Engine Specs

Rebuilding the Chevrolet LT1 Engine, Doug Anderson, Automotive Rebuilder, September 1999

http://www.automotiverebuilder.com/a...ents/99928.gif Thirty-seven years after the birth of the small block Chevy V8, the Generation II engine was introduced in the 1992 Corvette as the LT1. Although it shared many common dimensions, looked much the same and even had a few common parts, it was totally redesigned to provide more power with lower emissions and better fuel economy.
Compared to the 1991 Chevy 350 L98 with TPI, the LT1 made 20% more horsepower, got better fuel mileage, and had a much broader torque band with 90% of it’s peak torque available from just over 1,000 rpm all the way up to nearly 6,000 rpm.
GM Powertrain accomplished all of this by reverse cooling the engine so they could bump the compression ratio up to 10.5 to 1, tweaking the airflow in and out of the engine, and using sophisticated electronic controls for both fuel and ignition. This combination gave the LT1 300 hp in 1992 and ultimately led to the 1996 LT4 that used better heads, more cam timing, roller rockers and sequential fuel injection to make 330 hp .
Although the LT1 was only around for five years, there were two-bolt and four-bolt blocks, aluminum and cast iron heads, regular and H.O. cams that came with long and short dowels, and three different front covers. There was also the "Baby LT1," the 265 cid version that was the standard engine in the Caprice from 1994-‘96. With all that in mind, let’s take a look at this family of engines and see what goes where.
http://www.automotiverebuilder.com/a...nts/99928a.gif BLOCKS
350 - There are two blocks, one with two-bolt mains and one with four-bolt mains. They both have the same 10125327 casting number, so there’s no sure way to know which one you have until you get the pan off. However, if it came out of a Corvette, it should be a four-bolt block, and if it came out of anything else, it was supposed to be a two-bolt. GM used the two-bolt block for everything but the Corvette because it had plenty of strength and it weighed a little bit less.
265 - There was only one block used for the 265 cid version of the LT1. It’s a 10168588 casting that had the numbers "4.3" cast on the side, too. It’s real easy to spot if the heads are off because of the small 3.74" bore.
Getting the right cam in the right engine can be a little bit tricky because there were several variations over the years. There are essentially two different grinds used with two different snouts, depending on which distributor was used on the engine.
http://www.automotiverebuilder.com/a...nts/99928b.gif CRANKS
350 - The crank for the LT1 looks just like the one in the late 350 and has the same casting number 14088526, but it’s balanced for the lightweight pistons that were installed in the LT1. Be sure to keep these cranks separate so they don’t end up in a regular 350, and don’t ever use a regular 350 crank in a LT1. In fact, if you are short of LT1 cranks and don’t have a balancing machine in your shop, you would be better off using a crank from a 305 instead of a 350 because it’s actually closer to the balance specs for the LT1 crank.
265 - The 265 has it’s own unique crank with a 3.00" stroke. That’s the same stroke the original 265 had back in 1955; it’s funny how things go around and come back full circle. It’s a 10168568 casting.
http://www.automotiverebuilder.com/a...nts/99928c.gif RODS
350 - The original LT1 came with regular forged 350 rods, that were shot peened for localized hardness under the head of the bolt and nut. Powdered metal rods were phased in for the Corvette around 1994 and used in all of the LT1 engines by 1995. GM made the change because the powdered metal rods were cheaper to make and were much stronger than the GM high performance "pink" rods. In fact, they are supposed to be good for up to 450 hp. They are machined at the parting line so they can be reconditioned.
265 - The 265 rods are 0.240" longer than the ones in the 350. Both blocks are the same height, but the stroke for the 265 is 0.480" shorter, so the rods have to be longer to make up for half the difference. These rods can be identified by the single, raised dot on both sides of the shank.
http://www.automotiverebuilder.com/a...nts/99928d.gif CAMS
1992-’95 350 WITH ALUMINUM HEADS - The 1992 Corvette had a steel roller cam with a shallow hole in the snout that measured .450" in the front and tapered down to .240" at the bottom. It had a short dowel (.320") that was used to locate the timing gear and a hole with 16 splines in the center of the gear for the stub shaft that drove the early distributor. The 1993-‘94 H.O. cam had a few subtle changes, but all of the early H.O. cams are the same for all intents and purposes. They can be identified by the number "241" stamped on the barrel in front of the first lobe.
http://www.automotiverebuilder.com/a...nts/99928e.gif 1994-’96 350 WITH IRON HEADS - The distributor drive was changed on the iron-headed motors only in 1994, so the front of the cam and the timing gear were changed, too. The cam had a pilot hole that was bigger and deeper (0.500" x 1.0625") and it had a longer (.685") dowel pin that stuck out beyond the timing gear to drive the new distributor. This iron-headed motor was used in the Chevy Caprice, Buick Roadmaster and Cadillac Fleetwood, so it came with a milder cam that improved low end torque and reduced valve train noise. These cams have the long dowel pin and either "600" or "779" stamped on the barrel of the cam in front of the first lobe.
1995-’97 350 WITH ALUMINUM HEADS - In 1995, the aluminum-headed motors got the late, pin-drive distributor, so there’s a second version of the H.O. cam with the big pilot hole (.500" x 1.0625" ) and the long (.685" ) dowel pin. Look for a cam with the long pin and either "242" or "705" stamped on the barrel in front of the first lobe.
http://www.automotiverebuilder.com/a...nts/99928f.gif 1994-’96 The cam gear had to match the cam and the distributor drive, so there were two different gears used, depending on the year and the application.
The original cam had a small, tapered hole in the center and a short dowel pin. It was used with the cam gear that had the small hole in the center with 16 splines in it. It was connected to the distributor with a short drive shaft that was splined on both ends. The cam gear is a GM p/n 10128349. This combination was used from 1992-‘95 on the aluminum-headed motors.
http://www.automotiverebuilder.com/a...nts/99928g.gif GM had some problems with the early distributor due to both carbon tracking and moisture, so a new sealed distributor with a vacuum port was introduced on the iron-headed 265s and 350s in 1994 and used on all LT1s in 1995. The new distributor was located with a pilot shaft and driven by a pin, so both the cam and the gear were changed. The cam had a large, deep hole in the center for the pilot shaft and a longer dowel pin to drive the distributor.
The cam gear had a bigger hole and it didn’t have the splines that were found in the early gear. The pilot shaft for the distributor extends through the hole in the cam gear and seats in the hole in the cam; the distributor is driven by the long dowel pin that sticks up through the cam gear. The cam gear is a GM p/n 10206039.
350 ALUMINUM HEADS</B> - There were two versions of the aluminum heads used on the Corvettes, Camaros and Firebirds. The later ones have less material around the top of the intake ports and weigh about 2- 1/2 lbs. less than the earlier ones, but they are identical otherwise. Look for a 10128374 and possibly a 649.
http://www.automotiverebuilder.com/a...nts/99928h.gif FRONT WATER PUMP DRIVE SHAFT
Be sure to check the seal surface on the geared shaft that drives the water pump. If it’s grooved, it will leak and it will be your fault. New ones are available from GM (p/n 10219554) for around $40. That’s cheap insurance when you consider that the timing cover, chain and gears have to come off to replace it.
http://www.automotiverebuilder.com/a...nts/99928n.gif OIL PUMP
The LT1 powerplant uses the late model 350 oil pump with the 3/4" pickup tube. This should be fairly easy to identify.
HUB AND BALANCER
The balancer is a two-piece assembly with a pulley that bolts onto the hub. Separating the two made it easier to install the Optispark distributor on the assembly line and out in the field. The holes in the hub are offset, so the balancer only fits on it one way, but there’s no keyway in the hub to index the hub on the crank. This shouldn’t be a problem unless the damper was drilled at the factory to "trim" the final engine assembly.
If it was drilled a lot to compensate for an engine that was out of balance, you could end up with a shaker, depending on how everything stacked up with the remanufactured engine compared to the original engine. If you encounter a balance problem on a remanufactured LT1, try rotating the balancer assembly on the crank 90° at a time to see if it eliminates the problem.