# FAQ - 1.8t Pistons



## groggory (Apr 21, 2003)

This thread will be indexed in the main 1.8t FAQ

*Other good discussions on 20v turbo piston choices*
Pistons for a 2L Stroker
Choosing piston diameter for increased displacement discussion

This thread is to cover the piston options available for the 20v turbo platform. Notice I didn't say 1.8t :thumbup: Many of these pistons will be part of your quest for increased displacement or modified compression ratio.

There are many other topics required to properly cover the topic of changing pistons. Where necessary, I will point this thread to the FAQ or to other threads to cover those topics in detail. Let's try to keep this thread mainly geared at the piston choices and their uses for various goals.

With that...let's get started......

*Terms*

*Bore* - Refers to the diameter of the cylinder. Stock bore is 81mm.

*Coating* - This refers to coatings that have been added to the piston in order to improve its performance somehow. Coatings are commonly added to the skirt and to the crown.

*Compression Height* - The compression height of a piston is the distance from the center of the wristpin to the top of the piston, not including domes.

*Compression Ratio (CR)* - It is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.[1]
Picture a cylinder and its combustion chamber with the piston at the bottom of its stroke containing 1000 cc of air (900 cc in the cylinder plus 100 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio.
A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher efficiency is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. It may be more helpful to think of it as an "expansion ratio", since more expansion reduces the temperature of the exhaust gases, and therefore the energy wasted to the atmosphere. 

*Crown* - This is a general term to describe the top of the piston. In the 1.8t platform there is never just a flat unmolested piston. There is always a mixture of dish, valve reliefs, coatings, and other treatments. The crown will commonly be coated with a thermal coating to help resist melting and pitting during high cylinder temperatures.

*Detonation* - 

*Dish / Dome* - This is in relation to the shape of the crown of a piston. This is commonly measured in cc. This is because you either are adding or subtracting from the combustion chamber's volume with Dish and Dome respectively.

*Displacement* - This is the volume of your cylinder including the dome in the head and head gasket thickness when the piston is at bottom.

*Drop In* - This is a loose term meaning you don't have to CHANGE anything else in order to use this piston. No piston is a true "drop in" unless you are replacing it with a piston from the same manufacturing group as the original that it replaces

*Locks* - Circlip, Wirelock, Spiral, etc

*Micro Welding* - (In relation to ring grooves)

*Oil Squirter* - This is a small nozzle that is fed oil from the block and squirts oil on the bottom of the piston. 

There are numerous oil squirters used in even the same blocks depending on what head and what car it came out of. For instance, in the 06A block the motors originally equipped with AWW and AWP heads have one style squirter while motors originally equipped with BAM / AZG / etc heads use another style squirter. This is important when you're choosing stroker pistons so that the piston does not contact the oil squirter.

*Oil Squirter Notch* - This relates to clearance(s) cut on the piston so that the oil squirters mounted in the block will not hit the piston at the bottom of the stroke

*Ring Lands / Ring Grooves* - These are the grooves cut into the side of a piston that the rings sit in. High quality pistons have very very flat ring grooves so that the square cut rings can seat properly. Lower quality pistons can have variations in the cut, which will reduce the effectiveness of the rings to properly seal in the cylinder.

*Rings* - On the 1.8t these are sold as a set as each piston has 3 rings:
The first ring is chrome faced steel.
The second is cast iron.
The third is the oil control ring and has 2 chrome faced steel rails and a steel separator. 

*Rod Length* - Connecting rod length is measured from the the center of the 'big end' (crankshaft journal end - rotating) to the center of the 'little end' (piston pin end - reciprocating). Standard length of 144mm in 1.8T formats: 144x19 or 144x20.

*Rod Ratio* - Can be calculated by dividing the rod length by the stroke. Common rod ratios using 144mm connecting rods (most of the rods out there for 20v motors) are:

1.5078 for 95.5mm stroke
1.5517 for 92.8mm stroke
1.6666 for 86.4mm stroke (stock). 

Understanding Rod Ratio is a key factor on revving, friction and engine wear.



blurb below on rod ratios said:


> Larger rod ratios will create a smoother running motor with less friction / wear and load on the piston/wall.
> 
> Smaller rod ratios will create greater wear / friction and load on the piston/wall.


*Skirt* - The piston skirt is the part of a piston that extends the lowest. It is tasked with keeping the piston from rocking excessively in the cylinder. The piston skirt is typically machined with small grooves to aid in holding and transporting oil to the cylinder walls to provide proper lubrication. In some high-performance applications, the piston skirt may be coated with a type of chemical which aids in lubrication and prevents scuffs from occurring on the cylinder wall.

In a combustion engine, the pistons are sealed inside of the cylinder walls by the piston rings. The rings, as they are called, are making contact with the cylinder wall while the piston rides up and down, centered by the rings in the cylinder wall. At the top and bottom of each stroke, as the piston is changing direction, the piston rocks. It is then that the piston skirt makes contact with the cylinder wall, setting the piston straight once again to continue its journey.

Depending on the stroke of the crankshaft and the length of the connecting rod, the piston skirt could be in danger of making contact with the crankshaft at the very bottom of its travel or stroke. This is especially common in high-performance engines known as stroker motors. In a stroker motor, the engine's stroke has been altered by swapping to a longer throw on the crankshaft and also changing the length of the connecting rods. The piston pin location is changed, creating a new location for the piston to connect to the connecting rod.

In the typical stroker application, the engine block needs to have notches ground in the bottom of the cylinder walls to prevent the crankshaft and connecting rods from making contact with the block. Often, the bottom of the piston skirt must also be clearanced to avoid making contact with the connecting rod as it spins around the crankshaft throw. When clearancing a piston skirt, it is wise for individuals to make the same cut on both sides of the piston skirt. This maintains balance within the reciprocating components. The most minute removal of material can cause the components to be dangerously out of balance, leading to catastrophic engine failure.

One of the telltale signs an engine has been operated while low on oil is a scuffed piston skirt. As the piston travels up and down the cylinder wall, the lack of oil can result in the piston's skirt scrubbing or scuffing the cylinder wall, leaving the telling scuffing sign. When this occurs, it is often time to replace the pistons as well as to bore the cylinders to remove the scuff marks.

*Barrel Skirt*

*Round Skirt*

*Slipper Skirt* - A Piston with the lower edge cut away so that the Piston skirt is short on the two sides not used as thrust surfaces. Such a design lightens the piston making it easier to accelerate and decelerate, wastes less power, and is easier on the bearings. Cutting away the skirt also allows the Connecting rod to be made shorter but leaves enough room between the Counterweights and the pistons so the overall height of the engine can be reduced. 

*Skirt Coating* - Anti friction for initial start up or Anti Wear for longevity of motor

*Stroke* - Refers to the length the piston travels from bottom to top. Stock stroke is 86.4mm. Common strokes are 80.0, 92.8, 95.5, 100.0 plus a few others, but these are the most common.

*Stroker* - Refers to a motor that uses a longer than stock stroke in order to increase displacement. Stroke: Standard (as stock), De-stroked (shorter than stock) and Stroker/stroked (longer that stock)

*Valve Reliefs*

Wrist Pins - This is the diameter of the pin that connects the piston to the connecting rod. 19mm Tapered rod useage / 20mm Typically pre-19mm useage and aftermarket standard - Tool Steel, Heavy Duty, Severe Duty are also terms used by various manufacturers of aftermarket pistons when it comes to the levels of pin strength, materials and quality

*Specifications of a Piston*

* Wrist Pin Size

* Compression Height

* Crown Height

* Valve Reliefs / Angle

* Coatings

*Materials*

2618 Aluminum Alloy - Stronger than 4032, but has a higher thermal expansion. Used by JE in many of their pistons. 

4032 Aluminum Alloy - This material is not as strong as 2618, but has a lower thermal expansion. This allows the engine to be built 'tighter'. This material is commonly used by Wiseco and SRP. JE uses 4032 in certain applications.

Mahle 124 Alloy - Also known as ISO 4032 Aluminum Alloy

Mahle 138 Alloy - Cast piston Alloy (not used in the Mahle Motorsport Powerpak lineup)

Mahle 142 Aluminum Alloy - Used in most of the Mahle Powerpack line of pistons and is the alloy that VW uses in their OEM pistons. This is a combination of 4032 and 2618 alloys. There is no ISO designation for this alloy.

Mahle M-SP25 - Also known as ISO 2618 Alloy

*Crown Coatings*

JE Thermal Barrier Crown
The thermal barrier crown coating is applied to the piston dome and is designed to reflect heat into the combustion chamber. This increases exhaust gas velocity, greatly improves scavenging potential, and extends piston life by decreasing the rate of thermal transfer.

*Skirt Coatings*

JE Tuff Skirt ®
JE Pistons trademarked coating Tuff Skirt is a lubricating, anti-friction / anti-wear coating applied to the piston skirt designed to withstand many different types of endurance racing. 

*Mahle Grafal skirt coating*
This is a proprietary skirt coating used by Mahle on their powerpack pistons. Mahle markets this as an anti-friction coating that also offers impact absorbing qualities; reducing piston noise and decreasing stresses in the piston skirt.

*Pistons*
** I'm going to organize these by manufacturer for now. However, I may create names for the pistons for use in this thread and then cross index them by bore.

*Aries*

*CP*

*JE*
Discussion on Updated FSR Forging
The FSR line of pistons is a slipper skirt forging, only designed specifically for boosted applications. It has a larger, stronger skirt on the side of the piston which receives all the side loading during the high pressure combustion process. The opposite skirt is smaller and weaker, for light weight. The pistons still use a full width wrist pin and large, wide pin bosses to carry the load of a turbo/supercharged engine without wearing out or ovaling out the pin bosses. 

*Mahle*
The Powerpack line of pistons is their performance offering

*INA Custom Stroker Pistons*
* Series: Powerpack
* Mass: 
* Bore:
* Advertised CR:
* Crown Coating:
* Pin Size: 20mm
* Skirt Style:
* Skirt Coating:
* Fitment in 06A AWP / AWW blocks
* BAM / AZG / etc require the use of 06A AWP oil squirters as they are different shape and do not clearance the skirt.

*IE Custom 10:1 Pistons*
Link
* Series: Powerpack
* Mass: 
* Bore:
* Advertised CR:
* Crown Coating:
* Pin Size: 20mm
* Skirt Style:
* Skirt Coating:
* Designed for 92.8mm stroke crankshafts
* Not compatible with TT225 blocks due to oil squirter differences

*Probe*

*Ross*

*Wiseco*

*Wossner*

*Rod Ratio*

Excellent read on rod ratios

More good reading on rod ratios

There are limited choices when it comes to changing the rod ratio on the 20v platform unless you use a custom length rod or can adapt an off the shelf rod to work in your application. People commonly incorrectly assume that 2.0 pistons will work in a 1.8 without much modification or trouble. They will work, but require a custom rod to make up for the compression height difference or will require use of the crankshaft that the pistons were designed to run with. This problem is typical of people trying to make do with what they can afford or have readily available. 

Larger rod ratios will create a smoother running motor with less friction / wear and load on the piston/wall. 

Smaller rod ratios will create greater wear / friction and load on the piston/wall. 

Case in point, the G60 1.8 with its 86.4mm stroke and 136mm rod (rod ratio = 1.5741). By switching out to a longer rod and shorter compression height piston [1.286" compression height in a 220mm deck height block with a 144mm rod and 86.4mm stroke (rod ratio = 1.6667)], the motor will rev smoother with less wear. That is one of the speed secrets for the G60 guys introduced many years ago.


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## groggory (Apr 21, 2003)

*Piston Installation DIYs, Tips, and Notes*

*How to check true displacement*
The advertised displacement and your true displacement may differ. This can happen if a head or block has been surfaced, bores have been changed, non standard head gaskets have been used, etc

*How to choose the right ring gap*


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## groggory (Apr 21, 2003)

POST3


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## groggory (Apr 21, 2003)

POST4


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## groggory (Apr 21, 2003)

POST5


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## Big_Tom (Aug 19, 2007)

:beer:


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## Rheinland Technik (Apr 2, 2010)

*Terms*

Bore - Refers to the diameter of the cylinder. Stock bore is 81mm.

Crown [I would suggest sub-grouping this as Crown/Top with Compression Height/Crown Height, Dome/Dish, Valve Reliefs/Angle, Coating - there are a few more details that I will leave out at this time]

Dish [Dish / Dome - see above]

Drop In [Loose term, as no piston is a true "drop in" unless you are replacing it with a piston from the same manufacturing group as the original that it replaces]

Locks [Circlip, Wirelock, Spiral, etc]

Oil Squirters [Block specific feature, though standard on most 1.8Ts, refer to it as Oil Squirter Notch when relating to a piston feature]

Rod Length [Standard length of 144mm in 1.8T formats: 144x19 or 144x20]

Rod Ratio [1.6666 for 86.4mm stroke / 1.5517 for 92.8mm stroke / 1.5078 for 95.5 stroke - understanding Rod Ratio is a key factor on revving, friction and enine wear]

Slipper Skirt [Skirt Design: Barrel/Full/Round versus Slipper]

Skirt Coating [Anti friction for initial start up or Anti Wear for longevity of motor - thermal crown or top coating as mentioned above in Crown]

Stroke - Refers to the length the piston travels from bottom to top. Stock stroke is 86.4mm. [80.0, 92.8, 95.5, 100.0 plus a few others, but these are the most common]

Stroker - Refers to a motor that uses a longer than stock stroke in order to increase displacement. [Stroke: Standard (as stock), De-stroked (shorter than stock) and Stroker/stroked (longer that stock)].

Wrist Pins - This is the diameter of the pin that connects the piston to the connecting rod [19mm Tappered rod useage / 20mm Typically pre-19mm useage and aftermarket standard - Tool Steel, Heavy Duty, Severe Duty are also terms used by various manufacturers of aftermarket pistons when it comes to the levels of pin strength, materials and quality].

*Materials*

2618 Aluminum Alloy - Stronger than 4032, but has a higher thermal expansion. Used by JE in many of their pistons. This is the material the OEM uses. [Actually 4032 is used in stock alloys for closer tolerances due to the lower thermal expansion]

4032 Aluminum Alloy - This material is not as strong as 2618, but has a lower thermal expansion. This allows the engine to be built 'tighter'. This material is commonly used by Wiseco [SRP uses 4032, JE in come applications use 4032].

*Mfg Model Lineups*

JE

Mahle
* Powerpack

Wiseco[/QUOTE]

[CP, Aries, Ross, Wossner, Probe plus a few more]


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## groggory (Apr 21, 2003)

Fantastic! I'll work on integrating this and expanding


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## Rheinland Technik (Apr 2, 2010)

As for rods ratio is concerned, there is limited choices when it comes to changing the ratio unless you use a custom length rod or can adapt an off the shelf rod to work in your application. People will commonly assume that 2.0 pistons will work in a 1.8, which is a false positive. Yes they will work, but require a custom rod to make up for the compression height difference or use the crankshaft that the pistons were designed to run with. Typically a "noob" mistake, trying to make do with what they can afford or have readily available. The larger the rod ratio, the smoother the motor will run with less friction / wear load on the piston/wall. The smaller the ratio, the greater the wear / friction and load on the piston/wall the motor will see. Case in point, the G60 1.8 with its 86.4mm stroke and 136mm rod. By switching out to a longer rod and shorter compression height piston [1.286" compression height in a 220mm deck height block with a 144mm rod and 86.4mm stroke], the motor will rev smoother with less wear. That is one of the speed secrets for the G60 guys introduced many years ago.


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## groggory (Apr 21, 2003)

Everything up to this point has been integrated into the first post


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## speed51133! (Aug 5, 2002)

i would add an entire section on rings. There are a few different types, total seal, OEM rings, etc...

ring gapping is also important and not really talked about much. there are different gaps for different applications. not really one gap fits all. what the bentley states is fine for oem use. for high boosting cars i would not just use the gap that is used oem.

i do not know all the ins and out specifics, but wouldnt mind seeing all the info consolidated. it is important to check gaps, position them in the right spot, and file rings when assembling an engine.

have one of the forum sponsors maybe type out the proper procedure and reccomended things. there are a ton on you tube...


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## groggory (Apr 21, 2003)

speed51133! said:


> i would add an entire section on rings. There are a few different types, total seal, OEM rings, etc...
> 
> ring gapping is also important and not really talked about much. there are different gaps for different applications. not really one gap fits all. what the bentley states is fine for oem use. for high boosting cars i would not just use the gap that is used oem.
> 
> ...


Thread updated with some more information and space to put this information in.

That's a great idea.

Looking for more info everyone. Chime in if you wanna help out here.

Also, I'm going to get pictures of a lot of the common pistons going, so please post up pics of all the common ones. I'll dig through and get what I need from your posts.

Thanks!

Question: Are all piston ring sets created equal? Should you pair say, a Wiseco piston with Wiseco rings? Mahle pistons with Mahle Rings? Etc?


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## kamahao112 (Nov 17, 2007)

another very useful thread !:thumbup:


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## [email protected] (Jul 1, 2009)

here is a good paper on rod ratios. It illustrates how many variations have been used over the years.

http://victorylibrary.com/mopar/rod-tech-c.htm


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## groggory (Apr 21, 2003)

^^bump

Keep the good information coming. I'm going to start adding a bunch of the piston choices to the list above. Many of you are far more versed on this than I am so please keep tossing in your $.02. I'll integrate it into the write up.


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## vtraudt (Mar 1, 2010)

groggory said:


> Question: Are all piston ring sets created equal? Should you pair say, a Wiseco piston with Wiseco rings? Mahle pistons with Mahle Rings? Etc?


Have engine (previous owner, AEB) with Mahle pistons. Want to put new rings on. Can someone chime in?


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