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Building a 2.7 engine for track

I wanted a slightly more powerful engine in my track racer together with a manual transmission (it used to be an Automatic!), so the use of the 2.7 liter block I had laying around was a perfect choice. I also had an E30 cylinder head laying around, which is equipped with larger intake ports that will help the engine flow better.
Read on for the details and the process of building this engine!

The theory behind 2.7 engines
In the E21 chassis, M20 (small-six) engines could be had in two flavors: carburated 2.0 litre (122HP) and fuel-injected 2.3 litre (143HP). While these engines offer enough power to enjoy yourself in an E21, it's nice to have just a little more when racing on a track.. There are a few options to increase power output of an M20 block, but I decided to go with the most cost-effective solution: increasing displacement.
A complete solution would be to drop an M20B25 engine from a 325i E30, which would be a straightforward swap (everything fits save for a few small issues). However, I would have had to find a complete 325i engine and this would not be as cheap as building my own stroker from various parts I have laying around.
There is a special version of the M20 engine, the M20B27. That's right, a 2693cm³ block with 84mm bores and 81mm stroke. However, all versions of this engines were tuned for fuel economy, and they all developped around 120-125HP, which puts these 2.7 variants in the same power category as the 'regular' 2.0 litre M20. However, thanks to their displacement advantage, these engines had lots and lots of torque.
The trick is to use a 2.7 shortblock and drop a regular cylinder head with regular camshaft to unlock some 160-165HP. This page is by no means an attempt to guide you through the descisions and different 2.7 set-ups that are possible, I did my own research and made my own conclusions before starting the project.
Here is the list of engine parts selected from various models:
- Shortblock from 528e
- E30 323i cylinder head
- 320/6 intake manifold
- Solex 4A1 carb from 728
- Ignition setup from E21 323i
This particular setup will result in a 11:1 compression ratio. I plan to use the stock dual 323i exhaust, a regular 323i gearbox (with mechanical speedo outlet) and the rest of the 323i parts (cabling, cooling system, etc.)
As I said, with this setup I should be good for 160HP and 240Nm torque (these are conservative estimates).


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