Stock pistons?
 

1995 - BPY1-11-SA0A
1999 - BPZ0-11-SA0
2001 - BPZ3-11-SA0
MSM - BPZ4-11-SA0

Does anybody know what the real difference are between these stock pistons.

Compression ratios?
Compatibility usable with NA, NB1, NB2 heads?

9:1, 9.5:1, 10:1, 9.5:1

yes all interchange

I think compression. I ran a early set in my 99 engine as the 99's were if I remember right a half higher, like 9.5 verses 9

FWIW: Factory 94-95 pistons are 8.8:1. They are superseded by the new part number, for 9:1.

Yes, I tried to go with them a few years ago and had to go with the 9's

For completeness JDM 10.5:1 pistons are BPZ2-11-SA0. I ordered some on MazdaComp in December but they haven't arrive yet.

Good to know. I think I'm stuck with stock spec USDM internals for an SCCA CSP car. I guess I can use the stock overbore pistons though. it will be a 2001 motor.

Where are you sourcing oversize oem pistons from?

You can always jb weld some quarters to the top of the pistons to increase compression.

lol'd

Anybody?

If it's a 2001 Motor in CSP you can only use 2001 Pistons. Update Backdate does not apply to individual parts within the engine. I.E. you can't put a VVT head on a 95 block...you have to swap the whole engine.

Unless I am TOTALLY misremembering that.

Even if you could you would want to use 01+ pistons anyways for the compression.

IIRC someone got a custom set of JE pistons at the .050 overbore limit made for stock specs at one point.

Yep. but you are allowed stock over size pistons. Even if they arn't much oversize. Matt seems to be going the route of buying his 2001 engine in parts for me to assemble.

Mazda sells OEM pistons in .25mm and .50mm oversize. The 2001 oversize ones are $33 each cheaper than standard size from Mazdamotorsports.

Thanks, that's what I was after.
It looks like they sell JDM spec pistons .75mm over as well.