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From page 2
Pistons - Cast, Hypereutectic,
or Forged?
Most shops will
reach for OEM cast replacement pistons when
assemblying a stock bottom
end. There is nothing wrong with cast, unless you plan
to add a power
TRW/Sterling Pistons have
huge valve reliefs for 2.02" valves, but the
head volume is a gapping 8cc! |
adder or high compression. We
like to step up to hypereutectic simply because it offers
more strength than cast, and they experience less thermal
expansion than cast, meaning you can run a tighter piston
to wall clearance for better oil control and less scuffing.
Ultimately this translates to more power due to higher
cylinder pressure.
Many people scoff at cast or hypereutectic and immediatley
ask for forged aluminum pistons, without considering the
draw backs. While forged is undoubtedly the strongest
of the three pistons, that does not mean you will make
more power. First of all forged pistons are very heavy
- the Federal Mogul forged replacment piston for 5.0L
engines weighs 80 grams more than its cast or hyper counterpart.
The greater the reciprocating weight, the more power the
engine needs to turn over the crank. Secondly, as detailed
above, forged pistons have larger than stock valve reliefs.
This increases the head volume and lower compression ratio.
So unless you absoutely need a forged slug (forced induction,
high compresion, etc) you will save money and increase
power with a lighter hypereutectic piston.
Balancing Act
We called four reputable engine rebuilders and
machine shops in the Northern California area to inquire
about their beliefs on engine balancing. Suprisingly,
none of them included balancing as part of a standard
engine rebuild. They all charged between $175-$250 extra
to balance a rotating assembly, and in fact most of the
shops did not even do balancing in-house, they sent it
out to another shop if you opted for it.
Most rebuilders assume that because they are using OEM
replacement parts, that balancing will be within factory
tolerances. (Afterall, they tell you, Ford doesn't balance
each individual engine off its assembly line.) Take our
word, this is not a safe assumption -always pay the extra
$150-$200 to get an engine professionally balanced. If
it comes down to spending a couple hundred dollars on
balancing, or something questionable like torque plate
honing the cylinders, you will do more for horsepower
and life of the engine by balancing it.
We observed as much as a 30 gram difference between the
Silvolite replacment pistons and the stock pistons that
came out of our engine. According to Bay Area Balancing
guru Tom Benoit, this is more than enough to cause a noticiable
vibration, and accelerate bearing wear. Furthermore, machining
the crank and rods, installing a new replacement damper
and flywheel, and even a new clutch, are all things that
can drastically effect engine balance.
This is state of the art balancing
- a Hines HC500 micro-computer balancer. Before the rotating
assembly is spun, the piston and rods are
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weighed
and equalize to the lightest one in the set. The weights
are recorded, and then bobweights matching the total rotating
weight of the piston, rod, rings, bearings, and even the
weight of the oil, are attached to the crank main journals.
Finally the harmonic balancer and flywheel (plus pressure
plate) are attached to the crank. The "replica"
rotating assembly is spun by the computer at several hundred
rpm, while it records the amount of out-of-balance and
the angle it is located at. The specialist then either
removes or adds weight by either drilling holes or welding
metal in the counter weights. Our balance shop (Bay Area
Balancing) shoots for less than 1 gram total out of balance
-in contrast, Ford specifications are abut 6 grams.
Completed Shortblock
Eventhough it took
a couple weeks, and two attempts at assemblying the motor,
in the end we got exactly what we wanted. The final short
block assembly had the correct H3101 hypereutectic pistons,
sitting at virtually zero-deck (measured at 0.003"
under). With 60cc aluminum heads we will have a pump-gas
friendly 9.55:1 compression ratio. 
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5.0L Short-Block
Specifications
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| Bore |
4.020" |
| Stroke |
3.000" |
| Compression
Ratio |
9.55:1 |
| Piston
to Deck height |
0.003"
below |
| Piston
to wall clearance |
0.015" |
| Piston
top-ring end gap |
0.025" |
| Piston
2nd-ring end gap |
0.018" |
| Main
Bearing clearance |
0.0015" |
| Rod
Bearing clearance |
0.002" |
| Rod
side clearance |
0.018" |
| Main
Bearing Journals |
0.010"
undersize |
| Rod
Bearing Journals |
0.010"
oversize |
| Crank
endplay |
0.003" |
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| 5.0L Short Block Part
No's |
| Piston
4.020" |
Silvolite
H3101 |
| Rings |
Hastings
2M 5504 |
| Bearings |
Federal
Mogul |
| Block/Crank/Rods |
1989
5.0L |
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| 5.0L
Short Block Costs: |
| Standard
rebuild |
$795.00 |
| Machine
for Zero Deck |
$100 |
| Balancing |
$200 |
| Tax |
$101 |
| (core
charge) |
($400) |
| Total
Short Block |
$1196 |
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