Frequently Asked Questions - Pistons

  1. My ring pack has 3 rings, but my piston only has 2 ring grooves. Did I get the wrong ring pack? Or was the piston made incorrectly?
  2. Why do I have an extra set of Spiral locks?
  3. Where can I get more stickers?
  4. What is the difference between lateral and vertical gas ports?
  5. What is the difference between CP-CARRILLO and BULLET Series Pistons?
  6. What is Cam and Barrel shape?
  7. What is an X-style forging/piston?
  8. What are non-rotating wire locks (KRAMM LOX)?
  9. What are billet pistons?
  10. Ring orientation
  11. Ring end gaps?
  12. Ring Dimension terminology
  13. Piston to wall reference chart for different bore types.
  14. I want to supply CP-Carrillo with a model to make my new pistons, what’s the best way to do this?
  15. I broke a ring during the install, can I just use OEM rings with this piston?
  16. How much ring end gap should I run? (Answered on pages 2 & 3)
  17. How much lift will your piston take?
  18. How long does it take to make Custom Pistons?
  19. How do I request a catalog?
  20. How do I know my piston to wall clearance, and where do I get the measurement? (Answered in question: “Piston to wall reference chart for different bore types.”)
  21. How do I identify Tops, 2nds and oil rings?
  22. How do I identify my CP-CARRILLO or BULLET Pistons?
  23. How do I cut ring grooves?
  24. How do I become a dealer?
  25. Do you have a minimum quantity of pistons I need to buy?
  26. Can you coat my pistons?
  27. Can I purchase rings for your pistons?
  28. Can I order direct?
  29. Are all your pistons forged?

Q: My ring pack has 3 rings, but my piston only has 2 ring grooves. Did I get the wrong ring pack? Or was the piston made incorrectly?

Neither. What you have is a 2-ring piston designed to utilize the top and oil rings ONLY. Simply throw away your second ring and install as normal. NOTE: If you see a V-shaped groove below the top ring groove, that’s actually an Accumulator Groove and you can’t put a ring in it.

Q: Why do I have an extra set of Spiral locks?

CP-CARRILLO and BULLET include double Spiral locks with most off-the-shelf pistons. Most shelf pistons that are designed to use Spiral locks utilize 2 per side (4 per piston). For instance, an 8 cylinder motor would come with 32 Spiral Locks whereas a 4 cylinder would only come with 16.  Wire locks only require one per side (2 per piston).

Q: Where can I get more stickers?

Contact your WD or send your name and address to sales@cp-carrillo.com and we will put a decal package in the mail for you.

Q: What is the difference between lateral and vertical gas ports?

Lateral gas ports are channels drilled at the bottom of the top ring land that assist in ring seal. These channels allow combustion gasses to enter behind the top ring and improve ring seal by forcing the ring against the cylinder wall during combustion. Gas ports are most commonly used with back cut rings, which have less friction and better performance characteristics. See Figure 6

Q: What is the difference between CP-CARRILLO and BULLET Series Pistons?

Both CP-CARRILLO and BULLET are high quality forged pistons, made from 2618-T61 Alloy. CP-Carrillo pistons are designed for high performance racing engines and are available for many "race specific" applications. Additionally, CP-Carrillo can be custom made in as little as 3 days to your specification. BULLET Series Pistons are large production runs on centralized manufacturing cells made from dedicated “Bullet” forgings. An application specific forging, as well as manufacturing in larger quantities reduces machining time. We pass the savings on to you, offering a more economically priced part, made on the same machines as a traditional CP!

In addition, the BULLET Series features a quality 1.2mm, 1.5mm, 3.0mm ring package and includes Chromoloy wrist pins with wirelocks. The 1.2mm carbon steel nitrided top ring is extremely durable and offers reduced friction over 1.5mm and 1/16" top rings. A 1.5mm Napier (hooked face) 2nd ring is used to improve oil control over conventional taper-faced rings.

Q: What is Cam and Barrel shape?

Based upon a few different variables, cam / barrel shape is the curvature built into the piston to insure the correct amount and rate of expansion. As the motor approaches operating temperature, the cam insures that the aluminum piston and the aluminum/ steel/ cast iron cylinder all achieve optimum operating temperature / shape at the same time.

Q: What is an X-style forging/piston?

X-Style forgings are designed to minimize friction and reduce weight without compromising strength. With the use of bracing and ribs, the forging is configured by adjusting the weight balance between high and low stress areas. This design enables the use of a shorter pin for added strength and weight savings.

See figure 5

Q: What are non-rotating wire locks (KRAMM LOX)?

They are designed to directly replace standard wire locks with no additional machining to the pistons and will not rotate in the lock groove. Click here for more information

Q: What are billet pistons?

Billet parts originate as solid blocks of aluminum and are normally used in the rare instances when forgings cannot produce the optimum design.

Q: Ring orientation

Q: Ring end gaps?

Due to the wide variance of expansion rates typical of power adders (nitrous, turbos, etc.), air cooled versus water cooled, marine applications, etc., it can be difficult or impossible to give ring end gap recommendations that will be accurate across the board. Please be aware that the information provided is only a guideline and that any concerns should be addressed with your engine builder. All information is provided in inches of ring gap per inch of bore. EXAMPLE: A recommended ring gap of .0040 per inch on a motor with a 4.000 inch bore would yield a ring end gap of .016 inches as .0040 x 4.000 = .016



DOMESTIC AUTOMOTIVE: Normally Aspirated (no power adders) up to 600hp.


DOMESTIC AUTOMOTIVE: Normally Aspirated over 600hp and turbo/nitrous applications below 750hp.


DOMESTIC AUTOMOTIVE: Turbo/Nitrous applications above 750hp.


SPORT COMPACT: Normally Aspirated to 300hp


SPORT COMPACT: Turbo/Nitrous applications to 450 - 750hp


POWERSPORTS: Normally Aspirated


POWERSPORTS: Turbo/Nitrous applications

Q: Ring Dimension terminology

Q: Piston to wall reference chart for different bore types.

Your pistons should have come with a Spec Sheet that will have the recommended piston to cylinder wall clearance written on it, as well as where the piston should be measured. As always, you’ll want to consult with your engine builder to verify whether that is the correct clearance for your application. NOTE: You cannot accurately measure your piston to wall clearance by sliding a flat feeler gauge into a round hole next to an elliptical object (piston).

EXAMPLE: Bore = 3.898 / Piston measurement at gauge point = 3.895 / Remaining piston to cylinder wall clearance = .0030

Q: I want to supply CP-Carrillo with a model to make my new pistons, what’s the best way to do this?

If any form of model is provided (old piston, mold, cylinder head or 3D CAD model) for manufacturing new pistons, please make sure you take the following steps to ensure a proper sample is received:

If sending a piston sample, make sure it is clean and piston sample needs to be the least damaged out of the set, remove all rings, locks and wristpins.

If you are sending a Mold from cylinder head this mold needs to be made out of a hard material (e.g. Bondo ®) and should include “X” and “Y” centerlines (representing the bore CL) and backside of mold needs to be completely flat.

If sending a Cylinder head include gasket, valves, spark plug, dowel pins (if possible) and please remove valve springs. CAD 3D models are also an excellent source of information and often times more convenient, talk to your CP-Carrillo salesman for the appropriate file type. For any other types of models/samples please talk to your CP-Carrillo salesman for proper instructions before sending samples.

Q: I broke a ring during the install, can I just use OEM rings with this piston?

No, OEM rings will not fit; you would have to get another CP ring set.

Q: How much ring end gap should I run? (Answered on pages 2 & 3)

The required ring end gap varies for each application. A spec sheet/ installation sheet is included with piston and ring orders to help you determine the proper ring end gap. Click here to download the form. If you have further questions, please contact our technical sales department at 949-567-9000

Q: How much lift will your piston take?

This value depends on the engine and piston part number. CP-CARRILLO and BULLET Pistons are designed with valve pocket depths to fit most popular camshafts. We strongly recommend checking your piston to valve clearance during assembly.

Q: How long does it take to make Custom Pistons?

It depends on the level of customization. We can make custom pistons in as short as 3 days, but the engineering part can take longer. Custom piston turnaround can vary at different times of the year. As a baseline, you can generally assume approximately 5 weeks from the time we receive all of the pertinent information to the time the parts are ready to ship. We do offer an expedite service for rush jobs but you’ll want to contact your distributor/engine builder for further information. Please keep in mind that certain operations/features must be sent out for processing and CP/Carrillo cannot be held responsible in those circumstances.

Q: How do I request a catalog?

Send your name, mailing address, phone number and indicate which catalog type you like (Automotive/Marine or Powersport) you'd like to receive to sales@cp-carrillo.com or call 949-567-9000 and we are happy to send you one.

Q: How do I know my piston to wall clearance, and where do I get the measurement? (Answered in question: “Piston to wall reference chart for different bore types.”)

Each CP-CARRILLO and BULLET Series Piston kits include a piston spec sheet with a piston to wall clearance recommendation. Always measure CP-CARRILLO and BULLET Series Pistons at the recommended gauge point, usually .500" up from the bottom of the skirt or where otherwise indicated on the spec sheet. Subtract this dimension from your finished bore size to determine your piston-to- wall clearance. If you have further questions, please contact our technical sales department at 949-567- 9000

Q: How do I identify Tops, 2nds and oil rings?

See figure 1. Assuming your top and second rings are of different thicknesses you can simply measureyour rings and compare them to the groove dimensions. (SEE DRAWING) In instances where the top and second rings are of the same thickness the top ring will generally be of a shiny silver/copper color whereas the second ring will be of a dark grey or black coloring. Both rings will normally be marked with a dot(.), number, or letter that will aid in determining which side of the ring will face up toward the dome of the piston.

If the rings don’t have a dot or letter to mark “up”, check the ID of the ring and they should be beveled. The inner beveled edge of the top ring will face up towards the cylinder head, and the inner beveled edge of the second ring will face down towards the crank.

Additionally, some second rings will have a tapered hook groove on the OD. This hooked edge will face downward as its function is to scrape oil back down into the crank case. See Figure 4

In the rare instance that you receive a ring with no designation, though it could mean the ring manufacturer has determined that it will work effectively either way, we recommend that you contact us for clarification.

All of our oil rings for 4-stroke applications utilize a 3-piece design which consists of two thin oil rings separated by an expander (wavy) ring.

PLEASE NOTE: DO NOT ALTER YOUR EXPANDER. Oil ring gap specifications are for the top and bottom rails only! Oil ring expanders are designed to butt against each other and when installed along with the rails allow the ring to have the correct tension when seated in the cylinder.

You may also have a piston that requires the use of a rail support, that rail will have a dimple to prevent rotation.

Q: How do I identify my CP-CARRILLO or BULLET Pistons?

How do I identify my CP-CARRILLO or BULLET Pistons?

Q: How do I cut ring grooves?

You don’t, we do. Attempting to alter the ring groove(s) of your CP piston could severely compromise the integrity of the part. The good news - if you have the correct rings and your piston is in good condition there should be no reason to alter the ring grooves.

Q: How do I become a dealer?

If you are interested in becoming a dealer, please complete a dealer application form located here. Email completed to sales@cp-carrillo.com or fax 949-567-9010

Q: Do you have a minimum quantity of pistons I need to buy?

While our custom parts are generally made in a 4 piece minimum order, shelf parts may be purchased as singles. We also stock replacement hardware for all of our shelf parts and most customs.

Q: Can you coat my pistons?

Yes, we can coat our pistons per request.

Q: Can I purchase rings for your pistons?

CP-CARRILLO stocks a complete line of piston rings for your shelf and custom piston orders. All BULLET Series and CP-CARRILLO Sport Compact shelf piston kits include rings. Most CP-CARRILLO Powersports piston kits include rings as well.

Q: Can I order direct?

We don’t sell retail, but we have a list of established distributors that stock and advertise our products on our website.

Q: Are all your pistons forged?

Yes all of our parts all are forged. All CP-CARRILLO and BULLET Series pistons are forged for maximum strength and durability. We predominantly use 2618-T61 and some 4032.

4032 is a high silica (glass sand) content material that has good scuff resistance and allows tighter piston to wall clearances, however this is at the expense of strength. The greater the silica content, the more brittle the material, so 4032 does not lend itself well to high cyl. pressure applications such as those found in Super charged, Turbo charged, or Nitrous Oxide applications, with relatively light piston weights. 4032 has been used in some low boost applications in OEM and in some high boost diesel applications, but the pistons are much thicker and heavier than there 2618 counter parts, in an effort to keep them from failing. 4032 is also more expensive to machine, because it wears out tooling quicker. 2618-T61 on the other hand is a low silica content material, so it is more ductile/forgiving, so it is the material predominately used in high cylinder pressure applications. However, 2618 does require more cylinder to wall clearance because of the lack of silica and it reduces anti-scuffing qualities.

↑ top