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

[JiXer]

Yeah, Im sure I wasnt the first to think of this, but its a tough thing to search for and I couldnt find anything solid.
I have sooooo many other projects I ned to finish first, but I really wanna mock one of these up some day soon.
And then find a cam and porting guru to really maximize the potential.

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.

[digger]

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

this

the two b25 blocks i remember measuring were 206.2mm so piston 0.5mm proud. with a 1.75mm gasket thats a 1.25mm clearance between piston and head

[LJ851]

this

the two b25 blocks i remember measuring were 206.2mm so piston 0.5mm proud. with a 1.75mm gasket thats a 1.25mm clearance between piston and head

This is what i measured as well.

http://www.r3vlimited.com/board/showthread.php?t=285315

[JiXer]

Damn it! Really?
That's the only number I have seen. I don't have the means to measure that accurately and I don't have a block with a crank in it. I'd really just need to be close enough to not bother with the wrong pistons. The actual mock up would determine everything for final assembly measurement.

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

[digger]

Damn it! Really?
That's the only number I have seen. I don't have the means to measure that accurately and I don't have a block with a crank in it. I'd really just need to be close enough to not bother with the wrong pistons. The actual mock up would determine everything for final assembly measurement.

if you plan on a new engine just find a second hand block and use it. that way you have measurements.

[JiXer]

if you plan on a new engine just find a second hand block and use it. that way you have measurements.

Im sorta shifting this conversation over to the e30tech post...

http://www.e30tech.com/forum/showthread.php?p=1374882#post1374882

[Accota]

Since e30tech is dead ...

So has anyone actually shaved M52b28 pistons and recut valve pockets in them?

Based on 7mm crown thickness, would shaving 2.3mm and cutting 2mm valve pockets in them make them too weak?

leaving 4.7mm crown seems acceptable but 2.7mm at valve pockets seems very thin.

Application is M54b30, trying to boost CR to 11,3:1

Thanks

[nando]

Ixer did it, but he never finished that motor (or at least he never posted about it).

if it's an N/A application I bet it would be fine.

[Accota]

Ixer did it, but he never finished that motor (or at least he never posted about it).

if it's an N/A application I bet it would be fine.

Yes only NA, with 264/252 cams

THere's also the M52b25 piston which has ch 32.8 and the material above the top piston ring seems even thicker. But I presume has nothing to do with crown thickness?

Stock M54b30 has about 6mm crown thickness, 4mm between top piston ring and top