The dome volume you have for those pistons isn't correct, try running that exact calculation with a 0.026" gasket and 50cc combustion chamber and see if that comes out anywhere near 10:1.

The dome volume is from another site, but even aftermarket upgraded pistons range from -16 to -23 so its all I can go off of. 

 

The quench for the Cometic gasket is 0.030. I called them.

 

Why use 50cc combustion chamber? EJ22E single port P1 heads are only 41CC.

 

remember this is a EJ253 (NOT 25D) with phase 1 EJ22E single port heads.

Edited April 26, 20187 yr by iluvdrt

I'm trying to get you to reverse calculate the proper piston dish for the ej251/3, which has a 50cc combustion chamber. If you do that you'll see they have an 8cc piston dish. Plug that number into your calculations for the 22e heads and you'll get the correct compression ratio for your combo.

If I use all the same data as before with a 8CC piston dish the compression drops to 8.1

 

If I use the data you suggested in your first post with my original data than the compression is 7.49

Forged Weisco stock pistons are -16 for the Piston dish. If I plug that number in using my original data than my ratio is 10.5:1

 

JE pistons are also -16.5

Edited April 26, 20187 yr by iluvdrt

If I type in the bone stock numbers for a complete 253 using a +8 piston dome it says the compression is 7.49. I don't think that dome volume is right Bratman. EJ253 is 9.5-10:1 

 

If I use all stock data for a 253 with a -12 dome its 9.25 which is way more realistic. -16 piston (which is what replacement pistons are) is 9.7:1. and that is with stock 253 heads and 0.026 quench. That's pretty realistic as well.

Edited April 26, 20187 yr by iluvdrt

I'm not sure where you're getting anything in the 7s with these numbers.

 

Those are aftermarket turbo compression pistons from JE, and the 16cc pistons sound more like ej25d at 9.7:1.

Edited April 26, 20187 yr by 86BRATMAN

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.submariner.org/thepno95/TWE%2520Compression%2520Calculator%2520ver6%2520-%25202017.xlsx&ved=2ahUKEwjShtK399jaAhWpdd8KHSy5B1QQFjAAegQIBhAB&usg=AOvVaw2jny25j3_6lk0HLJDPXO3c

 

Hopefully that link copied correctly. This is a pretty accurate and easy to use Subaru compression calculator.

So the dish is -8 and not +8? I was using +8

So with the 22E heads what are you coming up with? Obviously I keep punching in the wrong numbers lol

 

Thanks for the help

11.88 using your chart with 41CC heads and a piston dish of 8. If that's the case, guess Ill have to tune it.

That's what I came up with as well with, it's definitely not a combination I'd recommend running on a stock ecu. If it weren't for this going into an ea81 chassis I'd recommend going to 25d heads because the compression bump isn't as drastic. But that opens up another bag of fitment issues with the timing covers and frame rails.

253 deck clearance is nowhere near 160 thou. You probably read that in metric, which would be .16mm, or .006"

 

160 thou would wreck the quench. 6 thou plus the gasket would be in the ballpark for quench. You're going to find the compression much too high as I said though.

 

The aftermarket pistons WILL NOT WORK as they are pin located for 257 rods. They will sit way over the deck with an NA rod length.

 

GD

Edited April 27, 20187 yr by GeneralDisorder

Well thanks for the help everyone. Looks like this is a total no go.

 

Ill put new gaskets on it and save it for my sons 05 impreza OBS.

 

 

Oh, checked when I got home and its a EJ251 but that doesn't make a difference. Still too high.

Edited April 27, 20187 yr by iluvdrt