Cheap 11.5 CR on an M52b28

[CoreyZ]

M50b25tu pistons (just a vanos M50) in an M52b28 with b28 rods and crank. Been mentioned before in other old threads but I thought I'd put it in one place again for anyone new looking at this.



Rough measurement of piston to deck of stock M52b28 pistons


Same with M50b25tu pistons



e: Better CR calcs

You can use deck height, piston compression height, head gasket thickness, and cylinder head volume to calculate compression, but I can't find decent measurements. The height of the piston at top of stroke should be 209.55mm, but the deck height for an M52b28 block I saw was 208.XXmm. Not the case as you can see.


Compression ratio = 10.2:1 = swept volume + (Cyl. head volume, HG volume, clearance volume, ect) : (Cyl. head volume, HG volume, clearance volume, ect)

10.2 = (465.5cc + X ) / ( X ) where X is the sum of those hard to measure volumes.

9.2*X = 465.5cc. X ~= 50.598cc.

If those compression heights are accurate (seems reasonable) the reduction in volume is 4.045cc.

50.598-4.045 = 46.552cc

(465.5cc + 46.552cc) / ( 46.552cc ) = 10.99 CR

I didn't measure CH and we're going by BMW's CR, so there still could be issues, but you're right, it's 11:1. Still pretty decent for very little $$ spent!

[Northern]

I've never seen calculations of what this came out to before, just people saying it would be 11+

Thanks for that.

[whodwho]

This appears to net you .8 so looks like it is closer to 11.0

"Total displacement is slightly decreased" - Unless you change the bore or stroke the "total displacement" will not change

So here are some numbers and a CR calculator to work with

M50B25 Vanos 32.55mm CH
M52B28 31.82mm CH

32.55 - 31.82 = .73 - your 1mm difference is actually .73

Change the piston CH and you can check the displacement and CR - http://www.zealautowerks.com/advance...00,7200,1500,0

* The volumes and HG thickness may not be valid they were adjusted to make the final CR of the M52B28 as a base

[CoreyZ]

Sorry, meant cylinder volume.

Of course, I started with 465.5 for the total cylinder volume initially and that's neglecting the deck + HG + cylinder head volume, so it is off! Fixing

[King Mufasa]

are building this engine? or you were just toying with parts you had available?

[CoreyZ]

Yes

[King Mufasa]

like to see results

[emmanuel.dlc]

it's 10.99:1 I have one. 226whp and 209wtq with stock m50 cams

[Humour]

hi guys and gals,

apologies for being a newbie and resurrecting an old thread first of all.

I find the information very interesting and I'm wishing to build my knowledge on the subject of BMW engines.

In line with the discussion here, has anyone considered pairing an M52TUB25 Rods (140mm) with M54B30 Pistons into an M52B28 short block?

If my understanding is correct, this will increase the rod ratio from the M52B28 default 1.61, to 1.67, which is beneficial. Also to my knowledge the M54B30 piston is around 5~6mm shorter than the M52B28 piston as well as including a newer implementation of rings design (smaller + closer spaced).

I know that the M54B30 RA in the M52B28 block is a proven 3 litre stroker upgrade, but this moves the rod ratio down and thus would be prohibitive to making power and revving in the high rpm range for say a track only application.

I would appreciate any feedback/opinions on this combination of components and perhaps some guidance on compression calcs using these components....

there is some useful info on another forum about pistons I am listing below but it does not include the M54B30 piston unfortunately.



Humour

[I5_E30]

The M54B30 has a piston compression height of 28.32, with a rod length of 140, and a crank stroke of 86 (43). puts you at 211.32. The M52 has a deck height of 210, you will be 1.32mm above deck with that set up.

https://catalog.mahle-aftermarket.com/eu/modules/motorComponent/specs/detail.xhtml?filterId=966910

[Humour]

Thanks for the feedback I5_E30.

Isn't the M52B28 crank stroke 84 instead of 86, or am I missing something?

[I5_E30]

Sorry about the wrong info, you are right it is 84mm for the M52B28.

[Humour]

in which case based on the numbers you have stated and my understanding that puts TDC with those components at 0.68mm below deck?

Theoretically then that is 1.87mm difference at TDC using the M54B30 piston with an 140mm rod.

In reality as measured by Corey@Track.One in his exercise there is a possible deck height difference of 0.5~1.0mm from the specified 210mm, instead measured in the 208.XX range.

It is questionable whether this combo will clear the valves or mate with them. and that's before high lift cams are added to the mix.

No obvious price vs. performance advantage even with a slight raise in CC (IF valves can clear), but if the RA had to be taken apart anyway the M54B30 is a lighter and a better OEM piston design as well as cheaper than a forged piston set, so combined with a decent H-beam 140mm rod that combination will aid in lightening the RA assembly as well as slightly improving the rod ratio and arguably increasing the compression ratio to somewhere in the 11:1 range (no hard calcs. done here just speculation on my part). Just leaves the small "IF" it will clear the valves lol My feeling is that without some machining work to the pistons its a non-starter.

[drew_step]

I didn't measure CH and we're going by BMW's CR, so there still could be issues, but you're right, it's 11:1. Still pretty decent for very little $$ spent!

How did this turn out? I'm think about doing the same thing and was wondering if the high compression ratio gave you any trouble. What did you end up doing for tuning?

[The Dark Side of Will]

The M52 has a deck height of 210

Is the M54 deck height 211mm?