Al Rilma - few impressions mainly about forced induction

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Sooo take this all with a grain of salt, as I didn’t perform proper comparative tests or anything like that (that would take much more time), but those are my general impressions after playing with some engines a bit.

  1. Turbos spool later and/or slower - it seems like the spool slope is less upright, which makes simple one turbo setups less viable for high boost applications - which I guess makes sense, but it still feels excessive, especially when comparing the same engines from stable and their open alpha clones. Also…
  2. There’s absolutely zero point of using two parallel turbos when one can be used - it literally has no benefits and several drawbacks, which I guess should not be the case. Oh, and I mean one larger vs two smaller, with the same target output, if that wasn’t clear. IIRC in the stable version it at least improved responsiveness (quite logically), which is no longer the case. Also, again, haven’t really tested that, but it feels like two parallel turbos really don’t act like a single turbo of that size would on an engine half of the size. Like, twin turbo I6 doesn’t act like two single turbo I3s welded together. And while that was the case on the stable version too (which always kind of bothered me - like, why?) it feels somewhat more pronounced now?
  3. If the engine has forced induction, it usually makes more power with an extremely low cam profile. On performance heads (at least below ~7000 rpm) zero is the best cam profile for power with a turbo and/or supercharger. With standard heads it’s still sth like 15-20 I think? It creates a high torque peak early in the rev range, which I think can be undesirable sometimes (less smooth curve, more stress on internals or gearbox). Again, I don’t think it behaved like that in the stable?
  4. Should high and low pressure turbos be the way they are? It feels like the high pressure is the base one, and the low pressure is “on top” of that. When I tried to build an engine with that setup it actually seemed to have a better curve when the high pressure turbo spooled first, and then the low pressure one - shouldn’t that be in reverse? I might be misunderstanding the way it should work, but it certainly feels very odd.
  5. I think there’s a lack of communication of the flow effects of the chosen head, manifold and header types. Especially the heads - I don’t think their flow is clearly indicated anywhere, and sometimes they are the limiting factor.
  6. Flow percentages seem all over the place in forced induction engines - either that, or the manifold and header scaling is all over the place for them. 100 % is often simply impossible with more advanced forced induction - the headers and manifolds are oversized even on minimum.
  7. Engines are way heavier than they used to be! Differences are like 200 → 250 kg I think. Cars seem a bit heavier too… but I don’t think it’s as consistent? At least the weight distribution seems to make more sense than it used to in the stable - now 50:50 on a normal FR car is not some miracle.
  8. Twincharged engines are nice. Compound turbos are weird, but pretty nice too.
  9. The new reliability system is so much better.
  10. High revving N/A engines seem down on power a bit? One example I have is a modern 3.3 DOHC engine - in stable it made 350 hp and around 420 Nm I think (yeah, that torque was unrealistically high), now I couldn’t really get its clone above around 335 hp without sacrificing something (but the torque is more realistic). I haven’t yet tried remaking the Valkyrie V12 replica to see how that would turn out (which was difficult, but possible in stable), but I have doubts.
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A minor update - it turns out I didn’t delete the Valkyrie V12 replica, so I cloned it and adjusted to the changes… and it makes a bit less power than on stable, but that still means the same power as the real engine, at the same revs, just with the torque peak being 10 Nm lower and 1000 rpm later (at the correct revs it’s 25 Nm down from the real engine). Although this uses race heads, which I’m not sure if it’s intended. I mean, I had to use race intake even on stable, and IIRC that looked more or less like what Aston Martin is using IRL, but still worth noting.

Edit: oh, wait - the GM LT6 is as impossible as before - around 640 hp on stable, 637 hp on open alpha… if WES11 is to be passed in a rough Corvette replica. That basically requires pre-cat, and a pre-cat requires at most tubular mid headers, which limit the power on such a high revving engine. With long headers it’s making even more power than the real engine (670 hp vs 693 hp without adjustments). I haven’t put the Valkyrie engine in a car before - now I’ve done it, and guess what, it also can’t pass WES11, it tops out at 8 with the power intact. At WES11 it makes around 125 hp less!

Something about forced induction

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This is the same engine, stable and open alpha. 3.0 DOHC I6 with a single turbo giving 0.4 bar of boost. 42 hp and 46 Nm down! And that’s precisely the kind of application in which, I think, a simple, single turbo setup should be perfectly fine.

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BTW, I’ve found some context for high boost single turbo viability.

  • Ingenium P300 - 2.0 engine making 300 PS @ just 5500 rpm with a single twin-scroll turbo (although it has MultiAir, which may help a bit)
  • Mercedes M260/264 - 2.0 engine making 299-306 PS at around 6000 rpm with a single, twin scroll turbo, and a less magical valvetrain
  • VAG EA888 - apparently they all have single turbos, even the one making 333 PS at 5600 rpm (that’s a 2.0 from the Golf R)
  • VAG EA855 - 2.5 making up to 407 PS (at least ignoring Donkervoorts) at 5400 rpm with a single twin scroll turbo
  • BMW B48 - it seems the 306 PS version of this 2.0 also uses a single twin-scroll turbo. Oh, and reaches its peak power as early as 5000 rpm.
  • Toyota G16E-GTS - a 1.6 making up to 305 PS at 6500 rpm with a single single-scroll turbo

Also, there are engines which I discarded, as I couldn’t really tell how their forced induction works:

  • Stellantis Hurricane - “twin turbo”, but is it parallel or compound? No idea, but it makes up to 540 hp and over 700 Nm. And the peak power is likely before 6000 rpm, as the redline is apparently at 6100. Oh, and I didn’t really look for twin turbo engines (for parallel twin turbo context), so it’s not that relevant here anyway (I thought it might use a single turbo).
  • Mercedes M139 - “electrically assisted” turbo. How much difference does it make? No idea, therefore out the window it goes.
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