CP-Carrillo Tech Talk - Part 1

What are some of the latest trends used in modern piston design?
Reducing friction, propagating loads, and increasing ring seal. These key factors, accompanied by manufacturing improvements, the latest hardware options and design feature updates are constantly redirected in today’s markets. CP-Carrillo has been able to incorporate features into pistons that were not available in the past. When evaluating rod/stroke ratios and block/sleeve lengths, we can choose a perfect skirt profile from our unlimited amount of cam and barrel options. The cam is the shape from the floor of the oil ring to the bottom of the skirt. The cam is the shape around the circumference of the skirt. Depending on the type of forging and location of the material – this choice is crucial to have perfect stability, without creating unneeded friction. The operational sequence and roughing versus finishing of ring grooves are huge in maintaining minimal clearances. The machining approach for wrist pin bores plays a huge roll in the way loads are decreased and clearances are created to suit the needs for certain applications.
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Identifying your pistons…
At CP-Carrillo we get calls from customers all the time, while tearing down a motor for a refresh and trying to identify their pistons. Here is a quick guide to help you out. If you’re lucky enough that the pistons were manufactured within the last 8 years or so they will be identified by laser markings under the pin boss. A custom piston will have a 6 digit job number while a shelf part will have both a job number AND the part number laser engraved on it. Now if your piston happens to be older and does not have these markings this is where it gets a little trickier. In this case the best way to identify the piston is to send it back into us to be reverse engineered and identified. However if that is not an option such as overseas customers or time constraints there are some things you can do to help us narrow it down either over the phone or by email. First thing to look at is the forging number (example “CP546” in images), a finish bore size, compression height, pin diameter, dome height/ dish depth if it has one, ring groove widths, pocket depths and more may be required depending on the amount of jobs manufactured that fall within your specifications. So have as much information ready before calling and we are happy to walk through it with you and identify your parts for either spares or replacement sets.
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Can a specially designed racing piston improve performance?
A purpose built racing piston can heavily improve performance by evaluating the conditions it will see and then engineer and build specifically for it. With the various types of racing in the world today, it requires more attention to detail than ever before.
In drag racing alone, there are tremendous differences between the classes and each one requires a different approach. In bracket racing, it’s not necessary to have a low safety margin and get every last ounce of performance out of a piston since the vehicle is designed to run on an index and be “easier” on parts than the professional classes. In Top Alcohol the RPM is high and they benefit from a reduction of weight, but where the weight is removed is very critical.
In Pro Stock, it’s a constant hunt for every last bit of power and although a reduction of rotating and reciprocating mass in crucial – there is also a minimum weight requirement that has to be considered. Nitro classes cycle through parts faster than any other form of racing, but some teams have more of a budget than others. It’s a constant battle of performance and longevity, but we have a solution for each and every one of them.
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Did you know....An Accumulator Groove is a groove machined in the second ring land to increase the volume between the top and 2nd ring. During the combustion process some residual gasses from blow by get past the top ring, this groove creates more space for these gasses to accumulate and reduce pressure in between the top and second ring keeping the top ring on its sealing surface and reducing 2nd ring wear.
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Our sport compact shelf pistons offer valve reliefs that are deeper than stock, to accommodate high lift camshafts and 1mm larger diameter valves. When it comes to getting the most out of your custom pistons, having actual valve diameters and camshaft specs ensures we can more easily reach the compression ratios required. Even when maximum dome heights are not required, having the adequate pocket depths help us maintain a safer and stronger piston design and allow us to more adequately obtain the needed piston volume. Deep valve reliefs might require a dome, and having shallow reliefs could require a flat top or even a dish piston for the same compression ratio.
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Did you know that Bearing tangs are often one of the most misunderstood features of a connecting rod? Most people assume they are there to hold the bearing shells in place and keeping them from spinning or rotating. This could not be further from the truth, since what really holds the bearing shells in place and prevents them from rotating in the connecting rod housing is bearing crush. Bearing crush is created by the two halves of the bearing shells butting up against each other, as the connecting rod cap is tightened to the main body of the connecting rod. This in turn seats the back of the bearing shells firmly into the housing bore, keeping them under constant pressure. Bearing tangs are only used to laterally locate the bearing shells within the connecting rod housing bore. Some connecting rods have distinct upper and lower bearing shells, that have different bearing tangs, so that they can only be put into the connecting rod or cap half. Some connecting rod bearings in modern engines do not even use any bearing tangs for bearing location. #themoreyouknow  #bearingcrush #bearingtang #CPCarrillo #carrilloconnectingrods #carrillo #rods #connectingrods #enginetech #engineering
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How can we make the best racing piston for you? Although CP-Carrillo has a great database of a variety of engine specifications, it is nearly impossible to have every single spec of all engines out there. So we rely on customers to provide these details. Aside of providing bore size, stroke, cylinder head volume, deck clearance and gasket values, we often times need combustion chamber details and valve location to aid the design. Below is a brief description of the most common ways to deliver details for your new racing pistons…
CAD files (computer aided design) or Drawings software like Solidworks you can send us your 3D file preferably as IGES, STEP or PARASOLID , unfortunately digitized files from laser arms are not always very smooth and workable for us so we rather to digitize cylinder heads or molds “in-house”, our digitizing includes a pre-process of cleaning , smoothing voids, edges, sharp corners and elimination of negative angles (drafts) that can be an issue once the file is transferred to our CAD program. This method is becoming very common and is the quickest way for us to plan a piston since these files skip the inspection process unlike the other ways.
Sample Piston - is the most common way to let us know what you want. Make sure the piston is not damaged. This sample piston will go through a lay out process in our inspection department, so send us the best part out of the set.
Combustion Chamber Mold - very common but requires a little bit more of work, you need the correct materials (CP-Carrillo has available kits), chamber free of carbon deposits, oil, etc. scribed center lines on the flat back face of mold are needed so we now where cylinder centers are on X and Y. Our moldkits include all needed instructions.
Cylinder Head, - this is preferable if you want to skip the extra work of making a mold, we basically extract all needed information: valve location, sizes, and angles, spark plug info., volume etc. We can even digitize it and keep a record for you, perhaps not the most cost effective due to shipping fees but is the most reliable and accurate method of obtaining dimensions (don’t forget to send dowels & gaskets with it).
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Thermal Barrier….
Combustion temperature is translated through the piston, into the rings and then into the cooling system. The thermal barrier reduces the temperature in the piston crown and transfers that temperature out the exhaust. Each engine builder and tuner has their own approach on the benefits and CP Carrillo has options when needed and wanted. When a piston goes through continuous heat cycles for long durations of time a thermal barrier seems to be most advantageous.
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WPC?!?
WPC is an anti-friction micro shot-peening treatment to the surface of the (any) part. The peaks and valleys scoop up oil and increase the surface hardness of the material. CP-Carrillo started using WPC on our motorcycle pins, as they helped with protecting the pins at high RPM from galling, but now use WPC on a variety of pistons and rod bearings as well. WPC will treat the whole piston, not just the skirt area, providing the anti-friction treatment on the skirts but also of the ring grooves, and wrist pin area as well. The wrist pin bore area is one of the highest stressed areas of a piston: as not only is the wrist pin floating and rotating inside, but it also gets the pull and tug from inertia and compressive forces acted on through wristpin via the connecting rod and crankshaft.
Next time try your CP Pistons with WPC treatment and see what it can do for you. Due to the fact there is virtually no dimension change, we can add the treatment to already finished pistons, such as pistons on the shelf, and keep the same piston to cylinder wall clearance upon install.
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Does reduced piston weight increase horsepower and if so why? Reduced piston weight helps more times than not, as long as the weight is removed in areas that don’t jeopardize the pistons integrity. If a piston is used in a race engine that needs every last ounce of power advantage to win, but lasts all season, then it’s too heavy. There’s a fine line between a failure and “just right” and this comes with a lot of design experience and communication with the racer. The more monitoring that is done on the end users side, the better and helps us understand where we can make changes and what we can get away with. Post-run inspection by us and the customer is the key to continuously push the limits on their design.
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Is there such a thing as too little or too large a clearance? What are the pros/cons of each? Does too much clearance cause rings to “wear out” sooner – true or false?
Too little will cause piston scuffing, which generates material transfer between cylinder wall and piston, wristpin galling, excessive heat, and other unwanted conditions. Too much clearance will cause reduction of ring seal, excessive blow by, rings to wear out quicker than normal and depending on stroke and cylinder length – it could increase piston “roll over” at TDC and BDC which intensifies the piston movement, possibly causing skirt collapse and multiplying the excessive piston to wall clearance. If too much piston to wall is used, the piston can essentially start “beating itself up” in the bore, especially at BDC if/when it sticks out the bottom of the block or sleeve, which can also cause excessive skirt wear as well as cracking.
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When selecting a connecting rod for your application, you have a choice between shelf/ catalog rod or custom designed. Most shelf rods are designed to work in a wide range of application simply because do not always know type of racing, HP or RPM the end user is planning on.
To get a better balance of weight and strength ratio, we can custom design a rod based on compressive and inertial loads. By using the engine parameters such as: Bore x Stroke, HP, Power RPM (Compressive), over-rev RPM (Tension) and piston assembly weight, we can calculate stresses and design for the application (drag (high stress), road race/ endurance (medium stress), or street (low stress).
For example
The image shows rods for a turbo 4 cylinder and customer requested rods to make 1400hp and 10,500rpm
On the left is a shelf rod where the beam and bolts would have been at the limit and the pin end strap and big end area would have been over the allowable stress
Rod on right is a custom rod with a larger size bolt and increased the cross-section of the rod, to stay within allowable stresses and can handle the request HP and RPM.
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All pistons are designed using Solidworks here at CP Carrillo. Having CAD models at our fingertips makes it possible to dissect, measure, and weigh pistons long before production. The engineering team can help supply 3D pdf models for customers to see and approve before manufacturing.