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I have a early 1979 US 320i with a tired m10 and 4spd. I want to swap in a m20 motor and 5spd transmission. I found a euro m20b27 motor with a blown head gasket for cheap. It is supposed to be the early 11:1 compression ratio. I know that in it's original form it has around 120ish HP, which is sufficient, but we always want more. So my thoughts are this, run the stock bottom end, use an 885 325i head and intake with motronic 1.3. Any of you euro guys that have actually seen and worked on one of the high comp. motors (not just heard of) know if this is a good setup? If not, what would you recommend for getting a little more power out of this particular motor? Ideally 180-200 hp would be nice, however I think anything above 150hp would be satisfatory. Ultimately the car is being setup for spirited driving on the back road twistys with a pack of e28's. So I'm not looking for a 500hp speed demon dragster, just a really spunky daily driver that I can have some good fun with on the weekends.

You can only use the 885 head on the 27 6 kb bottom end (129hp) with the 325i stylish pistons. The 27 6E A (122 hp) engine has the flat pistons and that can only be used with the e21 type "200" or e30 type "731" head.

So to begin it all depends wich bottom end you have there.

To build the high comp. engine you are talking about you need to have the 27 6 kb engine with 885 325i head but you have to ditch the original eta pistons for 1988 onwards 325i pistons .. shave 2mm from the bottom end and use an adjustable cam gear .. rocker arms and crank can be used from the eta bottom end .. if you rework the cilinder head 210hp is possible with a comp ratio of 10.6. If you use the standard pistons with the same head mods 195 to 200 hp is possible with a comp of 9.4

For more info you can also use the search button on this forum plenty to find about 2.7 strokers

Gerrit

Am i right in thinking the 320/6 had the 27 6e a bottom end? If this were to be mated with the 731 head and 38 dgas weber would there be any performance increase or would you have to get uprated cams to make the most of the bigger head?

The motor is originally out of a euro 525e e28. What was the original engine management?

Also, I want to keep the a/c system functional on the car. Living in Texas, it is a necessity. I pretty sure that the m10 compressor will not bolt up the the m20 block. Can a m20 compressor be bolted up and the original lines be reattached? Not certain if there is a major difference between a/c lines from m10 and m20. I should add that I don't know jack about working on a/c systems. The current system has already been converted to r134.


Another question while I'm thinking about it. Will a stock e21 m20 drive shaft fit, or will I need a custom length shaft?

You need the m20 box and the m20 prop. The m10 gearbox is way shorter in length.

how do you meassure the 2mm which needs to be milled off the top of the eta block?

Take it to an engineer shop and have them machine it off.

You can use an 885 head on the stock eta bottom end. With 11.0:1 pistons you will get a CR of 10.0:1. Pistons will not hit the valves with a stock cam. You do not have to use the 325i pistons and deck the block. You may see 180 hp from this build, I have around 170 hp from a budget stoker build using the later 10.2:1 CR eta pistons with 325i top end bits.