1970 – 1974 LS5 Corvette Engine Ultimate Guide
By the early 1970s, the thriving automotive performance scene had reached a crossroads. Increasingly stringent emissions standards had begun taking their toll on subsequent offerings from some of the nation’s most renowned automotive manufacturers. It seemed as if the power wars of a decade prior had finally reached an end, though not by choice.
In a bid to retain sales, many of these same manufacturers were slow to dial back the output associated with their most prestigious models, instead opting to engineer around de-tuning related matters. No exception to this generalization, General Motors sought out any means of retaining the Corvette’s performance acuity. This desire ultimately gave rise to the company’s illustrious LS5 454 cubic-inch big-block.
454CI (7.44L) History
Up until the latter half of the 1960s, the Corvette had been motivated most notably by small-block powerplants. However, during the pre-emissions era power wars, several robust big-blocks were featured beneath the Corvette’s hood, on an optional basis.
Although newly implemented anti-smog mandates of the day threatened to stifle the production of such engines, GM had no intentions of removing its numerous big-block offerings from the Corvette’s options sheet, until absolutely necessitated by non-compliance.
One of the Corvette’s most significant selling points had been that one could quite literally order a production race car, by selecting the right combination of RPO codes at the time of purchase. This was a principle that had endured for the better part of a decade, and one that many, such as famed engineer Zora Arkus-Duntov, did not intend to let go by the wayside.
At the same time, GM had already begun subsequent detuning of their passenger sedan models, in a bid to reach compliance with federal emissions mandates. However, most felt that such detuning would have little overall effect on sales, so long as the Corvette’s stellar performance attributes remained largely intact.
As a result, the 1970 model year could have easily been referred to as a show of force. Though the legendary L88 and L71 powerplants of just a year prior, had been unceremoniously retired, GM did have two new engines at the ready, which were set to fill this void. Small-block lovers were presented with the 370 HP LT-1, while big-block aficionados found solace in the introduction of a 390 HP LS5 V8. The LS5 actually served as a stroked version of GM’s earlier 427ci big-block, now featuring a total displacement of 454 cubic inches.
454CI V8 Specifications and Technical Configurations
The 1970 LS5 featured a standard cast-iron block, which housed a forged-steel crankshaft, with a total of five main bearings. While most 454ci V8s were of a two-bolt main design, a number of four-bolt main LS5s have been recorded.
Attached to this crankshaft, was a set of I-Beam forged steel connecting rods, which featured forged aluminum pistons at their opposing ends. These pistons were attached to their corresponding connecting rods via chamfered wrist pins.
While the LS5 maintained a 4.251” cylinder bore, the engine’s stroke was increased to a full 4.00”. This brought total engine displacement to 454 cubic-inches, with an effective compression ratio of 10.25:1. It is widely believed that the LS5’s stroke was increased to improve combustion efficiency, thereby minimizing emissions output.
The 454ci LS5 also featured a set of cast-iron cylinder heads, and a General Motors’ “High-Performance” hydraulic lifter camshaft. This camshaft was reported to have been the same model as that used in other GM big-blocks, most notably the L34, L36, and L68 (part number #3883986).
Also universal between multiple GM big-blocks was the LS5’s use of 2.06” intake valves and 1.72” exhaust valves. Valves of this size would remain standard fare for the entirety of the LS5’s 5-year tenure, with the 1971 LS5 serving as the only exception.
The 454ci LS5’s heads were fitted with a cast-iron low-rise intake manifold, which was somewhat more restrictive in design than those manifolds featured on prior GM big-blocks. This intake was topped with a Rochester 750-cfm four-barrel Quadra-Jet carburetor.
All things considered, the 1970 LS5 equipped Corvette produced 390 HP, and 500 lb-ft of torque, while covering ¼ mile in just over 14-seconds. The 1970 Corvette also posted 0-60 MPH times under 7 seconds.
LS5 Specs Index
- Horsepower: 390 hp @ 4,800 rpm
- Torque: 500 lb.-ft @ 3,400 rpm
- Compression Ratio: 10.25:1
- Displacement: 454CI (7.44L)
- Cylinder Bore: 4.251” (107.98 mm)
- Stroke: 4.00” (101.6 mm)
LS5 (454CI) Additional Uses
The 454ci LS5 big-block continued to be offered for use within the Corvette’s engine bay until 1974, when it too, ultimately fell victim to the era’s emissions standards. Prior to being discontinued, the LS5 underwent substantial detuning.
In 1971, just one year after its initial release, the LS5’s output was reduced to 365 HP. By 1974, the LS5’s output was rated at only 270 HP, though at least part of this performance reduction can be explained by the subsequent restructuring of industry standards toward output measurement. The LS4’s latter ratings were measured in terms of net output, rather than gross horsepower.
During its tenure, the LS5 also appeared under the hood of additional Chevrolet models, such as the Chevelle, Monte Carlo, and El Camino. The famed big-block also served as a staple of the company’s C/K Series truck line.
A Dying Breed
For all intents and purposes, the early 1970s served as the final days of General Motors’ original line of high-output big-blocks. By the end of the decade, such engines would serve as little more than an afterthought, as Corvette’s list of optional powerplants dwindled significantly.
Today, the 454ci LS5 is remembered as one of the final GM big-block offerings to have come out of the 1960s/1970s power wars. Although the LS5 was certainly not the most potent of such offerings, its performance acuity was undeniable enough to hold a special place in the history of Corvette performance.
I recently bought a big block for a street rod I’m building, not sure what I have. Can anyone help identify it
Here are the casts and stamps on the block
Casts are, at the oil filter is hi perf pass 22, At the trans flange is 3963512 and H19 70 On the right side
Stamps are front left side of the block 5301, on the stamp flange is TO826CRR
Heads are 3993820 and F10 71
Is this possibly a ls5 or a frankistien 🤔
I did a little digging around and found the following:
The 3963512 on the trans flange is a block casting number and applies to the following engines:
3963512 427 68-69 Pass 385, 425 HP
3963512 427 69 Chevelle, Camaro COPO
3963512 427 69 Corvette Late 69
3963512 454 70 Corvette, Pass 360, 390 HP
3963512 454 70 Chevelle LS6, 450 HP
3963512 454 70-71 Pass, Chevelle, Monte Carlo
3963512 454 71 Corvette 365, 425 HP
3963512 454 73-75 Chevelle
H19 70 is a date code – I believe it translates into the date the block was cast – H=August, 19 would be the 19th day, and 70 would be the year. The block was cast on August 19, 1970. This would be consistent with an engine purposed for a 1971 model year car.
The 3993820 stamping indicates the type of cylinder heads for a big block Chevy. Specifically: Oval Port, Cast Iron, Open Chamber Cylinder Heads for an LS5.
F10 71 is most probably a casting date for the heads. Same translation – F would be June, 10 would be the tenth day and 71 would be the year. So the heads were cast on June 10, 1971.
Assuming your block was a factory install, the heads on this car may be a “Frankenstein” as you put it…namely, the dates would indicate something installed post-production, unless the car was a late build in 1971 (model year production usually starts around September and ends in June/July).
I hope this helps. If you have further questions, please feel free to reach out to me directly at [email protected] or by replying here.