compression

[sunnysr]

I have had a look in the wikki and im a little confused what compression ratio i am at ,i have a tech 1 sport so i am assuming its a early motor so will the compression be 9:4:1 as i read in one bit of wiki or 9:75:1 ..i got these two numbers from the wiki(one in the building a 2.8 section and one in the m20 piston section ) i have no understanding of compression numbers i am going to look that up in a min .my understanding is late motors had lower compression they were 8:8:1 ?? I am all a bit confused google is not helping much because of American market .and how do i check what motor i have i just bought a spare one but dont know if its early or late ...thank you for any help

[Grrrmachine]

The best thing is to check the engine number itself, as that will tell you whether you have a high or low compression motor. These days there's no guarantee that an E30 has the engine it left the factory with.

Get under the car on the passenger side, and look for a machined flat area on the bottom of the block, exactly where the block meets the sump. Use some sandpaper to clean it up if necessary.
The engine number is stamped in two rows. The top row will only be a few characters:

25 6E = high comp
25 6K = low comp

[sunnysr]

on the engine in the car its impossible to read ,why they wrote in such small letters hardly stamped on is anyone guess ,i have cleaned it and everything and can read most of it except the last bit so cant see no e or k ,very frustrating ..thanks for the reply ,do you know the correct compression ratios for both motors ,i suppose i will find out when i come to strip it down because i am building it as a turbo motor but it will make difference to what bits i will need .thank you