Naturally aspirated better than turbo for highway cruising at constant speed ?
Posted by Pale-Revolution-5151@reddit | askcarguys | View on Reddit | 98 comments
Want to buy my first car and will mostly do highway driving 6000miles/10,000km per year. Ideally want at least 1.5L maybe 2.0L. Just wanted to verify if my driving is mostly highway will little to no overtaking at constant 75mph/120kmph will the naturally aspirated engine be better than the turbo? Let's say Mazda 3 vs VW Jetta.
GeckoV@reddit
The turbo engines are more efficient because they are smaller and run much more loaded without turbo, but still provide a lot of power when needed. An NA engine of the same peak power will run worse when just cruising as the volume is oversized.
Paqza@reddit
Why would it be at peak power while cruising? Peak power is needed for accelerating.
sisyphus_met_icarus@reddit
He means an engine rated for the same peak power. Not that it's at peak power while cruising
Paqza@reddit
Is that actually true in practice, though?
the_Q_spice@reddit
I mean, yeah.
I just moved from a VW 2.5 NA to a 1.8T this year.
The 1.8T makes 20 more peak horsepower, the same peak torque, and is AWD.
The 2.5 was FWD.
The 1.8 makes about 4-10mpg better fuel economy across all loads.
GeologistPrimary2637@reddit
Finally someone who gets the point of actual downsizing.
In regular traffic and sane acceleration, you're almost guaranteed to get much better fuel economy in a downsized turbo car than a larger cc engine of the same power. Where people don't get the fuel savings is when they realised they now have a small cc turbo engine giving the same power as a large cc engine and go 100% throttle from stop light to stop light.
It's not because it doesn't feel as powerful, rather, in some parts of the world, bigger cc cars with more power were usually reserved in higher brackets that regular people couldn't buy previously.
Illustrious_Law182@reddit
I hear from german friends that small engine with turbo is no good.
Big engine and turbo lasts forever.
The_Truth_Flirts@reddit
I mean my n55 is getting pretty much the same average mpg as the kia niro 1.6 na, the mg 1.0t etc. It beats them cruising from 50+ mph.
BrickLorca@reddit
Ok
SailingSpark@reddit
You would be surprised how little power a car needs when cruising down the highway. Thst kind of driving is better for a car than stop and go city driving.
I used to do about 25,000 miles a year, 90% of it being highway. At the time I had a 4 cylinder BMW with all of 140hp. It did great on the highway.
BisexualCaveman@reddit
1 gallon per hour flow rate makes about 15 horsepower.
So if you're going 60 MPH and getting 30 MPG that means you're burning 2 gallons per hour.
Thus, you're actually only using 30 horsepower in that situation.
SailingSpark@reddit
using that as a ballpark figure, I used to get 35 or so on the highway by my hand calculations. So my little boxy hatchback (the E36 318ti) was reasonably aerodynamic and efficient by 90s standards.
BisexualCaveman@reddit
BMW and Mercedes back then weren't QUITE as crazy heavy as they are nowadays, kinda makes sense.
The way they really cost you back then was parts and paying for premium, although I'm not sure if the 1.8 you had actually called for it.
I was a Mercedes diesel guy back then.
Paqza@reddit
I'm well aware. You should tell the guy I replied to.
RoxieMoxie420@reddit
He is saying that if a 2.0 L making 180 hp peak and a 1.5L turbo making 180 hp peak both going at 70 mph the 1.5 L would keep the speed just as well and get better gas mileage.
ImplementLogical4130@reddit
Depends on gearbox and differential. So also on torque if the rpm are low
PetriDishCocktail@reddit
You're exactly correct... I remember watching a TED talk with one of the Chevrolet Corvette engineers. He let slip that the c8 Vette only needed 24.6 horsepower to cruise down the freeway at 55 mph and that it needed 40 HP at 70 mph.
He mentioned trying to get a 465 horsepower( 6.2 liter) V8 to cruise down the highway nicely at low RPM making such a little horsepower (well averaging 30 miles per gallon) was quite an engineering challenge.
jnyc777@reddit
Not necessarily, as the smaller engine running at the same speed will be working harder to keep the speed as the bigger engine will be cruising along. A 2010 Chrysler 300 (v6) was getting the same mpg. Highway as my 2013 vw tdi. Gearing or transmission choice, weight, tune, some cars are tuned for sport and some for gas meisers. Mazda has the skyactive engine that runs lean and from what I’ve been told by a friend that drives one gets better fuel efficiency and a 1.5lT
BrickLorca@reddit
At a higher speed you're running the smaller engine harder and using boost to make up the difference. On my F-150 2.7L EcoBoost (regular cab, 8 foot bed, RWD), I don't really dig into boost until about 55/60 mph?
Don't quote me on that, but I can get this box moving quite fast before engaging the turbos. At the end of the day, with a set of 42lb/tire all-terrain tires and a headache rack sticking out above the cab, I'm averaging 24ish mpg highway, 26ish mpg rural roads (45 mph average or so).
I didn't believe in turbos until I bought this thing, and I only got the 2.7 instead of the 5.0 because I'm poor. Now that I've read up on the engineering in the Nano, I'm a believer of small displacement forced induction supremacy.
jnyc777@reddit
A v6 also has power enough to maintain highway speed even in a f150 without a turbo! Turbos definitely add efficiency! They are great pieces of engineering! But a 1.5-1.4lt at highway speed will definitely be working harder than say a 2.4l naturally aspirated. Now I haven’t driven the same vehicle is both to say definitely which would be more efficient fuel wise, I’m just contemplating because of such a small engine
Signal-Confusion-976@reddit
A NA engine will not run worse than a turbo. Once up to speed they cruise along just fine.
Bulky_Employ_4259@reddit
It’ll run worse in the sense that it’ll use more fuel.
GeckoV@reddit
It will have more pumping losses due to partial throttle and more friction losses due to larger size
Bulky_Employ_4259@reddit
That’s a borderline ideal use case for any engine. Turbo or NA would be equally suitable.
Datboi_Markus@reddit
If only car companies told you the mileage their vehicles got so you could compare them
Dzessito@reddit
Those numbers are not real world accurate.
JCDU@reddit
No but they're comparable to each other, everyone cheats by a similar amount.
If one claims 45mpg on the highway and the other claims 50, the truth might be 40 and 45.
Datboi_Markus@reddit
This guy gets it
MrSNoopy1611@reddit
I currently drive a 900cc turbo 3 cylinder and get with 80% highway 4.7L/100km while my 1.6 FSI i can at best get down to 5.8L/100km although its a little older. In terms of HP they are the same. Although i am a little slower than you with mostly 90 - 100kph
Anon-Knee-Moose@reddit
I personally found that I got worse than advertised mileage with a turbo because it was hard to resist taking advantage of the extra power.
In theory my ecoboost fusion should get about the same mileage as my 20 year old civic, in practice its quite a bit worse.
saladmunch2@reddit
I hate how my 2013 awd 2l ecoboost fusion gets 23mpg avg. Compared to my old 2003 malibu v6, which i got close to 30mpg. I suppose thats the trade off I get for getting awd.
HB97082@reddit
Yeah, I don’t understand the recent obsession with AWD.
Bananahamm0ckbandit@reddit
I drives me crazy lol.
Does it snow where you are? AWD SUV!
Do you have a kid? AWD SUV!
Do you eat lunch? AWD SUV!!!
A front wheel drive car does perfectly fine on snowy roads, manufacturers are just fear mongering to sell expensive vehicles.
saladmunch2@reddit
I know what you mean, my fwd malibu did fine in snow. Even if there was like half a foot, car was like it was on rails even only having $80 allseason uniroyal tiger paws on it. Winter can be pretty bad up here and I generally have atleast an hour commute to work so anything to make it a little bit better is nice, i had the opportunity to get the awd so i did it since it will be nice for the conditions im in. I leave before 5am so not much traffic to deal with but sometimes more rough roads.
mpgomatic@reddit
Gotta stay outta da boost.
BrilliantTruck8813@reddit
I used to take this to heart until I got a C8 Z06. High-strung N/A motors win the bad gas mileage award, especially when heavy on the throttle 🤣
Prestigious_Tiger_26@reddit
And there's the catch. When you're not boosting, it's slow AF where you're actually getting decent acceleration in an NA engine.
mpgomatic@reddit
Not necessarily. It all depends on the engine and driver’s familiarity with it.
Anon-Knee-Moose@reddit
Well thats just silly
SevroAuShitTalker@reddit
I swear, at least half the comments I read on thos sub are outright wrong
JCDU@reddit
If I've learned one thing over the years it's that most "car guys" don't actually know how cars work.
bmanxx13@reddit
I get better mpg on my 5.0 v8 than I did on my 3.5L ecoboost (2 turbos) cruising at 75-80 on the highway. As long as you stay out of boost as much as possible the engines are efficient.
Samsonlp@reddit
The downside of turbos is they operate at higher pressure and rpm compare to na engines. They wear out faster and are mechanically more complicated. A lot of engineering has been done to mitigate this in modern cars, but it's still a thing. Otherwise all a turbo does is push more air into an engine, this allows more fuel to burn, so the engine produces more power. It does this by facilitating higher compression with more air/fuel in the cylinder than just raising compression without first compressing the air coming in.
Any given engine might have a different rpm sweet spot for efficiency, but that's is more connected to your transmission. If your car is at an inefficient rpm then, yeah, cruising at highway speed is less efficient. You might need to slow down a touch. That's true whether or not the engine has an na engine, turbo or supercharger.
BrilliantTruck8813@reddit
Turbos operate at a lower rpm compared to na engines.
Because of physics an NA engine has to spin more rpms to move the same amount of air. Generally apples to apples a turbo is less harmful or stressful. It’s the ancillary bits or displacement differences (turbo motors can be smaller and be more efficient) that changes that equation
Samsonlp@reddit
I don't think we disagree. And you're absolutely right on principle. But the way turbos are used is to put a smaller engine in a larger vehicle to produce the same power. So instead of an NA v8 in 4100lb vehicle you have a turbo 4 cylinder and 8 to 17 speed transmission. It generates plenty of power but because of the application it's doing up to 8,9,10k rpm half the time. Similarly the crank case and every other component is under much higher pressure, leading to pcv issues, oil on valves, and busted seals, and all the other stuff.
BrilliantTruck8813@reddit
Uh what turbo 4cyl are you talking about? Most turbo 4s have a redline under 6500rpm. Very few go higher than that. And the comparison of a 4 and an 8 gets murky due to even vs odd-fire
Samsonlp@reddit
Performance cars, 2 Liter turbos.
BrilliantTruck8813@reddit
Where? What performance cars? Name them. Almost every manufacturer has popular turbo 4 that doesn’t rev over 6500. Certainly not 8, 9, or 10k rpms.
Samsonlp@reddit
You're right. 9k in a Honda s2000. That's too weirdly specific. I had some memories crossed between an (ironically naturally aspirated) 1.3 L motorcycle engine, the 7k redline on my current inline 6 and a Santa Fe I drove that would would absolutely fly but the transmission jumped smooth and clean at the quiver of the pedal to to near max rpm.
Secure_Public6076@reddit
Nailed it. Turbos help the engine produce more useable power (torque) at lower rpm.
Samsonlp@reddit
See above reply, yes, but the manufacturers aren't adding turbos to big displacement, they are using smaller engines in larger applications, so the rpm is always higher for the same load vs the old NA strategy.
nanneryeeter@reddit
They don't necessarily operate at a higher rpm. I've towed the same exact load with a 3.5 ecoboost and a 5.7 hemi. The ecoboost will bumble along at 2000-2500 rpm while the hemi would be at 4000+.
Samsonlp@reddit
Good transmission has a lot to do with that. But yeah, as some other replies said, if displacement is the same, turbos produce more power at the same rpm.
Numerous_Historian37@reddit
Having owned a handful of small engine turbo cars, 75mph is just outside some turbo engines efficient zone. You'll have more engine load and end up running max boost on every hill.
One car I had would get 40mpg at 65mph, but at 78mph was down to 29mpg. The average efficient zone seems to be 45-70mph in my experience.
One of the turbo cars I owned also came with an naturally aspirated engine, those would get better mpg at 75mph+ than the smaller turbo engine in real world driving.
Mammoth-Ad-3957@reddit
Most cars have turbo-chargers now because they can be more efficient. Any downsides have been compensated for - such as sound deadening.
Andreas1120@reddit
Turbos are more prone to heat issues and the turned itself wears.
1234iamfer@reddit
It doesn’t matter that much. The Turbo would probably run low boost, low rpm. Be little less noisy and little more efficient.
Mundane_Television23@reddit
For what what you described it literally doesn’t matter.
briman2021@reddit
Probably won’t matter a whole lot, without load on the engine the turbo won’t be making boost. Look at fuel mileage numbers and reliability reports for the models you’re interested in and go from there.
The one exception I would make would be if you drive in high altitudes, a turbo makes a huge difference. Driving through the mountains of Colorado with a 1.6 liter n/a motor was miserable, but with a 1.8 liter turbocharge motor it was the same as driving at sea level, still had all the power despite the altitude.
Only_Information7895@reddit
Highway driving, just cruising, not even the speed limit is more than enough for the turbo, unless you have a really big and strong engine.
Depending if uphill of flat it was making 0.7-1.2Bar (10-17 PSI). It isn't like a ton, but it is working fine. Not even high altitude, just around a 1000m.
StaarvinMarvin@reddit
At highway speeds in my 1.4 turbo suzuki swift I’m not making boost unless passing someone
RealSprooseMoose@reddit
My WRX never gets into boost on the highway unless I am passing.
IBringTheHeat2@reddit
It’s not like your turbos gonna need to be replaced the first 5 years you own the car.
Putrid-Function5666@reddit
Turbos are great for better mileage and more power...but...
Turbos create additional heat, pressure and friction, and additional moving parts to your engine. Replacing blown turbos can go anywhere from expensive to blown engines. Todays turbos are pretty reliable, but still these factors exist.
Recent-Program-5183@reddit
VWs will sip fuel, if you have a light foot. Stay under 2K rpms.
cookie-ninja@reddit
My 1.4L Jetta runs 6L/100km or about 40mpg in the city and 4L/100km or about 60mpg on highway. It's silly efficient.
Feels just as fast as a Mazda 3 with much more responsive in the city due to much better low end torque. Turbo mazda3 is much better but wasted on that sad transmission.
moonlite_equilibrium@reddit
Tell that to my gli 🥲
cookie-ninja@reddit
Well that's their second/third top performance engine. Drive it like I do my base Jetta and you to shall achieve nearly 4L/100kmph or 58mpg.
Recent-Program-5183@reddit
I have a turbo GLI too, 6 speed manual. Grandma mode great mpg. But, it's hard to Grandma when it's that much fun! Had a VR6 jetta. Same great economy si portaste bien.
moonlite_equilibrium@reddit
Yup same '16 gli 6MT.
Its my car for when the bikes are down or the weather gets real nasty. But its so fun to rev out.
My only complaint is electronic power steering. Would almost rather have a manual rack than this electric.
Signal-Confusion-976@reddit
They put turbos on cars to give a small engine more HP. This causes more problems. Higher maintenance costs and repairs. Either one is good for cruising down the highway. I would recommend a naturally aspirated engine over a turbo.
lunchbox651@reddit
Turbos are really just power in the latter half of your rev range. For cruising at a constant speed they don't make a difference. Just don't get something that struggles to get to 120 and you'll be sweet.
Only_Information7895@reddit
Mine is smaller, more like kicking in past halfway instead starts dying past halfway. My top HP and torque and nowhere close to redline because this. Most small cars are built like this.
sisyphus_met_icarus@reddit
Most turbos in modern commuter vehicles are sized for roughly 1500-5500rpm. The redline on these engines will often be around 6500rpm but there's little point in revving them that high, as the turbo becomes a restriction and power drops off
BrilliantTruck8813@reddit
This is false. Maybe true in the 90s but hasn’t been true since mid/late 2000s
lunchbox651@reddit
You are saying a turbo engages at all levels of the rev range or that it makes a difference while cruising at a single speed?
One-Butterscotch4332@reddit
I mean mine spools at 1,600 rpm with enough throttle
BrilliantTruck8813@reddit
Check the 335i from 2007. Made like 300ftlbs of torque around 1600rpms stock. It has no lag and is like driving a V8
BrilliantTruck8813@reddit
Yes. Unless it’s a very large turbo, those compressors ARE moving air even at idle. It’s not enough to pressurize the intake past ambient, but it definitely runs less vacuum without the motor working as hard
2fast4usky@reddit
depends on turbo size. almost any stock set up will ne power in lower rev ranges but mostly depends on pedal engagement
RingOk664@reddit
Engines with turbos are more prone to failure. Forcing hot exhaust back into the engine does provide more power but then your turbo can start to smoke when the seals or bearings fry. For longevity and reliability, NA is the way to go. Fewer oil changes too.
Only_Information7895@reddit
Turbos doesn't push exhaust back at all (EGR does that, but on wide open throttle even that is closed).
It has 2 separate part, the exhaust part spins it up and on the other side it sucks in fresh air from outside (through the air filter obviously) and compresses it towards the engine.
Cars with turbos also generally have an intercooler, my intake air temperature is only around 3 degrees higher than ambient temperature even if I go up a long steep hill.
StarsandMaple@reddit
They're all fine.
Turbo engines on paper are more efficient and they usually use a smaller displacement motor and the turbo is there to add power when needed.
In theory turbo cars tend to drink a bit more fuel in city mileage because it's harder to keep our foot out of it.
I've driven 92hp 4cyls NA, and 600HP+ N/A and Turbo cars. The chassis matters more for a good ride and comfort than anything.
SpeedyHAM79@reddit
Define "better". Better at what? Miles per gallon? Reliability? Every design has it's own benefits and drawbacks, and between turbo and NA it's very blurry depending on the manufacturer and vehicle.
jsaranczak@reddit
Better how?
Strange_Library5833@reddit
Depends how fast your going. If I ever get into the boost (either going 75+ or a little headwind), it'll absolutely crush mpg. If you can stay out of the boost, the smaller engine will be better.
roosterjack77@reddit
I have a 2015 Jetta TSI 1.8T. Love this car. Great auto transmission it is very pleasant to drive. Turbo makes this car fly. Its a big pain in the ass to work on. Ive changed 3 quick struts on the front in 4 years, total dogshit.
El_mochilero@reddit
Honestly - I think you’re overthinking it a bit. The turbos on those smaller engines spool up pretty quick, so you won’t really notice a huge difference in performance and feel.
I would just look at overall horsepower. 170hp is going to do a lot better than 150hp regardless of turbo/NA.
Ibdliquidator@reddit
Naturally aspirated all day
Overall-Tailor8949@reddit
Most automotive turbo engines only get help from the turbo when your right foot gets heavy.
RobertISaar@reddit
All else being equal, N/A has less things to go wrong and has the potential for better fuel efficiency.
guyfromthepicture@reddit
A turbo will be more efficient at a constant speed like that but I'd rather have a naturally aspirated car as well.
RobertISaar@reddit
Turbines represent an exhaust restriction to be overcome by the piston having to push the exhaust charge out through it, along with the compressor wheel having to draw fresh air through it, neither of which exist on a N/A application.
If you only need to generate 25HP, a high compression, N/A, small displacement engine operated at near atmospheric manifold pressure to minimize pumping loss is going to be tough to beat. Atkinson-type cycle.
Efficient-Ball4360@reddit
There's a reason Ford calls their turbo engines "ecoboost" care to guess why?
BrilliantTruck8813@reddit
That’s true but you’re ignoring that the engine doesn’t have to work as hard to maintain rpm since there’s nearly free air and more of it in the intake. The pistons aren’t working as hard to draw the air in.
In the end, the difference is minimal if engines are equal other than one having a turbo.
But that’s where the turbo wins since it will make more power with a far meatier powerband at the same displacement, so it can get away with lower displacement and thus get better mileage
H0SS_AGAINST@reddit
Yeah idk wtf they're talking about, a turbo may not be building boost but it does reduce pumping losses.
mpgomatic@reddit
I’ve spent way too many days driving around in circles on the highway, testing fuel efficiency.
A smaller displacement turbocharged engine can be more efficient at highway speeds than a larger displacement NA engine if you drive with a light foot. 🪶 🦶🏻
When the boost kicks in, efficiency drops. If the vehicle has a real-time MPG display, using it makes it easy to see. The more you, the easier it gets.
Careless_Studio_1293@reddit
If you’re buying new, it won’t matter much because modern turbos are very reliable and efficient. If you’re buying used with high miles, I might steer towards NA for reliability, because there’s less to go wrong.