286210 pistons and compression ratio

[YOUNG GUNS15]

So in my last motor build I opted to use PAI 286210 pistons in my build with .150 for valve reliefs. The head has not been decked, only cut for fire rings, block had .001 removed. I am using a standard thickness fire ring head gasket from haisley machine. Now here is the question, I bought the pistons as 17.5:1 compression ratio and was told that .100 is roughly a point of compression, so theoretically I am close to 16:1 compression ratio considering that .150 is a point and a half of compression. My question is are these 286210's really 17.5:1?

In this thread the 286210's are said to have 16.5:1 CR to start with. If that was the case I would be sitting at 15:1 CR.

http://www.competitiondiesel.com/forums/showthread.php?t=176501

Then in this thread from four years ago the 1.00mm oversized 286210's are 17.6:1

http://www.competitiondiesel.com/forums/showthread.php?t=84602


right now I am just confused, it seems like not all 286210's are created equal?

 

[Smokem]

Not sure what you are missing that I did not make clear in the other thread, you cannot accurately calculate compression without piston protrusion and gasket thickness. The compression values are different depending on what piston is being replaced, as the stock pistons have varying bowl volumes and compression heights.

 

[YOUNG GUNS15]

Let me add that the whole reason I went with the 286210's was to retain as much compression as I could with big reliefs, it would be kind of a bummer if they ended up being 15:1 CR.

 

[YOUNG GUNS15]

So replace a 1995 piston with the 286210, standard gasket, same protrusion, no releifs. where does it fall?

I might be over thinking this a little too much.

 

[Tate]

So in my last motor build I opted to use PAI 286210 pistons in my build with .150 for valve reliefs. The head has not been decked, only cut for fire rings, block had .001 removed. I am using a standard thickness fire ring head gasket from haisley machine. Now here is the question, I bought the pistons as 17.5:1 compression ratio and was told that .100 is roughly a point of compression, so theoretically I am close to 16:1 compression ratio considering that .150 is a point and a half of compression. My question is are these 286210's really 17.5:1?

In this thread the 286210's are said to have 16.5:1 CR to start with. If that was the case I would be sitting at 15:1 CR.

http://www.competitiondiesel.com/forums/showthread.php?t=176501

Then in this thread from four years ago the 1.00mm oversized 286210's are 17.6:1

http://www.competitiondiesel.com/forums/showthread.php?t=84602


right now I am just confused, it seems like not all 286210's are created equal?

Are you missing that standard and oversize pistons have the same bowl volume, but will have different cylinder volumes? Same piston in oversize will have a higher compression ratio because it has a larger swept volume, but the compression volume is (very close to) the same.

 

[Smokem]

If you want an accurate answer get the piston protrusion and gasket thickness.