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 Â 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 Â 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.
2 Replies to “K20 Head Swap onto K24 Block”
Came along your site here while doing some researching. Decent little site with decent info, thank you!
I’ve been researching in regards to try and determine what folks are doing for a head gasket when they get a K20Z3 bottom end sleeved which removes the coolant diverter item in the block and are intending to run the K20Z4 (RSP) or even the K20Z3 head? I have not yet been able to find any text yet referring to this however based on text relating to head swaps and Frankenstein builds it would possibly suggest that one would use a K20Z3 head gasket as it matches the head and maybe thats not ideal but the best option. I would love to hear from anyone who has any solid info regarding this specific combination.
You would want to stick with a Z3/RBC or Z4/RSP headgasket with a proper bore size and also retain the use of the coolant diverter as well. The diverter works in unison specifically with that K-series head type (RBC/RSP) unlike the K20A/A2/A3/Z1 PRB head that does not require one.