Prefacelift/facelift block similarities

Fri Dec 30, 2011 9:18 pm

Just a quick one here to see a couple of options, are the early high comp blocks changeable with the later low comp stuff?

IE could an 883 head from a late 325 be fitted to an early B20 block rebored to 84mm? The bottom end would be M52 crank, 130mm rods and late 325 pistons.

Fri Dec 30, 2011 9:39 pm

Yes, thats no problem. M20 blocks are all very simular, the b20 has no "steam holes" which are about 4mm round holes between the bores, it can be bored to 84mm no problem. I've used b20 blocks for this with no ill effects.

Other than that sounds like a nice recipie for a 2.8

Be careful when choosing the crank, you need an early single vanos, so the pistons and crank webs dont clash.

HTH

Fri Dec 30, 2011 10:59 pm

Cheers, I have the crank, according to my research it's the right one (no trigger wheel on the other end) from an early 1998 car, late pistons from my B25 - don't know what make yet - and 130mm rods. I have both a B20 and B25 but I want to build the engine from the B20 as it seems a good base.

Sat Dec 31, 2011 1:04 am

Personaly I think your much better off with the b20 block, nice fresh new bores. You can get the b25 rehoned ok, but honing is only a surface finish it does not correct any flaws, the worst of which is the wear ridge at the bottom of the bore. This part of the has never been used during its life as a b25, but as a b28, the pistons and more importantly the rings will be dragged through it on the down stroke and over it again on the way back up.

Not saying the b25 cant be used, but if you got the choice.................

Sat Dec 31, 2011 9:47 am

I'll use the B20 then, it seems to make a lot of sense for the sake of £150 for the rebore, especially as I don't really know the history of the B25 I'm running (£100 engine/box!).

Time to get cracking! Cheers.