m20b20 stroked to m20b25? Budget project

[bmwmaster81]

I think to do something new but am not sure to really try it. Some opinions of the experts would be good.

I got an m20b20 engine as a present. Since 3 Months its lying in the corner of my garagre.
Then i got some m54b22 80mm bore pistons for free.
I don't have the numbers here because am on my latop but my thoughts are to build an cheap stroker engine.

Crank would be from m52b28 84mm stroke.
Pistons and rods from m54b22

Result of my calculations are that it would fit perfect in the block. Just don't know cc of m20b20 combustion chamber to calculate cr.

The result would be an 2533 cm^3 engine.
What do you think, is it worth to try it? What numbers could i expect? Maybe more thorque and low end power than stock m20b25?

Would be really cheap to build but i just don't want to waste my time.

[digger]

sounds like its not going to work. id guess (but dont actually know) that the m54b22 piston and rod plus 84 crank will stick out the block alot

the m54b22 stroke is 72mm, so using a 84mm crank means it will stick out 6mm higher than it did. the m20 block is even shorter in height so it would be worse than 6mm

[bmwmaster81]

Yes you are right. Somehow i calculated completly nonsense. Have now my Data here and can't prove my last calculations.

Only possible way would be with eta 81mm crank.

40,5mm crank + 135mm (m54b30) rods + m54b22 pistons 29,6 = 205,1 mm


This schould fit and would result to 2442 ccm. Somehow less interesting......but for nearly no investment.......just bearings and gaskets...
Would be courious what numbers would come out.
Rotating assembly would be much lighter and a long stroke engine. With the m20b20 head and intake it schould have good low rpm torque.;D ?

[bmwmaster81]

Yes you are right. Somehow i calculated completly nonsense. Have now my Data here and can't prove my last calculations.

Only possible way would be with eta 81mm crank.

40,5mm crank + 135mm (m54b30) rods + m54b22 pistons 29,6 = 205,1 mm


This schould fit and would result to 2442 ccm. Somehow less interesting......but for nearly no investment.......just bearings and gaskets...
Would be courious what numbers would come out.
Rotating assembly would be much lighter and a long stroke engine. With the m20b20 head and intake it schould have good low rpm torque.;D ?

My first calculation was

42mm crank + 135 mm + 29,6 = 206,6 mm

hmm, could also work.....maybe better.......depends on cc of combustion chamber.........

[digger]

My first calculation was

42mm crank + 135 mm + 29,6 = 206,6 mm

hmm, could also work.....maybe better.......depends on cc of combustion chamber.........

that would work but its still only going to be a 2.4L engine. if you need bits from 4 different engines m20b20, m52b28, m54b30, m54b22 why not get a block with 84mm bore that way you can get a 2.8L

[bmwmaster81]

With 80mm bore x 84mm stroke it should have 2532 cm......

I already have an m20b28.......in my car.
All the parts are here and i got them really cheap, so why not use them...?

I just need an crank......all together sould be about 500-600 costs with new bearings seals and so on. And an new built 2.5l for that cost sounds good for me.

At the end i wouldn't know waht to do with it but thats the samllest problem.

[digger]

With 80mm bore x 84mm stroke it should have 2532 cm......

I already have an m20b28.......in my car.
All the parts are here and i got them really cheap, so why not use them...?

I just need an crank......all together sould be about 500-600 costs with new bearings seals and so on. And an new built 2.5l for that cost sounds good for me.

At the end i wouldn't know waht to do with it but thats the samllest problem.

it will be better than a b20 but doubt it will be better than a m20b25 OEM maybe a bit more torque but wont make as good hp without a bit of massage to the b20 731 head

[bmwmaster81]

Yes surely i will do some grinding to the Head ports and also chamber to lower the cr.
I have to take about 3cc out from each chamber to go from 10.8 to 10.3.

I bought an 323i Head which should be similar to the 320i, i got it very cheap and it had been refurbisched.





I will use that. In the chambers i will grind out all the edges around the valves and the see how much i still have to remove. Any tips how to grind the ports properly?

Is it true that 731 head doesn't tend to cracking like the 885 do?

I also dont't have experiance with the flat squisch. Are there some rules? how much space must stay between squish area and flat piston? how much is best for performance?

would be thankfull for any advice.:)