1970 – 1972 LT-1 Corvette Small-Block Engine Ultimate Guide
Throughout the earliest years of Corvette design and development, a definite trend began to emerge. In almost every case, famed GM engineer, Zora Arkus-Duntov, would always find a way to ring every last ounce of horsepower out of an engine. Ever the perfectionist, Duntov relentlessly sought out new and innovative ways to bolster the Corvette’s output, in a bid for performance superiority.
There are perhaps few greater examples of Duntov’s ideology relating to engine design and development, than the 1970 LT-1 small-block. The LT-1 served as a revised version of GM’s famed 350 cubic-inch platform and is often heralded as one of the manufacturer’s most beloved small-block powerplants. With 370 horsepower on tap, it is not difficult to imagine why.
The early 1970s were harrowing days for many automotive manufacturers. The horsepower wars of the 1960s continued, though increasing federal oversight began restricting that which was permissible in regards to emissions. Government agencies had established environmental mandates, which threatened to limit available powerplant options, in a bid to reach compliance.
This is a fact that was not lost upon Arkus-Duntov and his associates, as they recognized that increasingly stringent emissions standards would ultimately slow subsequent performance-related gains. In fact, the de-tuning of many General Motors’ passenger vehicles had already begun.
In order for the manufacturing giant to retain some level of performance dignity, the Corvette would have to have a strong showing during the 1970 model year. While the prior 427 big-block was bored to a full 454 cubic-inches, the Corvette needed added power to GM’s successful small block. The LT-1 would be one of the most significant upgrades to an engine GM ever made.
The LT-1 served as a high-output version of GM’s famed 350 cubic-inch engine platform. With a revised crankshaft, redesigned pistons, and a higher compression ratio, the LT-1 took on a life all its own and gained instant notoriety for its profound performance despite it’s diminutive size.
LT-1 Specifications and Technical Configurations
Much of the LT-1’s promise lied in its internal construction. This engine utilized a cast-iron cylinder block, which housed a 1018 alloy-steel crankshaft. This crankshaft was cross-drilled, as well as internally balanced, and featured Moraine 400 rod and main bearings.
The LT-1’s connecting rods were of a heavy-duty ⅜” bolt configuration and measured 5.700” in length while weighing just under 21-ounces a piece. Opposite the crankshaft, these connecting rods supported specialized forged TRW pistons, of a high silicone aluminum construction. Each piston was secured with the use of pressed chromium-steel wrist pins.
The pistons used by the LT-1 were of a slipper-skirt design and featured similar piston rings to those found on other engines within the 350ci small-block family. The first of these rings was of a cast-iron construction, complete with a molybdenum inlay. The second ring featured an inside bevel, and consisted of ductile iron, while the LT-1’s oil control ring was of a chromed steel build.
A solid-lifter camshaft was featured in the LT-1, which supported .4586” of intake lift and .4580” of exhaust lift. The engine’s intake valves opened at 38 degrees before top dead center, and closed at 94 degrees after bottom dead center. Likewise, the LT-1’s exhaust valves opened at 86 degrees before bottom dead center, and closed at 46 degrees after top dead center.
The LT-1 featured a set of proprietary aluminum heads, which were minimally restrictive and conductive to streamlined induction. These heads were fitted with sizable intake and exhaust valves (2.02” intake, 1.60” exhaust).
Atop the LT-1’s heads sat a specialty Winter aluminum intake manifold. This manifold was of high-rise, dual-plane configuration, and featured a divided plenum. Affixed to the LT-1’s intake was an 800-cfm Holley carburetor, which included racing-spec fuel bowls and center-hung floats.
At the end of the day, you would have a small-block Corvette (or Camaro) with horsepower rivaling most big blocks – with less weight. 370hp, and 380lb-ft of torque was astonishing from a mere 5.7 Liter motor. It actually had 1.1hp per cubic inches – something the 396 and 454 engines could only dream of.
1970 Corvette LT-1 Specs Index
- Horsepower: 370 hp @ 6,000 rpm
- Torque: 380 lb./ft. @ 4,000 rpm
- Compression Ratio: 11.0:1
- Displacement: 350 cubic inches ( 5.7L)
- Cylinder Bore: 4.00 inches
- Stroke: 3.48 inches
Vehicles Using the LT-1 Engine
Though quite legendary in status during the modern era, the LT-1 was rather obscure and short-lived during its production run. The LT-1 was only produced for three years (1970-1972), before being retired by General Motors, presumably because of concerns toward increasingly stringent emissions standards.
During its production run, the LT-1 was only used in the Chevrolet Corvette and Camaro (with the latter being rated 360hp), In total, only 1,287 LT-1 Corvettes were sold during the 1970 model year.
A Legendary Small-Block
Today, the LT-1 is remembered as one of GM’s most renowned small-block creations. The storied powerplant dished out a substantial amount of horsepower and responded willfully to even the most modest of jabs at the accelerator. In short, it is difficult to imagine anyone not enjoying their time behind the wheel of an LT-1 equipped Corvette.
Good story Josh but your numbers for H/P & torque were too high by 100 points.
That ain’t all… he lists the bore and stroke of a 6.2 LS motor. How much else is wrong with his specs?
The bore and stroke of a Gen 1 Chevy 350 has always been 4.00 bore and 3.48 stroke.
The 1970 350 LT-1 does have a bore of 4.0 inches and a stroke of 3.48 inches.
302 is 4.0 x 3.0
327 is 4.0 x 3.25
350 is 4.0 x 3.48
All of his specs are correct, the sanctioning body for drag racing in America, the NHRA actually assessed or “factored” the 1970 350 “LT-1” at 425 brake horsepower and 6,000 RPMs stock, with the addition of open headers.
70 LT-1 did not have aluminum heads. They were cast iron.
I bought a short block 1970 LT 1 corvette engine in 1970 and put my aluminum heads with solid lifters and it ran great
Not true. The LT1 has a cast iron cylinder block with aluminum heads in the Corvette, Camaro and Firebird applications, but cast iron heads on the Buick, Caprice, Cadillac and Impala models.
Not in 1970 it didn’t. There is a huge difference between the early LT-1 and the late model LT1. Get it right.
You’re all right. Having owned one, I know.
I have a 1970 LT1 with Holley 34R-11877A aluminum heads, 222cam dome pistons I cant find anything on web about the heads they came on it I got the Camaro new on rockers and airfilter it said 350-375 H/P
I had one too,I totally loved but I was too young
To really understand what I had
Wow, I’d be a bit embarrassed that a fair bit of incorrect info laid out here has not been corrected by now.
The 1970-1972 LT-1 did not have aluminum heads, neither in the Covette nor the Z-28 Camaro.I have a 1971 numbers matching, all original Camaro LT-1 Z-28. The heads are iron and have never been off the 53,000 mile engine.
If anyone has a 70-72 LT-1 with aluminum heads, those heads were not installed on a GM production line.
Maybe you are thinking about a normal production 350.
LT-1 350 engines all had c.i. heads from the factory. I was with my brother-in-law when he purchased one new in 1970.
Also forgot to mention the heads had screw in rocker studs and pushrod guide plates.
The 4 bolt main caps had special studs with a windage tray, special high volume oil pump, and baffeled oil pan.
They also offered this motor in 1969 as a crate engine, short block, and fitted block Only difference between it and the 1970 was the pistons had full floating pins
So you think that an LT-1 did not produce 370 BHP at 6000 RPMs OK, then ask yourself why is was factored at an actual 425 BHP at 6,000 RPMs for drag racing by the NHRA ? It does produce 370 bhp, meaning at the crank. This is a matter of actual NHRA racing history.
370 HP 1970 LT1 350″ engines were advertised in early 1970 Corvette literature but none was ever installed in production Corvettes. All Corvettes and Camaros got the more tractable 360 HP engines with milder camshafts. Lash on the solid lifter camshaft was spec’d at .030″ for street drivability, but more than specified HP was available for racing if the lash was reduced to a smaller clearance like .010″… giving higher valve lift and duration open… The 370 HP camshaft could be installed and qualify for ‘stock’ racing since it was specified in the early Corvette literature.
I bought a 70 Z/28 at Jerry’s Govans Chevrolet Balto. Md. Sept. 1970 They all had Cast Iron Heads, 780cfm Holley. The Cam had less duration on the intake lobe. The lash was .024 intake,.030 exhaust. The 67,68& 69 302 Zs used the old “fuelie cam” same duration on intake & exhaust .030 lash on both lobes. The Z/28 had a dual snorkel air cleaner. The Vette had a open element air cleaner. The Z/28 had a reverse flow muffler. The Corvette didn’t That is supposedly why they were rated at 370 versus 360 for the Z.
Your getting LT-1 1970-1972, and LT1 1990s confused. You are correct for LT1, however the discussion is about LT-1.
They made the LT1 in 1969 available as a fitted block, and I think short block.
I have one that as a fitted block was put in my 1968 Camaro rs/ss as a retro fit.
Those were as same configuration as the 1970 motors (11:1 trws) but had full floating, rather than pressed in piston pins. It had the same high nickel SPHP block with main bearings caps fitted with windage tray. My motor was fitted with the same LT1 heads having screw in rocker studs and pushrod guides, steel crank, forged rods. The oil pump was the high volume one.
I have the original receipt for the fitted block assy, and the part # was found in the chevy power catalog. The block came with a stamped ser# which did not correspond to any GM engine codes.
Josh is correct. The 70 LT1 motor is rated at 370hp but the Dyno showed 400+ at the wheels (ours). They were a beast in their day and they would walk all over the 454s. The 71/72 LT1 engines were rated at 350hp. I’m not sure that was true though, I think they rated them lower because of the tax. I dont recall the torque The 70 LT1 engines were blueprinted (we have a set along with the original title somewhere). There were 1,287 built in 1970. You can check the C3 registry for a list of features and number codes.