TPI 355 Machine Work - Something Old, Something New Part II

Ray T. Bohacz Apr 1, 2006 0 Comment(s)
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The time had finally arrived when GMHTP and RaceKrafters Automotive Machine Inc. were able to get back to work on our project TPI 355. As mentioned in our update on the series that ran in the January 2006 issue of the magazine, even though metal shavings were not flying, we were busy at work lining up the additional services of cryogenic processing and coatings to our research exercise.

In the update we touched on a problem that we discovered with the cam that we had chosen. In reality the camshaft supplied by COMP Cams, a roller hydraulic grind, was made to perfection and the bad readings we received from the Cam Pro Plus was from a batch of faulty stands that were production out-sourced by Audie Technology. Company owner Audie Thomas worked feverishly to determine his supplier had machined error into the cam holding stand and the problem was not with the manufacturer's cam grinding machine. As a matter of fact, the COMP Cams bump stick was made to such exacting standards that it looked as if it were custom produced for a NASCAR team, not an off-the-shelf part! COMP Cams has invested heavily not only in research and development to create the most efficient valve events, but also in advanced manufacturing processes and quality control. We are excited about the contribution this camshaft will make toward reaching our performance goal and thank COMP Cams for its effort.

The Probe Inc. forged piston and the Manley connecting rods were also masterpieces of quality and engineering. The piston is very light and features metric ring grooves for the lower-than-standard friction rings we wanted to use. Likewise, the Manley connecting rods just dripped of quality and not only measured exactly to standard, but were also light and strong. When held in the palm of your hand, both the pistons and connecting rods had the feeling of quality. There is an intangibility to quality that cannot be measured, but can be felt and seen. The Manley and Probe products definitely posses that attribute.

Bob and Craig Wise worked alongside the author during the machining steps that were used to prepare our engine. The most common mistake made by enthusiasts is that he or she does not understand the necessity for quality machine work and its impact on the end result. The machining is not only the result of the equipment employed, but more often the skill, finesse, and edict of the operator. I know with certainty that at the end of this series when all is said and done, a number of readers will try to duplicate our results with a local machine shop that may be very good, but is geared both physically and mentally toward general rebuilding. Or as we like to say in the industry, taxi cab-style work. The attention to detail that RaceKrafters gives to a project such as ours is the intangible difference that not only produces the extra horsepower, but makes the engine run better, smoother and longer. Engine machine work is akin to brain surgery. There is no place to save money or eliminate a step.

Since it is very hard to capture the true dynamics of proper machining procedure with still photos, extended captions will be used as we tell the story of how our little 355 is coming together. As was stated in Part I, not many street TPI engines are built to the standard that GMHTP and RaceKrafters Automotive Machine are establishing on these pages. We hope this series starts a Tuned Port revolution!

What Is Camshaft Inspection Equipment?
Simply put, Cam Pro Plus is a software and sensor package for the study of lifter and valve motion. With the cam mounted on a test fixture and spun either manually or by an optional electric motor, each lobe can be measured and graphically reproduced for analysis. A highly accurate rotary sensor produces 3,600 counts per revolution, allowing measurements to 1/10 of a degree.

Further, a linear sensor is included that has a resolution of one micron (0.00004 inch) to measure the movement of the valve or follower. Not limited to external use, Cam Pro Plus can be fitted with a fixture that allows you to read the cam while it's in the engine.

Interfaced through an IBM-compatible PC, it allows the operator to view all characteristics of the cam grind. Originally developed for quantitative analysis of cams in the pursuit of engine performance, many advanced engine shops are using this system to quality control the cams they purchase. It is disappointing that every cam is not manufactured with the same quality, and it is common to discover variations in lift, base circle runout, and duration, along with inconsistencies in the ramps.

The function of the cam is to smoothly open and close the valves as far and as fast as possible. Thus, the smoothness of the profile is paramount in deciding the life expectancy of the valvetrain and its components. The closing force for the valve is applied by the valvespring, but dynamic concerns for valve life must be ground into the cam to control the speed at which the valve moves.

Modern cam-profile designs are a computer-generated balance of competing concerns for engine performance, emissions production, specific fuel consumption, valvetrain life, and cost. The cam profile consists of a base circle, opening and closing ramps, and polynomial-generated curves for the main opening and closing events. The terms opening and closing are derived from the direction of valve travel. You may see the terms acceleration and deceleration used instead of opening and closing, but these terms are not technically accurate since the lifter and the valve experience acceleration and deceleration during both opening and closing events. The whole purpose of the cam is to move the valves (usually by lifters, pushrods, rocker arms, and valve springs) in a manner that will allow the engine to experience an efficient combustion event. The Cam Pro Plus enables the engine builder or hobbyist to measure and analyze the shape of the motions produced by the cam and the velocities, accelerations and jerks inherent in those motions.

Cam-Lobe And Design Terminology Ramp: The portion of the cam-lobe event from zero lift (base circle) to the defined opening or closing point.

Base-circle radius: The portion of the cam contour at zero lift (valves closed).

Flank: The section of the cam lobe between the ramp and the nose radius.

Nose radius: The radius that is tangent to the flank and the maximum lift point. Also, the instantaneous radius at the maximum lift point of the nose of the cam.

Inflection point: The point on the lift curve where acceleration (of the lifter) changes from positive to negative or vice versa.

Main event: The portion of the cam-lobe profile from the ramp to the nose. There are two main events--one each for the opening and closing halves of the profile.

Velocity: The rate at which position changes. In most instances, it is expressed in terms of distance versus time (mph, feet per second, and so on). When dealing with camshafts, time is replaced by degrees of camshaft rotation. This allows the study of camshaft profiles to be independent of the engine speed. The cam-follower position in Cam Pro Plus is expressed in units of inch/degree. A metric equivalent can also be displayed in mm/degree.

Acceleration: The rate at which velocity changes. It is expressed in cam logic: inch/degree or thousandths/degree.

Jerk: How fast the acceleration changes. It is expressed in units of inch/degree.

To further establish these terms, consider the analogy of a high-speed train traveling a short route. The train at rest in the station has zero velocity, acceleration, and jerk. The moment the train starts to move, all three measures increase. Leaving the platform, the engineer brings the speed up to 5 mph and holds it there until the train clears the station. During this period, velocity is steady (5 mph), acceleration is zero (no change in velocity), and jerk is zero (no change in acceleration). This is analogous to a common cam-ramp design known as a constant velocity ramp. Having cleared the station, the train increases speed until it reaches maximum cruising speed. During this period, velocity is rising, acceleration is positive (increasing velocity), and jerk depends on the engineers skill in smoothly accelerating the train. This portion of the trip corresponds to the opening main event before the inflection point. This being a short run, the train must slow down as soon as it reaches cruising speed. During this period, velocity is decreasing and acceleration is negative. This portion of the trip corresponds to the opening main event after the inflection point. To complete the return journey as soon as it reaches its destination, which corresponds to the nose of the cam.

Duration: The amount of time in crankshaft rotational degrees that it takes for the lifter to travel from a specified lift point on the opening side of the lobe until the same lift point on the closing side. Unless you know the specified lift point, a duration number does not tell you much. Unfortunately, this is often omitted, and there are different standards in use as to which lift point should be assumed when the lift point is not stated.

The following are the standards:

Old Chevrolet specification 0.020-inch lifter travel
Aftermarket 0.050-inch lifter travel
Advertised 0.004-inch lifter travel
SAE 0.006-inch valve travel

Since the aftermarket value of 0.050-inch lifter travel is the most common for the readership of GMHTP, that will be used to explain duration. If our cam is rated at 236 at 0.050-inch, that means it requires 236 degrees of crankshaft rotation for the cam to move the lifter from 0.050 inch-lift to a fully open valve and then back to 0.050 inch. The advertised duration, which is measured at 0.004-inch lift, will always be longer than at the 0.050-inch duration. Now let's consider two cams with identical 0.050-inch durations but different advertised durations. This would have to imply that the ramp on one cam is steeper (or quicker) than the other since the amount of rotation to travel from 0.050-inch lifter height open to this value on the closing side is the same, but the arc of travel needed to drop down to a 0.004-inch lifter displacement varies.

Once you analyze this scenario, you will conclude that the cam with the lower numerical advertised duration and a constant 0.050-inch value is ground with a quicker opening. This is established by the fact that it requires less rotation of the cam in crankshaft degrees to bring the lifter down the additional 0.046-inch to the advertised standard. If you engage a conversation with an OE engineer about cams, their standard of including the multiplicative effect of the rocker arm ratio can really confuse an individual conditioned to the advertised or 0.050-inch method.

Lobe centerline: This represents an imaginary line, referenced from the true center of the base circle out to the end of each lobe, expressed in crankshaft rotational degrees. Intake centerline values are found in the crankshaft's rotation ATDC, while exhaust centerlines are found at travel BTDC. Lobe centerlines are commonly thought to be the actual midpoint of the flank and are usually close to that, but different ramps on the opening and closing sides may change that reading. For this reason, the true center of the cam core is used as a reference. For those who use the intake-centerline method for degreeing a camshaft, you can now see (if the phase of the camshaft is off) how it will require a different amount of crankshaft rotation to find this point. When using the intake-centerline method, lower crankshaft rotational degrees represent the cam as being in early, or advanced. This statement is correct since in relation to the crankshaft's rotation ATDC, the valve event happened sooner.

Lobe-separation angle: LSA is measured in camshaft degrees and refers to the amount of rotation it takes to travel from the intake centerline to the exhaust centerline. As this number grows, the distance between the centerlines is spread out. Often LSA is considered an indicator of overlap, or the period of time that both valves are open on the same cylinder. Because it is a partial function of LSA, overlap can be calculated with fair accuracy using duration and LSA values. The issue concerning this is that you need accurate duration numbers at 0.006-inch to calculate overlap at the industry standard.

The following equation can be used for approximations of overlap. For single pattern cams (duration being equal on both the intake and exhaust lobes):

Overlap = Duration - 2x(LSA)

For split duration cams (different durations on the intake and exhaust lobes):

Overlap = Intake duration + Exhaust duration/2-2x(LSA)

Note that nonsymmetrical cam lobes will increase error when using these calculations.

Not being a single function of LSA, overlap is affected by changes in centerlines, ramp designs, and duration. The rumpty-rump sound that we all love in a performance engine is the hallmark of overlap. Used to help scavenge the cylinder, overlap is a function of the complete cam design. The use of Cam Pro Plus enables you to quickly and accurately define overlap at any given point.

Holding The Horsepower
Power is useless if it isn't reliable, and that is where 300 Below Cryogenic Tempering Services become useful. The bane of all metal is the residual stress that remains from the manufacturing and machining processes. These are broadly grouped as thermal and mechanical stress. The first situation occurs when metal of any type is drilled, cut, machined, or welded, and is the by-product of the uncontrolled cool-down rate in the affected zone. Bending, forming, die-casting, or the rigors of machining impart mechanical stress as the molecules are forced or torn into a new shape. Engine components usually suffer from the two of them. Though both are catastrophic, thermal stress is dominant and more destructive. It makes bores go out of round, shifts line-bore paths, causes premature valvespring failure, and initiates other nice stuff like that. By removing the residual stress, the component becomes stronger and more stable.

Cryogenic processing incorporates a controlled deep-freezing process with a very defined warm-up rate. This process accelerates the molecules until they align themselves properly, which returns the intended dimensional stability to the component. Stability through stress relief adds power by keeping the bores concentric longer, thus maintaining ring seal; it increases the life of an aluminum connecting rod on the order of 300 percent to 500 percent and triples the usefulness of something as mundane as a brake rotor. Unlike heat treating that tends to warp or distort the piece, cryogenics has no impact and requires no additional machining. Dimensional tolerances should always be checked after each process; as the molecules return to their natural position, measurements may change. The molecules return to the position they maintained prior to manufacturing and machining. After the cryogenic process they stay this way.

The original deep computer-controlled cryogenic process was developed by Peter Paulin of 300 Below Inc. In the early '60s, NASA and the military experimented with freezing to -120°F for stress relief and dimensional stability. As with many technologies, the microprocessor allowed the full benefit of a process to unfold, and enabled 300 Below Inc. to develop this integration. Its documented cryogenic process has the ability to neutralize both mechanical and thermal stress with no negative effects. The secret is the way it is able to control the temperature drop from a computer cycle. The temperature of the part is lowered to -100°F through normal refrigeration (in a processor that resembles a chest freezer). Nitrogen gas then plummets the Fahrenheit to -300°, and the part remains in the processor for 24 to 36 hours, depending on its mass and composition.

Then it's time for the warm-up cycle to begin. The temperature is raised very slowly to 375°F and then slowly returned to room temperature. During the deep freeze, the molecular structure draws closer, and stops just short of absolute zero (-459.69°F), where no molecular movement exists. During warm-up, the molecules accelerate, and the grain structure of the metal takes its natural form, thus limiting distortion and adding strength and dimensional stability.

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