A typical rebuilder will
inspect the core block, make sure it is free of cracks
and warpage. The stock 4.00" bores are cut .020"
over (if you want more, ask for it, as most rebuilders
will overbore the least amount neccesary in order to
ensure the block can be used again down the line.) The
bores are then honed, the block is hot tanked, and then
cleaned. New freeze plugs and oil plugs are installed,
all the main and head bolt holes are chased with a tap.
New cam bearings are installed. The crank is cut and
polished, and the rods may or may not get resized depending
on their condition. Finally the short block is assembled
to factory specification for clearances and torque.
All this is fine for your neighbors Crown Vic, but we
feel that there are a few more steps that you should
ask for to gain a performance edge and increase reliability.
For example, it is not standard rebuild practice to
surface the deck, or align hone the main bearing bores.
These machining options are only done if the block requires
it or if you, the customer, specify it and pay extra.
Our shop conviced us that align honing was not neccesary,
since the core did not have a spun bearing or crank
damage. We agreed.
We did opt to pay $100 extra to get the deck milled
about 0.015". We did this to not only ensure a
dead flat surface for the head gaskets to seal properly
with the aluminum heads we would be using, but also
to increase compression ratio by ensuring the piston
is not below deck.
Furthermore, before you lay
down any cash, ask what new parts will be used, and
get part numbers. For example, will the shop install
new rod bolts? (May rebuilders do not.) What pistons
will be used? We ran into some trouble here - our rebuilder
stocks one piston for all 289-302 rebuilds. The piston
(Silvolite 1177) is actually 0.020" shorter in
compression height (height of the piston above the top
ring) than a true 5.0L replacement piston. This sort
of cost savings by the shop, will cost you power in
the end.
Eventhough we had paid $100 extra to have our block
machined for zero-deck (piston top is dead level with
the top of the bore) the fact that the shop used the
wrong piston, meant our piston was actually 0.018"
below deck. This seemingly minor difference would make
the compression ratio 9.0:1 rather than the 9.5:1 we
desired. More on pistons below.
Make sure you ask the rebuilder for all the part numbers
for the parts they'll use in your engine. Then look
up those parts in the manufacturers catalog or website,
and make sure they will yeild the results you want.
If you want to make changes, such as different pistons
or bearings, let them know up front, and settle on an
additional cost or credit depending on who will supply
the upgraded component.
Piston Problem
The following chart shows the problem we encountered
with the KB Silvolite replacement piston number 1177.
Our engine rebuilder carried this piston as a OEM replacement
for all 289 and 302 engines. However the 0.025"
shorter compression height results in an effective compression
ratio loss of one-half point. The 9.0:1 ratio would
significantly hurt power with our aluminum heads. We
identified the correct piston to be part number H3101,
and had the shop re-assemble the engine. (We did have
to pay an extra $50 for rebalancing.) Note that some
rebuilders stock a Silvolite 1195 piston, which has
the correct 1.605" compression height, but has
a 4cc dish! In other words, it's a compression killer,
do not opt for this piston unless you need to lower
your compression.
We were fortunate that our rebuilder uses Silvolte pistons
for the fact that these pistons are true flat-tops with
stock size valve reliefs, thus the head volume (volume
of the piston top) is only 3cc. We found the TRW and
Sterling flat-top pistons to have head volumes of 6
to 7cc due to the larger than stock valve reliefs they
use.
Unless you are planning to use 2.020" or greater
intake valve in conjunction with a "large"
cam (224 or greater duration, .500" or more lift)
there is no need for the huge valve reliefs. As the
numbers show, all they do is hurt compression ratio.
With the Silvolite piston we can easily achieve 9.55:1
with a 60cc combustion chamber, without any need to
mill the heads. With the TRW piston you'd need to mill
4cc from the heads (roughly 0.030") to achieve
the same compression. Continue
Part
No. |
Cyl.
Engine
Bore |
Compression
Ratio with 0.003" deck and 60cc head.
|
NOTES: |
Rings |
Head
Shape |
H3101 |
V8
302
5.0 L
4.000(IN)
101.6(MM)
FORD
ENGINE |
9.55:1
|
Hypereutectic,
not destroked. Flat top with four valve reliefs.
Not intended for race application.
APPROXIMATE HEAD VOLUME=3cc
Comp. Ht. 1.605
Pin Dia..9122 Offset |
2-5/64
1-3/16 |
 |
|
1177 |
V8
302
5.0 L
4.000(IN)
101.6(MM)
FORD
ENGINE |
9.09:1
|
Flat
top with four valve reliefs. Comp. Ratios with cyl.
heads: 51cc=9.7; 54cc=8.8; 64cc=8.3; 69cc=7.8.
APPROXIMATE HEAD VOLUME=3cc
Comp. Ht. 1.585
Pin Dia..9122 Offset |
2-5/64
1-3/16 |
 |
|