Engine internal specs... M20 vs. m10, m42, m50, m52, s50, s52, m54, s54 etc.

[JiXer]

Looking for info on pistons (diameter seems easy enough to find, but curious about wrist pin center to crown height/skirt bottom)
Also looking for rod length specs for same engines.

Gotta be a chart or post out there somewhere. But I cant seem to find it.

[dustyperez]

here is some of the specs

http://cars.forumsee.com/a/m/s/p12-15951-0209962--calcing-m5x-compression-ratio.html

[JiXer]

awesome!
Thanks!

[shadowracer]

You can try this... www.bmwheaven.com

[JiXer]

You can try this... www.bmwheaven.com

I see no engine dimension info there??

[digger]

I see no engine dimension info there??

http://www.bmwheaven.com/database/engine.php

[JiXer]

http://www.bmwheaven.com/database/engine.php

Thats what he said. Still no specific data in those links.

[JiXer]

Mass edit/delete. Keep reading below....

[Madhatter]

None of them are very good. All of those will be sitting 3+mm above the deck of the block. Some nearly 6mm when you factor in what you want to do with the block. 206.7mm is the height of the block you are trying to put it all in. The combination of stroke, rod length and compression height should aim to be around this amount to have the top of the piston level with the top of the block. Some of the suggestions you made would see the piston wedged against the head when you factor in how much the crown sticks out. As said in the other thread, if you want to run a 2.8L crank, use 130mm rods and 325i pistons, then you'll be sitting pretty. Only thing you have to worry about it crankshaft counterweights clearing, but thats going to be an issue with just about every combo, depending on exactly what crank and pistons you have.

I posted in your other thread on e30tech other internals I found that would work based on the math.

[shadowracer]

How bout these links.....?

https://www.zealautowerks.com/index

https://www.bgsoflex.com/displacement.html

[JiXer]

Crap, I had the wrong deck height to start with. Damn it!
Sorry. This thread afficially sucks. Will try to save it :) Stand by.
Also, keep in mind I have access to a mill and lathe so I can cut piston tops however I want. I also should have a head here that I can cross section for test fits.

[nando]

if you can cut the pistons, then use the M52B28 pistons, rods, crank, etc - the whole assembly. there's plenty of crown thickness on the M52 pistons to shave a few MM off and cut the valve pockets.

[JiXer]

Well, I'm editing/deleting my other list bc it was wrought with errors.
2 things changed in the basis for this. I actually need to use the iX block which is an M20B25 block which eliminates the chance of using a shorter deck early-m20b27. That and correcting my earlier error leaves me with a deck height of 206.7mm. Earlier I was confused and was using an M50 deck height.
So... this is what I have come up with.

2.8L
M20B25 Block (206.7mm)
M52B28 Crank (84mm)
M50B25TU Rods (140mm)
M54B30 Pistons (84mm / comp. height - 28.32 shaved 3.2mm down to 24.7)
*Might be a bit much to cut off the pistons?

M20B25 Block (206.7mm)
M52B28 Crank (84mm)
M52B28 Rods (135mm) (I believe these are forged and the 135mm M20 rods are not?)
M52B28 Pistons (84mm / comp. height - 32.8 shaved 3.1mm down to 29.7)
*Might be a bit much to cut off the pistons?

3.0L
M20B25 Block (206.7mm)
M52B25 Crank (84mm)
M52B28 Rods (135mm) (I believe these are forged and the 135mm M20 rods are not?)
S52B32 Pistons (86mm / comp. height - 31mm shaved 1.3mm down to 29.7)

There was mention on e30tech about using some 85mm pistons which would be PERFECT and it seems MB has TONS of options. I would need to do a little more research and part number digging, but to be realistic, I don't have access to MB like I do BMW parts. I basically have all of these internals available to me dirt cheap if not free.

[nando]

you'd have to measure the M54 and S52 piston crown thickness to determine how much you can shave off. IIRC, the M52B28 are ~7mm thick which is plenty. also, it's been done before.

[whodwho]

Careful using 206.7 as the block height in your calculations, that is the stack height of the stock B25 and not the M20 block height

75 /2 + 135 + 34.20 = 206.70 and we know the piston does not sit flush