Diesel crank... worth it?

[Reynard38]

I am picking up a 2.7 in the morning. I have a spare i head. I intend to totally rebuild the 2.7 with the correct components to make a solid stroker.
Question. Considering the limitations of the 2 valve head is it worth installing a forged TD crank? I need to keep the motor emmisions legal so any cam much over a 284 is out. I am thinking that since this engine will peak out at around 6000rpm max the standard crank should be up to the task.
Opinions....

[BimmerToad]

Metric Mechanic doesn't feel the TDS crank is worth it

check out

http://www.metricmechanic.com/pdfs/M20_Engines_Brochure.pdf

page 12

[SA E30]

If u can get it, it will be worth it, just as it's stronger than the eta crank... which is just a failsafe, as the Eta crank is plenty strong enough.

[Swede-E30]

At the time that I built my engine I was told over and over again that the diesel crank was the way to go. I figured if I took the time and money to rebuild/build a somewhat of a performance engine I didn't want to do it all over again.
When building my engine I actually ended up bying a brand new crank, I think it was $800 bucks or so. They are harder to find used, and will most likely need a visit to the machine shop before dropped in.
If you plan to go with a 284 cam you shouldnt have any issues passing emmissions, I didn't.
When dynoing my engine it didnt frop off until it hit 6300rpm and that was using a 284/272 cam. I am sure you will be ok using the eta crank though. They are cheap, easy to find and many people use them.
Good Luck!

[CarsSuck]

swede: how power did you end up making with that cam in the 2.7?

[Swede-E30]

188.8rwhp and 181.5rw lbft. I am running 10.2:1 compression so it may vary depending on set up.

-Martin

[nando]

diesel cranks are HEAVY

if you want forged, go with the M52B28 crank. it's lighter and stronger than either of them, and has another 3mm in stroke to play with. they should also be easier to find.

in short, the diesel crank is a waste of time (and money) if all you are building is an N/A stroker. for a regular stroker, all you need is a good e crank.

[volgapower]

yes diesel crank is heavy, but heavy duty as well...
my friend installed it and works like swiss watch...
he has approx 210bhp now on his 2.7

[Swede-E30]

I agree with volgapower.

Both Eta and diesel cranks were around when Alpina, Hartge and Racing Dynamics built their engines in the 80's. They all used the diesel crank.
Cut once measure twice that's my thing. I would hate to do it all over again.

[mrsleeve]

Like stated above, if all you are doing is a N/A stroker then a good ETA (cast) crank will be fine. If you plan on forced induction or NO2 in large amounts then the TD might be the better choice. I have 1 of each in the basement an you guys got me wondering, the TD is a few LBS more

ETA = 50 LBS
TD = 54 LBS

[nando]

4lbs is a lot of weight when it comes to the rotating mass

[JJGBMW323]

I knife edged my 524td crank.
I also lightened my 325i flywheel down to 11 pounds.

Knife edgeing and race ballancing my td crank cost $500 at the machine shop.
The bottom end that i have - the previous owner who built it, used an eta crank that i am removing...and installing the knife edged one.
Its a 2.8 stroker that uses MM pistons, and 325i rods and has been bored to 2.8 liters and built by Tyler who used to work at Bav Auto.

Not to sure what the weight savings is, but I got lucky and found a 524td at the yard, purchased the whole block and ripped out the crank for cheap.
There was another one at the yard, and I was going to save it, but it was crushed...

I have also heard that you can use a M50 crank or something as well,
but I fiqure what reinvent the wheel? Not to sure the diameter of the m50 crank is??

I also have a s50 crank, and may someday bump the displacement, but for the time being I am going to put the built engine into my 79 323i.

[nando]

M50 cranks have the same bearings as the M20. all you need is a sleeve for the front crank seal.

[mrsleeve]

4lbs is a lot of weight when it comes to the rotating mass

I know thats why I am gonna have mine balanced an lighted when I build my turbo motor, gonna take 4-6 lbs out of the counter weighting dont need it for a non diesel app. Turbo motors dont have 28:1 or more compresion ratios so why have all that extra mass if you dont need it but still get the strength of the forged crank.

[nefarious7907]

diesels are usually around 17:1 FYI

I agree with MM about the 524td crank, I would just go with an ETA one.