Common compression and squish numbers for the 4AGE and 7AGE

You should always calculate the compression and squish numbers specifically for your build however I am posting this to get you some general numbers for rough and quick calculation. It will help get a genral idea of where you want to be and what pistons to be looking at.
Once you are ready to order I highly recommend running your own numbers. Preferably using the details of your build including CCing your head and measuring your actual deck height.

For more info on doing these calculations read this page.

Due to great pricing they have given me and their willingness to talk about these details and refine and improve their designs I have decided to make Arias my primary go to company for shelf pistons.

Check the store via the links below to check out current pricing.

 All the piston manufacturers tend to get many numbers quite wrong meaning you should never trust any shelf piston specs. Always run the numbers yourself.

I have been working with Arias to improve their designs and now we have new shelf pistons that are all much more correct and ideal. I hate using the info below now because Arias has done so much to work with me on improving their designs however I already used them as examples and don't have the time to completely redo it. All of the new Arias designs use the stock compression height of 30.5mm. Stock dome volumes have been corrected for each head and we have also refined the design of the 16 valve pistons. 
The new pistons are available in 8.5:1, 9.5:1, 10.5:1 11.5:1 and 12.5:1. You can also adjust squish and combustion chamber volume to move each up or down slightly. 


Here are some general calculations using arias's old designs and information assuming an unshaved head and block and untouched combustion chamber.


Head Combustion chamber volume Piston Manufacturer compression ratio rating

deck clearance

Negative if above deck

Heagasket thickness

Calculated compression ratio Squish gap  
16 valve 4age 36cc Arias AP331669 8:1 -.0054 1.2mm 8.16 1.2054  
.8mm 8.44 .80054
8.6:1 .274 1.2 9.36 1.474  
.8 9.74 1.074
9:1 .274 1.2 10.01 1.474  
.8 10.46 1.074


10.7 .274 1.2 12.08 1.474  
.8 12.76 1.074
SIlvertop 36 Arias
9.2 -.2086 1.2 8.99 .9914  
.8 9.34 .5914


11.3 -.2086 1.2 10.78 .9914  
.8 11.31 .5914
Blacktop 38 Arias
8.5 -.2086 1.2 8.38 .9914  
.8 8.68 .5914
10.5 -.2086 1.2 10.33 .9914  
.8 10.8 .5914


16 valve pistons can be found here.


20v pistons can be found here.


courtesy of