right...I did a fairly large writeup of this a while back but can't find it.
firstly, principles. this exercise does not aim to get omfgzorz mad bhp yo!!! nor does it aim to chase peak bhp figures.
what we are going to do is increase the efficiency of the engine, making it produce more torque over more of the rev range. this makes it more driveable and (because bhp is ultimately a function of torque and revs) makes it produce more power.
secondly, blower choice. for a 2.0 I'd go for an eaton m42 from a BMW mini or merc 230 kompressor. this will be fine for up to 10psi of pressure. it is a positive displacement supercharger which means that it outputs a set volume of air for each revolution...note: not boost. boost is a bad thing. nasty, nasty boost.
thirdly, cooling. you can go up to around 6-7psi without the need to cool the inlet charge by the use of either an intercooler or a chargecooler. above this you will need to either find a way of routing the blower outlet to an intercooler then back around to the plenum chamber or find the space to package a chargecooler on the inlet side of the engine (Jag v8 chargecoolers are cheap and plentiful...use one side and sell the other
).
so we've got the basics out of the way; what we are wanting to achieve, what we will use to achieve it and cooling...
now you have an option. do you want to stay with 6psi, leave out the cooling side, stick with stock internals and get an engine which doesn't really suffer ay greater wear and tear than a stock engine?
...or do you want to go for 9-10psi, an intercooler or chargecooler, risk the chance of the stock internals letting go, upgrading the internals and spending more money for an engine which will ultimately be more powerful?
with either choice, you will need to look up the map for your blower on the eaton website and use it to work out what pulley ratio you need. but what engine rpm to use as a reference? well the easiest way to do this is to find a point in the rev range where you feel the engine pulls hardest.and use that...for a bit more accuracy, get a rolling road printout and find where your peak point is in the torque curve.
mounting and plumbing...you will need to find space for the blower to go where it won't foul steering components and so on. if I recall correctly, the intake is on the left hand side of your engine bay...so you should be okay mounting it under the plenum. once you have decided your location (remembering that you need a clear belt run to the crank pulley), you will need to mount the blower solidly to the engine. try and triangulate mounts for stiffness.
you will need adapter plates for the blower inlet and outlet. CR500DOM on the
www.retro-rides.com forums makes these (expertly CNC'd. well worth it...and if you haven't signed up, do it. its a great resource and I'd love to see a build diary on there
). these plates basically turn the odd-shaped inlet and outlet into standard-sized circular ports.
after that its 'simply' a case of mounting everything up, getting it plumbed up and running with your ECU.
on the intake side of things, you can either retain the stock TB and plenum, replace it with a bigger TB (328?) or replace the whole setup with an ITB rig...with a six, I'd go for two sets of TBs from a triumph triple and a custom plenum. you should be fine for flow with them until you start nudging 400bhp-ish.
all said and done, though. I would simply drop a 535i engine in. 211bhp from the word go and then fit a blower or turbo in the future for 300+bhp.
*n
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