Modified Mustangs & Fords
347ci Small Block Build - Hammer Time! - Part 1
Part 1 In A Four-Part Series. We Build A Powerful Summit Racing 347ci Small-Block With MCE Engines
Mr. Clean, Mr. Clean, Mr. Clean
Think your block and heads are clean? Guess again. When McAfee gets a block back from Motor Magic, which has already cleaned the block, he goes to work with the detail of Felix Unger of The Odd Couple. He uses a rifle-cleaning kit to clean deep into oil galleys with soap and water. He also uses a high-pressure mix of petroleum-based solvent, soap, and water to get passages hospital clean. His logic is grassroots-even the tiniest iron or steel particle can score a bearing or damage a piston, rendering a new engine useless in short order. McAfee's job as a builder is to ensure engine reliability, covering details most of us miss. Thorough cleaning prevents contaminates from doing engine damage.
Cleaning begins by completely disassembling the block-knocking out all cam bearings, removing freeze and oil galley plugs, and chemically dipping the block. Some machine shops employ a hot-cook process to bake off all the crud, followed by a shot-blast that makes the iron look new again. After that, a shake-out process removes all of the steel shot. A complete water/soap washing should always follow to remove hidden debris.
Because we wanted to establish a power baseline, we decided to begin with CNC-ported 351W heads from PowerHeads. Using 351W heads has been a low-buck 289/302 upgrade for ages. When you're huffing 347 ci through them, 351W heads make even more sense. PowerHeads does a nice CNC-ported head for less than $1,000-which also maintains a stock appearance, if that's important to you. Ports and bowls are CNC-machined, then hand-detailed to a nice finish. New stainless valve guides, valves, and hardened seats are also included. Valve sizing is also increased to 1.94/1.60-inch intake/exhaust. Stock 351W valve sizing is 1.84/1.54-inch intake/exhaust.
|Powerheads 351W Flow Figures|
Over-The-Top Dynamic Balancing
Automotive Balancing in Southgate, California, does all of McAfee's balance work. Think of MCE Engines and Automotive Balancing as right and left-brained. McAfee and Rocky Bowen work together in order to achieve above-average engine-balancing technique. McAfee likes reciprocating parts within 1 gram or less of each other, which takes time and commitment. Bowen is committed. McAfee is quick to add there's no such thing as "perfect" balance. The best you can do is get it as accurate as possible. For him, that means a reciprocating weight within less than 1 gram, which is darn close considering current balancing technology. Call this splitting hairs, but the result is smooth operation.
A Balance Of Power
Vibration comes another way when static and working compression aren't cohesive. Static compression is what happens when you crank the engine and check compression. Working compression is what happens when you throw in fuel and air, and light it. Heat energy changes compression depending on cylinder and combustion chamber dynamics. To get all eight bores working in unison, each has to have uniform volume above the piston, which is known as compression height and deck height. What happens to the piston and rings at light-off also affects working compression. How well will the rings seat? This is an unknown until you whirl it around and light the mixture.
How much volume is there above the piston at top dead center? The distance the piston travels from bottom dead center to TDC is live volume. What's left above the piston at TDC is called dead volume. The dead-volume area is called the combustion chamber. Chamber size affects compression. Valve-relief size, no matter how small, affects compression. Even the area above the top compression rings affects compression. Are the valve heads dished or flat? This also affects compression.
Dynamic (working) compression is when an air/fuel mixture (which decreases volume because fuel drop-lets are considered mass) is moved through the chamber. When you ignite the air/fuel mixture, the chamber temperature rises to approximately 2,200 degrees F, depending on humidity, ambient temperature, and atmospheric pressure.
McAfee says all eight cylinders must have identical compression for the power-and load-exerted on the crank to have any chance of being uniform. When you have a loafing cylinder due to compression variations, the engine runs rough and costs power. McAfee begins his compression insurance policy by cc'ing every chamber and piston to get them all spot on.
During assembly, it's important to take things slow and go step by step. Set the crank; then carefully set each of the caps. Each one should be snugged first; then check the endplay, which should be 0.0004-0.0008 inch, with a maximum of 0.0012 inch. If you're going to rev it high, aim for 0.0008 inch. Torque main caps beginning with No. 3, followed by 1, 5, 2, and 4. Torque them in third values, and check crankshaft freedom with each one. You should be able to move the crank by hand at the snout. If it binds and won't turn, bearing clearances are too tight. Once all caps are torqued, check the endplay again.
It's important to note all pistons must be bore-matched, meaning each bore is honed to match the piston. Ring-end gaps must be checked on all eight bores. This is what real blueprinting is-a precision fit of all components.