Modern Engine Blueprinting Techniques. Mike Mavrigian
longevity. OEM production may allow a certain tolerance range for areas such as piston-to-wall clearance, bearing clearance, deck height, etc. But when blueprinting, you decrease the tolerance range significantly. For example, if an OEM specification allows a clearance of .020 inch, +/– .005 inch, you try to achieve exactly the optimal .020-inch clearance when blueprinting. You’re refining all clearances while greatly minimizing allowable ranges.
Let’s look at a specific example. Say that an engine manufacturer lists piston ring end gap at .003 to .005 inch for a specific engine application. Rather than varying end gap while staying within that tolerance range, you can tailor the gap to the application at hand. An ideal end gap for a road-racing endurance application might be .0045 to .005 inch. For a drag racing application this might be better suited to .0035 to .0040 inch. This is just one example.
By initially considering the published clearances, you can then fine-tune the gaps in order to obtain the best dimension for an application. Much of this depends on the engine builder’s personal experience with various ring end gaps for specific racing applications. In blueprinting you narrow down various clearances in order to achieve the ideal clearance, instead of simply falling into the wider range acceptable for the average street engine.
Areas to Consider during Blueprinting
• Flaw inspection of all components (checking for cracks/flaws)
• Main bore position and alignment, which includes line boring the main bore
• Position (relative to the main bore) and alignment of the cam tunnel
• Block deck accurizing, including height (distance from the main bore centerline and correction of deck angle)
• Cylinder bore indexing (establishing accurate centerline)
• Lifter bore accurizing (establishing lifter bore centerline and angle)
• Bellhousing dowel location accurizing
• Correction of the crankshaft’s main journal alignment and spacing, endplay, rod journal alignment and spacing, stroke throw length, and clock-position of each throw (angularity of the rod throws)
• Indexing cylinder heads (correcting intake port centerline; scribing cylinder bores on the deck surface of the heads for consistent chamber layout
• Static weight matching of all pistons, rods, rod pins, and rod bearings
• Crankshaft dynamic balancing using bobweights to simulate static reciprocating weight packages
• Inspecting and correcting (if needed) crankshaft main and rod journal diameters
• Connecting rod dimensions and checks (big-end bore diameter, pin-end bore diameter, center-to-center length, checking for bend and twist)
• Checking piston pin bore centerline-to-dome distance (and verifying that this is equal on all pistons)
• Measuring the camshaft for journal diameter, straightness, lobe spacing, lobe lift, and ramp angles
• Measuring all pushrods for length and straightness
• Inspecting all lifters for length and diameter
• Measuring cylinder head combustion chambers for volume and (if needed) machining to equalize all chamber volumes
• Measuring all intake valves for height, stem diameter, and head diameter
• Measuring and equalizing all valve seating depths
• Valveguide sizing for desired valvestem oil clearance
• Measuring all valvesprings for open and closed seat pressure and height, and checking for coil bind at the fully closed position
• Checking rocker arms for proper geometry and contact at the valve tips through the rocker arm’s arc
• Inspecting and verifying crankshaft counterweight to block clearance, connecting rod big end to block clearance, connecting rod big end to camshaft clearance, etc.
• Intake port matching (of intake manifold-to-cylinder head)
Part and parcel of blueprinting involves inspecting everything. Never assume that any new or used component is dimensionally correct. Don’t just take it out of the box and bolt it on. Blueprinting involves close examination of absolutely everything. Where variances exist, depending on the specific component, the part must be machined for correction or replaced with another that matches the desired dimensions. The golden rule is to assume nothing and measure everything.
Parts Selection
A true blueprinting job is very time consuming and labor intensive. So it doesn’t make sense to start the job with inferior or questionable parts. Buy the highest-quality components that you can afford, and don’t try to skimp.
Regardless of your component selection, if you’re going to invest in a blueprinting approach, it’s highly advisable to perform a flaw detection on components such as the block, cylinder heads, crankshaft, and connecting rods and check for cracks and porosity. For the block, this also means checking for cylinder wall thickness at each bore location. If you start the job with questionable or unknown parts, you’re just defeating the purpose.
The quality issue aside, also consider the type of material and construction (for instance, when choosing between a casting, forging, or a machined-from-billet piece). As an example, depending on the manufacturer, a cast-iron crankshaft might be dependable up to, say, 400 hp. If you plan to produce more power, moving up to a forged crank is recommended. Select the parts based on the application. By choosing a component that is stronger and more resistant to failure, you increase your chances of avoiding a failure when producing increased power and/or increasing engine speed.
Can’t Blueprint?
Certain race sanctioning body rules may not allow blueprinting (old SCCA showroom stock road racing as an example). However, there are ways around such nonsense. Even a stock engine can be improved, and mildly blueprinted by mixing and matching engine components in order to improve the engine’s dynamic operation. Instead of machining various parts in order to optimize, an alternative may be to spend the time to locate stock parts that provide the improvement.
For example, an engine’s original set of connecting rods may be specified as having a 6.000-inch center-to-center length. But, as a result of mass production and a factory tolerance range, your engine may actually have rods that vary in length from 5.996 to 6.002 inches. Instead of “illegally” machining to correct, you can take the time to create a matching set of rods that actually measure 6.000 inches. This may be aggravating and tedious, but it’s a way around a silly ruling. The same holds true for OEM camshafts; if yours doesn’t measure at the published specs, you can hunt through several others of the same part number until you find one that’s on the money.
Remember: Blueprinting involves much more than simply balancing the crankshaft. This is serious business that goes far beyond the simple re-assembly of an engine with new parts. It’s an investment in time, skill, labor, and money.
To achieve the highest level of precision engine building, you must perform diligent detective work and pay close attention to detail. When using flaw detection equipment, you are searching for damage that’s more and less apparent. And many kinds of damage are not easily recognizable to the naked eye. Flaw detection equipment and technology help you discover potential problem areas in your engine components. A variety of testing methods are available for inspecting individual components for cracks or porosity, as well as prejudging cylinder wall thickness prior to block cylinder boring.