How to identify a M20B25?

Post Sat Jul 06, 2019 9:16 pm

Right, probably asked before but as I can't search for the terms 5E or 5K (@ Steve

) I'll ask again.........

How do I tell if a potentially bodged 325i M20B25 is a 5E or 5K?

It is in an '88 facelift shell and has 173 motronic box but the early 2 vacuum pipe throttle body.

Thoughts?

Post Sat Jul 06, 2019 10:41 pm

My first thought is what does 5E and 5K mean?

Post Sat Jul 06, 2019 11:34 pm

Cloggy Saint wrote: ↑
Sat Jul 06, 2019 10:41 pm
My first thought is what does 5E and 5K mean?

Sorry, finger trouble I meant to type 6E or 6K

I am trying to work out if it is a High Compression 9.75:1 which I believe is the 6E or the later low compression 8.8:1 which I believe is the 6K.

It makes a difference to a few bits I'm getting for the engine.

Post Sat Jul 06, 2019 11:41 pm

Ah, never heard it referred to as that before. Don't really know the answer but a compression test would be the obvious solution.

Post Sun Jul 07, 2019 10:53 am

Cloggy Saint wrote: ↑
Sat Jul 06, 2019 11:41 pm
Ah, never heard it referred to as that before. Don't really know the answer but a compression test would be the obvious solution.

Good thought but a compression test won't give you the compression ratio, The only difference was a change in the height of the squish band on the piston giving a lower compression ratio but helpfully the critical piston measurement is missing from the wiki, even if I did wait to take the piston out and measure it.

I can't clearly make out the block writing next to the sump with the engine still in the car. I was hoping to identify it before I took it out.

I thought I had a Low Compression 6K but the throttle body vacuum is wrong for that. It may be I have one of the last of the High Compression 6E converted to Motronic 1.3.

I was hoping someone may know what other changes happened when the engine went 6E HC ot 6K LC other than piston, throttle body and Motronic version.

Post Wed Aug 14, 2019 11:20 am

Well I have got to the bottom of identifying the engine by attacking the number plate on the bottom of the block. Turns out it is an early 6E low compression. Not ideal for what I want to do but there are ways around it involving bits from a 6K.

I am still at a loss as to the difference in throttle body design. Some have two pipes going to the servo with a (three way non return valve) and some have one pipe (with a simple in-out NRV)

Curious to know what the purpose of the two pipes is. It is not the change from FL/PFL, HC to LC or motronic 1.1 to 1.3 because FL 325i Low compression 6E motronic cars have both designs.

Post Wed Aug 14, 2019 7:03 pm

K-katalyser

Post Wed Aug 14, 2019 7:23 pm

sweep wrote: ↑
Wed Aug 14, 2019 7:03 pm
K-katalyser

No can't be that, The 25 6K is the early high compression engine from a chromie, way before the cat cars here. The FL cars that had emissions kit had the later 25 6E engine I'm sure of it.

I know what they are just not all the differences between them (apart from pistons)

Still unsure why some throttle bodies have 2 servo outlets and others have 1.