441-inch Small-Block Chevy - Sonic Treasure

Seven hundred and ten fuel-injected, street-drivable normally-aspirated horsepower from a 441-inch small-block Chevy hardly sounds like a budget deal, but the truth of the matter is the block, at only $75, was a steal. If you think that's good, how about a 302 Ford block that, when punched out .60-over and equipped with a Scat 3.40-inch stroke crank, delivered 352 inches. The block for this project motor was from a salvage yard and set us back a whole $50. This street driver, without blower or nitrous, went on to produce 525hp and 465 lbs.-ft. of torque. Normally, for engines of this stature, one would expect that heavy duty (and usually expensive) factory blocks would be mandatory. So how, you may ask, especially in the case of the usually fragile 302 Ford, was it possible to get away with such big cubic-inches generating huge overbores and still have the engines live? Was this simply dumb luck or smarts? Well, if it were not for bad luck we would not have any luck at all so, biased though it may be, there is only one option left.

In our world, building project engines is a way of life and building powerful ones, a passion. Each one, regardless of inches, has cubic effort put into it and having it grenade on the dyno is a major disaster. Such an event not only impacts magazine copy dates but also has a serious negative effect on the thickness of your wallet! So how do we minimize such disasters? Two words-sonic tester. This is a piece of equipment that allows the measurement of the thickness of a homogenous material from one side only. Before we go into the implications and cost analysis of using such a device, let us give you a little history and also a basic explanation of its function.

This author's first experience with sonic testing was back in the days when Cosworth first started to dominate Formula One. Back then, Formula two and three were feeder classes for F1 and as such relied on power from stock block race engines. I was running a derivative of an F3 engine in a one-liter Ford Anglia road racer. This 61-inch short-stroke big-bore pushrod Ford engine made an ear-piercing 109hp at the rear wheels at some 10,000-rpm. I remember getting the block sonic tested at Cosworth and it cost what then seemed an arm and a leg. Since then, the value of sonic testing has become vastly more appreciated and as a result their use has proliferated. During 1997, this author found that one manufacture of Sonic testers, StressTel, had the price down to almost $1000, so it had to go into the tool box. Currently, the same unit from StressTel is now under $1000. Granted, that is still far from peanuts but, in our experience, the payback is so good not buying one would have proved far more expensive.

The mode of operation of a sonic tester is easy to understand. Essentially it comprises a sending/receiving probe and a box of electronics to analyze a signal return time. The diagram shows the principle of the probe's mode of operation in conjunction with the data processing box. When sound encounters a sudden change of material density in its path, it is reflected. If the speed of sound through the material/medium is known, then the distance to that change in density can be accurately determined by measuring the time it takes for the sound to return to its source. As the diagram shows, the probe emits pulses of high frequency sound that travel through the part being tested. These sound pulses are then reflected by the opposite surface and picked up by the receiving side of the probe. Given the right calibration, it is possible to measure the thickness of a section of cast iron or aluminum to less than five-thousandths accuracy. This has great implications toward producing relatively cheap power and torque increases while retaining reliability.