The combination of a high...
The combination of a high 13:1 static compression ratio and short cam timing created cylinder pressure that nearly pegs a standard compression gauge, registering 240 psi while cranking the engine. Testing was done with VP 114-octane race fuel. We will explore using an electronically controlled water/alcohol injection system to make it run on pump gas at a later date.
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.
After breaking in the cam...
After breaking in the cam to establish a contact pattern and making a few preliminary pulls, the valvetrain was removed to install the inner springs of the 930 valvespring assemblies. The dual spring gives 142 pounds of pressure on the seat and 353 pounds of pressure at max lift.
With preliminary numbers that looked encouraging, we allowed the engine to cool down and installed the inner spring to the valvespring assemblies. Our loads were now quite high for a flat-tappet application, just in the range of what would normally be used with a serious flat-tappet cam. The 930 is a conventional dual-spring with a 1.509-inch outside diameter, and has proven to offer good rpm potential with a typical high-performance flat-tappet camshaft. We also took this opportunity to make a jetting change, leaning the carb six jet sizes at the front and rear. The dyno was set to make a pull to 6,000 rpm. The results showed the jetting to have helped lift the power curve in the lower rpm ranges, and revealed some interesting insight on valvetrain control. The curves carried virtually parallel through 4,600 rpm, although the engine was making an average of 10 lb-ft more torque across the range with the more appropriate mixture. At 4,600 rpm, the single outer spring dropped off like a stone, while the dual spring with its increased loads carried on with the slope of the power curve as straight as a bullet. However, at 5,400 rpm, the gig was up, and the valvetrain became unstable with an immediate nosedive in power from there up. Peak numbers were now 551 lb-ft, at 3,500 rpm, and 560 hp at 5,500 rpm, right where the valvetrain went unstable. The low apparent peak torque is deceptive, since the engine's torque curve was extraordinarily flat. At 4,800 rpm, the engine was making 550 lb-ft, within one lb-ft of the torque reading at 3,500. In fact, looking at the average torque over the full test range from 3,100 to 5,500 rpm-the point at which valvetrain instability became apparent-the engine delivered an average of 544 lb-ft, which was very unusual.
We could see the engine in this configuration was going to come up short of our goal of 600 lb-ft of peak torque. However, the slope of the horsepower curve before the onset of instability showed the potential was there to meet the 600hp target, if only it would rev more cleanly upstairs. We had a set of Comp's high-tech Beehive springs (PN 26120), which have tested to provide unusually good valvetrain control in other applications. We made the spring change, installing the new Beehive spring at 1.880 inches, which provided spring loads of 155 pounds on the seat and 377 pounds over the nose. This is about as much spring as can be run with any reliability on a conventional flat tappet, and the Beehive winding significantly reduces inertia at the valve. We used a steel retainer (PN 964) and a modified lower locator to fit the Indy heads. Interestingly, the change to the Beehive spring did almost nothing to improve the rpm potential of the valvetrain. Peak torque improved slightly to 556 lb-ft at 3,500 rpm, with the same flat curve varying little and holding nearly constant to record 554 lb-ft at 5,100 rpm. Peak power nudged up to 559 hp at 5,400, at which point the valvetrain became unstable and power began to plummet.
 Back up and running, the 446...  Back up and running, the 446 was put to its first serious pulls, running from 3,000 to 6,000 rpm. Torque was nearly constant from the bottom of the pull to 5,400 rpm, at which point the hydraulic cam valvetrain went unstable. Power stood at 560 hp and 551 lb-ft. |  RPM capability in our valvetrain...  RPM capability in our valvetrain was clearly holding back peak output. Searching for the magic bullet to stabilize the system, the conventional dual springs were swapped to Comp's Beehive springs (PN 120). The spring change had little effect on rpm potential, prompting us to look elsewhere for the source of instability. |  We had an Indy 440-2 intake...  We had an Indy 440-2 intake available for testing. The intake was box-stock, except for a port match. We found it added a little power over 4,500 rpm, but the trade-off was losing the torque of the 2D dual-plane down low. The single plane intake's benefit up top would have been more apparent had our combination been able to work in that rpm range. |