3.0 stroker theory

[E46Twist]

Okay so I am still deciding between turbo, swap, and m20 stroker build. Last night I was doing some more digging and wondered if I may have found a good combo. I'll just shoot it S50 crank (86mm) m54B30 rods and pistons (135mm + 28.32mm). Now this would give you and assembled height of 206.32 which is just a little more than an eta and less than a m20b25. So pistons would need little if any shaving. I am guessing there is a flaw in my maths because I have not seen it documented. Also any thoughts on what the CR would come out to be?

"Fast is Sexy"

[nando]

it doesn't sound right. using an entire M54 rotating assembly (crank, rods, pistons) results in having to shave the pistons, and the M54 stroke is 2mm less than the S50.

M54 pistons have quite thick crowns so it may still be feasible but I don't think it will be a drop in assembly. even if the assembled height worked you'd still have to cut reliefs for the larger valves of the 885 head.

[Liquidity]

What are the benefits of going this far with the 2-valve engine versus using the M54 right from the start? Is it because it will look stock? Or because you already have all the parts? I'm seriously asking because this really seems like so much time money and work to end up with less power anyways. Modifying cranks, grinding blocks, machining pistons, I'm trying to wrap my mind around the point of it all when an M54 can be picked up for $500.

[nando]

sigh.. this argument again. comparing a stock, high miles junkyard motor to a freshly built modified one. also unless I'm mistaken an M54 makes about 230-240bhp stock which will be less than a properly built 3.0 M20.

[E46Twist]

Liquidity, I will just leave that you are comparing apples to oranges with that question. I like the m20, it fits well, and is easy to work on.

Back to the main question at hand. If the eta is 206.2 flat top pistons and works could you not just skim .12 off of the 206.32 of the s50US. Also iirc S50 crank is 86mm m54b30=s52=89.6mm so the s50 stroke is shorter. Am I wrong or am I wrong?

"Fast is Sexy"

[E46Twist]

I am not claiming to know whether this will worm well or not just arguing to form a good consensus, yep I'm an engineer haha.

"Fast is Sexy"

[digger]

28.32mm seems like a BS number. its unliely the compression height is that small on a OEM BMW piston. m50/52/54 are tall decks than the m20.

m54b30 has 211mm deck height
throw = 89.6/2 = 44.8mm
rod =135mm
comp height if at deck =211 - 44.8 - 135 = 31.2mm approx

so

86/2 + 135 + 31.2 = 209.2 so 3mm above deck so you need to machine them

[Liquidity]

sigh.. this argument again. comparing a stock, high miles junkyard motor to a freshly built modified one. also unless I'm mistaken an M54 makes about 230-240bhp stock which will be less than a properly built 3.0 M20.

That's with catalytic converters, stock exhaust, stock airbox, stock tune, etc etc. It's a 4-valve engine no matter what way you look at it so it will breath better right off the bat. And when you say properly built, that would entail real custom pistons and rods to fit this motor with a balanced crank, not some frankensteined motor with pistons from this, head from that, crank from there where here him her... That's not a proper build, it's just throwing parts together to end up with something inferior.

[digger]

it costs a lot to build a proper stroker M20 to make 240+bhp, every aspect needs attention

[whodwho]

That CH does match notes I had:

M44, 30.4mm CH, 84mm bore
M42, 31.65mm CH, 84mm bore
M43, 31.65mm CH, 84mm bore
M40, 31.65mm CH, 84mm bore
M20, 34.09mm CH, 84mm bore
M50B25 (VANOS), 32.55mm CH, 84mm bore
M50B25 (non VANOS), 38.2mm CH, 84mm bore
M52B28, 31.82mm CH, 84mm bore
M54B30, 28.32mm CH, 84mm bore
S50B30 (USA), 32.8mm CH, 86mm bore
S50B32 (USA), 31mm CH, 86.4mm bore

FYI that is going to be closer to a 2.9(2859) than a 3.0

[E46Twist]

Okay really let's put the motor thing to rest. I said a swap was a possibility but it would be an s50. Back on topic, does anyone know the b30 comp. Height? I was readying a thread where some on put this rotating assembly in an M50 block(210mm) and was 4mm below deck. I found a few sources saying they were 28.32mm and if you look at one its not too hard to believe.

"Fast is Sexy"

[E46Twist]

Okay just dug up some more info. Tdc pistons sit ~3mm below deck so we get 89.6/2+135=179.8, 211-179.8 -3 = 31.2-3 = 28.2~28.32. So a small shave should do the trick. Now it is just a question or CR

"Fast is Sexy"

[digger]

wow 3mm down the bore.....seems pretty gay if true.

for CR M54B30 head is 34cc

[E46Twist]

Yep its a true story, also I was talking about compression ratio

"Fast is Sexy"

[digger]

Yep its a true story, also I was talking about compression ratio

"Fast is Sexy"

should be able to work out the CR knowing what you have and the head cc