Which one to Turbo?

[clyde20]

Hi Guys....and girls if any

I have a '86 525e and want to do an engine swap and turbo it. I am stuck between an m30b35 and m50b25.

- Which one can take more boost in stock form?
- Which one will be more reliable ?
- Which one will work out cheaper including maintenance?

Thanks

[turbodan]

Nothing wrong with the M20, but between your two options the M50 is the only choice in my opinion.

[jodystevens]

Nothing wrong with the m50, good engine and fairly reliable but the m30 is a real workhorse and dead reliable.

[turbodan]

M20 or M30 is pretty much a toss up. Boost makes up for the difference in displacement, it just depends on what kind of personality you're looking for. The M30 is a midrange motor, the M20 likes to rev. My B27 made peak torque from 4000 RPM through about 5200 and peak power at 6400. It pulled all the way to 7K. The M30 can be made to rev too but with the stock head and intake manifold it is not very eager to do so.

Since the guy already has an M20 in the car I can't imagine going through the trouble to swap in a slightly larger 12 valve motor. The M50 takes a big step forward in cylinder head design and comes with coil on plug from the factory. Big perks there. Either an M50 or M20 would be much better on fuel than an M30, turbo or not. Between all three motor, all stock, the M50 has the highest HP capability. 24 valves and modern combustion chamber design is the big advantage.

[Shadow]

m50 for mpg, m30 for power.