K20 Head Swap onto K24 Block

I got tired of googling around sifting through posts on what the proper combination of components are required for swapping a K20A2/Z1/Z3 head onto a K24A1/2/4 block. Thanks to K20A.org forum I’ve compiled the proper ‘combo’ parts list below.

First off, a little head comparison info.
If you didn’t know, the K24A2/TSX head isn’t as “performancy” as a Type-S head CFM-wise. Hence why a lot of folks switch over to a Type-S head or simply because they are piecing together a K24 build and need a head. There’s a thread on K20A.org where member DRAG ran the most commonly used stock K-series heads through a CFM flow bench  and made a nifty comparison chart (view thread HERE).

Stock-vs-stock CFM flow bench results are as follows from best to meh:

• RSP head / JDM K20A (FD2) – 1st best flowing cream of the crop / best flowing factory head found on the JDM FD2 K20A CTR engine. Rare AF to find in the states. Head looks similar to that of a K20Z3 & K24A2 head w/side mounted water neck. Also is the only K head that is factory ported – has an ‘NSX’ port job. Usually stamped with “RSP-2” on the head casting.
• PRB head / JDM K20A, K20A2/K20Z1 – 2nd best flowing head CFM wise. Most common head used for K20/24 builds. Found on the RSX-S K20A2 & K20Z1 engines & JDM EP3/DC5 K20A engines. Has front mounted water neck. Typically stamped with “PRB-1” on the head casting.
• PPA head / K24A1 – 3rd best flowing head. Found in the CRV with K24A1. This head isn’t really used for typical street builds. Its used for drag race ‘vtec killer’ builds since it does not utilize the typical 3-rockers per exhaust & intake nor has the provisions for lost motion assembly use on the exhaust side of the head. Typically stamped with “PPA-1” on head casting. 4piston has done some port job wonders on this head and increased CFM substantially.
• RBC head / K20Z3 – 4th. Found on the 06-11 Civic Si. Shares the same head layout as a K24A2 head w/side mounted water neck, but doesn’t have the same port angle as K24A2 head nor smaller ports. Typically stamped with “RBC-2” on head casting.
• RBB head / K24A2 – 5th. Found on the 04-08 TSX. Shares same head layout as K20Z3 and FD2 head w/side mounted water neck but ports are not the same, are smaller and flow weak vs. all heads listed above. Typically stamped with “RBB-2” on head casting.

When swapping a K20A (EP3/DC5), K20A2, or K20Z1 head onto a K24A1/A2/A4 block the following parts are required:

• CRV / K24A1 head gasket – Honda P/N 12251-PPA-004
  This gasket matches a K24A’s 87mm bore size  and also shares the same exact coolant passages as a Type-S head gasket + head. You can’t/don’t want to use K20A2/Z1 headgasket because it has a smaller 86mm bore size and the gasket will hang into the cylinder bore.
• Remove coolant diverter – if present
  If left in place, may cause overheating issues (says the internet). The PRB head isn’t designed nor requires the use of a coolant diverter.
• Use K24A headstuds
• Use K24A timing chain

When swapping an RSP or K20Z3 head onto a K24A1/A2/A4 block the following parts are required:

• TSX / K24A2 headgasket – Acura P/N 12251-RBB-004
  This gasket matches the K24A 87mm bore size and has the proper coolant passages for the RSP, K20Z3, and K24A2 heads.
• Coolant diverter MUST be used
• Use K24A headstuds
• Use K24A timing chain

An easy rule of thumb is that a head gasket matches the head its designed to work with.

Credits to K20A.org forum & it’s members for information shared in this article.