Details by Shaun Perry, HCI Motorsports.
When it comes to building a high horsepower engine, today's
enthusiast certainly has it easier than his predecessor. The
advancements, and assortment of aftermarket cylinder heads,
intakes and camshafts has made the task of making big power
no longer something only the pro's could achieve. Yet don't
be fooled into thinking that the average enthusiast armed
with a Summit catalog is just as capable an engine builder
as the seasoned professional. The experienced race engine
builder is still enjoys a comfortable margin of power over
us average wrenches. In fact, it's quite likely that all the
great technology has only resulted in too many choices for
you and I, resulting in mismatched combinations that perform
well below their potential. The pro's, on the other hand,
have sorted through all the permutations and developed detailed
techniques on how to make it all come together in a big way.
So what's the likelihood someone one of these pro's will let
you in on their secrets? Pretty unlikely, but every now and
then one of the nice guys takes pity on us and throws a few
tips our way. Shaun Perry builds engines at HCI Motorsports,
a Sacramento, CA area performance engine builder. Recently
Shaun put together a 347 stroker using off-the-shelf parts
you'll all recognize, but power numbers which will shock you.
When it was all said and done the engine was put into his
wife's 1991 Mustang, where it rolled out 421 horsepower at
the wheels. Do the math, that is about 500 at the crank. So
how the heck is this done, for surely if we bolted together
a 10:1 347 with Victor Jr. heads and intake, it would be an
accomplishment to come home with 380 horse at the wheels.
The secret is in the details, and Shaun is in the mood to
share. Let's check out his notebook.
As this will be a naturally aspirated motor there is no need
to go with anything beyond the factory 5.0L roller block.
Besides cutting the cylinder bores 0.030" over, and parallel
decking the head surfaces, there is no specialized machining
procedures. Shaun likes to improve oil return by chamfering
the oil holes at the rear of the lifter galley until they
are even if not lower then the lifter bosses. The floor of
the lifter galley is sanded smooth, and the oil drain holes
are also chamfered.
This 347 uses a Scat 3.40" cast steel crankshaft, Probe
Ultralight 5.315" forged 4340 steel rods, forged Probe
flat top pistons and cast steel wrist pins with spiral locks.
Shaun prefers Scat's cast steel crankshaft for its radiused
counterweights. He likes to further radius the counterweights
so that they are "blunt like that of the nose of a submarine."
Polish the radiused counterweights and journal ends to a smooth
surface. The crank also receives oil hole chamfering, grinding
ten- thousandths off the main and rod journals and machine
The Probe 5.315" Ultralight rod was chosen to keep the
pin out of the oil control rings. The Ultralight rod has a
weight of 530 grams, resulting in a significant overall reduction
in rotating mass. The shorter rod also has some benefits by
increasing rod ratio compared to a typical 5.400" length
rod. Shaun polishes the rod and removed all sharp edges prior
a surprise that in this particular application an expensive
"zero gap" style piston ring is not selected. Shaun
goes with a standard Perfect Circle Moly file-fit set. Ring
gaps on this motor were filed to .024 top, .024 second. The
reason for a fairly wide second ring is two fold as Shaun
explains. "The second ring is a cast ring and thus expands
more with heat then the top. Additionally, gapping the second
ring larger greatly decreases the chances of ring flutter
that can happen if the second ring gaps closes due to high
cylinder temps from lean air-fuel ratios or detonation. Ring
flutter causes blowby and a loss of cylinder pressure, with
the net effect being a loss of power.
locks are a cheap upgrade that we recommend as unlike wire
locks, spiral locks are installed flat against the pin &
boss. The wire locks round surface distorts the aluminum piston
under high engine loads with makes removal of the pins during
a freshen up very difficult. This typically results in galling
of the piston/pin which makes a paperweight out of an otherwise
crank scraper is a good idea to keep oil off the crankshaft.
This motor is using a Milodon crankscraper along whit ARP
main bolts& studs. Adjust the crank scraper to scrape
the rods as the crankshaft rotates. The Milodon scraper needed
significant massaging to get it to scrape properly. Rod to
scraper clearance is adjusted to 0.050".
height is checked with a dial indicator & degree wheel.
This motor came in at .018" in the hole, so custom Cometic
MLS headgaskets were chosen to bring quench into spec. A motor
like this should have quench between .035-.045". Quench
on this motor came in at .045. Ideally it would have been
closer to .035", but Cometic's thinest gasket for this
motor is .027" thick.
Those who know Shaun are well aware of his penchant for camshaft
selection. It's not often that Shaun goes with something out
of a catalog. For this engine he specified a reverse-split
cam. This is a common practice amongst top Ford engine builders
using aftermarket heads and EFI applications. The greater
than 70% exhaust to intake port flow on modern heads means
combustion gasses are easily expelled. Rather than biasing
more exhaust duration builders would rather shove in more
charge. For this 347 Shaun specified a 246° intake and
240° exhaust duration @.050, with lift at .576"/.555"
respectively. Degree the camshaft using the .050 method. That
is, find TDC, setup the dial indicator on the lifter &
turn the motor over till the dial indicator reads .050 lobe
lift. Note the degree on the wheel, repeat on closing side
of the lobe, then repeat on the exhaust lobe. Compare the
valve events to the cam card and adjust as necessary. In this
case the cam measured at 244°/239° duration and accurate
on the lift, close enough to run with.
Cylinder head preparation
had previous success with the Victor Jr head, so it was no
surprise they were chosen again for this motor. Although 210cc's
seems large to some for a small block Ford, this motor needs
the volume for the intended power levels. They are not taken
as is, and a fair amount of work is done by Shaun to ensure
the combination works as planned.
Starting in the chambers, the valves are unshrouded to allow
a clean path for airflow around the sparkplug which is key
during the overlap phase of the powerstroke. All sharp edges
are knocked down and the combustion chamber surface is polished
smooth but not mirror.
exhaust portwork is crucial in attaining a broad powerband.
Too large of a port and low end will suffer, while too small
and top end power will be limited. However, with
the smaller exhaust lobe on the camshaft a higher flowing
port was needed. The port was widened .100", and the
straightened. The valve guide boss was narrowed, then the
port was sanded smooth.
intake ports on these heads were heavily massaged. The area
around the valve guide was widened and smoothed. The short
turn radius was lowered -a tactic which can virtually ruin
the heads flow characteristics if done incorrectly. On this
set of Victor Jr's the short turn radius significantly choked
the port. Lowering it allowed for a larger window for the
airflow to enter the valve. Shaun notes however that not all
Victor Jr's are like this. On older versions the intake port
floor is lower then new designs and thus does not need to
be lowered any further. The port was then widened to promote
a straight shot at the valve. This resulted in cutting through
to the pushrod hole. Although easily fixed, it was not desired.
The fix was to drill the pushrod hole to 5/8" and press
in 5/8" O.D. aluminum tubing. Red Locktite was
used to lock the insert in the head and seal from any potential
Shaun selected the Victor 5.0L EFI manifold for this motor
for its short runner length which works well in the 6000+
power range. However while it might be reasonable to assume
the same brand intake and cylinder heads will yield a perfect
alignment, Shaun would never make this assumption. "Port
matching of the intake to the heads is critical in extracting
every last bit of HP out of the motor." Once the heads
are installed on the shortblock, mock up the intake using
old intake gaskets (already compressed). Using a wire hook
an flashlight to aid in feeling any ridge in the transition,
and how far is needed to port the intake to match the heads.
the manifold is port-matched to the heads Shaun goes back
and ports the entire lower intake runner, ensuring a slight
tapering of the cross sectional area (larger at the mating
of the upper manifold to a smaller port at the head). This
will give a velocity stack effect and increase torque production.
Too much taper however is not a good thing. Shaun aims for
a 2-4% taper from the widest to narrowest point. Calculate
the area simply by multiplying
length x width at both ends of the intake port & divide
the top area by the bottom, then subtract 1. This will give
a close enough average of the percent of taper. A negative
taper (going from small to large) of more than 7% in any area
will result in the airflow leaving the port walls and creating
turbulence. An intake whistle can be heard if turbulent airflow
same porting technique should be applied to the upper manifold.
Measuring often helps prevent porting too much. Tapper on
the upper intake should also be between 2-4% from plenum to
base. Maintain as consistent a cross section as possible.
The plenum cover can also be addressed. As the air enters
the TB it slams into the plenum cover then must make a 180
degree turn and enter the runners. Smoothing the plenum cover
will help eliminate a boundary layer, increasing airflow velocity
and very slightly increasing the plenum area which gives the
airflow more room to make the 180 degree turn.
the most restrictive point of the upper intake is just after
throttle body. The airflow is squeezed into a rectangular
shape before opening up in the plenum. Measurements on this
particular intake when un-ported revealed an area at the smallest
point equivalent to a 65MM throttle body diameter. Since a
75MM TB was to be used, the area was enlarged significantly.
Although it still seems small in this picture, it was opened
up 30% from as-cast.
Shaun Perry's build techniques were
put to the test at Force Fed Performance's chassis dyno in
Sacramento, CA. With the motor in his wife's 1991 Mustang
GT, the dyno rollers measured
out 421 horsepower at 6000 rpm and 388 ft.lbs. of torque.
Think it is spinning to unreasonable levels? Peak power occurs
at a tame 6000 rpm. Must have unfriendly compression? It's
|Engine: 347cid - Shaun Perry,
Vehicle: 1991 Mustang GT, T5
Dyno: Force Fed Performance, Sacramento, CA