Engine builders...help!

[ADEN]

Before you judge i am in a place with only very limited resources and no shipping means.

So i made my new combination that i have a problem with:

B25 block
m50b25 NV pistons
m20b20 130 rods
731 head

Problem now piston is 1mm below deck i am stuck now i already assembled the block i did the CR calculator and result is 9.47:1 is this comp. Ok? Btw i am using 87 octane gas.

please see below the result and review my numbers i might even got them wrong.

[jbontke]

I don't think that is a bad compression ratio. Do you not have access to parts or shipping?

[ADEN]

I don't think that is a bad compression ratio. Do you not have access to parts or shipping?

Thank you for your feedback. Unfortunately no shipping but we have few shops that sells bmw parts but m20b25 didn't make it here only b20s so that's why b25 parts are rare.

My concern that the parameters i put in the calculator (attached picture) might be wrong, I need somone to take a look at them and confirm if they are correct or not?

here is a screenshot from the deck clearance calculator

[jbontke]

I pulled this pic form the forums

[jbontke]

The pistons have different profiles on the top, each for a different cyl head. Your m50 pistons are not on there, but hopefully the image above will help some. What may not help is if the piston profiles are vastly different from the cyl head. You may get strange cyl fill and compression that could cause pre ignition or incomplete combustion. That may be more noticeable at full throttle.

[digger]

Gasket thickness is either 1.75mm or 2.05mm if it’s an oem gasket.

Do you know the cc value of m50nv pistons ?

may wish to check p to v

[ADEN]

Gasket thickness is either 1.75mm or 2.05mm if it’s an oem gasket.

Do you know the cc value of m50nv pistons ?

may wish to check p to v

1.75mm commpressed?

This means thay i will get even lower CR.

The m50b25 early pistons 10:0 CR according to https://www.e30zone.net/e30wiki/index.php/M5x.
These pistons have a very light dish that i estimated .5 in my calculations they are the same as the ones in the pictures.

[ADEN]

The pistons have different profiles on the top, each for a different cyl head. Your m50 pistons are not on there, but hopefully the image above will help some. What may not help is if the piston profiles are vastly different from the cyl head. You may get strange cyl fill and compression that could cause pre ignition or incomplete combustion. That may be more noticeable at full throttle.

Mine are M50 10:1 CR and they are almost flat pistons as the 731 needs flat piston i think i am good on this issue .