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SMALL BLOCK CHEVROLET - TECH HIGHLIGHTS

SMALL BLOCK CHEVROLET - TECH HIGHLIGHTS
 

The small block Chevy is the most popular engine in the enthusiast market. As a result, anyone should be able to assemble an engine that will meet their needs. It is the engine for which the greatest assortment of parts are available, and is the one most enthusiasts are likely to be familiar with. There are a few areas that require special attention, some of which could cause problems even for an experienced engine builder.

 

One potential problem area is in the valvetrain. Like many small blocks, the Chevy has a relatively short valve spring installed height. The spring diameter is also rather small at about 1.25". These dimensions make it difficult to increase spring pressure and travel for performance cams. All small block Chevy springs listed in our catalog are designed to work at an installed height of 1.69", +/- the difference that our retainers make You MUST have an additional .060" of spring travel available at maximum valve lift. We offer retainers which provide additional installed height over that of the stock part. This increase allows the standard diameter VS739R spring to work with cams that would otherwise cause it to approach coil bind. While this definitely works, we consider the machining of the heads to accept the larger diameter double spring combinations to be well worth the added effort. Just remember that this is a task for a skilled machinist, as some Chevy heads are very thin in the spring pocket area.

 

On small bore engines the use of exhaust valves larger than 1.58", or intake valves larger than 1.88" may require the cylinder bores to be notched for clearance. Other critical areas to check include piston to cylinder head interference, piston deck clearance, valve to piston clearance. Connecting rod bolt to camshaft interference can occur in stroker engines using the 400 crank, and should be checked and remedied if found during an engine test assembly.

 

Camshaft selection can be very critical in computer controlled vehicles. Overlap, duration, and the resulting manifold vacuum must be carefully considered when making your selection. Some systems are less forgiving than are others, and may require recalibration of the computer to deliver acceptable performance. Few such combinations will be emission legal. We have a selection of cams which have been granted E.O. numbers, making them street legal in all 50 states.

 

Valve to piston clearance is dependent upon piston dome configuration, camshaft and valvetrain characteristics, and cylinder head design. Check clearance and make modifications if it is less than .100. Check whenever changing cams, pistons, cylinder heads, valve sizes, or rocker arm ratios. The clearance is reduced if you mill the heads or go to 1.6:1 rockers, and will change if you advance or retard the cam timing. Valve to piston contact will destroy your engine, so check carefully before trying new parts!

 

Piston to cylinder head contact can be a problem in some engines. The piston domes are designed to work with various factory cylinder heads that were available at the time of initial development. The vast array of aftermarket heads now offered, along with the extensive modifications being made, can create problems unless interference is detected and corrected during the trial assembly of the engine. Clearance of .050-.060 should be considered the absolute minimum.

 

Unless assembled by a professional, an engine's deck clearance will be the result of tolerance stack-up rather than careful planning. This dimension is critical to getting the desired compression ratio. A common problem is determining whether a block's deck surface has been previously machined. If you are not sure of the block's past, have your machinist check the actual deck height before ordering pistons. Many small block Chevrolets have been rebuilt over the years, and it is not uncommon to get a "core" that has seen multiple machining operations.

 

Compression ratios in this catalog were calculated with a gasket thickness of .038. Many of the resulting ratios will differ from factory "advertised" data. We have not changed the pistons, but are using a more realistic approach to stating compression ratios, using several popular cylinder heads. Gasket thickness will vary by manufacturer and application, so use the ratios in this catalog as a comparative guideline.



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