With the bottom end already built, the smaller 78cc chamber of the Indy head shot the compression ratio of our combo way up-to no less than a full 13:1. What to do? A change back to a flat-top piston would have brought the combo back to exactly the targeted ratio, but the super-high compression was intriguing. No, it wouldn't be expected to run on pump gas by itself, but it would very likely work with water or a water/alcohol injection. Newer high pressure/high atomization systems have become popular on highly boosted street turbo and mechanical supercharger applications, so we decided to keep the high ratio to experiment with such systems in a high-compression normally aspirated engine. The potential benefit-if it works-is more torque production, and better part-throttle efficiency and fuel economy. It's a pretty wild approach, so don't start building your own Mauler until the full series is completed, all the data is in, and all the cards are on the table.
To The Dyno
That pretty much sums up the build and the theory behind it. The engine was taken to Westech Performance Group for preliminary testing to get an idea of how the theory works out in practice. This project is by no means the type of thing you build with full knowledge of what to expect, slam on the pump for a report card, then ship out the door. Our first testing was more of a progress report, a check to see how close it is to being on target for the objectives we set, and to determine what, if anything, will need closer examination or changes. The engine was equipped with the ported Indy dual-plane intake we featured in a previous story, topped with a Mighty Demon 850-cfm carb. With the radical flat-tappet cam, we were very careful in the cam break-in procedure. The cylinder heads were equipped with Comp's springs (PN 930), set up at an installed height of 1.900 inches, using Comp's titanium retainers (PN 721). The springs deliver 142 pounds of seat load and 353 pounds over the nose with our cam, which is pretty stout for a flat tappet. For break-in, the inner springs were removed, and the springs were installed on the heads with the outer springs and dampers only. This reduces the load considerably, until the cam and lifters establish a wear pattern.
For this testing, we used VP 114-octane race fuel. The distributor was dialed in for 34 degrees of total timing, and it fired instantly. The engine speed was brought to 2,200 rpm for a break-in cycle of 30 minutes. The break-in went perfectly. With the outer springs and dampers only, the springs were providing 103 pounds of seat load and 270 or so pounds at max lift. With the outer springs only, dyno operator Tom Habrzyk and I decided to do a couple of preliminary pulls to gauge the air/fuel ratio, and to see how the low spring load copes with the intense camshaft action. Our first pull was to 4,500 rpm, followed by another, raising the limit to 5,000. The engine did run up to 5,000 rpm before any audible valve float occurred; however, the data showed, as expected, compromised control with the very light spring loads. Power on this first-look pull reached 490 hp at 4,900 rpm, with torque coming in at 540 lb-ft at a low 3,700 rpm. The mixture was very rich, registering in the low-to-mid 10s over the course of the rpm range.