Could someone please explain a blockguard and ductile iron sleeves to me???

i have seen them, but i really have no idea what they do? Also I have a question when people refer to "ductile iron sleeves". Im guessing the sleeves slide into cylinders to increase cylinder strength, but my questin is this. say i have my LS block with bore of 81mm, and im wanting a bore of 84mm, now i can just get my block bored 84 mm, but there would be really weak cylinder walls right? so if i want to put in ductile iron sleeves that were 84mm, would the cylinder walls have to be bored out to like 86mm, so that the 84mm sleeves would fit? Anyways, i am obiously confused about both a block guard, and ductilve iron sleeves, so could someone please explain them to me, thanks.

First of you have to understand the way the 4 cylinder engine is designed. The sleeves you talk about are the cylinder walls. They are the walls that contain the combustion process. They have a small space all around them betweenn the sleeves and the block which is where the coolant flows to keep temperatures in a non-damaging range. This makes for great cooling but the tops of the sleeves aren't attached to anything. Which is fine for what honda intended but if you somehow modify the engine to rapidly increase and decrease the compression rate, either by turbo-charging or nitrous oxide, you run the risk of damaging or even shattering the tops of the sleeves. They simply weren't designed to withstand it. The block gaurd effectively gives the tops of the sleeves, something to hold on to. It strengthens them so that rapid compression changes don't dramatically affect them. The downside of course is that the space for coolant travel is reduced.

And as for cylinder re-sleeving, that's an EXTREMELY expensive process. The amount of money that you get from the extra 2mm could be better used elsewhere. As for how far you can safely bore out the stock sleeves, the smarter ppl in here can tell you. They can also correct any errors I've made :)