m20b25 Head Questions

[Dooin180]

Hey guys this is my first post so here it goes.
I have a question about the m20b25 heads, I am buying a new head and i found a good deal on ebay for a 885 head. I am looking to swap it on thinking my head was already an 885. well its not, its a 731 head. Im mainly wondering if a direct swap is possible and if not what to do and how much of a pain is it. And i have tried looking around for an answer and there was one post here that didn't give a strait answer and it was a different car; and then i found this which just confused me more. http://www.e30zone.net/e30zonewiki/index.php/M20#Head
Thank you for your help. :D

[AwakenNoMore]

M20 sub forum here should help you, here's a thread with some info:

http://www.r3vlimited.com/board/showthread.php?t=182216&highlight=head+differences

[jeffnhiscars]

If your car has an eta engine the 731 head is a great NA option cause it gives you higher co pression than an 885 head. The other possibility is that you have an m20b23 engine which is where the 731 was born.

[Dooin180]

Well That kind of helped but not quite.

To put it as simple as possible. If i take a completely stock 1990 325i with m20b25 engine with 731 head, can i put the 885 head on and start it right away?

Is it a strait swap essentially?

[AwakenNoMore]

m20b25 is supposed to have an 885 head so yeah, its a direct swap.

[digger]

Many people put the 885 onto the ETA but it is also 84mm bore.

The question of whether the 885 head with its O/S valve fits directly onto a M20B20 or M20B23 block both of which have 80mm bore or whether the bigger valves hit the top of the smaller bore I’m not 100% sure. It would be very close, you could modify things to get it to work if you really really had to, but why not just get the right head.

[Dooin180]

Well originally i believed i was getting the correct head. (not knowing there was multiple)

So now my predicament is whether or not it really is an m20b25 engine just with a swapped head.

I pulled this from the block (13 m87) if any one knows if there is a way to decipher this or if it will even help me figure out what engine i have is greatly appreciated.

And also thanks to all of you who have responded.

[digger]

are there any codes like 25 6k 1 or 27 xx x?

what does the rest of the engine look like?

if your head is 731 it is unlikley to be a m20b25 as that head wont fit directly on due to piston and combustion chamber interfence

could be a ETA bottom end, if you have a little camera scope thing have look into the spark plug hole

post up some pics of the intake manifold, coolant system, fuel system etc there might be more clues

[Dooin180]

Absolutely, I will get some pics up tomorrow when it is light out.

[digger]

i sat a 84mm gasket (~85mm ID) onto a 885 head and there is about 3mm clearance to the valve edge. with 80mm bore there would be 0.5mm clearance which seems too close to risk

[Dooin180]

ok so i got pics but they are to big to upload and i dont have time to fix it right now.

but i found two things that may help.

first I found these on the side of the block (20 6K A) and below that (23444302) hoping these may tell me what block it is.

second the car had a spare ecu in the trunk when i bought it. i kept it still and was wondering the difference between that one and the one in there. found nothing at first.

But now i have looked again and there is the beginning of the VIN number on one of the stickers. The one that is out of the car has the same VIN as the car itself. whereas the one in the car now is different. they are both Bosch motronic 173.

[digger]

That's a BMW m20b20 (20 6k A is the give away, 20 means 2.0L 6 means 6 cyl etc) that did come with a 731 head. 80mm bore 66mm stroke. big port 885 head on teeny-tiny engine = not so much fun

[Dooin180]

Awesome! thanks for all your help. i guess that solves this then. Till next time.