Block Talk (Part 2): Why Chevrolet Performance’s Bowtie Big Blocks are a Great Foundation for Performance Builds

Certain Chevrolet and aftermarket cylinder heads are engineered with extra head bolt holes or can be modified with additional head bolts. Our Bowtie block has four extra bolt holes for each head. More bolts equal more cylinder head clamping force and less chance of blown head gaskets. That’s a big plus for engines running high compression, nitrous, supercharger, or turbo.

The Bowtie block has more metal around the lifter bores than a standard production block. This allows you to safely sleeve the bores for use with keyway roller lifters, repair worn bores, or install oversize lifters (all Chevrolets use a rather small 0.840-inch diameter lifter). The lifter valley is also machined in areas adjacent to the lifters to ensure clearance for roller lifter tie bars.

On late model big Chevy blocks like the Bowtie, the oil gallery is placed up high next to the cam tunnel. This keeps an engine builder from hitting the gallery when clearancing the block for a very long-stroke engine combination. Earlier big Chevy blocks have the main oil gallery positioned between the oil pan rail and the main journal tunnel. That limits options for clearancing the block for long-stroke crankshafts. An extra bonus with a Bowtie block: less chance of a grenading connecting rod hitting the oil gallery.

Brass core plugs are installed in the CNC Bow Tie blocks. Brass is superior in because it doesn’t rust and is better looking than plain steel. Circle track engines usually have these plugs pinned (two or three pins on the circumference) or epoxied in place so they don’t pop out. This isn’t necessary for a street engine.

Most Bowtie blocks have “siamesed” cylinder bores. That means there are no water passages between adjacent cylinders, which allows you to machine larger bores for extra displacement. Big Chevy blocks like this have a maximum core diameter of 5.060 inches. They also have reinforced decks to improve head gasket sealing. Don’t worry about cooling with siamesed bores: there are a lot of street-driven engines with siamesed bore blocks.

The pointer shows where our block has been clearanced for a long stroke crankshaft. This prevents the crankshaft counterweights and connecting rod caps from hitting the block casting. This particular block will accept a 4.50 inch stroke crank with no further modifications. Combined with the as-delivered 4.560 inch bore size, you can use this block to build a 588 cubic inch engine. Boring the block to the maximum bore size increases the potential displacement to 598 cubic inches. Some extra clearancing work and a 4.75-inch stroke crank lets you build a 632-cubic-inch monster.

Chevrolet Performance Bowtie blocks come with a choice of a one-piece rear main seal or an old style two-piece rear main seal. In the case of the big Chevy block, the seal type has nothing to do with the crank flange bolt pattern, but it does require a dedicated crankshaft.

The Bowtie block casting is designed to accept an external oil cooler. The back of the block has a direct port to the main oil gallery (just behind the intake valley) for use with a dry sump oiling system. The block will even accept a vintage style clutch ball stud.