Search our catalog for Nissan VQ35 pistons and you'll find two Wiseco sets that look almost the same: both are 95.5 mm, both fit the 2003–2006 350Z and G35, both are forged. One is listed as a -10cc dish and the other as a +7cc dome. Same block, same bore. The whole difference sits in the top few millimetres of the piston, and it changes how hard that engine squeezes every charge of air and fuel. This guide explains where that small cc number fits, what else sets your compression ratio, and how to read the rest of a piston title before you order.
Compression is about the space that's left
When the piston is at the bottom of its stroke, the cylinder holds the swept volume plus everything above it. When the piston comes up to top dead centre (TDC), only a small pocket of space is left. Compression ratio compares the two: the total space at the bottom divided by the space left at the top. Make that leftover pocket bigger and the ratio falls. Make it smaller and the ratio rises.
That leftover pocket isn't one thing. It's four separate volumes stacked on top of each other, and the piston crown is only one of them.
Here's what the four volumes in the diagram are:
- The chamber in the head. The pocket cast into the cylinder head over each bore. It's fixed by the head design, and it gets smaller if the head is machined.
- The head gasket. The ring of space inside the gasket's bore, as tall as the gasket is thick once it's clamped. A thicker gasket adds space; a thinner one removes it.
- The deck gap. The distance between the top of the piston and the block's deck at TDC, across the whole bore. Machining the deck shrinks it.
- The piston crown. The shape of the piston top. This is the number in the title.
Why a minus sign lowers compression
Piston makers describe the crown as a volume measured against a flat top. A dish is a bowl cut into the crown, so it adds space above the piston and is written as a negative number: -10cc, -16cc, -19cc. A dome rises above the flat line and fills part of the chamber, so it takes space away and is written as a positive number: +5cc, +7cc, +14cc. A flat-top piston sits close to zero.
So with everything else unchanged, the -10cc VQ35 piston gives a lower compression ratio than the +7cc one. Boosted builds often choose a lower ratio than a naturally aspirated engine, which is why so many forced-induction pistons are dished. But the right number depends on your boost, fuel and tune, so settle it with your tuner before you choose a part number.
The same cc doesn't mean the same ratio
Because the crown is only one of four volumes, a cc figure can't tell you the compression ratio on its own. The same -10cc dish produces a different ratio in a different engine, because the chamber, gasket and bore are all different. You can see this in our listings: Wiseco sells a Mitsubishi turbo piston with a -10cc dish, a Toyota turbo piston with a -16cc dish and a Nissan turbo piston with a +14cc dome. All three say "turbo", yet one is domed. That only makes sense once you remember the head's own chamber is part of the sum.
Some makers skip the cc figure and print the ratio instead. CP's EJ257 piston and ring sets are titled "CR (8.2)", and its VR38DETT set "CR (9.0)". Wiseco does both, depending on the part: its KA24 sets come as "9:1 CR" and "10.5:1 CR", while its VQ35 sets give cc. A ratio printed on a listing can only be true for one combination of head chamber, gasket and deck. Change any of those and the ratio moves, so ask the piston maker or your machine shop which combination the figure assumes.
The rest of the title, decoded
Piston titles pack several measurements into one line. Wiseco's LS sets spell them out, for example "4.030in Bore 1.304in CH -3.20 CC". CP's import sets use brackets, such as "Bore (99.75mm) - Size (0.25mm) - CR (8.2)".
| Title callout | What it describes | Example from our catalog |
|---|---|---|
| Bore | The cylinder diameter the piston is made for. Your block has to be finished to suit it. | CP K24 sets at 87.0 mm and 87.5 mm |
| Size | How far the bore is over standard. STD means the factory size. | The 87.0 mm K24 set is "Size (STD)"; the 87.5 mm set is "Size (+0.5mm)" |
| CH (compression height) | The distance from the centre of the wrist pin to the top of the piston. With the crank and rods, it decides how high the crown sits at TDC, which is the deck gap in the first diagram. | Wiseco LS sets at 1.304in CH and 1.110in CH |
| cc | Crown volume: negative for a dish, positive for a dome | CP's N55/S55 set at -9.7cc |
| CR | Compression ratio for one combination of head, gasket and deck | CP EJ257 sets at 8.2 |
Compression height is the callout most often overlooked. Two pistons can share a bore and a cc figure and still sit at different heights in the cylinder, because the crank's stroke and the rod length also set where the crown ends up. That's why pistons sold in a rotating assembly kit are matched to the crank and rods in the same box. Some shorter titles drop the labels altogether, like "1.378 X 85.5". When a number isn't labelled, check the description or ask before you assume which measurement it is.
What else moves the ratio after the pistons arrive
Choosing the piston isn't the last word on compression. Three later decisions change the other volumes in the first diagram:
- Head gasket thickness. The gasket's compressed thickness is part of the space above the piston. Our guide to choosing an MLS head gasket explains how thickness and bore are listed. Pick the gasket with the pistons, not after.
- Decking the block. Machining the deck surface flat brings it closer to the piston and reduces the deck gap.
- Machining the head. Skimming the head's sealing face makes each chamber slightly smaller.
Tell your machine shop which pistons and gasket you're using before any of this work starts. The engine build order checklist shows where these decisions lock in.
Where block reinforcement fits (and where it doesn't)
On an open-deck aluminum block, a boosted build often adds block filler to support the cylinder walls. It's worth knowing that it doesn't change any of the four volumes. Following the EPOXY54 Installation Guide, the epoxy is poured into the water jacket and stops 1–2 mm below the deck. It sits around the cylinders, not above the piston. The EPOXY54 product page says the deck surface stays untouched and the epoxy can go in before or after machine work without affecting dimensional accuracy. So your compression ratio is set by the pistons, gasket and machining, and you can plan it separately from the pour.
EPOXY54 gives open-deck blocks closed-deck strength without machining. It has 21,000 psi compressive strength and a thermal expansion rate closely matching aluminum, and it's a DIY install in 5 steps. It supports the cylinder walls of a sound block. It is not a crack repair. Our glossary of engine block terms covers the rest of the vocabulary you'll meet in a build.
Before you add pistons to your cart
| Question | Who answers it |
|---|---|
| What compression ratio suits my boost and fuel? | Your tuner |
| What bore will my block be finished to? | Your machine shop, after measuring |
| Which head and gasket does the listed CR assume? | The piston maker, or us by email |
| Does the compression height suit my crank and rods? | The piston maker or your engine builder |
| Which gasket thickness am I running? | You, and decide it with the pistons |
Browse every piston we carry in Pistons. If the block is open deck, add EPOXY54 to the plan. For a full parts list on one engine, our VQ35DE build parts list puts the pistons in context. Not sure which listing matches your engine? Email support@epoxy54.com with your engine code and power goal before you order.
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