High compression

[ed325i]

Is this a early high compression piston ?

[Ant]

from the valve cutout depth I'd say yes, but the skirt is shorter than normal.

KS or Mahle ??

[ed325i]

Mahle.
Its got + 83.98 stamped on the top

[e21Jason]

Hi

Could the skirt be mmodifed to clear the rods in an early 2.7 conversion

Jason

[ed325i]

The engine is not a 2.7 as it has the longer 2.5 conrods.

[e30world]

use that as bin

[chu346]

use that as bin

[tristan325]

use that as bin

Seems to be a regular response to his posts.

[kam-325i]

That looks like a low compression piston to me..........

Is the top of the piston "dished" in ?

[ed325i]

That looks like a low compression piston to me..........

Is the top of the piston "dished" in ?

Yes its dished, is the high compression not ?

They came from an engine which had no engine number so I cant tell that way, the car was running a early injection system with a 073 ECU.

[kam-325i]

My 325i engine is marked as the "Low Compresion" engine, and it has those type (the dished) of pistions fitted.

AFAIK the higher compresion pistons have a flat top.

Like this......

[Simon13]

i've got some late 8.8 pistons and Alpina pistons also, and the one pictured looks different to them

[kam-325i]

Is this Fact ?

Flat top Pistions = High Compression.
Dished Pistions = Low Compression.

Pic below is of my Low Compression 2.5, you can see the dish in the pistons.

[ed325i]

Mine has got a bigger cut out for the valves.

[Ant]

top pic is a high comp piston

lower is a post 88 8.8:1 CR jobbie.

KS/Mahle pistons do vary but all M20B25 pistons are the same basic shape, flat tops in B20 and ETA/323 only

THAT, is a fact

[kam-325i]

Mine has got a bigger cut out for the valves.

Thats a low compression piston. The same as fitted into my block.

[ed325i]

The piston with the bigger cut outs runs closer to the valve making it high compression. Thats what I think ?

[kam-325i]

Please dis-regard all my previous posts in this thread....im getting confussed !!!!!

The piston with the bigger cut outs runs closer to the valve making it high compression. Thats what I think ?

That makes sense,

But my engine is marked up as low comp and the pistons look the same, with the deep cut out for the valves......

[Ant]

given that were looking @ pix, not dimentions,I still vote higher CR, reasoning...... the deeper cutouts are there because the piston crown height is taller on the High CR pistons, and thus relieved more to clear the valve on full lift.

the lower CR pistons have less of a beak on the frontside, the overall shape is similar though, with a corresponding reduction in the valve pockets, the head is unchanged High or Low comp, all have same dims and valve sizes.

the only surefire way is get the part number from inside the skirt and match it up.

the 885 heads are oddball to the B25( and super Eta) because its a hemispherical combustion chamber shape, the piston "bowl" completes the shape.

[kam-325i]

So, could there be high comp pistions in my block ?

[e30world]

ur want help?????

[kam-325i]

ur want help?????

eh ?

[ed325i]

So, could there be high comp pistions in my block ?

What is the engine number on the block ?

84B25E is the 9.75:1 CR variant 84B25K for 8.8:1

[kam-325i]

mines defo stamped as the low comp block....... B256K

[maxfield]

ur want help?????

WTF!!

All of your posts/threads make no snese what so ever!!!

Buck your ideas up half of the zone must be pissed off with all your postss!

Sorry to rant on this thread but his posts make no sense what so ever

[snoops]

i know they dont make 'snese' do they?

[maxfield]

Bully