Being a K-series Rain-man hurts my brain. Here’s a slew of trivial K-series things the average joe may or may not know… (updated periodically)
Idle Air Control Valve (IACV) cross compatibility
IACV’s from the following engine/vehicles are cross compatible with OEM RSX Type-S K20A2/K20Z1 + aftermarket throttle body’s due to sharing the same IACV mounting flange pattern:
- 02-04 CRV (K24A1)
- 02-06 Base RSX (K20A3)
- 02-05 Civic Si (K20A3)
03-05 Accord, 03-06 Element and JDM 03-08 CL7 K20A all share the same IACV’s that are NOT cross compatible with the RSX Type-S throttle body nor aftermarket equivalent because of their different flange mounting pattern.
However, if you disassemble a K-series IACV and disregard the metal chambered body side, the actual sensor side (black body) are the same, and are cross-compatible with either the RSX or Accord metal chambered body.
Just about 99% of all aftermarket K-series tb’s are templated from the 02-04 K20A2 throttle body when it comes to bolt pattern and the IACV, TPS, and MAP sensor fitment.
OEM Cable Driven Throttle Body’s that are RBC/*RRC/*RSP Manifold Compatible
Honda has a couple factory drive-by-cable (DBC) throttle body’s that bolt right up to an RBC/RBB/RAA/RRC/RSP’s throttle body flanging without the aide of a throttle body adapter plate. Said manifolds typically come with a Drive By Wire (DBW) type throttle body. These DBC tb’s are found on the 03-05 Accord, 03-06 Element, and semi-rare 03-08 JDM CL7 Accord Euro-R K20A engines. However, their bore sizes are not all the same. The accord/element tb has a small bore size of 59-60mm and the CL7 K20R tb has a bore size of 62mm (equivalent to a K20A2/Z1 tb). The accord/element tb has a throttle pulley that supports cruise control while the CL7 K20R tb does not have c/c support. Regarding the IACV all 3 of these tb’s share the same type of IACV mounting pattern and not compatible with any other oem K-series tb’s such as the K20A2/K20Z1 RSX Type-S or JDM DC5/EP3 Type-R tb’s.
An important aspect of these tb’s is they lack a MAP sensor unlike the K20A2/K20Z1 tb’s. So you must rely on the intake manifold for map sensor mounting.
*The RSP manifold can support these DBC tb’s but a special type of tb adapter plate MUST be used in order to compensate for the RSP’s short tb flange that lacks an IACV provision.
*The RRC manifold can support these DBC’s tb’s with a small caveat; small modification needs to be made to its lower inner bore to provide an IACV vacuum source.
K20A2 vs K20Z1 OEM Throttle Body Differences
The 02-04 K20A2 and 05-06 K20Z1 oem throttle body’s might look identical on the exterior but have one small but major difference that can actually become and unforeseen issue: the MAP sensor vacuum source. If you take a gander on the backside of either of these tb’s, you will find the K20A2 tb’s map sensor vac source has a small recessed channel that runs parallel to the bore and then accesses the bore for a vacuum feed – this is a long running style Honda has used with most of their tb’s way before K-series. Honda/Acura for some dumb reason, made a small update on the K20Z1 tb by changing the vacuum source to a got damn single small. This hole relies on the K20Z1’s PRB intake manifold’s flange to access the MAP sensor. It’s the dumbest sh*t ever. So, when you use this particular tb on any other intake manifold – besides a K20Z1 PRB manifold – it WILL pose an unforeseen problem because of that small MAP vac hole. What happens is that MAP sensor hole gets choked off because no other manifold (oem or aftermarket) has a K20Z1 style map sensor vac hole provision, not even your typical RBC throttle body adapter plate. With a choked off MAP vac source, you will experience engine performance issues when revving up and past 2500-3500rpm. The engine will stumble past 3500rpm and will be easy to misdiagnosed for the unknowing.
FIXES
(1 – best) Grinding a channel from the K20Z1’s MAP vac hole to the mouth of the bore. This by far, is the best option as this will forever fix this issue no matter what manifold this tb is used on.
(2) Modify a K20Z1 thermal throttle body gasket. Thanks to this gaskets thickness, you can extend the opening of the MAP vac hole to reach the tb mouth for a proper vac source.
(3) If using an RBC/RRC/RSP manifold, use the MAP sensor on the manifold side instead of off the Z1 throttle body. But leave the map sensor on the Z1 tb as a dummy-plug tho!
USDM 02-04 RSX Type-S K20A2 and 02-05 Civic Si EP3 K20A3 engines both share the same PRB intake manifold and throttle body. The 05-06 RSX Type-S K20Z1 also uses a PRB intake manifold and similar throttle body as the K20A2 but received some small (dumb) changes at the map sensor and IACV feeds.
While Honda changed up the wiring and ECU type between 02-04 RSX and 05-06 RSX models, that carry over into the 02-05 EP3 Civic Si, it remained 02-04 wire & ecu type into 2005.
JDM K24A RBB vs USDM K24A2 suffix number internet overhype/hysteria.
coming soon.
K24 short block deck height is 19mm(1in) taller than K20 short block deck height.
The 07-09 CRV K24Z1 engine is a unique freak!
While the engine stamp ID is “K24Z1” one would assume its a typical K24Z era engine w/single exhaust port – NOPE! It’s 85% K24A and 15% K24Z. It uses an ECO K24A RAA short block/crank/rods/pistons and an ECO K24A RAA cylinder head (ie. 4-port intake & exhaust port head) + intake manifold, same eco engine you’d find in an 03-07 accord (K24A4), but it uses a K24Z’s girdle with relocated oil filter and does retain a 50 degree VTC gear just like its 02-06 K24A1 predecessor. Also the K24Z1 oil pan (PN# 11200-RZA-000) is interesting, its like an aluminum version of a K20A3 steel pan that caters to a balance shafted oil pump.
The CR-V has always seemed to be Honda’s little secret lil sandbox car.
The USDM 06-08 K24A2 TSX received updated engine components the rest of the world did not receive.
Particularly, the intake camshaft (larger profile), larger plenum RBB intake manifold, larger bore tb, 1mm larger (36mm) intake valves (altho useless/non power adders because the valve seat is still 35mm), and beefier rods at the big end. Again, there’s a lot of dumb internet hype surrounding this specific engine with the purists blowing their load over a few hp gains when comparing to the older 04-05 K24A2 variant and JDM K24A RBB variant (which is equivalent to our 04-05 K4A2).
Moving on, the 09-14 TSX K24Z7 and 12-15 Civic Si K24Z3 engines both share the same large profile intake camshaft, and its possible to use in a previous gen K24A RBB series engines if desired. The K24Z (R44) cam gear MUST BE USED as the K24Z intake camshaft is a few millimeters shorter than a K24A2/RBB intake camshaft and the R44 cam gear compensates for that. The K24Z cam lobes are narrower than the K24 RBB cam lobes but this doesn’t pose as a problem to the K24A roller rockers at all.
The K24Z VTEC lobe is a little smaller than the 06-08 K24A2 intake cam but the K24Z’s smaller primary + secondary (non-vtec) lobes have larger profiles than the 06-08 intake cams non-vtec lobes, meaning you will/should make a little more power before VTEC crossover with the K24Z cam, but the 06-08 K24A2 intake cam could make more power on the VTEC lobe due to having a slightly larger profile. Something to think about if you’re hunting for the most power with OEM parts.
Upgrading to a 50 degree VTC gear on a performance K24A engine will unlock some fatty mid range power once tuned.
K24 & K20 short block trivia..
All K24A generation cast short blocks are stamped “RAA” regardless if they are ECO or performance based. The RAA part numbering is usually associated with the ECO variant K24 engines, but Honda uses the same block casting for performance K24A RBB/K24A2 engines as well with the addition of plumbing for of the oil squirters.
Japan’s K24Z (R40) variant engine is actually block stamped with “K24A” and not “K24Z” like you’d assume to help differentiate. They threw a block identity curve ball with this engine for some reason. Typically the K24Z era engines have an “R40” stamped cast block, so the naming scheme for this JDM variant is K24A R40 if you pay attention to the JDM engine yard sellers. Its just a full blown K24Z era engine in disguise (ie. 4-port intake single exhaust port cylinder head) with an R40 cast short block. This is the JDM K24A variant that a lot of internet people claim/assume an 11.0cr JDM K24A engine exists, which it does but isn’t an 11.0cr K24A RBB engine. Without looking into details a bit deeper these peeps assume the wrong shid. I blame most of this confusion on Wikipedia. If you look up K24 details on their site you’ll see what I’m talking about. But not too long ago, I went and made some small changes to their listed 11.0cr K24A information to help dispel further confusion.
ECO variant RAA K24A – USDM K24A4/A8 (RAA) and JDM K24A RAA short blocks use PPA stamped rods, RAA eco crankshaft, RAA pistons, 6.5″ diameter crank pulley, balance shafted oil pump, steel oil pan, no oil squirters, no oil cooler/heat exchanger, runs a coolant diverter, RAA water pump housing. JDM K24A RAA engines might use the funky “RFE” type water pump housing just like the JDM K24A RBB engine.
Performance variant K24A – aka JDM K24A RBB, US K24A2 (04-05, 06-08), UK K24A3 – RAA cast short blocks w/plumbing for oil spray jets, RBB 10.5cr pistons, RBB performance crankshaft, RBB rods, 6-1/8″ diameter crank pulley, uses coolant diverter, balance shafted oil pump, steel oil pan, all except the UK K24A3 do not have an oil cooler/heat exchanger (K24A3 runs a cooler). The JDM K24A RBB has its own one-off type “RFE” stamped water pump housing that has a completely different mounting style for its accessories (alternator, p/s pump, and auto tensioner). Aside from the several exterior differences, the cast block/crank/rods/pistons are all the same between the US 04-05 K24A2, JDM K24A RBB and UK K24A3. The 06-08 K24A2 received some updates the rest of the world did not get, specifically with the updated beefier yet slightly lighter RBB rods and updated RBB pistons with slightly bigger valve reliefs to accommodate the 1mm larger intake valves (non-power gainers btw) with no change in compression ratio.
…more soon