M20B25 Rebuild

[digger]

They are heavier than the m52 crank, then you also have the shorter rod length.

Budget strokers look good on paper, but you will find many many threads about those who were hoping for more power. Just be realistic with the limits of what you are doing and have fun.

Most budget strokers are 885 head on an eta though.

A 2.8 budget oem build compared to a 2.8 build with a 5mm longer rod and forged 85mm Pistons with 0.5 to 1.0 extra compression can be hard to justify for some who simply want a hot street engine.

The 2.8L oem option is proven as the eta crank option with 2mm deck reduction it's a far cry away from slapping a 885 head on an eta which was proven years ago to be only an upgrade from an eta baseline and not much else

[packratbimmer]

With a little research I found that the compression would be 9.4 to 1 or 9.8 to 1 with the block decked .5MM. Sound correct?

[digger]

yes that correct. i would definitely take the 0.5mm (nominal) off the block to eachive the proper deck clearance if doing this method as it optimizes the CR and combustion chamber characteristics

[Malcolm206]

Ok so I've read several threads on 2.8L stroker builds, and from my understanding you need the following:

id consider a 2.8L all you need in addition to a stock build is

ETA rods
M52b28 Crank
Modify the B25 piston skirts or the M52 crank counterweights
Sleeve for oil seal

As well as decking the head a little, an adjustable camshaft gear, and probably upgraded injectors? And then also getting the crank rebalanced.

Does anyone who's done this know how much/can estimate how much is costs to have the piston skirts/crank counterweights modified and have the oil seal sleeve fabricated?

[digger]

Ok so I've read several threads on 2.8L stroker builds, and from my understanding you need the following:



As well as decking the head a little, an adjustable camshaft gear, and probably upgraded injectors? And then also getting the crank rebalanced.

Does anyone who's done this know how much/can estimate how much is costs to have the piston skirts/crank counterweights modified and have the oil seal sleeve fabricated?

PM forcedfirebird

and deck the block not the head

[Malcolm206]

PM forcedfirebird

and deck the block not the head

Right, meant to say that.. Thanks for all the help, I appreciate it Digger!

[ForcedFirebird]

Machining costs vary greatly by region. A small town in the middle of Indiana isn't going to cost the same as a high production company in Miami, but as a guide, figure at least $100 to shave the bob weights and $200 to have the rotating assembly re-balanced. Again, just a round about figure, depends on who is doing the work.

The eta crank/rods, 325i pistons and decked block is almost as powerful as a 2.8 with m52 crank. Figure bout 175-180whp with a cam (up about 40whp from most worn stock engines).

[Malcolm206]

Machining costs vary greatly by region. A small town in the middle of Indiana isn't going to cost the same as a high production company in Miami, but as a guide, figure at least $100 to shave the bob weights and $200 to have the rotating assembly re-balanced. Again, just a round about figure, depends on who is doing the work.

The eta crank/rods, 325i pistons and decked block is almost as powerful as a 2.8 with m52 crank. Figure bout 175-180whp with a cam (up about 40whp from most worn stock engines).

Perfect, that's what I haven't been able to find on anyones' build threads. I'll be having the work done in a relatively small town, but I know the (2) guys at a shop that does custom engine builds in town that do good work for a reasonable price.

Anyone have a guess on what the sleeve for the oil sleeve would cost to have made? Or if anyone is selling them for using an M52 crank in the M20?

For a daily driven car that I won't be autocrossing or racing at all, would you recommend a 284/272 cam?

[digger]

MM sell them

http://metricmechanic.com/engine-parts/

its 200 with the bolt and washer. im sure you can find one for $100 or less but make sure the material ihardness is good and surface finish mint and dimensions are good.

[ForcedFirebird]

We make them for $85.

https://wot-tech.com/m20-crank-seal-spacer.html

We re-use the stock bolt and shave the back of the thick washer so it seats on the crank snout properly.

[Malcolm206]

We make them for $85.

https://wot-tech.com/m20-crank-seal-spacer.html

We re-use the stock bolt and shave the back of the thick washer so it seats on the crank snout properly.

Would you say the m52 crank is a worthwhile upgrade over the eta crank for the extra ~$400 for the seal and machine work? Or is it so similar it's not really worth it.

[ForcedFirebird]

More displacement will make more power in the end, just depends on how far you want to chase every ounce of power.

[Malcolm206]

According to this build, if you have a 97 or earlier m52 crank, you don't need the extra machining on the crank/piston skirts. http://www.bmwforums.com.au/showthre...-factory-parts
Don't know if that's true or not, but I think I'm going to go with the m52b28 crank with eta rods and b25 pistons like digger recommended. Does anyone have recommendations on cam, injectors, and ECU chips? As of right now leaning towards m50 green top injectors and either a Dinan or sssquid chip.

Thanks for all the feedback.

[mr2peak]

Not all early year M52 cranks are equal from my research, the euro cranks seem to have smaller counterweights. Euro M52 blocks are also alloy, so a different crank wouldn't be entirely unexpected.

284/272 cam might or might not clear stock pistons with a .5 block deck. Everyone says "they might" because it's too close to make a proper decision without measuring the actual piston/valve clearance of your block/rod/piston/head etc. 272 is the safe choice. I'm in the same position, not sure which way to lean.

[digger]

yeah some cranks clear but i dont think those exist in US engines or are very rare. A few years back at one point i imported an early m52b28 crank from the US as i couldnt find one locally and it was cheaper that way. Unfortunately it ended up being the big counterweight version. another bigger stroke ultra rare crank came up for sale in the UK so i decided to go "big" so i put the m52b28 in storage.

below pics shows what is in store, shown is with 135mm rod so with 130mm rod the pistons sits 5mm closer to crank so its pretty cosy





you need to clearance the skirt, you may be able to away with just the skirts but perhaps not?

otherwise counterweights need to also be reduced a little depending what you find and the resource or skills of people you have access to.

if its a street engine only then a 272 is a good balance, matches the compression nicely and will run nicer on motronic, if you think you may do more later on (ITB, headwork, more cam) then look at deepening the valve pockets now as it will be much easier, there is heaps of meat below.