E30 Zone

Hi there, im gathering parts for a 2.7 turbo build, and have the crank and rods now, a friend has a m20b20 block for me (i have read in a few posts that the b20 block can be bored to 84mm)

i was wondering if there are any differences between an early pre-facelift b20 and a post-facelift b20

ie compression ratios etc arent affected by the crankcase but are there any differences beween the two engines?

also does anyone know where i can get a spigot bearing for my eta crank? (im not even sure if i need one) can someone clear this up for me please

thanks all

i have a 1983 m20b20, and i can tell you the wall thickness is 6mm on the 80mm cylincers. so boring it up to 84 till put that wall on 4mm

i have a 1983 m20b20, and i can tell you the wall thickness is 6mm on the 80mm cylincers. so boring it up to 84 till put that wall on 4mm

4mm doesn't sound enough! do you know what the wall thivkness on the b25 is by any chance?

your power stroke only last for 40 degrees max if your lucky, the centre of your bores are never exposed to peak pressures, only the top 10mm ish of the bore.

4mm will be fine and has proven to be fine in the past.

Ok then, i have read it in a few posts that both b20 and b25 blocks are the same except for bore size (the main reason i would like to start with a b20) i'l have a quick measure up of the b25 block i have tomorrow,

my main question though to anyone who might know is, whats the difference between the early and late blocks, if any? someone please clear this up for me as i have an early low mileage block on hold.

thanks for the help lads

i think the difference was the pistons used, ie early blocks hi comp pistons

Is bore the only difference between the b20 and b25 blocks?

Gortour wrote:Is bore the only difference between the b20 and b25 blocks?

The 2.5 has some small coolant holes that a 2.0 block doesn't. Which isn't essential tbh. They are really bar this and bore size like for like

Thanks for that Simon. Vaguely remember someone saying the 2.5 had either extra oilways or waterways, hence the question.