M52B30 Stroker Compression Ratio Question

[werfer]

Alright so let’s say I’m planning on building an M52 stroker with a M52B28 aluminum block from a ‘97 z3 and M54B30 crank, rods, and pistons. What head gasket thickness could I go with to get an 11.5:1 compression ratio? I’ve been searching for a while but am having trouble finding all the measurements I need.

[gdavid]

I would have to dig deep to find the exact cylinder head volume, dish area (very small for the M54b30) to calculate it but I believe it is generally the same as the m54b30 ratio of 10.2:1 with a stock HG because the deck height is the same and the head dimensions are very close. The info is buried in PEI330Ci's and Someguy2800's various threads. To get to a 11.5, you will have to have to shave the head, and/or the block.

[werfer]

I thought the stock head gasket thickness was .069” and yielded a 10-10.5:1 CR with the stroker setup? So wouldn’t going to a .027” or .03” head gasket increase the compression?

[pbonsalb]

Who sells 0.027 HG? Cometic? Could gain some by decking head within allowable limits or even a little over.

[werfer]

Yeah Cometic sells .027”

[werfer]

So for my setup the bore would be 84mm, stroke 89.6mm, combustion chamber volume 36cc. All I need to know is the m54 piston dish volume and deck clearance and I should be able to calculate compression ratios for various head gasket thicknesses. Unless any of my numbers are wrong?

[gdavid]

Yeah, that would get you there. Didn't know such a thin HG was available.

[gdavid]

I have also seen a number of 31.3 referenced as cylinder head volume so I believe the 36cc number includes the dish volume and volume outside of the piston and above the compression ring.

The numbers on this thread look right https://www.bimmerforums.com/forum/s...pression-ratio but I know that others have measured it with water (or oil) and documented the process.

[werfer]

Interesting, if that’s the case then I think compression should be 11.73:1 for a .027” HG and 11.63:1 for a .03” HG.

93 octane should be sufficient for an 11.73:1 CR on this motor right? I don’t see why not but just wanna double check.

Also, if anyone else can confirm any of these numbers that would be great.

[werfer]

Alright, so from what I can find, cylinder head volume is 36cc, piston dish volume is 0, and deck clearance is 1.88mm if my math is correct. Assuming all that is right, CR will be about 10.9:1 using a .027” HG. Not quite the 11.5:1 I was aiming for but not too bad either. Could easily get the rest of the way by shaving the head if I want to.

[gdavid]

After a lot of digging I found this old thread on another forum were PEI330CI measured the combustion volume for an m54b30 with water and plexiglass and provided the volumes for the block at TDC and Head (which is m54, probably very close but cannot be assumed the same). He measured a distance of 3.7 mm above the piston to the deck and a volume of 17.4cc, again this is a m54 block but the bore and deck height is the same as the m52 and the exact pistons you will be using.


https://www.bimmerboost.com/showthre...lopment/page10

[werfer]

Deck height on m54 is different than m52.

TDC = Stroke/2 + rod length + piston compression height = 89.6/2 + 135 + 28.32 = 208.12mm

M52 deck height is 210mm so deck clearance should be 1.88mm

[gdavid]

I should probably just quit this thread because I keep learning of my own ignorance. I thought the m52 and m54 had the same deck height.

So the deck height of the m54 is 211mm would make the difference in volume 5.5cc. Using PEI330Ci's measured volume of 17.4cc and subtracting the difference of 5.5cc would mean 11.9cc is the volume of the valve reliefs in the m54b30 pistons (which are very small) plus the outside volume above the compression ring. This assumes the 17.4 was accurate and water wasn't leaking past the compression ring during measurement, the guy is pretty meticulous so I'm assuming he sealed it somehow.

Again, I've shown my ignorance at least twice now so I'm just here for discussion but genuinely interested as I'm in the middle of putting my own m52b30 engine into a project car. I used a stock head gasket.

[werfer]

It’s probably going to be a little while before I actually get around to building my motor (gotta finish remodeling the house first). I just want to have everything planned out for when the time comes. I’ll be putting it into an e36 compact. Should be fun.

[Mike WW]

I thought the m52 and m54 had the same deck height.

That was my understanding also from some, but not extensive research. I've read that the 3.0 rotating assembly is plug and play into a M52 block with the possible exception of the pan, depending on what the M52 came out of.

[6inarow]

Deck height on m54 is different than m52.

TDC = Stroke/2 + rod length + piston compression height = 89.6/2 + 135 + 28.32 = 208.12mm

M52 deck height is 210mm so deck clearance should be 1.88mm

For this very reason, I've researched my butt off and found that m44b19 pistons fit, with an 85mm bore, and offer a compression height of an 30.4, instead of the m54b30 at 28.32. Thatll put the piston .2mm over deck on a 210mm deck height m50/52. I've also read and found out that s52b32 pistons have a CH of 31.00mm, making the m44b19 piston recipe work just right.

Btw, I'm building a 3.05L stroker with m44 pistons, m54 rods, and s52 crank, with m52 head and m50nv valvetrain with vanos, OEM ls1 throttle body, 3.5 HFM, m50 manifold, and pink top injectors.

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