Okay, so correct me if i'm wrong, when it comes down to the Z3 saying VTEC across the engine and not across the engine, all it means is how many valves will run at certain RPM's?
Let's make it simple. There's no such thing as a "Non VTEC" 8th gen Accord. All 8th gen Accords have VTEC.
The V6 has 2 different versions: the "VCM" iVTEC found in the automatic transmission equipped V6's. And the non VCM regular VTEC (not iVTEC) V6 found in the manual transmission equipped V6's.
The 4 cylinder has 3 variations (2 of which are slight variances of the Z3): The K24Z2, and the K24Z3. The Z2 is found in the Accord sedans, in the model trims: LX, LX-P, and SE (SE is a Canada only car). The Z2 was more restricted in terms of it's ECU tuning, and the exhaust being smaller diameter than the systems on the Z3 models, as well as the muffler being more restrictive. The K24Z2 is an iVTEC engine.
All of the 4 cylinder 8th gen Accord coupes (yes, all trim levels: LX-S, EX, & EX-L, both manual and automatic transmissioned) all came equipped with the Accord tuned version of the Z3, which are all iVTEC engines. The Z3 version has a larger diameter exhaust system than the Z2, and a higher flowing muffler, and more performance oriented ECU tuning.
The other variable of performance between the Z2 & the Z3 is the transmission and the PCM tuning. The Z2 is geared a little differently, and the PCM tuning is not intended for performance, but rather for economy and efficiency.
The automatic transmission in the Z3 equipped cars is more performance oriented in the PCM tuning, and has "sportier" gear ratios.
Now, for the "3rd version" of the K24Z, being the 2nd version of the K24Z3, which is the Acura TSX version, not the Accord version. It has slightly higher compression than the Accord, different ECU tuning, and electric power steering instead of a traditional power steering pump. Further, the TSX with automatic transmission has a magnesium transmission case which is approximately 9-10 pounds lighter weight than the Accord transmission case. The TSX also comes with a performance tuned PCM and oriented transmission, and is a little more refined than the Accord's transmission.
Furthermore than that, the 2nd gen TSX ('09-'14) has the option of paddle shifters for it's version of the K24Z3 with 5 speed automatic transmission.
The other variation on the 2nd gen TSX with K24Z3 is that they had the option of a 6 speed magnesium cased manual transmission with close gear ratios.
There are other variations of the K24Z series, but not in the Accord or "Accord related platform being the TSX".
As stated by someone else, the K24Z2 & Z3 in the Accord utilizes iVTEC only on the intake cam, not on the exhaust cam. The only thing the exhaust cam has "special" is the "VTEC-E" feature as mentioned, in which what it does is only activates 1 exhaust valve per cylinder below 2,500 rpm, once the engine reaches 2,500 + rpm, a mechanism is activated which operates both exhaust valves.
The purpose of the "1 exhaust valve" per cylinder in low rpm is optimization of fuel efficiency and low rpm torque delivery. It's actually not a bad thing, it helps reduce emissions, more effectively uses fuel, generates more power and torque in the low rpms, and is helpful in performance applications by optimizing swirl and quench for more effective ignition which helps reduce knock, ping and predetonation. But that's a totally different conversation.
