On our end, we saw some of the benefits Delahanty spoke of. Charlie Long, owner of Charlie's Automotive, uses a CNC-machining center for just about all the machining operations on a new block except honing the cylinders. As part of the process, he also uses the CNC to locate all the critical dimensions on every block to determine what needs to be corrected. After measuring everything from the main and cam journal bores, lifter bores, squareness of the deck, and even the dowel pin holes for locating the cylinder heads, Long says everything was correct to within a few thousandths of an inch-well within the acceptable margin and better than most blocks he's seen. Of course, this was only a single block we checked, but if the rest of them spec out this well then engine builders will certainly be happy.

This block also has numerous other features. It's available in either 9.2- or 9.5-inch deck heights and is based on Windsor dimensions except for the main journals, which are the larger 2.75-inch Cleveland size. If you are racing an open class where the cubic inches aren't restricted, Ford engineers say that the displacement can safely be upped to more than 460 cubic inches.

There are also splayed, four-bolt main caps (the caps are nodular iron), screw-in freeze plugs, siamesed bores with coolant holes drilled between each pair of cylinders, a front crossover for the lifter galleries, diesel-grade iron is used in the casting with a tensile strength of 41,000 psi.

The Heads Ford's engineers had a tricky proposition on their hands when it came to retooling for the N351 cylinder heads. Like mentioned previously, the tooling that was being used was old, and that led to headaches when trying to cast high-quality cylinder heads. Engine builders and racers were demanding better cylinder heads, but Ford engineers knew that if they produced a new head that was significantly better, NASCAR wouldn't allow it in the Late Model Stock division.

"What had happened over time is the tooling had gotten to where we could not produce a repeatable, quality cylinder head," explains Delahanty. "So the decision was made to retool the thing, but let's retool it to address dimensional controls and repeatability while still keeping it within the very tight box that NASCAR has defined for Late Model Stock Car racing. So our goal was to retool the cylinder head without changing any of the performance qualities while still taking advantage of any new manufacturing technologies that have come along since the head was first introduced in the late '90s. It was a delicate balancing act to keep the same performance capabilities while also significantly reducing any blueprinting or prep work that was necessary before these heads are ready to race."

After much work, Ford had a new set of N351 heads that it felt met the criteria. To prove it, both Ford and NASCAR representatives met at the Charlie's Automotive shops where Long tested both old and new heads back-to-back on the flow bench and running on a dyno. Because NASCAR found no real performance advantage if the new heads are legally prepped, it has approved the new N351 heads for racing.

The improvements that Ford did make, however, should make these new heads easier to work with for both the engine builder and racer. Take a closer look at this block and heads and next month we'll start bolting parts together on our Ford Late Model Stock engine.

On The Flow Bench Airflow for the new N351 head is measured in cubic feet per minute of air at 28 inches of water

Valve lift (inches) Intake Exhaust
0.100 67.6 54.2
0.200 141.5 104.1
0.350 193.8 131.4
0.450 213.2 147.1
0.550 228.0 157.2
0.650 241.1 165.7