Sonic Testers: A Surefire Method Of Detecting Metal Treasure
By David Vizard
Most of you have probably seen those TV commercials for metal detectors and the subtle suggestions that they could help you find a fortune in buried treasure. Maybe – but it is a real long shot at best.
There is, however, for the performance engine building business, what I perceive as the equivalent to the treasure seeker’s metal detector. The results, though, are usually anything BUT a long shot. Here I am referring to a sonic tester. This electronic device allows the measurement of metal thicknesses that have only one side inaccessible.
Examples of such are cylinder bore wall thickness, main webs, intake and exhaust port walls, etc. If I had to pick any single "tool" out of my shop and say "this was the most productive." I would have to say my sonic tester takes the prize. In a nutshell, here’s why. It made me money and paid for itself big time in just the first year. What it did for me it can more than do for a regular performance shop simply because of a greater number of customers and engine turnover.
Big horsepower numbers mean greater block stresses. Worrying about whether or not your customer’s block is going to hold up because you know how to make power is, to say the least, frustrating. If you are good enough to make enough power to put the block at risk, the life of that engine can become a source of mental stress.
In the days when sonic testers were a rare commodity I had what I felt was more than my fair share of grenaded engines. Every one of them was a carefully crafted high dollar deal and the resultant failure represented a financial loss at least double the worth of the components the engine contained. Most sonic testers were just outside of my financial budget, but in the late ’90s I found that StressTel had introduced a low cost sonic tester and I made a point of getting one the next working day.
Initially my main concern was to cut catastrophic engine failures so as to reduce the resultant financial loss. As effective as that has been it is far from the #1 payback due to having such a device. We are all aware that the easiest way to give a customer greater street performance is to add cubes to the engine. The easiest way for a machine shop to do that is to overbore the block but without a sonic tester that is also the easiest way to fall foul of unreliability problems.
In the first year of ownership my sonic tester not only weeded out many thin blocks, but also revealed some gold in the form of extra thick blocks. One wrecking yard and one swap meet trip netted two 400 SB Chevy blocks that looked for all the world like the original models for a Bow Tie race block. Except at the point the bores are siamesed these blocks could be bored at .060˝ over and still leave the cylinder walls at over .300˝. By repitching the bores a small amount I was in a position to safely bore either of these blocks at .100˝ over for 423 cid instead of the normal 406 cid.
Both these blocks cost $75. Compared to the substantial four figure number for a race block, that looks like a really good savings. Still, on the SB Chevy theme it’s accepted among many engine builders that for a 350 any bore over +.030˝ could get a little dodgy for a high performance application. The consequence is that there are a lot of +.030˝ blocks that are discounted for such use. The truth is that probably as many as a third of these blocks will go to +.060˝ and still leave the cylinder walls at or above the average block selected on the basis of minimal visual core shift.
If you have a dozen +.030˝ blocks it is not out of the question that at least four of these would be good for a 500 hp application at +.060˝ and the resulting extra 5 cubes certainly won’t hurt. With a sonic tester like my T-Mike R, these blocks now become usable high performance inventory as apposed to dime-a-dozen cores.
By any standard, Ford’s so called "thin wall casting" presents performance engine builders with some major block reliability challenges. The heads available today, not to mention blowers and nitrous, can easily out-power a typical 5.0L block. Fortunately for us Ford’s casting techniques – though commendably accurate for what it is – still have sufficient variables to produce both good and bad blocks.
A stroker motor project with Coast High Performance in California called for a stout block. Before resorting to a FoMotorCo performance block I paid a visit to some Ford oriented dismantlers in the Los Angeles area. A day’s scouting around turned up a Mexican cast block with at least as much material thickness as a Ford’s sportsman block. Even at +.060˝ this block still had cylinder walls and the associated areas thicker than an above average stock bore size block.
The block set me back $50 and resulted in a 352 cid 525 hp motor. The lesson here is not only did I save almost a grand on the price of a block, but I also reduced or possibly eliminated the chance of a block failure and got a bonus 5 cubes.
OE blocks are not the only candidates for sonic testing. While demonstrating the sweep feature, which shows the thinnest section within that sweep, on an aftermarket block I discovered a thin patch. In a highly localized area the cylinder wall, normally about .400˝ thick, was down to less than .100˝.
The block was intended for a ProMod type application and was going out of the country so reliability was a major factor. Had I not found this anomaly the block, under the pressures of 1,600-1,800 hp, would have certainly failed almost right away. Not only would it be embarrassing to have a $30,000 motor fail on the first pass but also shipping it back and dealing with all the associated customs/shipping hassles would have made it a financial nightmare.
Let’s face it, adding cubes is about the most satisfying route to more performance. Your boring machine can generate big bores, but without a sonic tester you can never be sure if you’re boring toward trouble or boring toward money.