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Gen II LT1 Engine Build

New Love For A Forgotten Engine: Keith Dorton and Automotive Specialists upgrade a daily driver Gen II LT1 with 21st century tech

Jeff Huneycutt May 31, 2017
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These days if you mention General Motors’ LT1, most will automatically assume you are talking about the modern all-aluminum wondertech V-8 with direct injection, variable valve timing, and a very healthy 450 horsepower right from the factory. Or maybe they will think you are talking about the famous high-performance version of the standard small-block that appeared in Corvettes and Camaros in the early ’70s.

But they probably won’t assume you mean the short-lived second-generation small-block from General Motors that debuted with a bang in 1992 but died with a whimper by 1997. GM’s second-generation small-block had some good ideas, like reverse-flow cooling that moved coolant from the radiator to the cylinder heads first where it is needed most, and electronic engine management controls. And at its peak, it did produce 300 horsepower and 330 lb-ft of torque, but there were also some really serious issues that held the engine back.

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When it came to weaknesses for the LT1, first on the list has to be GM’s abysmal Opti-Spark ignition system. On the drawing board, the optically triggered ignition probably seemed like a great design, but in real-world conditions the Opti-Spark turned out to be so susceptible to moisture that you couldn’t even use a garden hose to clean around the engine. The engine that was designed to be the successor to the famous Chevrolet small-block ended up leaving more people stranded on the side of the road than a Buffalo snowstorm.

By 1997, GM mercifully installed the last production LT1 engines in a handful of Camaros and Firebirds, and so began the reign of the much more successful LS1. The LT1 was unloved by performance enthusiasts, never embraced by the aftermarket, and largely faded from thought.

Of course, that doesn’t mean that all hope is lost for the LT1. Recently, engine builder Keith Dorton, owner of Automotive Specialists in Concord, North Carolina, took on an LT1 engine build for a customer that wanted to keep the LT1 in his car but definitely wanted more power and dependability. We thought this particular build was interesting because it is almost a complete rethink of the LT1 platform. And while Dorton definitely pulled out all the tricks for this build to squeeze out an extra 229 horsepower—while still running pump gas—all the parts used are off-the-shelf. And then when the NOS nitrous system is armed, that power number jumps all the way up to 644. Besides the usual machine work, this is a build an experienced engine guy can pull off in his own garage.

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1. Without the LT1’s distinctive front-breather intake manifold, the engine resembles a standard small-block Chevy, but there are still lots of LT1 uniqueness hidden inside.

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2. LT1 engines used cast-iron blocks with both two- and four-bolt main caps. Only Corvette engines were equipped with the stronger four-bolt caps. This block came with two-bolt mains, so to help increase internal rigidity Automotive Specialists machined the block to accept steel four-bolt main caps from Pro-Gram Engineering.

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3. Even though there aren’t a ton of speed parts manufactured specifically for the LT1, the good news is many LT1 components are interchangeable with a 350 small-block. The block utilizes small-block 4.400-inch bore spacing and 2.450-inch main journals so a 350ci small-block crankshaft will drop right in place. Dorton chose a forged 3.750-inch stroker from Lunati.

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4. All LT1 blocks utilize a one-piece rear main seal like later-model small-blocks. When ordering a crank, do make sure you specify it works with a one-piece main seal.

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5. The plan for this engine is to bump the displacement up from 350 cubic inches to 383. To handle the extra 0.250 of an inch of stroke, the block did need to be clearanced as you can see here.

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6. Dorton also went with Lunati for the high-strength H-beam connecting rods. They are sized at 6.000 inches and mated to Mahle pistons. Because the valve configuration is the same as a first-generation small-block, both the pistons and rods will interchange.

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7. After double-checking stretch, Automotive Specialists’ Tony Corrente torques the rod cap bolts in place.

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8. Comp Cams ground up a steel hydraulic roller cam for the build with 234/242-degrees duration at 0.050 on a 110-degree lobe separation angle. When matched up with a set of Comp Cams Ultra Pro Magnum 1.5:1 ratio rocker arms, the valve lift will be 0.543 inches for the intakes and 0.541 for the exhausts.

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9. The front view of the block makes it easy to spot an LT1. Notice the four holes where the water pump bolts up. Unlike a 350 small-block, the intake manifold on an LT1 is dry. So the water pump feeds coolant to the block through the top pair of holes, which are passages that feed directly to the cylinder head (you can see the hole in the deck of the block just in front of and above the number one cylinder). Hot coolant is returned through the lower pair of holes. Also notice the large hole at the top of the block that will be covered by the timing cover. That’s for mounting the bearing that holds the water pump spur gear. Dorton plans to use an electric water pump, so this hole will be plugged.

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10. Here’s a look at the piston tops in the block. At TDC, the flat-top pistons are 0.004 in the hole to maximize the quench area, so the valve pockets are mirrored at the intake size to help keep the compression ratio to a manageable 10.5:1.

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11. Cloyes provided the high-strength, double-roller timing set. In front of that on the crank snout is the crank reluctor from EFI Connection that will be used by the modern engine management system Dorton is using, which will be a significant upgrade over the flawed Opti-Spark ignition.

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12. The stock timing cover has a port for the Opti-Spark ignition, which won’t be used on this build. A billet aluminum cover from EFI Connection is used that deletes the Opti-Spark provisions for a crankshaft position sensor port.

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13. Air Flow Research (AFR) manufactures an excellent aluminum cylinder head casting for the LT1 with fully CNC cut intake and exhaust ports as well as the combustion chambers, so Automotive Specialists ordered up a pair with 65cc chambers. Here, Jeff Dorton uses a single-point seat cutter to machine the valve seats with their own five-angle recipe for the intakes and a radius on both sides of the seat for the exhausts.

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14. The AFR heads bolted right up with a set of ARP head bolts and a composite gasket from Fel-Pro between the deck of the block and each cylinder head. The valves, springs, and retainers all came with the cylinder heads.

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15. The stock front-breathing intake manifold wouldn’t work with Dorton’s plans for more power and modern EFI controls so a Holley single-plane intake that’s part of its HP EFI system will be used. To make it fit, the LT1 bolt pattern had to be plugged (which you can see here) and new holes drilled for the standard 350 small-block intake pattern.

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16. Ultra Pro Magnum rockers in a 1.5:1 ratio for both the intakes and exhausts round out the valvetrain.

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17. The Holley HP EFI system is set up with a throttle body that integrates with a port fuel-injection system. Because the port orientation on the LT1 is the same as the first-generation small-block, after the manifold boltholes in the heads are redrilled, everything bolts up and works exactly as it should. Notice also the spacer underneath the throttle body. That’s the fogger for the NOS nitrous system.

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18. What’s cool about adding nitrous to Holley’s HP EFI system is the simplicity of getting everything to work together. All that’s needed is a single nitrous solenoid. Instead of a separate fuel solenoid to keep the engine from going too lean, the Holley HP EFI system simply recognizes the change in the air/fuel ratio when the nitrous is fired and adds the appropriate amount of fuel. An Aeromotive fuel regulator is mounted to the fuel rail to handle fuel pressure management.

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19. Because the LT1 has a dry intake manifold, the thermostat is located in the water pump housing. For dyno testing, Dorton wants to manually control water temp and flow through the engine so the thermostat is removed.

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20. The front accessory drive system is all controlled by Jones Racing Products.

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21. Back in the ’90s, the best the stock LT1 could produce was 300 horsepower. Naturally aspirated, Dorton’s version made 529 horsepower at 6,200 rpm and 506 lb-ft of torque at 4,800 on pump gas. Better still, the torque doesn’t drop below 450 from 3,200 rpm all the way through 6,100. And once the 100hp shot of nitrous hits, peak power jumps to 644 hp and 612 lb-ft.


Air Flow Research (AFR)
Valencia, CA 91355
Lenexa, KS 66214
Pro-Gram Engineering
Barberton, OH 44203
EFI Connection
Automotive Specialists
Concord, NC 28027
Southfield, MI 48034
Ventura, CA 93003



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