[oldman]

The Blackwing has an absolutely tinny tiny intake port and intake manifold and associated head port which is also outside the the V. The intake ONLY works with twin turbo. To feed a much bigger 5.5 liter the engine would have to grow 30% or so and to get a conventional layout intake in the V, that could also breath would add another 10% or so. Ford 4.6 and 5.0 engines are HUGE, the 5.4 DOHC is even bigger. The only way to get a DOHC engine to breath NA is to raise the intake port and that makes the engine even bigger. The Blackwing uses FI (20 PSI) to achieve what essentially is mediocre power from a FI DOHC engine. 550 HP from a twin turbo V8 clean slate design is not very good. Then comes the excuse oh it is only 4.2 liters, LOL. Internal engine size is not a design criteria in the USofA. Lastly the Blackwing was limited in HP because of engine bay heat.... a killer for sure on a performance car with GM ready to race warranty. That what happens when you fill an engine bay up with a huge engine and two turbos. How many times has GM been bitten by a heat problem?


So say the new DOHC engine does produce 600 HP NA and GM could "fit" it into the Camaro, what do they get? The engine will produce less hp and way way way less torque than the LT4. What "race" or street driving will this new engine / chassis excel at? The LT4 > Voodoo, why would GM put a a slightly bigger Voodoo along with all the problems associated with DOHC high revving engines. GM would be LAUGHED at when this Z/28 DOHC would inevitably be matched against the GT500 and the ZLE, even more so if the LT5 goes into the ZLE (completely believable).

To my mind the only reason for a DOHC 600 HP NA engine is for marketing on a base Vette, assuming the Camaro 7th gen will be mid engine OHV with a choice of transmissions.
Up to 60K you get a Camaro mid engine OHV with choice of transmissions and NA
up to 70 K you get a C8 DOHC NA 600 HP
upto 80K you get a twin turbo C8 700 HP
above 80K gets you a high boost twin turbo C8 at 900 HP.

essentially the Camaro remains a "poor man's Vette", and finally loses the useless backseats;

Back to the Blackwing "The Blackwing was meant to differentiate the top-level Cadillac from the rest of GM's products.... the small-block V8 could fit the Omega platform.... the supercharged small-block... wouldn't fit the character Cadillac was striving for."
Which is essentially what I'm saying a DOHC V8 NA for the Vette is more about marketing than performance. It the engine does not have to have NA performance, it makes more sense to build a Blackwing type engine with small ports and FI (better torque, better smog, better MPG, smaller externally, more responsive), but alas GM would not have an entry level NA DOHC V8. If it were me, I would say:

Mid engine Camaro OHV your choice of transmissions.
C8 2021 DOHC twin turbo base 650 HP low boost, DCT with no thought of good breathing NA DOHC.
C8 High boost up to 900 HP, DCT


Here:
"Given Cadillac’s abrupt change of course, it’s amazing that the Blackwing engine even made it into production. The few examples of the twin-turbo V-8 were hand-built in Kentucky, at the Bowling Green plant where the Corvette is assembled. Each engine was constructed from start to finish by a single employee, one of just six appointed to this role. One source estimates that the Blackwing cost General Motors $16 million to develop—around $20,000 per example. You get the sense that the team behind it wanted to show Cadillac was capable of producing a world-class engine, even if the production run was extremely small."