Crank srokes & Rod lengths - fill the blanks!

[Sean]

Ok, I need some facts that I can't seem to find out.

Here's a list of cranks, and the strokes I know. Can anyone tell me if all the below is correct?

Cranks
M20B25 Crank --------- 74mm --- Cast
M20B27 Crank --------- 81mm --- Cast
M20B27 Diesal Crank --- 81mm --- Forged
M52B28 Crank --------- 84mm --- Forged
S50B30 Crank --------- 86mm --- Cast
S52B32 Crank --------- 89.6mm - Forged


Rods
M20B25 Rod --------- 135mm --- Cast
M20B27 Rod --------- 130mm --- Cast
M20B27 Diesal Rod --- 130mm --- Cast
M52B28 Rod --------- 135mm --- Forged
S50B30 Rod --------- 135mm --- Forged
S52B32 Rod --------- 135mm --- Forged


The reason I'm getting all this is because I'm trying to find the best pair for a stroker. I want to go either 86mm or 89.6mm stroke - yea huge - but with that I'm going to need longer rods. Has BMW made any rods longer than 135mm? I kind of want to go with 140-143mm to help the rod stroke ratio - if that's even possible?? (am I just gonna run out of room in the combustion chamber?)

The other question I have is, between the S52 and S50 did the cranks change? I'm under the understanding that the S50 has a Cast 86mm stroke cank and the S52 has a Forged 89.6mm stroke crank?

Help me out! :)

[Sean]

Found this page: http://www.bmwworld.com/engines/m52.htm

Looks like the M52B20 has a rod length of 145mm.

Pair that with the S52 crank at 89.6mm stroke

If that works in an M20, you'd have a killer rod/stroke ratio and a 3.2 liter motor! (right? - or am I thinking wrong?)

145/89.6 = 1.61 r/s ratio - not too bad actually

Anyone know where I could get ahold of those rods?? lol Can anyone tell me if that would work in the m20 block with massively modified pistons?

[plotfi]

bump

[whodwho]

bump

What part you are looking for information on?

Here's a list of cranks, and the strokes I know. Can anyone tell me if all the below is correct?

I know this is an old thread...

M20B25 had a 75mm stroke

Some more strokes to add to your collection
66 mm (2.6 in) (M20B20)
75 mm (3.0 in) (M20B25)
76.8 mm (3.0 in) (M20B23)
81 mm (3.2 in) (M20B27)

M54B22 had a 72mm
M54B30 had an 89.6 as well

M50tu had 140mm rods
M52tuB20/b25 had 145mm

Not sure you could use 145mm you would have a tuff time putting 140mm rods with an 89.6 crank, MM uses a 135 & 138mm(not sure I think a smaller pin) rods with 89.6 & 86mm cranks with their kits.

I am using 135mm with a 89.6 and it creates some challenges with fitting the rod small end between the pin and head of the piston(had to be milled for room). It also impacts the ring pack, the pin is up past the oil ring

[plotfi]

stroker

I am wondering why S52B32US with identical Rod/stroke ratio might be more long lasting than MM 3.2 m20 engine. There is a difference of .4 in bore diameter.

What part you are looking for information on?


I know this is an old thread...

M20B25 had a 75mm stroke

Some more strokes to add to your collection
66 mm (2.6 in) (M20B20)
75 mm (3.0 in) (M20B25)
76.8 mm (3.0 in) (M20B23)
81 mm (3.2 in) (M20B27)

M54B22 had a 72mm
M54B30 had an 89.6 as well

Not sure on the 145mm, but a M50tu had 140mm rods

Not sure you could use 145mm you would have a tuff time putting 140mm rods with an 89.6 crank, MM uses a 138mm rods with kit.

I am using 135mm with a 89.6 and it creates some challenges with fitting the rod small end between the pin and head of the piston(has to be milled for room). It also impacts the ring stack, the pin is up past the oil ring

[digger]

I am wondering why S52B32US with identical Rod/stroke ratio might be more long lasting than MM 3.2 m20 engine. There is a difference of .4 in bore diameter.

only difference is going to be piston design such as shorter height, slitted (weaker) skirt that MM use to package it in the block, slightly larger cold clearances due to forged material vs cast and proper assumptions of piston growth (temp profile) during machining/manufcturing leading to more wear on pistons and bores particularly when engine isnt warmed up. i think an OEM S52 would last longer than MM if street driven as it had more engineering go into it.

i dont think the bore size has much to do with life, as the amount of meat in the walls is reportedly similar (according to MM) though i dont have an S52 block to compare. when you go thinner the walls move around more and the rings arent going to seal as well. that's why with big boost or anything like that you might even lose more through rings on power stroke than you gain from the extra CC.

i do wonder if the S54 and S52 use a slighty different material in the block though

i thought the S50B30US stroke was 85.8mm not 86mm ?

plus modified crank nose allows some diesel cranks to be fitted with 90mm stroke e.g. M57B30

and to answer the 2006 question you cant use a 145mm rod with 89.6 stroke in an m20 block without using a deck plate