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.

Block Preparation
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.

Rotating Assembly
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 polishing.

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 to install.

It's 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.

Spiral 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 good piston.

A 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".

Deck 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
Shaun's 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.

Proper 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 exhaust port was needed. The port was widened .100", and the walls were straightened. The valve guide boss was narrowed, then the port was sanded smooth.

The 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 vacuum leaks.

Intake Manifold
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.

Once 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 is present.

The 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.

Perhaps the most restrictive point of the upper intake is just after the
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.

The Results
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 just 10:1.

Engine: 347cid - Shaun Perry, HCI Motorsports
Vehicle: 1991 Mustang GT, T5
Dyno: Force Fed Performance, Sacramento, CA



In This Article:
The days of one horsepower per one cubic inch are long gone. In fact with today's engine technology, that is barely respectable at the wheels. We get the build secrets for a 421 rear-wheel horsepower, 347 cubic-inch stroker, from one of HCI Motorsports engine builders.

421 RWHP EFI 347 cid
Edelbrock Victor Jr., (Ported)
Edelbrock Victor 5.0 (EFI) w/ 75mm TB. (Ported)
Injectors 42lb/hr
Camshaft Custom Hyd Roller
246°in/240°ex Duration
.576"/.555" Lift
110° LSA 111.5° ICL
Lifters Sherman Racing Products
modified to go solid after .025" preload
Valvesprings Comp Cams PN: 917
Pushrods Comp ProMagnum 6.250"
Rockers Comp ProMagnum 1.6:1, 7/16" stud
Block Factory 5.0L
Crank Scat cast steel
3.40" stroke
Rods Probe Ultralight 5.315" I-beam
Pistons Probe Forged Flat top
Rings Perfect Circle Moly
Hardware ARP























HCI Motorsports
5112 Bailey Loop
McClellan CA 95652
(916) 643-2291

Sherman Racing Products Donaldsonville, LA 70346.

Force Fed Performance
7333 Roseville Road, St. 1
Sacramento, CA

2700 California Street
Torrance, CA 90503

Probe Industries

2555 West 237th Street
Torrance, CA 90505
Phone: 310-784-2977

Cometic Gasket
8090 Auburn Road
Concord, OH 44077


Tech Archives Project Cars Readers Cars Feature Cars