M50B25 vs M50B20 block

[leomarcus]

Hello i have a ful m50b25 non vanos , i need a new block but in italy not easy to find.

I found a m50b20 block thas has same measure , oil passage , block height etc..

Seems the only difference is bore 80 instead of 84 mm

Do you think i can get 84 mm bore from m50b20 block without trouble?

In order....is material the same?


thanks

[Pierre3400]

Well, i can understand its hard to find an M50B25 in italy, but they are normally EVERYWHERE otherwise.

The only difference between the M50B20 and M50B25 is the bore side B20 is like you 80mm and teh B25 is 84mm. If you bore the B20 up to 84mm then the only difference you will be able to find is. on the B20 is says Ø80 on the side. They are cast the same way, and share the bearings all over.

I have been playing around with all of this for many months now. I have an M50B20 with the M50B25 crankshaft, and the M52B25 conrods making the M50B20 have 2260ccm. So i am very sure all the parts will fit.

In most cases its cheaper and easier to get the full engine. Ofcourse i dont what its like in Italy. But a rebuild with headgaskets and everything takes time, and will cost also.

Consider it.

[xlDooM]

Just out of curiosity, what happened to the block? Usually the head takes the fall long before the bottom does.

[leomarcus]

i have already all part for m50 b25 (second kit of forged piston,new hg ns,
I got detonation on 2 cylinders (2nd and last) after 20 minutes of monza at 1 bar track day

I have 8.5 cr, mls ,etc

now i am rebuilding engine, i have to find also whawas trouble because i got 11.5 afre and 850c on egt that are not out of line.

I just want know if cast were same.

[Pierre3400]

I just want know if cast were same.

Cast is 100% the same. I know the bored out m5b25's have a hard time holding alot of preasure because the walls become thin and crack.

I ave seen M52B28 blocks used. But ofcurse this will never hold preasure, but if you bore them out ALOT and stick in the cylinder tubes in, i believe i say they used ones from Fiats. Lighter block at the end of day, but this is pursuit any weight lost is time/speed gained.

[coffeeandcigars]

"Cast is 100% the same."

This is not true, M50B20 has thinner walls. My casting 1735813 has ca. 5,3 mm thick walls, at the thinnest point i can measure it.

[spyderg0d]

The b20 blocks only have 80mm pistons. The block is different. I'm afraid any oddball mix of parts will just leave the ecu confused. Best bet is repair,replace, or swap.