It really depends on what you want.
It's easy enough to select the correct turbo(s) for an engine once you've decided on how much power you want.
If you look at the compression ratio of the 325i, it's only 9.7:1 which is low by modern standards (compared to 10.4:1 for the Peugeot Mi16 Turbo engine I'm building) which means it can take a reasonable amount of boost without problems.
The fuelling and ignition can be the biggest problems if done wrong, hence the mappable ECU and session on the rolling road to get it all perfect.
Intercoolers are dirt cheap on e-bay (around £40 for one of the excellent Cosworth ones).
Also, for a daily runner, forged pistons are pretty useless due to the excessive piston-bore clearance required which means you need to start up and warm up before you can drive away, further lowering your efficiency.
Then there are factors like lowering the CR unnecessarily wil drastically reduce your fuel mileage, whether on or off boost.
Not including engine prep (by which I mean getting the lump up to a good, standard condition) you can easily build a very effective low boost system for around £1500 which buys you an extra 70ish bhp (at 6psi) taking the output of a 325i up to a meaty 240bhp.
It's tempting no?
More power, turbo style
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GT6-M3 wrote:
use, knock sensor for that full boost moment & ya ya ya aye tell you what why not just buy a 540 manual/M5/M3 & have done with it?/