How to Identify a Small Block and a High Nickel Block on a Chevy

by Richard Rowe
Motor - Hot Rod image by Jeffrey Zalesny from

Chevrolet has produced the small block engine in dozens of different configurations since it was first introduced in the mid-1950s. General Motors alloys all of its cast iron blocks with a certain amount of nickel, but for some time, cast them with a far higher nickel content than it does today. The high nickel content made the block stronger and more resistant to wear, but it must be used with caution. Many high-nickel content blocks were cast with relatively thin cylinder walls, and can only be safely over-bored by about 0.030-inch.

Step 1

Identify the block casting number, which you can find on the top of the bell-housing ridge (where the transmission connects). If you see a "++" after the casting number, then it's a high-nickel block.

Step 2

Remove the harmonic balancer and crankshaft pulley from the front of the crankshaft. Remove the water pump and timing cover from the front of the engine. Identify the block casting just above the crankshaft main journal.

Note the numbers you see there. They indicate the block's nickel and tin content by volume. If you see both an 010 and 020, the block has 10 percent tin and 20 percent nickel by volume. An 010 or 020 by itself indicates the block's nickel content as 10 or 20 percent, respectively.


  • A two-bolt main high-nickel block with chrome-moly studs all the way around is safely good for about 700 horsepower, which is comparable to a similarly-equipped factory four-bolt block with the same hardware. However, the ultimate in factory block strength comes in the form of the splayed-four-bolt-main block (as opposed to the standard straight four-bolt-main block), which is good for about 950 horsepower.

Items you will need

  • Socket set
  • Harmonic balancer puller
  • Gasket scraper
  • Mirror
  • Flashlight

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