Engine builder Charlie Long...
Engine builder Charlie Long was one of the first people outside of Ford to get his hands on Ford's new 351 Boss block and N351 racing cylinder heads. Here, he compares the casting to Ford's own blueprints for Circle Track.
The writing was on the wall a couple of years ago: Ford's tooling for the N351 cylinder head casting was wearing out, and if something wasn't done, that casting stood a chance of going the way of the dodo bird.
The problem was the N351 head wasn't exactly a new design. Very few people use it for street applications anymore. But like the venerable Chevy 23-degree cast-iron head, the N351 is still the most popular option for Ford racers in any class that still has "Stock" somewhere in the name. In many classes, in fact, it's the only Ford head allowed. That head is a constant; engine builders and race series alike are familiar with it and its potential for power production. The recipes have all been worked out for making good racing between Chevys and Fords with the current packages, so you can imagine that many racers, engine builders and series owners were more than a bit nervous at the thought of the N351 going away.
But that was before Ford announced that it has recommitted itself to the Saturday night racer. And the manufacturer has backed up that claim with lots of new products for everyone from the circle track racers to drag racers. Of course, at Circle Track we're a bit partial to the stock car racers, so when Ford announced the new Boss 351 engine block and brand-new N351 cylinder head castings, we were interested. And of course, we wanted to provide you with a more in-depth look than a cut-and-paste of Ford's press release, so we hooked up with Ford and race engine builder Charlie's Automotive to detail a complete engine build specifically for NASCAR's Late Model Stock class with the new Ford block and heads.
In order to give you as much information as possible, this build will be broken into installments in the magazine. And since this is one of the first race builds anywhere with this block and heads we'll devote the first installment to taking an up-close look at Ford's new hardware.
Long uses a CNC-machining...
Long uses a CNC-machining center to perform almost all the machining work on a new block (honing is still done by hand). One of the benefits of having a piece of CNC equipment like this on hand is he can also use it to accurately measure all the critical points on a block.
The Block Ford got the ball rolling more than a year ago when it announced the completely new Boss 302 engine block. And since the Windsor 302 (that the Boss is based upon) and the Windsor 351 share so many dimensions, most felt it was only a matter of time before a Boss 351 became available. And now it is here with plenty of upgrades over the stock 351 Windsor that will make it attractive to race engine builders.
Previously, Ford has offered many different versions of the Windsor to fit the needs of different racing classes. The Boss 351 is designed with what Ford calls the best assets of several different blocks in order to make it a viable candidate for many different types of motorsports. Consolidating several different part numbers into the Boss block hopefully will allow Ford to maintain costs and keep the Boss 351 block affordable for racers. Currently, the street price is less than $2,000, keeping it in line with other performance blocks.
"There were a number of different blocks that have come and gone over time," explains Mike Delahanty, Ford Racing's new Short Track Program Manager. "Some were optimized for short-track racing, while others were optimized for drag racing and other types of motorsports. And the idea with the Boss was to create one block that had the best properties of all of them.
"The improvements we've made are numerous," he says. "First of all, we're using a higher grade of iron that will provide better wear resistance, better ring seal, and better dimensional stability over the life of the engine. And from a design standpoint, this engine block was designed in the world of CAD. This really has the benefit of being designed from the ground up in the computer. That not only helped optimize things like the water jackets to make the cooling more efficient, but it also makes it a lot easier to check all the dimensions of a new block so that when a customer receives the block, it is dead on. So, there is less time involved on his end in blueprinting and bringing the block up to spec."
We'd have to test over a dozen...
We'd have to test over a dozen to be able to tell definitively, but our one example of the new Ford block measured out very close to the blueprints. Long only had to perform a few finishing machining functions-like the final hone in the cylinder bores-before the block was ready for assembly.
One nice touch with this new...
One nice touch with this new block is the siamesed cylinders come from the factory with cooling passages already drilled between the bores. This helps pull heat away from the top of the cylinder bores but still keeps the strength inherent in the siamesed design.
If you are used to working...
If you are used to working with stock Ford blocks, you should be aware that the cam bores in the Boss block have a common diameter and aren't stepped down like you are used to seeing. This should allow for better machining tolerances, but if you are using a conventional cam, it does require a special set of cam bearings with a common o.d. Also, all the oil galleries are tapped for screw-in plugs instead of the stock press-fit plugs.
Out of the box this block...
Out of the box this block weighs in at a hefty 201.2 pounds. Some of that extra beef adds strength, but some isn't useful to stock car racers. For example, you can see a lot of extra material around the lifter bores. This is so drag racers can open them up for significantly larger lifters, but that isn't allowed in circle track racing so it does wind up being a small penalty.
Four-bolt mains on the center...
Four-bolt mains on the center three caps come standard, and the caps are nodular iron. The main journals are the larger 2.75-inch Cleveland size for added strength in the crank.
All the freeze plug holes...
All the freeze plug holes are tapped for brass screw-in freeze plugs. A very nice touch.
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.
In the foreground is a new...
In the foreground is a new N351 cast-iron cylinder head. Behind it is an older N351 head cast from the old tooling. As you can see, the changes are minor. The area around the lower head bolt holes has been beefed up slightly, and while the same headers will fit both heads it appears the exhaust flange on the newer head extends out slightly farther.
Another comparison shot. On...
Another comparison shot. On the left is the old-style head and on the right is the new head. As you can see, the chamber in the new head has a slightly sharper curve right around the spark plug hole. Engine builder Charlie Long tested both heads back to back and says that despite the differences, the two heads produce the same power. What is evident, however, is the casting quality of the new head is much better. Engine builders should see less core shift, casting flash, and overall aggravation.
One change you should be able...
One change you should be able to notice is the slightly different shape of the exhaust ports. Ford's Mike Delahanty says this was done to make casting the heads easier and does not affect performance.
"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)
Everything that affects valvetrain...
Everything that affects valvetrain geometry was kept the same. So if you already have a valvetrain package that works on your existing Ford race engine package, it should also bolt right up on the new heads and work just as well.
Charlie Long cut the seats...
Charlie Long cut the seats in our new heads in preparation for the build. Like before, the Ford's as-cast seats are not flame hardened.
Another change to this block...
Another change to this block that engine builders should be aware of is it has crossover galleries to the lifter galleries at both the front and back of the block. This is to make sure both galleries get plenty of oil when racing big, flat-tappet camshafts. But if you restrict oil flow to the heads, be aware that you will have to either cut off flow in one of the crossovers or restrict both.