There's no doubt that the Chrysler Corporation manufactured some of the best automotive engines of the muscle car era, with unsurpassed power and endurance. As these engines age, however, finding a good, low-mileage block suitable for a performance build isn't getting any easier. Let's face it, high-performance V-8 engines like Hemis, 340s, or 440 HPs or Six-Packs in factory muscle cars usually got worn out by the first or second owner, and have either been rebuilt two or three times or discarded by now. And if you get lucky enough to find an engine that hasn't been rebuilt several times there's still a good chance that corrosion or core shift could cause thin cylinder walls, rendering the block unusable.
Building a high-performance engine requires a careful balance of power versus the weight of the engine, and for this reason all manufacturers make some compromises in terms of materials used and the amount. Additionally, cast iron blocks are prone to a condition called core-shift, which can result in some areas of the block, especially the cylinder walls, to be thinner than others. This anomaly isn't just found in old engine blocks, but new ones as well, so before you bore your block oversize it pays to have it checked to ensure adequate cylinder wall thickness. Muscle Motors let us follow along as they checked the bores in a block they were building for a customer using a sonic tester.
Sonic testing a block may sound high-tech, but the technology has been around for many years. In simple terms, electronically generated sound waves are sent into the metal through a probe, and reflected back to the probe by the metal. The time it takes for the sound waves to get back is measured and then electronically converted to a dimension. Sonic testers are very convenient for checking thicknesses in areas that are inaccessible to conventional measuring equipment, like the cylinder walls of an engine.
To properly sonic check a block, it must be tested in several critical areas for material thickness. Facing the block, if the engine spins clockwise (like automotive Mopar V-8s), there is an area of the cylinder called the major thrust which will be on the left side of each bank of cylinders. This area of the cylinder gets the most abuse so it's important to have plenty of material here. Opposite the major thrust is the minor thrust, which should also be checked. The front and rear of the block should be checked as well, because the areas between cylinders are generally the thinnest.
If thin areas are found, there are several solutions that a machine shop like Muscle Motors can offer to correct the problem. In some conditions, offsetting the boring bar slightly can save material on one side of the cylinder, though we'd only recommend this for mild builds or to save an ultra-rare engine block. Typically, a thin cylinder is sleeved to correct the problem. If multiple cylinders are thin, however, it may be best just to find another block that's in better shape. So before building your next engine, find out if the block is good before you spend your money by having it sonic tested, not after you build it by cracking a cylinder wall.
Above Building and installing...
Above Building and installing a new engine for your Mopar is an expensive proposition, especially if you aren’t sure of the condition of your factory block. This month we’ll show you how easy it is to have your block sonic tested, so you don’t have to guess if it will last.
1 Building an engine for...
1 Building an engine for your Mopar is an expensive and time-consuming proposition, and you don’t want to have to do it twice. This month we’ll show you how you can ensure proper cylinder wall-thickness before you pay for expensive machine work.
2 A good machine shop like...
2 A good machine shop like Muscle Motors has the electronic equipment to sonic check a block, ensuring adequate cylinder wall thickness. The proper thickness depends somewhat on the intended use of the engine, but .275 inch is generally accepted as a minimum thickness for a high-performance build.
3 Using a probe, the sonic...
3 Using a probe, the sonic tester can access areas where conventional measuring equipment can’t be used. There are several areas which must be checked, such as the major and minor thrust areas of each cylinder, as well as the front and back, and areas between cylinders.
4 Testing in multiple areas...
4 Testing in multiple areas is advisable, as sometimes a cylinder will taper or be egg-shaped due to factors such as wear, previous machining, or core-shift. Compared to the cost of machine work and parts, we consider sonic testing money well spent.
5 Once complete, Muscle Motors...
5 Once complete, Muscle Motors gives its customers a printed sheet with the measured cylinder wall thicknesses, so they can see for themselves whether the block is buildable, needs to be sleeved, or simply needs to be replaced.