2.9 stroker build

[iloveshaorma]

hey guys i want to upgrade my m20b20 to a 2.9 stroker and i am wondering what parts i need to do that?
i want to bore the 2.0 block to 84mm and from what i understand a m50 crank will work(modded of course to fit) and i don't know what else i need. it's going to be a cheap project so i really need your help. tell me what i have to get extra knowing that i already have an m20b20 motronic from an 88 model in europe
thanks a lot

[The Humjet]

You won't be able to achieve this stroker combination with the block you have at the moment. The bore spacing is smaller and the deck height is shorter to accommodate smaller and shorter crankshaft stroke. Puting 84mm pistons on your block with require your block bored out .160" oversize in each cylinder with cuts very close to the water jackets if not you'll be breaking through. And the m52b28 crankshaft will push your piston a fair bit above deck height.
What you would need to do to archive a "2.9" stroker motor is to get your hands on a m20b25 or m20b27 block it already comes with 84mm bores and taller deck height, keep the 130mm rods you have in your m20b20, m52b28 crankshaft (not m50), and a set of pistons. You can go with stock m20b25 pistons which will make it a 2.8l or you can get a set of oversized 85mm pistons to achieve the 2.9l displacement.
This combination works really well for the guys who already have an m20b25. I don't know how well it would work with your 731 cylinder head. They don't flow as well as the 885 heads found in an m20b25, and they have a different combustion chamber shape so I don't know what will happen when you match it up to a b25 piston could it have valve to piston clearance issues? will it have the right squish or "quench". Being on a budget this doesn't sound like the right swap for you
Your better off starting with an m20b25 or even doing an m50/52 swap which is now starting to sound easier along with you gaining more power out of the box.
Another easier option you could do is buy a complete m20b27 block and bolt you head onto it. And keep all the motronic 1.3 ecu and wiring. And you will end up with a nice 9.8:1 cr. It's not a 2.9 but it should go better than what you have at the moment.

[digger]

The bore spacing is the same although the bore size is smaller.
i thought the deck height was the same for all M20 blocks (or close to it). Many of the UK guys use 80mm bore blocks for the 2.7L engines

[The Humjet]

Interesting then ignore what I said I'd follow what digger mentioned instead ^^^
Boring a block out .160" seemed a lot especially after looking at my old m20b23 block which also has 80mm bores seemed it would be cutting it close. In theory deck height should be lower because the crankshaft stroke is shorter and the rods are iirc also 130mm which is same as the eta. But I haven't really haven't taken measureme these are all calculated guesses.

[tinkwithanr]

Bore spacing is definitely the same, but like Humjet said the deck height is probably lower, I can't say by how much though.

[iloveshaorma]

Bore spacing is definitely the same, but like Humjet said the deck height is probably lower, I can't say by how much though.

my mechanic has done this before from a 2.0 to a 2.5 or 2.7 mine is the largest 2.9. i will have to bore the block 4mm from 80mm to 84mm(2.5 2.7 bore). sorry i just woke up so in short i will have to bore the block from 80mm to 84mm and the deck height to be the same. i want to bore my block for the serial number to remain the same i don't want no trouble

[hijack]

Hi,

I would like to build a 2.9 stroker M20 by using B20 block, and I heard there are people who have achieved this 84 mm bored B20 block, but they 2.7 or 2.8 liter engine. Not and 2.9.

I will change of course the head with #885, intake manifold with throttle body and ECU etc. I want to use iemotorsports.com specialized pistons and maybe crank for building.

http://www.iemotorsport.com/bmw/E30-...iepistons.html

http://www.iemotorsport.com/bmw/E30-engine/m20-29.html just crank from here.

My concern is height of the M20B20 block actually, even if I use 130mm rod.

Do you think pistons might stick out? Will be any valve/head-piston hitting or knocking issues?

[digger]

what is the deck height?

its likely the same as the others given they still build 2.8/2.7L in the UK with them. most likely any difference is small and you can remove material if its taller and use a thicker gasket if its smaller, as needed .....

not many people haved bore the 80mm blocks out to 85mm id sonic check it

i would buy the pistons alone, the shipping for crank will be prohibitive when you should be able to source one locally