How many times have we heard a fellow gearhead state “I’ve now collected all of the parts I need to assemble my engine, the end is in sight!”…or so they thought. To say that the devil is in the details of an engine build would be an understatement. Even having the best parts money can buy cannot guarantee a successful engine build. But how is that possible if only the best parts were acquired? The popular phrase engine blueprinting can be the final detail needed to bring about a successful build, but don’t be misled by this commonly overused descriptor.

Ask anybody attending hot rod night at the local cruise spot and four out of five people will certify that the engine in their ’68 Chevelle is definitely blueprinted, and thus better than the same engine sitting in the car next to theirs. Yes, it is possible that blueprinting has contributed to their engine satisfying their needs better than the engine in the next car. Or, there is also the chance that they bought into sales hype, and there haven’t been any (or few) actual blueprinting operations performed to their engine.

Stem Diameter

Measuring valve stem diameter is made simple with a standard micrometer. Make sure to measure at several points while rotating stem in hand as well as up and down the stem body.

As an example of misusing these descriptors, refer to the highly overused word billet. If one heads to the parts store, everything that is billet is inherently better for some reason. But according to Webster’s Dictionary, billet is simply defined as “a comparatively narrow, generally square, bar of steel, especially one rolled or forged from an ingot.” So why don’t these ideas agree with each other? Many moons ago it was too expensive to build all parts by forging a raw ingot and machining a part from that piece. In those days, a billet was the forged ingot that only high performance parts were born from. Arguably, those parts commonly produced more favorable results. But time would not let go of the billet superiority and it has become a common descriptor of a component’s construction technique with an implied quality level.

If you’re looking to set the standard in performance… ‘bust out the wallet and call the best in the business.’ ~Derrick Hubbard, Comp Cams

Just as buying a billet part can lead an engine builder down a path of ignorance, so can buying onto (or paying more for) a blueprinted engine.

“Blueprinting is a term everybody uses, but its strict definition is not understood by many. Adhering to its strictest definition requires significant fixtures and measuring tools that can put a large hole in anybody’s wallet,” says Comp Cams‘ Performance Account Manager, Derrick Hubbard.

Starting again at a basic level, Webster’s defines blueprinting as “a detailed outline or plan of action.” Simple enough; one would hope when building an engine (or paying for one to be built) a plan is defined and followed. But many moons ago blueprinting had a novel and strictly applied definition.

Weighing Valve

A simple nutritional scale will make quick work of determining the mass of a valve or other small parts.

The Proof Is In The Example

In an attempt to corral the wild misuse of the word blueprint as it refers to an engine build, we’ll refer to its traditional intent as well as as provide examples of its importance and application in today’s “billet is better” culture. For starters, we’ll use the working definition of engine blueprinting as “striving for a mechanically-optimized engine assembly, whereby minimizing energy losses in order to maximize system output.” Focus will be only on the mechanical efficiency portion of engine blueprinting, leaving engine design (choosing compression ratio, engine and head sizing, etc.) for other discussions.

Use a simple flat edge to determine if head is dished or flat.

To help us illustrate just how detailed a blueprinting effort can become, we visited Southwest Racing Engines in southern California where owner Steve Schlingmann was on hand to give us examples of blueprinting techniques they use to characterize an intake valve. Although the part itself appears very simple, there are many physical attributes to a valve which can lead to its successful use and just as many that can lead to its failure. Whether out of the box or reclaimed during a rebuild, checking the dimensional tolerances is a great place to start.

“You can’t afford to overlook details when your customer is relying on your engines. They need to know you’ve taken care of every part in every way possible before delivering their engine,” says Schlingmann.

Measuring Seat Angle

Don’t over complicate things; sometimes a simple angle finder can help to characterize a valve seat angle. In the case of multiple angle valve jobs a more robust angle finder may be necessary

Obviously, starting with a brief look at the part number doesn’t hurt. But if the part number is correct, why check dimensions and compare against spec/tolerance? First lesson in engine blueprinting; assume NOTHING! Webster’s defines tolerance as “an allowable amount of variation of a specified quantity, especially in the dimensions of a machine or part.” Most variation is born in the manufacturing processes due to wearing of cutting tools, abrasive stones, wear and calibration of machines and even measuring equipment.

Additionally, environmental contributors such as material or ambient temperatures can change part dimensions at time of initial construction and time of measurement. Lastly, remember that valves are typically made by the hundreds and thousands, so engineers and machinists are challenged with determining the quickest (and most cost effective) methods of achieving stated tolerances, which may not be all of the tolerances you focus on when building your own engine. So expect to have instances where additional part modifications or reorders must be made after receiving.

Using a straight edge, it is easy to visually inspect to confirm flat or dished head.

After confirming environmental conditions weren’t outside of 65-85°F, Schlingmann went about defining valve characteristics for a standard Ford 351W. The list of characteristics is as follows:

    • Material: may be difficult to define beyond part description from manufacturer without an alloy analyzer, but one should confirm that material description matches intent and clearances are intended for that specific alloy and expansion coefficient at operating temperatures.
    • Head Diameter: measured across head at least four locations while spinning valve within micrometer.
    • Stem Diameter: measured at several angular locations while spinning valve within micrometer AND measured at several longitudinal locations up and down the stem.
    • Overall Length: with valve sitting on a flat table, measure overall length of piece and compare to spec/tolerance.
    • Face Angle/Margin width/Seat width: Face angle will show the angle of face machined surface of the valve where it seats in the head. Margin width is the width of the non-angled margin space on the side of the valve head. Seat width is the width of the face angle section that was measured previously.
    • Valve Lock Location: length from tip of valve to locking groove on stem.
    • Valve Lock Style: refers to the type of stem locking device/groove. There can be several styles that are similar but will not work together.
    • Hollow/Solid Stem: may be difficult to determine without manufacturer documentation. Compare against engine design intent.
    • Sodium Filled: again, may be difficult to determine without manufacturer documentation. Compare against engine design intent.
    • Valve Dish or Flat Face: easy to determine using flat edge across face of valve. If dished, measuring dish volume may be encouraged for comparison against stated tolerance or against the other valves in the engine.
    • Stem Narrowing: measured at several angular locations while spinning valve within micrometer. If narrowing confirmed, compare against engine design intent.
    • Polishing: both visual inspection as well as review of manufacturer’s specs. This may also include polishing or burnishing of valve seats to confirm continuity between valves.
    • Hardened Stem Tip: determining if the tip of the stem is hardened or if the entire part is finished to throoe same surface hardness.
    • Valve Mass: total part mass. Part mass compared with spec and tolerance. Part mass compared to other valves on the engine
    • General Part Condition: checking for any visual blemishes, machining heat marks that don’t belong, pitting and so on. This may also include mag testing to confirm no cracks exist on the part. Confirm the part is straight! This is a common issue for parts not stored correctly.
Cracked Valve Head

Checking part condition is critical. Visual, mag, and other means of inspection should be able to locate a valve crack as shown here.

Where Do We Go With This?

As we’ve seen above, a simple valve can be measured against at least 15 metrics; some useful, some less useful. Now, multiply these efforts across all of the valves in your engine. Now add heads, springs, valve stem locks, rockers, pushrods and so on and you’ll see how this highly detailed amount of dimensional measuring can quickly add so much shop time to a build that the cost or timeline is simply beyond the means of most weekend warriors who just want to attend cruise night.

“A fully documented blueprinting effort can devote pages of notes and measurements to a single piston, valve, or lifter bore depending on what you’ve asked your builder for and what type of racing you’re expecting to do,” says Hubbard.

“Every engine builder, whether a home builder or professional, should be blueprinting an engine.” Jim Blakesley, H&H Flatheads

If you’re looking to set the standard in performance for your racing discipline/class, Hubbard warns “bust out the wallet and call the best in the business.” True in many racing situations, you should expect to see an engaged builder when you’re forking over larger sums, such as being present for initial engine startup, chassis dyno tuning, or even track-side support during initial phases of an engine program.

So is blueprinting worth extra money? One could argue yes and no. If rebuilding a mild small-block Chevy, documenting part numbers and comparing basic dimensions to those listed in a standard rebuild manual or the tolerances listed by the bearing and ring supplier is critical and 100% worth paying for. Whereas paying an additional $5k in shop time to highly document the same mild engine would be a waste of resources and time.

Valve margin width

Measuring valve margin width can be accomplished using a simple dial caliper.

“Every engine builder, whether a home builder or professional, should be blueprinting an engine. There are certainly different levels of detail some should go to when building, but nobody should be installing parts that haven’t been measured and compared to OEM specifications,” says Jim Blakesley of H&H Flatheads.

On the other end of the performance spectrum; if building a high performance sprint car engine (or multiple engines), there is a high value associated with being able to build multiple identical engines which allow race to race continuity, the ability to track performance gains/losses associated with new part installation, or be able to discover a potential problem before it destroys another engine. What price tag can be attributed to such an undertaking? That depends on your performance/racing goals, overall budget, your relationship with your engine builder/parts suppliers and additional factors special to each engine program.

Valve Lock Groove

Measuring valve lock groove and location along the valve stem can help avoid using the wrong locks or and/or spring bind.

The next time you’re speaking with your engine builder, ask them what they mean by blueprinting. Think to yourself; how does that vary from the phrases “a detailed outline or plan of action” or “a documented set of tolerances and setup practices?” If it doesn’t, and you’re paying extra for blueprinting, you may want to reconsider your builder. But if you receive an answer that is conducive with the build level you’re expecting, that is a good sign of things to come. Note–it never hurts to ask: “what documentation will I receive with the engine?” Some builders consider blueprinting documents proprietary, but Blakesley confirmed that “you should expect at least a build sheet listing all parts used in the build and a balance card showing final balance details of rotating assembly.”

As comforting as it can be to see that pile of new part boxes stacked high on the work bench, knowing your dyno session or first drive is only days away, Agatha Christie summed it up perfectly when she wrote “sometimes what you think is an end is only a beginning.”