Eta vs 324 2.7 Crank

[87mtech27]

Had a 324TD 2.7 crank on my watchlist but bleeding forgot all about it

Anyway the question I want to ask is which is the better crank to use for a 2.7 stroker?

Alpina used diesel forged cranks and Hartge most likely did as well due to them being stronger than the eta cast cranks despite forged cranks being heavier for the very reason of withstanding higher revs and not breaking under load.

However, rumours from across the pond suggest the diesel crank is prone to snapping, is this true?

[jimbom30cab]

Not sure about the diesel crank but i've heard many people who have used the ETA crank and i've never heard one story about problems with it

[87mtech27]

Eta cranks do appear to be safer, just not sure why the likes of Alpina would use forged cranks from M21 engines. I guess the second hand diesel cranks live a harsher life so already fragile or people abuse them more in strokers whereas those using eta cranks are more careful.

BTW does anyone know is 325i crank is cast or forged?

[reggid]

M20b25 is a cast crank

[87mtech27]

[jimbom30cab]

A light flywheel on a ETA crank really wakens up the lump, it's quite a rev happy engine.

Also worth thinking about lightening and balancing the crank, i think Simon13 did this to the bronzit and it was a little flyer.

[87mtech27]

Lightening and balancing is a must IMO if everything is out for a rebuild.

Iirc Si13 chucked in M5x 2.5 crank and rods into the M20 as they was lighter? The engine would definitely feel more active and alive.

[steve_k]

If you are going to use an M5x 2.5 crank & rods then get the block rebored by about 1mm & use some +1mm pistons to give a cc of 2554 not a hig increase but a nice improvement over stock.

[reggid]

Why would you put a 2.5 crank and over bore when you can put a 2.8 crank and stock 130 rods and b25 Pistons

[steve_k]

Why would you put a 2.5 crank and over bore when you can put a 2.8 crank and stock 130 rods and b25 Pistons

there is that but it all depends on what you have to hand & what you want to do.