Have Turbos Been Nerfed for 4.2?

Hi guys, I’ve been having a lot of fun with the 4.2 update because of how technical the turbo tuning is. But I’m just wondering, prior to the update I could get close to (and at one point crack) 40% engine thermal efficiency which made turbos really OP. With 4.2 I can’t even crack 30%. Am I just tuning it wrong?

For the sake of comparison, tuned for efficiency and reasonable performance:
3-Liter, Inline-6, NA: 30%+ Thermal, 200kw (260ish hp)
3-Liter, Inline-6, Turbo: 25% Thermal, 160kw (210ish hp)

And the turbo engine has the most disgustaaaang torque curve I have ever made (even with vgt) and an exhaust the size of a prolapsed anus.

I truly depise this engine

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What are the torque numbers? Power is only one part.
That torque curve looks absolutely perfect. Full boost before 1800 rpm? Nice.
Then flat torque up to 4000 rpm, that is what modern car makers strive after.
It would be perfect for hauling a trailer.

BTW most cars spend their entire running life between 1500 and 4000 rpm.


Thanks for the compliments, but its a far cry from the old engine’s I’m used to making that would have a flat torque curve from 2000 to 5000. I am a bit concerned about efficiency though as it seems that 4.2 has made it basically not worth putting a turbo in the car. Like 25% is pretty bad compared to 40%. And this was with a VGT with maxed out exhaust size.

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Efficiency is bugged, its getting fixed.


Turbos aren’t magic efficiency generators. I don’t know what the old game was doing to get turbos to have over 40% TE, but that’s really just not how it works.

Efficiency has some bugs in general, but turbos aren’t supposed to be magic “I want efficiency” buttons.

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I admit that the old turbos were OP, that much is clear. I previously stated that they were and I agree. 40% I know is a bit high, but it is doable without turbos (2016 prius atkinson cycle engine achieved this) and should be doable with turbos as well.

But what made it OP was that you could get both higher efficiency and higher power. My opinion is that you should be able to have one or the other, as is the case in real life. Not both as in old Automation.

But I think if we take a look at today’s standard cars, almost every instance of turbos are actually being used as magic efficiency generators as opposed to magic power generators. My suggestion is that at least if I’m tuning for maximum efficiency, it should give figures with higher efficiency per displacement. But it should also have the ability to be magic power generators at the expense of efficiency. Otherwise, the economics of a turbo simply don’t work out. As of now it works only as magic power generators, albeit one that is disgustingly inefficient compared to increasing displacement and cylinders.

The example I showed you actually shows that Naturally Aspirated engines with a higher power output can still provide higher efficiency. That doesn’t sound right to me especially since I was trying to make the most efficient turbo straight 6 possible. But of course I am wondering if I am simply tuning it wrong in Automation 4.2.

It’s still the case now, you just have to tune differently.

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If you don’t mind, could I challenge you to tune a better turbo car in 4.2?

I’ve made a vw golf looking thing in automation. It uses a 2.5l 4 cylinder engine producing 158ish hp (118kw) and returns 5.4 liter per 100km (43mpg US, 52mpg UK) using 91ron/87aki octane. It runs a 6 speed dsg and medium tyres sized 205/55 r16. Its a fairly rough draft and not super optimized.

Can you make a similarly specced 1.5l - 2.5l car with a turbo making the same or better fuel economy? Realistically I think it should be possible but I haven’t figured it out in new Automation. Btw feel free to use higher octane numbers as in real life.

I won’t accept your challenge as I run into the exact same issue. I really like the fact that they nerfed the turbo’s as the previous turbo system was OP in all aspects, also that the turbo tuning is way more realistic regarding the pressures etc.

However, I indeed have the same issue where even the most efficient turbocharged engine that I can design is not even close to the same efficiency as my NA engines.
Yesterday I made one 3.0L NA V6 engine that reached about 27% efficiency with about 6.5L / 100km estimated fuel usage in the car. Then I made the most efficient 2.5L and 3.0L Turbo V6 engine with a flat torque curve and the best turbo parts selected. I also tried single and twin turbo setups and each pressure in the range of 0.4 bar up to 1.2 bar, also tried all possible combinations of compressor, turbine and tuning sliders. I kept an eye on the turbo pressure graph and on the intake and exhaust pressure graphs. All other engine components were equal and the quality sliders on default. I deliberately tried to keep the turbo engine around the same performance index / power range as the NA engine.

Somehow the best efficiency that I achieved was around 23.5%, and the car did 8.3L / 100km at best with an optimized gearbox.

I do know that in reality turbo’s are no magical products that make an engine twice as efficient, but as far as I have learned from practise, a good optimized turbo should be able to make an engine produce more torque in the low rpm, have a similar power output in the high rpm and have a slightly higher efficiency compared to an equal NA engine (probably due to the higher torque in low rpm making it easier to stay in an optimal rpm range which is also significantly bigger).

Right now, it seems that the turbo’s in automation have only 2 purposes:

  1. Get massive low-rpm torque to build truck-like heavy duty engines
  2. Get massive high-rpm power to build sports/racing engines.

It feels that fuel economics right now is in not a single way a suited purpose for the turbo’s.


For post-2010 engines in particular, it makes turbocharged engines less viable in-game than they are in real life.


Have a look at mine.

model_2___trim_2.car (13.5 KB)

You have to remember engine efficiency is calculated MAINLY on its compression ratio.

That’s why diesel engines are always considered more efficient, they have 20+ to 1 compression ration.

So the more compression, the better efficience. It means the more boost the less compression ration.

Have a look at valve spring strenght, the stronger they are, the harder it is the engine to push them so it lower fuel efficiency.

Then, tyre width is important. The larger, worse is rolling resistance.

Tyre thickness has a big influence in 4.2, the thicker the more the tyre wall deforms and so heats up and uses energy. So it increases fuel consumption but if we had tyre pressure we could master that parameter.

Try an overdrive gear. It will lower engine rotation in relation to the speed of the car.

Underbody protection can improve air flow and so fuel consumption.

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I believe nowadays turbos engines are popular because they can use the lower engine size for engine pollution.

In optimal configurations the less size the less fuel has to be used for the homologation. But when you use these engines in normal operation they can’t produce the official figures.

You have to remember the amount of fuel is directly linked to the amount of air (beetwen 11 and 18 to 1 for petrol and 15 to 85 to 1 for diesel). So the more air, the more fuel, the worse fuel consumption. You can trick that with VVT or EGR strategies but it’s not available in the game.

You have to observe you can’t do all the strategies in the game the motorisation engineers can do in real life, so your result cannot be as realistic as you want to.

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This is a very good engine. No doubt about that. I have checked it and I’m getting 4.7 liters per 100km. There is one small issue though, when I made the original post it was in automation 4.2.5, in 4.2.6 I tried remaking my engine (now it can only be 2.0 in 4.2.6 due to stress) with your design choices I’m getting 4.5 liters per 100km on 91 octane. Also, there were a few choices that didn’t conform to the original specs, like tyre size and type. That’s ok though, I understand what you were doing.

A few things though, your engine has much more torque in the lower end (270+ nm compared to 200nm) which irl is very good.

I know about the overdrive, hard tyres low profile, areo, and compression ratio (actually cams and timing up to 70 is more beneficial). I tried not to make it too focused on being only efficient which is why the tyres is 55 profile and non existent overdrive. I think 4.2.6 has made it close to par to naturally aspirated engines, but slightly below which imo is fair enough.

I would make a hypermiling challenge on discourse but I suck at making pretty posts and using mods so it would be sh*t and unfair (I don’t even know how to do interiors), unfortunately. Otherwise I would make it a legit challenge.

Turbo engines are popular due to many factors, but one of them is that they’re just more efficient - in specific conditions. The problem with that is that in real driving most drivers don’t know or don’t care about it, or simply push those engines more, and they get out of these conditions, in which case turbo engines are less efficient than N/A ones. Size isn’t that important of a factor, since it’s somewhat negated by the turbo - it pushes more air into the engine, remember? And that means more fuel too. So the smaller size results mostly in less internal resistance. VVT is in the game, EGR isn’t, but it affects mostly pollutants emissions, not so much efficiency, so I’m not sure what you mean in that point. Also remember that it’s not a simulation, but a game, so even if some effect’s cause is not in it, the effect itself can be replaced with balancing the calculations right.

You don’t need any of that for an engineering challenge, so go ahead, I’d participate gladly! :slight_smile:


A bit off topic but super duper true. I have a friend who bought a VW Tiguan 1.5 turbo dsg, I myself have a Mazda 6 estate 2.5 NA automatic both from 2019. We drive similar routes and he is getting like 10 kmpl (10l/100km) and I am getting 11.5 kmpl (8.7l/100km). Of course my car has a smaller frontal area and lower drag coefficient than his but it was unexpected that the 1.5 turbo isn’t more efficient than the 2.5 NA.

Actually I knew about this phenomenon irl, which is why I chose a Mazda (and the lower drag is why I didnt pick a CX-5 among many other reasons). On paper the Tiguan should be much more efficient, but not irl.


I’ll think about it. Maybe when the release is stable.

I’m not familiar enough with all english terms to explain how VVTL, EGR, Injection time and timing and how car manufacturer have found loopholes in engine homologation with turbos.

I’ll try with EGR.

They use different strategies of EGR for both pollution and fuel consumption. In fact they are linked.
EGR is mostly used in low throttle loads. It recirculates exaust gaz through the intake to reburn exhaust gas. The consequence is a lower amount of O2 which means less fuel as well. The inefficiency of lower loads is due to the lower compression because of the partly opened throttle which creates a strong depression. So we use exaust gases to fill up the chamber and re-establish a higher compression and extract more power or use that to increase the AFR. I hope I’m clear…

About VVTL, on low loads we can differentiate one intake valve from the other and keep one closed to create a swirl effect and improve air and fuel mixing which lowers fuel spots and improves fuel efficiency and pollution. Many engines used this strategy before the arrival of direct injection, some fiddle a bit around like the TwinPort from GM.

With VVTL we can also increase Retard Exaust Closure and leave the exaust valves open after Top Dead Center to rebreathe hot exhaust gases and improve cold start ability. Mazda does that with its diesel Sky-activ engines because of a 16 to 1 compression ratio.

During the homologation, engine are under very little load so turbos doesn’t engage so the 0.9L 130hp turbo 3 cylinder engine runs as a 0.9 45hp NA engine. The rest of the engine range isn’t sollicited so the “correct” fuel consumption goes under the radar.

The gains on efficiency on the newest engines come from as you said internal resistance. Improved pistons, bearings, electric waterpumps, lubricated timing belt, oil quality etc…

I remember the first sign of this “cheat” was the Mk5 Golf GT. It had a twin charge setup 1.4L 170hp 4 cylinder engine. Journalists back then notified the difference beetween the official figures (really cheated of course as we know VW) and the reality where they couldn’t get the car under 8l/100km.

The game now. Of course it’s a not a simulation, otherwise it would be unplayable or we all would be Turbo Yoda or engine management specialists, which we are not. I tried to explain it was impossible to get exact real life figures because we cannot be as precise as irl.

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After a bit of fiddling, I managed 4.4 with 95ron so your tune is spot on!!

With a 1.5 3 cyl I have full boost at 1100rpm and 4.3l/100km.

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That is no more fully the case with WLTP - while still not perfectly accurate, it involves varied loads. I’ve seen some engines’ consumption ratings go waaay up in the switch from NEDC to WLTP :smiley:

As for VVTL and EGR - interesting stuff some of which I didn’t know, although that would affect turbo and N/A engines more or less equally, so I don’t see a link to the supposed turbo nerf in the game. Oh, and VVT in the game is already sorta magical like that - it doesn’t improve engine’s efficiency much, but it lowers the car’s consumption quite noticeably.

And I don’t agree about precision - as I said, in the game we don’t necessarily need precision for real life figures, since the devs can emulate what can be achieved via precision with a right balance of the calculations. For example yesterday I’ve got some engines very much like Toyota’s Dynamic Force, despite not having dual injection nor various other minor solutions they used for those engineering marvels.

Anyway, I’m off to check out your engine - I’m curious, as so far I wasn’t able to build anything efficient enough with a turbo.

Ok, so I’ve checked it out and it just confirms the nerf IMO, and a big one. What I see would get sth like 35-40% efficiency in 4.1, assuming the tech would be there, while in 4.2 it gets 31%. Then I compared it to one of my “magical” N/A engines, a 2.5 I4 (35% efficiency), and the confirmation continued - 4,7 l/100 km in the 2.0 turbo, while the N/A 2.5 got… 4,0 litres. And it’s just 0,1s slower to 100 km/h, as it has a few HP more with almost 50 Nm less. Can be the other way with a slight retuning of the gearbox, while keeping the economy. I have to admit though, my engine is a bit more expensive, I guess mainly due to being larger (but I still think turbos shouldn’t be that cheap, especially as advanced ones as in this engine).