compression ratio of ahu pistons

[ShoulderMan]

Is there a set compression ratio on the ahu piston,  are all the ahu piston compression ratios the same.
  does anyone know the compression ratio of the ahu piston.

  thank you
 -Ron

[ShoulderMan]

I think that answer might work.
 
  I know the 1.9l tdi engines made  between 17.5:1, 18.5:1 and a 19.5:1 that is with
 
79.5x95.5 bore and stroke
144mm rod length
26mm wrist pin
236mm deck height

is that becasue you can use a 1, 2, or 3 notch headgasket?  or because  one is N/A, one early turbo, and one a bigger turbo?

another question then,
 Ive heard you can interchange pistons between the 1z and the ahu,  can you also interchange with the "AFN"
and will 1z/ahu/afn pistons interchange with the newer 2000-2006 pistons

and if you can interchange pistons, utilizing the same rod length and deck height, 
you are saying that the compression ratio will(should) be the same regardless of the piston (ie: 1z/ahu)
and that it would be the cylinder head, and head gasket, that would change the stock c/r   (unless you open up or change the piston bowl)



 

[ShoulderMan]

Alright, after some more research,
 the a3/a4 searies vw's that ran 90-110hp engines used a 19.5:1 compression ratio
the a4 and up that hat 115hp or more used 18.5:1 c/r

 so, knowing this, i still wonder what they used to lower the c/r.  is it in the piston, gaskets, valve train,

  thanks

-Ron

[410]

My "guess" would be the size and shape of the combustion chamber in the piston.  But like libbybapa said, anything can effect the compression ratio in an engine.

[shortysclimbin]

OK being someone who has had LOTS of pistons in my hands, cced and changing bowl shapes, I can tell you The following:

• The mk3  AHU/ AAZ tdi's all had 19.5:1 CR pistons.  These pistons have slightly lighter pistons and dont hold up to heat as well
• The mk4 ALH/ASV all had 19.5:1 CR no matter what size. These pistons will directly fit into an older mk3 generation
• The PD pistons ranging from pd100-pd130 all had 19.5:1 CR, ofset bowls AND NO valve reliefs.
• The PD150 pistons had 18.5:1CR ofset bowls and valve reliefs, these can be used for direct placement into mk3/ mk4 VE engines
• Other pistons out there for the marine application have been fit into diesel engines with some machining to fit with larger bores and oil squirter grooves re cut. They are by no means plug and play
• The BRM pd pistons and CR pistons have the bowls centered, no valve reliefs, and range in CR from 19.5:1 to 17.5:1 OEM. More may be different I have yet to get my hands on a set.

Gaskets range in thickness and CAN drop you're CR about .5pnt, but I highly highly sugest avoiding this. This drastically reduces your squish area which negatively effects efficiency, smoke levels, and cold starting.  If you want proper maching contact me. I have been doing some bowl work on the side that people are quite happy with.

hope that helps clear up the mud
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[ShoulderMan]

Thank you.  this is good information to know.