I’ll use this topic for when I have some questions that are related to engine design
Currently, I’m on the Al Rilma open beta, patch 9
The wiki mentions that each fuel system has a maximum air-fuel ratio that it supports. Have the values changed since the page was last updated? (By the way, it would be nice if this value is displayed in the tooltip )
Is there also a minimum air-fuel ratio that each fuel system supports?
What’s the best way to lower the idle RPM, without sacrificing too much power and throttle response? From my experience, using a better balancing system, and increasing the balancing weight, don’t seem to be doing much to lower the RPM. Maybe I’m targeting too low of a value? (800)
Pretty sure idle value is purely determined by the balancing weight. Max balancing weight should give you 500rpm idle and minimum should be 2000rpm I believe? Unless this has changed recently.
That also depends on the layout, I3s have higher idle by default, I6s have lower… But I’m not sure if that’s tied to smoothness or just the cylinder count (which would make a difference for I6 vs V6).
Some engine configurations (such as I4) can also have provision for balancing shafts in place of harmonic dampers, but this doesn’t affect idle speed. Also, an I4’s idle speed is in between that of an I3 or I6 with the same family dimensions (bore/stroke). Changing the primary cam profile will also affect idle speed, but in addition to affecting efficiency, doing so also changes the engine’s overall output (unless VVL is fitted, in which case it only affects the power/torque delivery before the VVL threshold, and hence efficiency, although VVL profile adjustments will still affect output).
Usually maxing out the balancing weight results in a 1300 RPM idle, unless I drop the cam profile to something like 20. I do try to set the cam profile to reasonable values, even when targeting performance, which is why this outcome seems odd to me. I get this behavior on a wide variety of engine configurations as well
I hope that it’s using smoothness, othewise it’s penalizing low cylinder count engines even if an effort is made to make them buttery smooth. Would be more realistic as well
I tend to make smaller capacity engines (like 1L inline 4s. Does engine size affect idle speed in game?), so for most cases I usually use the harmonic balancer instead of balancing shafts
Changing the cam profile does indeed work, and is what I’m currently having to do if lowering the idle RPM is desirable (at a cost of performance, unfortunately)
From my understanding, in real life, idle RPM is mostly determined by engine smoothness, cam profile, and the efficiency of things being driven by the crank, like the water pump, and alternator. This means that it’s possible (although it admittedly it would take time, and be more expensive) to make inherently unbalanced engines to idle smoothly at a low RPM, if you manage to balance them correctly and pair them with efficient auxiliaries
Well Automation idle speeds are a bit weird… I know from experience that a N/A PureTech (modern 1.2 I3) idles at around 750 rpm, despite not being all too smooth overall. Granted, it does have a very low revs optimised cam profile, but still I don’t think getting that low in an I3 is viable in Automation.
Although 1300 rpm at max weight in an I4 is surprisingly high, are you using some race cam profile? If so, then that would seem pretty realistic I think.
Just today, I’ve made a 1L I4 with a 70 bore and 62 stroke, used quality 4 for every slider (tech pool is 0)
Engine redline is 8000, and I set the cam profile to 69. With the balancing weight maxed out, idle RPM was 1200, and using a harmonic damper or balancing shafts made no difference. I had to lower the redline to 5700 and the cam profile to 35 to lower the idle to 800
Damn, yeah, that’s a very sporty setup, no wonder the idle is high Seems like it’s not related to smoothness, but - in terms of engine layout - just to the cylinder count. And, of course, besides that to the balancing weight and cam profile. If you want both high revs and low idle you should consider using VVL.
Well it’s quite simple, you set the lower cam profile for the low revs, and higher for high revs, and set the RPM threshold at which the engine switches between them. So you can have that 69 as the VVL profile, and some 35 or even 20 for the regular profile. That way you have the best of both worlds at the cost of some more complexity and weight.
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Seems like it’s not related to smoothness, but - in terms of engine layout - just to the cylinder count. And, of course, besides that to the balancing weight and cam profile. If you want both high revs and low idle you should consider using VVL.