Over bore wall thickness

[Riceburner]

Getting a block that'll go to 89mm can be quite expensive, as I've found out. That's before you even start the build.

 

Unless you're a clown and you buy the big pistons before getting the block  Ha! 

[PB260Z]

OK whats with you lot & the sudden fascination with L28 blocks that will go to 89mm? ? ?

 

Can anyone tell be why an 89mm bore is superior to an 88mm or 88.5mm bore?

 

Preoccupation with size - bigger is better ????

[jock]

Gareth, you need a minimum of 120thou bore wall thickness AFTER boring to your desired size.

'Correctly' sonic testing the block before boring to pinpoint the thinnest part of the bore, is the only way to determine where you can bore & how big you can go.

 

Check out this photo of a L28 block that Les milled the top off:

(Don't despair - that block had a dirty great big crack running along the deck between the stud holes. It was only ever going to be scrap).

 

 

It's standard 86mm bore N42 block & if you look closely you can see how much core shift it has in the bore walls.

 

After going through & sonic testing 10's of L28 N42 & F54 blocks for customer stroker builds, Les has found no difference between the two types of block castings in relation to bore thickness's.

'Most' L28 blocks can safely be bored to 88.5mm (some like Gav's can't), a very small number can go to 89mm, and I've only seen two that can tolerate a 90mm bore safely (Owen's and the US L34).

 

It's just all pot luck - you can can't tell until the block is acid bathed & sonic tested.

Depending on the intended duty of engine , if it sees occasional full throttle work and not of a very high C:R then you can sneak it a little thinner, if it is a HP big C:R engine not so and for me if it is a 1 bar or greater turbo engine that generates high cylinder pressure then stay as close to std as you can, I have seen many split blocks as a result, not nice.