my stroker recipe: good/bad?

[guibo09]

so here is my plan for a 3.0L (2989cc) stroker. i would like to know if anyone has done it, or if they foresee a problem.

- m20b25 bored to 86mm with 885 head with some porting/polishing + valve job, MM beehive springs, new OEM rockers
- 85.8mm forged crank from S50B30 US (any other source for these?)
- 140mm rods from M50B25 vanos (any other source for these?)
- custom 11:1 or higher forged pistons with stock piston shape (most likely JE) 86mm
- 288 shrick cam (i will calculate the proper dynamic compression ratio based on cam for 91 octane)
- MSII
- exhaust/intake tbd.

the goal is to keep reasonable stroke/bore and stroke/rod ratios that are tested and true.

thanks for any input!

[SpecM]

I think 140mm rods come from NON-vanos m50s, but I'm not 100% sure

[guibo09]

I think 140mm rods come from NON-vanos m50s, but I'm not 100% sure

here is one source that says otherwise, although reliability is questionable:

http://www.bmwe21.net/forum/viewtopic.php?p=48743&sid=95528f7686b0eeee65beec5e26322e64

and another more reliable source:

http://www.turrisimotorsports.com/race_team/bmw_specifications/engines/M50B25/M50B25.htm

also just calculated wrist pin position relative to the block (in mm):

OEM: 97.5 bdc to 172.5 tdc
Stroker: 97.1 bdc to 182.9 tdc

so with the 140mm rod, there is no risk of the piston skirt exiting the block at the bottom of the stroke. now it remains to see if is possible to trim enough of the top of the piston to clear the head. im guessing bumping up the compression will help with this.

[nando]

AFAIK all M50s have 135mm rods. Maybe the M42 has 140mm? in any case MM specs a specific rod for their pistons and I think it's even longer than 140mm.

sounds like a decent build though!

[e30this]

No vanos M50s have 140mm rods.


rod lengths:
M50B25TU: 140 mm
M50B25: 135 mm (non VANOS engine)
M52B25: 135 mm
M52B28: 135 mm
M54B30: 135 mm
M20B20: 130 mm
M20B23: 130 mm
M20B25: 135 mm
M20B27: 130 mm

[nando]

ah, it's the choked out M50B25 "puke update" motor that has 140mm rods.

I think it would be easier to use 135mm rods and just have the pistons made to match them.. the both the S50 and S52 use that same length anyway.

[guibo09]

ah, it's the choked out M50B25 "puke update" motor that has 140mm rods.

I think it would be easier to use 135mm rods and just have the pistons made to match them.. the both the S50 and S52 use that same length anyway.

i think if i source the s50 crank and it comes with rods ill probably just stop my search there and use 135mm.

but if i do fall onto 140mm, i think i would be tempted to use them. a longer rod is always better unless they are much heavier than the 135mm. anyone have weight specs for the 140mm? i know the 135mm weigh 565g.

[SpecM]

ok, I've been wrong before

[Jesse30]

135mm rods will work fine just have your pistons made to work with them. 140mm wouldnt be worth much more effort.


i hate plugging their parts all the time but i've had a lot of time looking at the rods that ireland sells. get their 135mm forged rods. affordable and they get shit done. :D

they may even sell a 140mm if your really really keen on that idea.

[asubimmer]

No vanos M50s have 140mm rods.


rod lengths:
M50B20: 135mm (non VANOS engine)
M50B20: 145mm
M50B25TU: 140 mm
M50B25: 135 mm (non VANOS engine)
M52B25: 135 mm
M52B28: 135 mm
M54B30: 135 mm
M20B20: 130 mm
M20B23: 130 mm
M20B25: 135 mm
M20B27: 130 mm

[e30this]

140mm M50B25 vanos rods on the left and 135mm M54B30 rods on the right.

[guibo09]

thanks e30this for the killer photo!! :-D

yeah looking at the photo i can see why the 135mm are more popular, the 140mm look pretty much like the stock m20 rods, thick and heavy. i wouldnt be suprised if they are even heavier than the m20 rods.

so i guess i will go with 135 rods, hopefully i can pick up a crank and rod set from a s50b30.

[e30this]

I know a guy with a s50 crank, Im not sure on shipping to canada though.
I will talk with him.

[guibo09]

I know a guy with a s50 crank, Im not sure on shipping to canada though.
I will talk with him.

its gotta be from the 3.0L though, the s50b32 crank is 91mm i believe.

[nando]

I think it's closer to 89.6mm. but why are you so set on the S50 crank? the S52 crank will work too.