Deck Clearance for Honda D-series Turbo Build Aimed at 300 HP

I'm currently in the process of building a turbocharged Honda D-series engine with a target power output of 300 HP. The setup involves combining a JDM D15B block (P2A) with a non-VTEC D16A head (P2A-11), utilizing the stock crank from the D15B block.

The issue I'm facing is that the parts I've selected, including the crank, pistons, rods, block, and head, have resulted in a deck clearance of -0.1mm, indicating that the piston will be 0.1mm above the deck height. I'm concerned about potential interference between the piston and the cylinder head. Is this deck clearance acceptable for my power goal of 300 HP, or is it problematic regardless?

The negative deck clearance of -0.1mm was determined through calculations. The JDM D15B and D16 share the same rod length of 137mm. To accommodate the taller D-series YCP Vitara pistons, manufacturers shortened the D15B forged rods to 136.38mm, given the shorter block height of the JDM D15B. However, using D16 Maxpeedingrods conrods, which maintain the stock length of 137mm, along with the taller YCP pistons, has led to the increased deck clearance issue.

I calculated the deck clearance using the formula:

Deck Clearance = Deck Height - ((Stroke ÷ 2) + Rod Length + Pin Height)

- Deck Height: 207.45mm (D15B block)

- Stroke: 84.5mm (D15B crank)

- Rod Length: 137mm (Maxpeedingrods)

- Pin Height: 28.30mm (YCP Vitara pistons)

This calculation resulted in a deck clearance of -0.1mm:

-0.1 = 207.45 − ((84.5 ÷ 2) + 137 + 28.30)

Any advice or insights on whether this deck clearance is acceptable for the intended power level would be greatly appreciated.

Personally, I'd be OK with that - othrs may feel differently - but until you do a dummy build to confirm, it's just guess-work, because of tolerances in the block height - on that, have you had the deck checked for flatness and parallelism with the crank centre-line, as if that needs a light clean up and/or better finish for the head gasket, it will also affect the final values.

If you're still a bit concerned, you should have options for different head gasket thicknesses, possibly from different suppliers, that will change the piston to head clearances.

Great suggestion Gord, a thicker head gasket will raise the head away from the piston. A head gasket with a thickness of 0.030in (or 0.762mm) should give a clearance of 0.026in (or 0.662mm).

When it comes to deck clearance, I [read that a piston should be at least 0.035in - 0.040in](https://turbobricks.com/index.php?threads/help-with-piston-choice-please.17231/post-158431) away from the head for good quench.

By switching to a 0.060in head gasket, I will achieve a better deck clearance

However, I've run into a deadend, where the D15B engine is of a newer generation, where it has a 45mm rod journal (like the D15). It does not have a 48mm rod journal (D16). So, I do have a D16 block, but will need a crankshaft to make it work.

Thanks for your input

Might be worth checking the main bearing manufurers a they may have special, thick wall conversion bearings available, or can make them you your speciication, which may be a financially viable alternative?

Different engines, or rather cylinder head/chamber designs may have different "sweet spots", but rather than "re-inventing the wheel", you're probably better to use what other Honda folks have found to work.

I'm not sure about the mixing and matching, but I'd also suggest checking the rod's side clearance and whether the journal radius may be an issue - but some more modern engines use a reduced diameter for the radius, which would remove that issue.

When it comes to bearing designs, does the size matter?

Could you give more detail about what the concern is?

As a general rule, larger diameter and/or wider will give more load bearing capacity, but at the cost of increased drag and increased oil temperature.

The concern is the thickness of the bearing metal. That is, the thickness between the inside diameter (ID) and the outside diameter (OD). Example: Let's say my bearing has an OD of 105mm and an ID of 103mm. I wish to fit a crank with 100mm big-ends. So I increase thickness of the bearing by decreasing it's ID to 100mm (matching the crank) and keep the OD as 105mm. The bearing now has a thickness of 5mm opposed to its previous size of 2mm. The question becomes, what effects does the increased thickness have on the mechanical function of the engine?

When you say larger diameter, do you mean a bearing with an increased clearance give more load capacity but also increased oil temperature?

Bearing shell thickness is half the difference between the journal and the bore it's fitted into, in your engine's case it will be an extra 1.5mm, and while it will slightly reduce the heat transfer that helps cool the bearing, that's small compared to the oil passing through it.

By larger diameter and/or width, I mean the physical size of the journal, or rather the shell's dimensions, rather than the clearance.