The Millenia came with the 2.0 KF, 2.5 KL and 2.3 KJ as standard, depending on market and badge (Eunos 800, Xedos 9). However, despite sharing the 2.5's block, the KJ has one different engine mount to all the others which you'd need to account for.It's a K-family engine, so any of the other K engines should theoretically be "compatible", depending on what exactly you mean by that, including the tiny K8, the miller cycle KJ-ZEM, and the sonorous KL-ZE.
It's worth highlighting how absolutely awesome the KL-ZE can sound when tuned to the max (and with ITBs):
K-series motors sound great, but they're no Busso.
I know someone with a KL in an NB and it sounds phenomenal without being obnoxious like they can be in the hands of "enthusiasts".
I take it you've never heard a VR6 with ITBs?TWR V6 >>>>> Ferrari V6 > Honda VTEC V6 > KL-ZE / Busso > The rest
I take it you've never heard a VR6 with ITBs?
I mean...I'm not necessarily disagreeing with you (well, I am regarding the TWR as used in the 6R4*; re: obnoxious**), but there's something to be said for availability. The Busso was made for a quarter century (and sure, some sound better than others) and the Ks saw use in a wide array of cars with significant production figures...but you should be prepared to offer up your first-born to get your hands on the others.TWR V6 >>>>> Ferrari V6 > Honda VTEC V6 > KL-ZE / Busso > The rest
Busso sounds good, but not as good as the old Dino V6 and not as good as the NSX V6 (or anywhere near the 6R4's apocalyptic V6). I'd rate the KL and Busso about on par. Busso has more depth & bass but the KL has more melody, to my ears.