Water pump differences.... (k20a2/k24a2) clarified

HotWheelz · Mar 15, 2006

Some people have been wondering if the pumps were the same or different, i'll grab some pics later tonight (at work), but they are infact different, the actuall size of the k20a2 water pump is smaller by about 2-3mm on the pulley itself., i'll mesure them exactly and post pics. so the k20a2 water pump is underdrived from the TSX/k20a3's and k24a1/3/4's counter part. I noticed this and was quite intrigued. (if the waterpump system) does cavitate at highrpm, if you used the same crank pulley one could use this water pump and plug the cooler port.

the ECT question people had, you have to understand when you underdrive you are doing it to all the accessories. waterpump also. less rotation on the pump will draw less power, but less flow aswell.

something i'll test for certain on the dyno! mesurable hp if any.

so a k20a2 water pump, and crankpulley is a "factory" underdrived unit compared to a k24a2 engine. Also you if you use a k20a2 crank pulley when doing the tensioner bypass, you will need the aem pulley and might need to shim it greater because of the shorter radius, thus affecting belt clearances.

na200whp · Mar 15, 2006

good info. i can tell you for sure the new 06 SI (k20z) motors water pump will not bolt up to a k20A2 block. bolt pattern is different.

tony4380 · Mar 15, 2006

i realized that. the water pump that came off of my donor car's k had a bent pulley, so my friend had an k24a3 waterpump.the housing and all is the same... but yea the pulley size is slightly different.

measureable HP?? maybe... significant? we'll see. then again, every ounce counts!

HotWheelz · Mar 15, 2006

you should mesure the Z1 pump, take a mesuring tape, and mesure the whole diameter of the pump so we can compare.

chunky` · Mar 15, 2006

Interesting. I'm using a k20a3 crank pulley, a k20a2 water pump pulley, and all accessories from a k20a3 (civic si). I guess I didn't notice the 2-3mm of difference because it didn't affect how the k20a3 belt I was using went on.

iRSX-S · Mar 15, 2006

so using the k20a2 waterpump will gain more hp and have better flow?

and all i have to do is plug the cooler hole?

EvaUnit01 · Mar 16, 2006

interesting stuff, would this be for something like say a k24/k20 combo where some people use aftermarket oil coolers?

HotWheelz · Mar 16, 2006

A2 (TSX) block comes pre-tapped ready to roll, no other k24 block does.

EvaUnit01 · Mar 16, 2006

so just use the A2 water pump and aftermarket oil cooler, sweet.

mike323 · Jun 25, 2006

HotWheelz said:
Some people have been wondering if the pumps were the same or different, i'll grab some pics later tonight (at work), but they are infact different, the actuall size of the k20a2 water pump is smaller by about 2-3mm on the pulley itself., i'll mesure them exactly and post pics.

I just measure my K24A1 and my K20A2 water pump pulleys and they're both 128mm.

Mike · Jun 25, 2006

You sure about the base model K24s not already being pre-tapped? I just went and looked at a K24A1 we have and Justin's K24A2, the place for the oil cooler looked to be exactly the same on both motors.

jyr3x · Jun 26, 2006

good info...hotwheelz you got so much times in your hand...

winek · Nov 30, 2006

is there any difference on the placement of the pcv valve on the k20 water pump, ive got a custom intake for my k20 that the bottom of it is hitting the pcv valve on the water pump assembly and im wondering if the k24 pump is different

BOMrsxS · Mar 12, 2025

@LotusElise I know this thread is 20 years old but I found it from you linking it in another more recent thread. Last week I bought a BNIB OEM K24 water pump, part# 19200-PNA-003, because this past weekend I was set on buying a K24A1 block. While at the shop to buy the block they offered me a JDM K24A for the same price, which I took being it already had the oil squirters and I wanted to utilize those again as I did in my last build. I didn't think about the water pump differences while in that moment. Will this USDM water pump still work ok on my JDM K24A?

yaggs · Mar 13, 2025

Keep in mind that sourcing jdm ancillary parts might be difficult for future repairs. All of the belt driven accessories (alternator, ps pump, auto tensioner) must be the same style as the wp housing, whether its USDM or JDM.

gtimportfanatic · Mar 14, 2025

The thing that matters is whether the engine has an oil cooler or not.

katman · Mar 16, 2025

(spewing maybe too much info here...)

a PNA stamped wp housing is usually found on eco K20A3 and 02-06 K24A1 engine(s). While RAA wp housings are found on usdm Accord/TSX K24 engines. They also require their respective alternator or you'll have fitment issues because of the got damn slight differences in water pump flanging.

a PNA wp housing would require an alternator from a K20A1/A2/Z1 or JDM EP3/DC5 K20A Type-R. These typically are a smaller alternator body type.
an RAA wp housing would require an alternator from a 03-07 Accord K24Ax, 04-08 TSX K24a2, or K20Z3 (an easy visual indicator would be the front facing connector w/black plastic inner cover). These are generally a bigger sized alternator body than the latter alternators. So, if you try using this bulkier alternator type on a PNA housing you will experience unwanted fitment issues, however using the smaller body alternator on an RAA housing will not be a fitment issue.

The JDM K24A's have one off style wp housing and alternator w/no idler pulley provision, but I found out they actually share the same type of WP housing + alternator as our USDM K24Z R40 engines. I haven't had a chance to physically confirm actuality's but allegedly they're the same so there's a possibility you wouldn't be assed-out if say the JDM K24A alternator died on you. Personally I'd switch over to a USDM wp housing and alt if I ever picked up a JDM K24A RBB engine just to save on future hassles/annoyances.

BOMrsxS · Mar 20, 2025

Awesome thanks for the detailed info. Luckily for me I have no housing or alternator whatsoever. I just bought a new pump. So to save space I should shoot for the RSX housing and alternator. @HSPrzepa did you already pull that TSX alternator I asked you about?

Water pump differences.... (k20a2/k24a2) clarified

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