Chevy 427 Engine
Chevy’s 427 engine is a 7.0L big-block V8 produced from 1966 until 1969. The 427 is part of the Mark IV engine family, alongside the 366, 396, 402, and 454.
|L36||1966-1969||4-barrel||390 hp||470 lb-ft.||10.25:1|
|L72||1966-1969||4-barrel, high flow cylinder heads, solid lifters||425 hp||460 lb-ft.||11:1|
|L68||1967-1969||3×2 barrel||400 hp||460 lb-ft.||10.25:1|
|L71||1967-1969||3×2 barrel||435 hp||460 lb-ft.||11:1|
|L89||1967-1969||Aluminum heads||435 hp||460 lb-ft.||11:1|
|L88||1967-1969||Racing cam, high flow heads||430 hp||460 lb-ft.||12.5:1|
|ZL1||1969||Aluminum block with open heads, racing spec parts||430 hp||460 lb-ft.||12:1|
The L88 version of the 427 is the most desirable variant. With a forged crankshaft and rods, lightweight aluminum heads, four-barrel carb, the L88 is the most power capable of the engines with the exception of the limited production ZL1 engine. The ZL1 427 was virtually the same as the L88 with the exception of an aluminum block and 30% more free flowing heads.
Despite factory power numbers on the ZL1 coming in at 430hp, it is estimated that the ZL1 actually produced closer to 550hp.
The ZL1 engine was about a $5,000 upgrade. While this might be minimal in todays age, this doubled the cost of the car back in 1969. With only 216 L88 Corvette’s produced, and only a handful equipped with the ZL1, these Corvette’s generally fetch multi-million dollar prices at auction.
For awesome technical details on the 427 engine differences and the zz427 crate engine, check this article out.
Cars that use the 427 engine
- 1966-1969 Chevy Biscayne
- 1966-1969 Chevy Caprice
- 1966-1969 Chevy Impala
- 1966-1969 Chevy Corvette
- 1968-1969 Chevy Camaro
ZZ427 Crate Engine
Much of todays hype around the 427 is mostly with the ZZ427-480, a modern performance crate engine offered by Chevy. The ZZ427 is a modernized L88 427 built for performance. The ZZ427 has all forged internals, hydraulic rollers, four-bolt mains, and a cast-iron block.
Built off of the L88, the modern improvements on the ZZ427 have increased performance to 480hp and 490lb-ft. of torque. While the ZL1 and L88 engines were designed primarily for high-performance racing applications, the ZZ427 has a lower compression ratio making it a street-worthy performance engine.
Bore was slightly reduced to 4.25″ while the stroke increased slightly to 3.766″. The crank and rods are forged steel and the pistons are forged aluminum. Solid tappet lifters were replaced with hydraulic roller lifters. The ZZ427 uses aluminum heads and a cast-iron block just like the L88.
Chevy 427 Engine Specs
|L88 427 Specs||ZL1 427 Specs||ZZ427 Specs|
|Hrosepower||435hp||430 hp (est. to be closer to 550hp)||480 hp|
|Torque||460 lb-ft.||460 lb-ft.||490 lb-ft.|
|Displacement||7.0L, 427 cu. In.||7.0L, 427 cu. In.||7.0L, 427 cu. In.|
|Crank||Forged steel||Forged steel||Forged steel|
|Rods||Forged steel||Forged steel||Forged steel|
|Pistons||Forged aluminum||Forged aluminum||Forged aluminum|
|Cam type||Solid-tappet||Solid-tappet||Hydraulic roller|
|Cam lift||.527 intake, .544 exhaust|
|Cam duration||224 intake, 234 exhaust|
Chevy 427 Performance Potential
Before we break down performance potential of the old school 427’s and the ZZ427, we need to level-set on performance numbers. Until about 1971 car manufacturers rated horsepower based on gross SAE instead of net SAE standards. Gross power is essentially power of the engine on an engine stand with zero engine-driven systems such as water pumps, alternators, etc. Additionally, it usually has open headers and no restrictive exhaust systems. Ultimately it outputs a horsepower number that is not realistic when you drop the engine in a car with all the necessary systems.
The L72 engine was quoted at 425hp but dyno’d around the 290whp mark. 290hp at the wheels is probably more like 350hp at the crank, vs. the 425hp quoted. So while the ZZ427 engine doesn’t appear to make that much more power than its 50yr old predecessor, it actually makes significantly more power when you factor in the gross ratings the old 427’s used vs the net ratings on the ZZ427.
Additionally, because the L88 and ZL1 are multi-million dollar engines and very few were produced, we’re going to cover the performance potential of the lower-end 427 engines. The L71 and L72 are the most common 427’s still around today.
L71 & L72 427 Performance Potential
While slightly less performance oriented than the L88 and ZL1, the L71 and L72 were still highly capable engines. Producing 425 gross horsepower and doing 0-60mph in 5.6 seconds, these engines were top of the line with respect to performance back in the late 60’s.
The 427 is capable of producing approximately 500whp. However, it does require a handful of upgrades such as a forged steel crank, h-beam rods, and forged pistons, all of which did not come from the factory as they did with the L88 and ZL1. Outside of these internal upgrades you’re going to need just about every bolt-on modification possible as well as fueling upgrades.
Ultimately, these older engines are capable of producing some significant power, but not without significant cost.
ZZ427 Performance Potential
The ZZ427 crate engine is going to run you $10,000 to $12,000 for the engine alone. With a strong cast-iron block, and all forged internals, the ZZ427 is built for power. While the factory horsepower comes out at 480hp, a handful of simple bolt-on modifications can take this engine to the next level. Additionally, the ZZ427 is estimated to be underrated from the factory, with completely stock engines dyno’ing numbers that suggest closer to 525hp at the crank.
While these engines are capable of handling near 1000whp on the stock block and internals from the factory, many performance oriented folks prefer to VortecPro engines to the ZZ427. The VortecPro engines offer more horsepower for a fraction of the price.
Chevy ZZ427 Engine Problems
1) Excessive Oil Consumption
The ZZ427 is known to burn about a quart of oil every 100 miles, which is quite aggressive. Chevy and GM claim that oil consumption like this is common on their big-block engines. While high oil consumption is said to be somewhat normal, failing head gaskets and cracked heads are also common problems that plague the ZZ427 and can cause excess oil consumption.
One of the effects of the oil consumption is oil blow-by. Blow-by coats engine parts in oil and fuel and can reduce efficiency and performance. Over time as cylinder walls and pistons wear down more and more oil slips into the combustion chamber which can eventually lead to engine knock.
2) Head Gasket Failure
Head gaskets seal the heads to the engine block. On any engine gaskets wear down over time and cause oil leaks and need to be replaced. However, while a typical head gasket should last somewhere around the 150,000 mile mark, the ZZ427’s are known to run through head gaskets every 10,000 miles or less, not hundreds.
This problem is most frequently caused by incorrectly torqueing the head bolts. When the heads are over or under torqued, excess stress is put on the gasket which causes it to fail.
427 Engine Reliability
The old school 427’s are getting to be 50+ year old engines. As with such, problems are going to arise. With that being said, the block, internals, and other major engine components are stout and shouldn’t cause any problems at stock power levels. Throw additional power at it and you can expect various block and internal improvements to be made given the age of the stock components.
The ZZ427 engine is not an enthusiast favorite given a handful of problems the big-block crate engines are prone to. Reliability issues with cracked heads, head gaskets, and oil consumption in combination with not-so-impressive power numbers for the price lead many performance enthusiasts to look different directions for big-block crate motors. It’s not to say that the ZZ427 isn’t or can’t be reliable, but it will generally require some significant maintenance and upgrades to lay down big power reliably.