As noted last month,
the first part of a big block Ford power program is to select
the appropriate components and machine them properly. Part two
entails coordinating the camshaft and valvetrain with an engine’s
intended use, and then bolting everything together using proven
high performance techniques.
According to high performance
Ford specialist Norm Wizner, Wizner Performance, Lilburn, GA,
improper camshaft selection continues to be the most common cause
of a performance shortfall. “We’ve had great success with
our camshafts because we tie our recommendations to real world
driving situations, said Wizner. “Too many people really
believe that bigger is better. That’s not always true with a race
engine and it definitely isn’t true with a street engine.
“I can’t tell you
how many customers we’ve had with engines that just didn’t run
the way they should have. In almost every case, the problem was
a camshaft with way too much duration. When they installed one
of our cams, the difference was night and day. In fact, one guy’s
car dropped its quarter mile time by more than a full second.
It’s not that our cam was so much better than the one he had,
it was just matched to his engine combination better.”
As an example, Wizner’s
camshaft selection for a 514 cid engine he built for a customer
was one of his Street Boss Special hydraulic grinds with duration
at .050″, lift of 236 degrees for the intake lobes, and 240
degrees for the exhaust. Lift specifications are .566″ intake
and .580″ exhaust. This is a relatively conservative camshaft
considering the engine’s displacement, but it’s appropriate because
the customer for this engine wanted to use his existing dual-plane
intake manifold and 850-cfm Holley four-barrel carb.
With this type of intake
system, the horsepower peak is in the 5,500 to 5,750 range so
Wizner picked a cam that produces maximum power at this rpm level.
A second consideration is that with 11:1 compression ratio, excessive
duration takes cylinder pressures for a nose dive, which manifests
itself as poor low-speed and mid-range torque.
In light of the fact
that the 514 cid short block was topped off with a pair of Ford
Motorsport Cobra Jet aluminum cylinder heads, the cam choice might
seem a little too conservative. In fact, the relatively short
duration of this particular Street Boss Special tends to compensate
for the heads’ huge ports. So what might seem like a mismatch,
turns out to be a marriage made in heaven.
“The ports in the
aluminum Cobra Jet heads are big, so they don’t need much work,”
explained Wizner. “All I did on these was a bit of clean-up
in the ports and some blending in the short-turn radius. We’ve
spent a lot of time on the flow bench and developed a port shape
that really works well.”
Norm also said air flow
is another consideration. “With these heads, you’ve got to
concentrate on quality of air flow because if you fully port them,
it will really hurt horsepower. So we concentrate on improving
air flow without doing a lot of grinding. To go along with this,
we also use a relatively short camshaft to pick up the velocity
a bit and build cylinder pressure. What we wind up with is an
engine that makes good torque — 621 lbs./ft. at 3,800 rpm —
yet has enough port volume for decent top end horsepower,”
he said.
But the horsepower and
torque figures in the accompanying chart (See page ?) only
hint at the performance potential of this combination. With a
longer duration camshaft, a 1050 Dominator and single-plane intake
manifold, horsepower typically climbs to approximately 650 and
torque rises to about 675; some low speed drivability is lost,
but peak power is still within a reasonable rpm range.
One point to note is
that with any high performance 460-based engine, it is essential
that top quality head bolts are installed and carefully tightened
to the recommended torque. This is critical because 460 engines
have only two rows of head bolts. With so much space between bolts,
any sloppiness in the tightening sequence can easily lead to head
gasket failure. To guard against that, Norm uses premium quality
head gaskets (in this case Fel Pro 1028) and torques the bolts
in steps to 125 lbs./ft.
When the engine was all
bolted together and run on the dyno, the wisdom of the Wizner
approach was immediately obvious. In addition to the 620-lbs./ft.
peak reading, the engine produced more than 550 lbs./ft. of torque
over a 2,000-rpm band — from 3,400 to 5,400 rpm. Horsepower
wasn’t too bad either; 570 at the peak (5,400) and more than one
horsepower per cubic inch over a 1,400-rpm band, from 4,800 to
6,200 rpm.
Broad, flat power bands
like these are what make a street engine fun to drive. Throttle
response is immediate, the engine comes off-idle easily and the
driver doesn’t have to constantly work to keep rpm within a narrow
range at the top of the scale. That’s an important point to keep
in mind. Most customers for high performance engines think they
want horsepower, but they really want torque. Deliver an engine
with a broad, flat torque band, and you’re almost guaranteed to
have a happy customer.
High performance assembly
techniques
Parts costs aside, assembly
of a high performance engine is a more expensive proposition than
putting a plain vanilla engine together. The high operating speeds
and increased stress levels to which the engine will be subjected
leave less margin for error and demand that tighter tolerances
be maintained.
That requires a good
bit of hand fitting and massaging, which in turn takes time which
we all know costs money. Piston ring fit is one example. In a
standard rebuild, you simply purchase the rings according to bore
size and install them. End gap falls where it may. In contrast,
rings are typically individually fit to each cylinder in a high
performance rebuild.
Ring fitting is a tedious
operation that begins with the purchase of a .005″ oversize
set. Then a compression and second ring are installed squarely
in a cylinder and the ends filed until the desired end gap is
achieved. Although not as critical, oil ring rails should at least
be checked to verify sufficient end gap. That process must be
repeated for each cylinder.
According to Joe Moriarty
of Total Seal, Inc., “All ring manufacturers face the same
situation, it’s difficult to supply rings that suit everybody’s
need for end gap. Requirements vary according to piston type,
fuel being used and individual preferences. Bore diameter also
influences the situation. If cylinders are bored to a specific
diameter to achieve the required amount of piston-to-wall clearance,
it can be impossible to achieve the desired end gap specification
with standard ring sizes. File fitting rings is a lot of work,
but it’s the only way to be sure end gap is properly set.”
Several studies have
been done concerning the effect of end gap on ring leakage and
they all agree that establishment of proper end gap pays significant
dividends. Minimizing ring leakage increases horsepower and fuel
efficiency while reducing oil contamination and oil temperature.
So the end result is a better running engine that lasts longer.
Lubrication is another
consideration, and one that is often overlooked. It’s not at all
unusual for an engine to sit for six months to a year after it’s
been rebuilt. In many instances the car in which the engine will
ultimately be installed is also undergoing a rebuild process;
initial firing won’t take place until after the entire project
is complete.
That being the case,
the use of quality assembly lubes that will remain in place is
essential. If all you do is oil up the cam lobes with motor oil,
a cam lobe or lifter failure is almost guaranteed.
Clearances must also
be carefully considered in a high performance engine assembly.
Main and rod bearing clearances typically range between .002″
and .0025″, but the important point is that clearances are
set precisely — a tolerance of plus or minus .001″ won’t
cut it. The same is true of piston-to-wall clearances. Most high
performance forged pistons require clearances of .006″ to
.008″, depending on bore size and material. If the manufacturer’s
specs are ignored or taken lightly, you’ll wind up with pistons
that rattle, or seize in the bore. Neither of these conditions
is especially conducive to building customer satisfaction.
Most engine builders
who specialize in high performance work trial fit components during
machining and again prior to final assembly. So an engine is assembled
at least twice before it goes out the door.
