How do I build a 2.7?

[e21Keith]

I spent time collecting bits when I was into e30s but never got as far as actually building a 2.7.

These are the bits I actually have.

324d Crank and conrods
Cam kit with followers etc. new (not sure which one but it's slightly warmer, supposed to be the same as Alpenis)
6-branch manifold, not sure what this is off, e21, e30, LHD/RHD?

How do I go about building a 2.7, can I use the e21 323i bock and head or do I need to get myself a 2.5 from an e30?

Do I need to go Motronic or can I keep the e21 setup? I'd like it to look stock!

What else do I need?

[niske]

I also want to know, if somebody is done this earlier...
Can 320/6 or 323i block from E21 bore to 84mm like in M20B25?
I found conflicting informations on internet... someone claims that water cooling lines are too close to cylinders in earlier M20
and that is allegedly the reason why not to bore M20B20 from E21...

Otherwise, in my opinion, the best way is: M21 crankshaft, 130mm rods (320, 323, 325e), M20B25 block, pistons, head (885), electrics... and block need to be "shaved" for aproximately 1,5-2mm
also you can keep k-jetronic, I guess that is easier with 323i head (200) that gives higher compression ratio but less flow...

[uwbuurman]

M21 crank is to heavy, rather use the b27 one

[gerrit323]

2.5 block because you need the 84mm diameter cilinders or more easy try to find an early 2.7 122hp e30 eta block .. just bolt on the e21 head and it runs fine ..

[Duracel79]

Hi Keith,

I have built a few of these and there are many ways to go.

A Key point is you must use the pistons that match the head. 325 pistons with an 885 head or Eta pistons with a 200 or 731 head.
If this isn't followed you will either have:

ETA pistons with 885 head - Very low compression and possible valve to piston contact - pistons need valve cutouts machining to fix.
325 pistons with 200/731 head - major contact between piston and head - head combustion chambers need machining to replicate the 885 head chamber.

This is assuming the piston height has been corrected in the block.
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With the parts you already have, I'm not 100% what the length of the diesel conrods are but if they are 130mm they are useable.
You will need flat top 84mm ETA pistons to run in a 323i (200) head, I'd prefer using a 731 head as the chambers are the same but the ports are much better.

323i block can be bored out to 84mm quite easily. Best way to get a fresh bore rather than a worn 325 block that is not worn over the full stroke of a 2.7.
No need to skim the block down if you get ETA pistons.

I'd recommend a vernier pulley to time up the camshaft and ensure you get the best valve/piston clearance. Especially if you don't know the full spec of the camshaft.

This would are still work well with the std K-Jet if its working properly. There are Warmup regulators which allow adjustment which can help get the best out of the system.
Would help with the increased capacity.

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Best spec with stock (ish) parts would be

323i block bored to 84mm
Block deck machined down by 1.5 to 2mm
324d crank or ETA balanced
lightened & balanced 323i conrods
Early Pre87 (6E1) 325i pistons (new rings)
885 head lightly ported on the exhaust side
Vernier pulley to correct cam timing and get valve clearance

-----------------------------------

There are other variations such as the Super ETA available in the states which uses 325i style pistons in an 885 head but I doubt they are easy to come by.

Having said all that - If you could afford a set of new Forged pistons they can be specified to suit any head/conrod/block combination possibly giving the best of all worlds but they do come at a price!!

Hope some of this helps

Ben

[croma_man]

I'd only add to the Duracell spec :

port matching 885 head with the M20B25 intake manifold
288 Schrick cam
the very best thing that you can do to your stroked M20 is AFM delete and standalone ECU with pink injectors (currently in the making)

but this is already the "tuning and maxing out the stroked engine part"

[niske]

323i block can be bored out to 84mm quite easily.

Are you talking about early M20 block from E21?
Is that valid for 320/6 block too?
I'm asking you because there's opposit claims on e21.tricord.be

Thanks anyway!

[Duracel79]

323i block can be bored out to 84mm quite easily.

Are you talking about early M20 block from E21?
Is that valid for 320/6 block too?
I'm asking you because there's opposit claims on e21.tricord.be

Thanks anyway!

I've only bored out the 323i blocks, so cannot say about the 320/6.

Ben

[croma_man]

320/6 is not suitable for boring to the 2.5/2.7 spec.

[Duracel79]

Just to add, all the 323 blocks I have bored to 84mm have been post 1980.

Not sure if any earlier 323 blocks would be different.

Ben

[Jeroen]

I always thought the bare block for 320/6 and 323i was the same?

[croma_man]

I always thought the bare block for 320/6 and 323i was the same?

water passages on M20B20 and M20B23 prohibit the use of a bigger bore as in M20B25 and M20B27.

[Jeroen]

That's what I also believe to have heard

[croma_man]

That's what I also believe to have heard

I checked the pics in my topic, dont know for 100% sure, but on the pictures, the blocks look the same M20B20 and M20B27 (the water holes)...

maybe its just a internet theory that we all believed.

[Jeroen]

Could be, that's why I didn't post that thought at first, no experience myself.