M20 engines, b20 or b25 better for building b28

[tomislav]

I've heard a lot of conflicting stories about the m20b20 and m20b25 engines as to which is best to make an m20b28.

Ant at Atech as was, told me he uses b20's that are bored out cos they dont have the steam/vapour channels or whatever they are in the block.

Demlot tells me the b25 can handle consistantly high rpm's better than a bored out b20.

I have a b20 block at the engine shop waiting for my instruction to be bored out, decked etc.

Any opinions, preferably based on fact not guesswork, would be great.

Cheers.

Tom.

[tomislav]

Sunday lunch bump

[tomislav]

Anyone?

[Ant]

No issues with either Tom

if you are concerned use the B25 block and get it honed perfectly parallel all the way to the main journals, any oversize ( minimal) can be taken up in the ring gaps when you do the dummy build

use a good piston and run it up and down the bore measuring the gap piston/block wall , all the dims you need are in Bently/TIS and even the orange cover haynes manual !

B20 is same wall thickness when bore to 84mm as B25 , I bandsawed one of each to check many moons ago

HTH.

[Andyboy]

The problem might be finding a 2.5 block with really good bores due to their age, although in reality the blocks were cast from a very high quality iron and you should be able to find one. Get a machine shop to check the bores for taper and ovality, although if the cross hatching is still there you should be okay. Use a new piston compression ring and check the gaps at the top and bottom of the bore.
It's worth getting the bores rehoned using a diamond tipped plateau honer. This is worth the money because it will virtually eliminate oil consumption. I've used glazebusters etc before and they're not really very good.

Boring a 2.0 block out will be pricey and you can pick up a 2.5 short engine for £60.

[tomislav]

I had a perfect block done honed and everything else then i had a little garage fire (burnt the car and garage to the ground) and the block didn't look so good after that!

Now got a 2.0 block kicking about so i think i'll be using that then.

Cheers boys.

Oh yeah, Ant, you still tuning?

[Ant]

I might be persuaded outa retirement Tom

Have to fit in with working F/Time mind lol !

Bad times on the fire !, it was the second bout of flooding that ruined me

[tomislav]

Shit me mate, i never knew,

Is it worth PM ing you about tuning it once its (finally) built or an email, mobile?

[Ant]

Email me dude, I'm on there 24/7 and can pickup on the cell.

Still got the emulators and my brain so that should suffice

[tomislav]

I've not got ya email or phone tho mate, any chance you could PM them to me?

Or gimme a txt on 07814 491583 would be cool