pump Seal P/N 10217886

1 Front Crankshaft Seal P/N 10128316

1 Oil Pan Gasket P/N 10108676

2 Valve Cover Gaskets P/N 10108625

2 Exhaust Gaskets P/N 12552470

Also includes: 1 Distributor Seal(1995-1997 cars) P/N 12552428, and 1 Distributor Seal (1992-1994 cars) P/N 10128317, but only one of these is used depending on apllication.

Not included in the kit, but recommended is the "Extreme Duty LT1/LT4" timing chain kit P/N 12370835.

These are the basic components that make up the LT4 engine and performance please note other parts may be required to properly install these parts on your non-LT4 engine.

1993-1994 ignitions are different than 1995-newer LT1's and may require changing to the newer ingnition system.

Please check with a certified installer before performing this conversion.

Additional parts may be required.

GM PART # 12370835
CATEGORY: Belt or Chain, Engine Timing
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $301.17
OUR PRICE: $210.82
DESCRIPTION: Timing Chain Kit
This extreme duty timing chain kit is for 1995 and newer model "Gen II" LT1 and LT4 engines. To convert 1993 and 1994 engines, you must use camshaft P/N 10224242, distributor P/N 1104032, timing cover P/N 12552426, vac harness P/N 12554395, and vac fitting P/N 14082470. Included in this kit are the following steel gears: water pump gear, a camshaft sprocket, crankshaft sprocket P/N 14088784, and timing chain P/N 14088783. These parts are not the production replacement components, but this roller chain kit is a great performance upgrade. Use with pin drive camshaft only

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