M20 cylinder wall thickness question.

[Coyote_ar]

Hey guys, im trying to figure out whats the largest overbore i can have on my block.

My car is a 1984 320i, but the block was casted in 1983.

I measured the wall thickness through the water pump hole, and it measured 6mm.

If someone has a 325i/325e block laying around, could you please do the same measure?
Just stick the caliper through the waterpump hole, measure the distance from the wall to the front of the engine. Then measure the distance from the cylinder to the front of the engine, and then substract for the difference and that should be the thickness.

Im trying to determine if going for 84mm is too much (that would leave only 4mm on the walls).

I know some guys do the 84mm overbore on the M20B20 blocks, but those seem to be a newer cast, and have thicker cylinder walls.

Anyway, i would really appreciate if someone could measure that, regards.

[Simon13]

84mm is the standard bore size on 325i/e engine

[ross2009]

yeah seems to me the most simplist thing to do and will be cheaper is put a 325i in it ?!?!? no

[Coyote_ar]

Not a cheap option to change the engine down here, actually i will be spending almost 4000usd on the M20 and thats the cheap option

I must figure out how much overbore i can pull out.

[HairyScreech]

im sure for that kind of money someone here would ship you a 2.5 block.

[Coyote_ar]

its ilegal to import used engine blocks

and even if you get it here, you cant get it on the car registry (yes, chasis number and engine block number are part of the car registry).

so im basically stuck with this block, given that, i would like to see how far i can pull it before i screw it up.

[Simon13]

84mm, lots of people have done it here. Never heard of a problem either

[Coyote_ar]

yeah my logic behind this is that on 84mm blocks, people say its safe to overbore them up to 86mm.

And given that cylinder center distance on M20s is 90mm, if you overbore to 86mm, you cant have more than 4mm of wall thickness there.

Then if thats the case, and with 4mm walls you are ok, i can go for 84mm.

Well, if 4mm is to thin, i guess i will find out, specially since it will be a boosted M20B28.