as the title states…
why not?
tl;dr answer: Automation families work like Honda and not Toyota or Nissan. There are no SOHC K24s. There are no DOHC R18s.
Slightly longer answer:
Because game balancing.
When Tycoon mode is implemented the intention is to give the player a bonus of some sort for engines which are broadly similar. If you have a different head on your engine, literally half of your long block is a different engine entirely. See below:
[quote][size=85]Time taken to develop a block: a engineer-hours
Time taken to develop a SOHC head: b engineer-hours
TIme taken to test & validate complete engine: c engineer-hours
Time to develop New Engine 1: a+b+c
Time taken to develop DOHC head: d engineer-hours
Time taken to test & validate the new combination: e engineer-hours
Time required to develop a DOHC “variant” of New Engine 1: a+b+c+d+e[/size][/quote]
Heads don’t “bolt on” in real life. Broadly speaking, the RB26DETT and the RB30E are completely different engines; they share the same RB designation because some parts from one will bolt to the other. This is not intentional. Nissan did not design the RB engine family with this in mind. The fact that you can put the RB26DETT head onto an RB30 block is a convenient coincidence allowed by the fact that all RB engines use a similar short block for development and production reasons.
Also, I don’t see people putting OHC heads on Chevrolet small-blocks.
Honda’s a very bad example sohc dohc and vtech all in the same famiy. I’d say GM is better, many sizes of the same engines and Valve train changes only happened after family changes.
Honda J engines are SOHC, K engines are DOHC, R engines are SOHC. Yes, L engines are produced both with and without VVL, but are all SOHC. They all use the same blocks and head materials throughout the family, with exception of the K series engines, which have a different deck height for the K20 and K23/24.
As far as GM goes, I agree in the case of Family 0 and Medium Gasoline I4s, and the High Feature V6s. Meanwhile the Generation V small-block family of V8s contains a V6 and the Small Gasoline family contains both I3s and I4s.
I hope they add the ability to clone engine families since we can’t have different heads within the same family.
I think including that function has been mentioned already so you can lift and shift an entire family and amend the base details to cascade it down to each variant