M20B25 Rebuild

[Malcolm206]

I currently have a second motor sitting around, and in the fall I tentatively plan to begin a complete rebuild of the motor. It's going in my DD and I don't am leaning towards rebuilding my second motor and then swapping the two, but I wouldn't be entirely opposed to swapping in a different motor...

I plan on doing all the work myself with the help of some friends except any machining work that needs to be done. I'm wondering if it's worth my time/money to stick with the stock motor and if there are any worthwhile upgrades to the M20 "while I'm in there".

-Malcolm

[digger]

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

[Malcolm206]

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

What are the benefits for a 2.8L over a stock rebuild?

[digger]

more torque and power

[badwella]

I'm doing the 2.8l build soon. What about engine management? Can the stock ECU run the 2.8l? I'd assume it might need a beefier fuel map or something which you could get from a chip.

Of course, a standalone and a proper dyno tune would be the best approach.

Sorry if this is a stupid question. Just a little confused as some guys say it's fine to use the stock ECU with chip, but it seems in most guys convert straight to a standalone (at least in the multiple threads I've read).

[whitebulat22]

I don't know if it's been done but another cheap upgrade may be eta crank, eta rods, I pistons, and skimming the block down. Everybody's got an eta crank lying around somewhere, plus they're probably lighter than m52 forged cranks. Now you'd have more displacement and compression, which seems to be what m20s crave.

[digger]

can run a 2.8L on stock chip but better to get something a little more custom and 17lb injectors or so would help motronic requiring less adaptions. plenty of aftermarket options to with PNP MS or other setups depending on budget

2.7L with ~2mm decked block above also works, slighty less compression and displacment than 2.8L but still better than b25 if you screw it together properly and add a nice tune. you'll need a cam gear to fix the cam timing but thats not a big deal

[badwella]

Awesome. Thanks, Digger.

[stonea]

+1 for the 2.8

[Malcolm206]

Are there any downsides to the 2.8?


Sent from my iPhone using Tapatalk

[digger]

only whatever the cost difference and time/effort difference to do it compared to a bone stock rebuild.

[packratbimmer]

What is the compression ratio on the 2.8 build? Thanks

[SkiFree]

I don't know if it's been done but another cheap upgrade may be eta crank, eta rods, I pistons, and skimming the block down. Everybody's got an eta crank lying around somewhere, plus they're probably lighter than m52 forged cranks. Now you'd have more displacement and compression, which seems to be what m20s crave.

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.

[Malcolm206]

What do you think about a 323i head with eta crank and/or eta pistons, upgraded injectors (either m50 green tops or 19lb ones) and a possible tune?

[digger]

you need a good amount of head work on b23 to make it a decent prospect. It can work well but as always it's in the details