C3 Corvette Engine Build - Welcome To The Machine (Shop)

We needed to mill the cylinder heads to achieve the desired 11:1 compression ratio, but that caused piston-to-valve clearance problems. In order to correct this anomaly, we fly-cut deeper valve reliefs into our Mahle forged pistons.

Milling the cylinder head reduces the combustion-chamber size, increasing compression. We couldn't achieve the desired compression ratio by flat-milling the heads, but fortunately Dart leaves plenty of meat on the deck for angle-milling. Only a dedicated performance machine shop like APE can perform this procedure properly, so be careful when choosing a shop to do this type of work.

The Dart cylinder heads we're using come assembled and ready to install, but since we had to angle-mill the heads, complete disassembly was required. While everything is torn down, we'll perform a few tricks to ensure this engine makes great power and lives a long life.

Dart provides the complete specs for the valvesprings installed on the Pro1-CNC heads, but we wanted to verify for ourselves that there would't be any coil-bind issues-especially since we're using a fairly aggressive Comp solid-roller cam. The springs checked out just as Dart advertises, and will work perfectly with our combination.

Here's a trick you won't see many shops performing. Since the steel valvesprings can mar the titanium spring retainers, APE uses a conical grinder to chamfer each spring, eliminating sharp edges.

The Dart Pro1-CNC heads are ported and flow tested, and Dart publishes the flow numbers-so why are we flowing our heads? Since each flow bench is a little different, we wanted to get numbers on the APE bench as well. We'll use the information to evaluate our combination once the engine is dyno'd, and as a point of reference for future projects. As it turned out, the Dart ratings were fairly conservative-the heads flowed even more than advertised on APE's bench.

To ensure correct bearing clearances, the main caps are installed and tightened to the proper torque, then checked for alignment. Each bearing is then measured and matched to the crankshaft journals to achieve proper clearance. We found our Dart block and Scat crank to be properly machined from the factory, so no additional machine work was required to achieve the right oil clearances.

The same procedure is used to attain the proper connecting-rod oil clearances: Each journal is measured both on the crankshaft and on each connecting rod, then bearings are mixed and matched to gain the right clearance.

The Scat rods we got from Summit Racing were right on the money, requiring a minimum of work.

With critical dimensions verified, all of the parts are cleaned again before the engine is assembled for final clearance checks and pushrod-length measurements.

Pushrod length is one of the final dimensions determined before assembling the engine, as it depends on many variables such as deck height, the amount milled from the heads, lifter and camshaft design, and the thickness of the compressed head gasket. We installed our heads with pre-compressed head gaskets, then bolted on our Jesel rockers and used adjustable "checker" pushrods to come up with a length of 7.5 inches.

As a final step, APE will balance our rotating assembly, and then we'll be ready for final assembly. Next month we'll bolt our LS7-killer all-aluminum small-block together, then strap it to the dyno to see if we've achieved our goals!

After that, our 427 will be installed in Project C3 Triple-Ex for some real-world street and track testing.