Machine shop quotes, parts listings and build threads all assume you already speak the language. "Check your journals before you order bearings." "It's open deck, so watch the fire rings." "Pour to ¾ inch over the solute." If you're planning your first boosted build, those sentences can feel like a test you didn't study for. This glossary translates the block and bottom-end terms you'll run into most, in plain English, with a note on why each one matters when the boost goes up.
How to use this glossary
Terms are grouped by where they live in the engine, not alphabetically, so related ideas sit next to each other. Read a whole group once and the vocabulary in a parts listing starts to make sense. Where a term deserves more than a paragraph, we point you to a longer guide.
The block itself
Deck. The flat top face of the engine block, where the head gasket and cylinder head clamp down. When someone says "deck the block," they mean machining that surface flat.
Water jacket. The passage cast around the cylinders that carries coolant. In a boosted build it's also where reinforcement happens, because it's the space between the cylinder walls and the outer block.
Bore. The cylinder itself, and also its diameter. Piston listings quote bore size, such as the 84 mm and 84.5 mm piston options in our BMW N54 Rebuild Kit, and the piston, rings and head gasket all have to suit it.
Cylinder liner. A separate sleeve of harder material forming the cylinder wall inside a block. In most aluminum blocks the liners are cast iron, which is worth knowing when you read about fillers made for aluminum.
Sleeving. Machining out the original cylinder and fitting a new, usually stronger, sleeve. It's a machine-shop job, and it changes the bore you build around.
Open deck, closed deck, semi-closed deck. Three ways a block ties the tops of the cylinders to the outer wall: not at all (open), all the way around with small coolant holes (closed), or at a few bridges (semi-closed). This is the single most important block term for a boosted build. Our open deck vs closed deck guide shows how to tell which you have.
Sealing the top of the cylinder
Head gasket. The layered seal between block and head. It has to hold combustion pressure, coolant and oil apart at the same time. Its thickness and bore size are part of the spec, so match it to your pistons.
Fire ring. The raised ring around each bore opening in the head gasket that seals combustion pressure. If the top of the cylinder moves under boost, the fire ring is where the damage shows up first.
Head studs. Threaded studs that replace factory head bolts to clamp the head down harder and more evenly. Kits can vary in a way that affects block work: the ARP N54 kit, for example, comes in a Standard version and a High Boost version that requires drilling and tapping some holes in the block.
Ring seal. How well the piston rings seal against the cylinder wall. Poor ring seal means lost compression and more blow-by. A cylinder that distorts under load makes good ring seal harder to hold.
Bore distortion. A cylinder going out of round under heat, pressure or clamping force. Reinforcing the cylinder walls aims to reduce it.
Coolant passages. The holes that let coolant pass from the block up into the head. On a reinforced open deck they're drilled back through the filler, using the head gasket as a template so they line up.
The rotating assembly and measuring
Crank journal. The polished surfaces on the crankshaft that the bearings ride on. Their measured size decides which bearings you buy.
Undersize bearings. If a crank has been ground, standard bearings won't fit correctly, so oversize-thickness bearings make up the difference. That's why bearing options are listed as STD, +0.25 mm, +0.50 mm and so on. Measure before you order.
Bearing clearance. The tiny oil gap between bearing and journal. Too tight or too loose and the bearing fails, which is why clearances are checked during assembly, not assumed.
Compression ratio. How much the piston squeezes the air-fuel mix, written like 9.5:1 or 10.2:1. Boosted builds often choose a lower ratio than a naturally aspirated engine; your fuel and tune decide the right number.
Reinforcement and block filler terms
Block guard. A metal insert pressed into the top of the water jacket to brace the cylinders. Usually involves machine work for a proper fit.
Block filler. A material poured into the water jacket to support the cylinder walls. It adds structure; it isn't a crack repair. EPOXY54 is a two-part block filler epoxy that gives open-deck blocks closed-deck strength without machining.
Partial Fill. A fill of only the top ¾" of the water jacket, with coolant still flowing underneath. It keeps OEM coolant capability, so it's the choice for street cars.
Dry Block. A complete fill of the water jacket, with no coolant through the block. It's for track use only. Partial Fill vs. Dry Block compares the two.
Solute. A temporary filler, usually sugar or salt, poured into the lower water jacket before a Partial Fill. The epoxy sits on top of it, and once the epoxy cures the solute is dissolved with water and flushed out.
Compressive strength. How much squeezing force a material can take before it fails, usually given in psi. EPOXY54 is rated at 21,000 psi.
Thermal expansion. How much a material grows and shrinks with temperature. A filler should move with the block around it; EPOXY54's thermal expansion rate closely matches aluminum.
Two-part epoxy. A resin and a hardener that stay liquid separately and cure once mixed. The resin alone can't cure, which is why it keeps in the can until you mix it.
Working time. How long a mixed epoxy stays pourable. The EPOXY54 Installation Guide gives about 25 minutes after mixing and says to mix the whole batch at once rather than splitting it.
Putting the words together
Here's a sentence you might read in a build thread, now fully decoded: "Measured the journals, ordered STD bearings, decked the block and poured a partial fill before tapping for the high-boost studs." The builder checked the crank, bought standard-size bearings, had the block's top surface machined, filled the top of the water jacket with block filler while keeping coolant flow, and planned the stud-hole work around it. For how those steps fit together on a real engine, our N54 bottom end build order walks through one in sequence. And if you've heard that filled blocks can't cool or are only for drag cars, our block filler myths post sorts the facts from the forum lore.
Next step: reinforce the block
Once you're comfortable with the terms, the next decision is how to support the cylinders. If your block is open deck, choose your engine configuration and cooling option for EPOXY54; the EPOXY54 Install Kit adds a stir stick, drill bit and squeeze bottle if you don't already have them. Not sure your engine is open deck? Check Shop by Platform or email support@epoxy54.com.