E30 Zone

hey guys, this will be my first post on the forum. im interested in building a stroker motor to get my hp up. i have a 85 323i with a m20b25 conversion in it. i was thinking about a 2.8L build. can anyone tell me what exactly will be involved in a build like this and just so you know i am a apprentice mechanic so i will be doing most of the labour myself.

i was told you need a m52b28 84mm crank, eta rods and my b25 pistons will work. what else is need for the build or what needs to be modified?

my car currently has headers and sports exhaust, 19lbs injectors, stand alone microtech computer and a k&n pod filter set up so im ready to do the engine now and if in some way it helps i still have my m20b23 engine sitting at home.

Have a good rumage through the engine conversion section.You are looking for recent threads by temple30 and jazzman.Both detail 2.8 builds. Also have a look at andyboy's sticky on 2.7 builds. If you get stuck,let us know!! And post up more about your build and it's home.Welcome to the zone,BTW.

Get your 323 block bored out to fit the 2.5 pistons.
You can use the 323 rods.
You will need a spacer for the front of the 2.8 crank.

Get your 323 block bored out to fit the 2.5 pistons.

i have a 85 323i with a m20b25 conversion in it

must read better

welcome to the zone, essentially a 2.8 is a M20 B25 (325) block, pistons/rings and head, A M52 B28 (328,528,728) crank, M20B20 (320) con rods. Then you must machine a spacer to fit the M52 crank so the front oil seal sits in its place, this is fairly easy as you can use the old 2.5 crank as a guide and i even believe you can use the 2.8 crank pulley machined down.

Then basically bolt it all together (dont forget new stretch bolts for the con rods), a head skim cannot hurt but best news is no need for vernier pulley set required in 2.7 build as the timing belt is unchanged

I am also collecting parts to build this engine was gonna do a tech article on it once i get round to it

mrlee

mrLEE30 wrote:

Get your 323 block bored out to fit the 2.5 pistons.

i have a 85 323i with a m20b25 conversion in it

must read better


mrlee

Who must read better ?
He says he still has the 323 engine at home.

ok cool, so i will cruz with my m20b25 and i can use the b23 to build my motor, then swap heads when im ready.

so if i got this right ill bore the b23 to fit my 2.5l pistons, use the 2.3 rods(will these rods still create a 2.8L engine) and swap my crank which will require a sleeve to be made and the timing belt pulley to be swaped. give it a head reco with a schrick 284/272, new valve springs and a shave and port and ill be on my way.

will the the new crankshaft require different big end bearing and what about the rear main seal?

also ive already started looking up those threads on engine swaps, i found threads from jazzman but not temple30, maybe his name was spelt incorrectly but ill try check again. thanks for any advice guys and ill be sure to take plenty of pics through the built and post a project thread.

i dont know if this is a dumb question or not but would would happen if you used the b23 crank and rods with the b25 pistons and head, would it be to much stroke and smack the head?

http://www.e30zone.net/modules.php?name ... 78&start=0

http://www.e30zone.net/modules.php?name ... 09&start=0

b23 rods are same as eta ones 130mm (not that these affect the displacement anyway)

looking at relative pin positions

b23 crank throw is is 76.8/2 = 38.4 mm + rod 130 mm = 168.4 mm,
b25 is 75/2 = 37.5 mm + rod 135 mm = 172.5 mm

so the b23 option has the top of piston 172.5 - 168.4 = 4.1 mm down the bore compared to m20b25

its common to use eta 81mm crank and rods with m20b25 piston and head and that puts you 2mm down the bore and ~8:1 CR with late m20b25 pistons, so the b23 crank which has a 2.1mm shorter throw than the eta 0.5*(81-76.8 ) + the 2mm = 4.1mm as above

So its a no no without different pistons