Is there really no replacement for displacement?

A popular saying among (American) auto enthusiasts is “There is no replacement for displacement”. How true is this? (let’s discount forced induction which is, in the end, a way to cheat more displacement into the same cylinder)

Angle your responses to the fact that I will be using this info to shut someone up. :slight_smile:

How far have we come in engine technology? How much more, on the average, one can expect from engines of equal displacements across the decades? Say 70’s vs today?

I posted an affirmative response here.

That’s the post responsible for this thread.

You started a thread soliciting responses just to shut me up?

Small engine applications, (4 cylinder cars) benefit from a lighter, less massive engine. Because there is less mass to move they don’t require a large displacement engine. However the performance of a 4 cylinder engine suffers by that lack of displacement. Adding forced induction to those engines makes them perform like a large displacement engines, yet deliver the fuel economy closer to that of a normal aspirated 4 cylinder engine. win/win.

Larger vehicles, such as trucks, require more torque at lower RPM than a smaller, lighter car requires. So large displacement engines with their better bottom end torque are required.

The answer to your question is yes or no, depending on the application.

Which turbocharged 4 cylinder car do you own that “performs like a large displacement engine, yet deliver the fuel economy closer to that of a normal aspirated 4 cylinder engine.” ?

Well, my 2004 WRX gets mileage like a civic when I drive it under the boost point, and then rapidly becomes faster than most V-6 luxo-cruisers when I push the big pedal down more.

Certainly you see how that’s not " performs like a large displacement engine, yet deliver the fuel economy closer to that of a normal aspirated 4 cylinder engine".

The flat four in my dad’s old Porsche 944, for one.

Maybe it’s because I’m not that sophisticated, but my friends always used the phrase “There ain’t no substitute for cubic inches”.

…along with the basketball-related phrase “you can’t coach height”.

While this may ultimately end up being IMHO territory, I suppose it would depend on how you’re defining “large displacement performance.” Certainly you can drive turbocharged engines to be virtually indistinguishable from a natural aspirated one - just don’t spool the turbo (harder with an automatic, granted.) Likewise, keeping the turbo spooled gives you a huge amount of horsepower and torque at high RPM ranges - similar to big NA blocks.

What you really sacrifice with turbochargers is low-RPM performance, and I’ll concur wholeheartedly that the need low-end power is one of the reasons for big displacement engines to exist. Superchargers give you a kind of middle ground - less extra ‘omph’ but it’s always there. Either way you slice it, forced induction at least can emulate its bigger, throatier brothers.

Since 944s didn’t have flat 4s, your recollections are somewhat less than convincing.

Does your engine get the same fuel economy as a NA engine when you’ve got the turbo going all the time? If not, then you are not getting the same performance as a larger engine with the fuel economy of a smaller one. Without the turbo, you will necessarily get worse efficiency than a NA engine because turbo engines (before direct injection) generally have much lower compression ratios.

Without getting too technical, the basic answer is really “no.” anything you can do to a smaller engine can be done to a larger displacement engine of similar design.

Yes, you can turbocharge a 2.5 Liter W-4 engine and increase it’s power output from 120HP to 300HP. You could do the same thing to a large displacement engine and get similar results.

Yes, there are 9 second Eagle Talons out there with 2.0 liter turbocharged engines. They would be even faster with a turbocharged 4.0 liter engines (though visibility might become an issue at that point :cool:). I speak this as a fan of small turbo engines.

However, keep in mind the fact that, on the freeway, your WRX gets about the same fuel economy as a Z06 Vette.

Ha! Sorry, no. My BIL, proud owner of a Grand National that I affectionately call “The Monte Carlo”

Ok, After reading all the responses. As I said, I would really like to leave turbos out of the equation, for now.

My take is that engine design has improved a lot and that his big roaring engine from 20 years ago is comparable to smaller engines of today.

Then there was a recent “Top Gear” episode where they were testing old roadsters and they were kinda crappy compared to regular cars of today (much due to suspension, but the engines were certainly underpowered).

What I would like is to be able to say “2 liters of 1980 are 1.6 liters of today” or something to that effect. Is this the case at all?

I suppose it depends on what you intend to get from the displacement. If you’re talking about raw automotive performance, 0-60 and 1/4 mile times, etc. there have been remarkable advances over the last 30-40 years in production cars. Take a Corvette from 1969 and one from 2008, both with 427ci engines. The 2008 model is going to run rings around the old one, probably shaving 2 seconds off of 0-60 and more off of the 1/4 mile. Some of that is engine technology, some transmission, tires, aerodynamics, etc. Ultimately, though, you have the same displacement, and the new car kicks the living crap out of the old car.

In addition, the old Corvette is going to get a run for its money from just about any 2008 sporty car, even just the V-6 version of a family sedan. Sure, you can say it’s not the “same” as having a big block under the hood (and it isn’t) I don’t think the saying should be referring to the thrill of a big block, but the performance of the car.

The late 60’s / very early 70’s Olds 442 (400 cu. in.) was one of the era’s muscle cars. Just going to the later 80’s / early 90’s, the Oldsmobile Quad 4 engine (4 cylinder / 4 valves per cylinder / 2.4 Liter ~ 150 cu. in.) in your average rental car would do 0-60 and the 1/4 mile faster with a higher top speed in the 1/4 mile. The engine delivered close to 30 mpg; about 3 times the original 442.

In terms of modern design: cams, ignition systems, fuel injection, sensors, cylinder shape; today’s engines far outpace the older carbureted V-8s of the muscle car era. Modern suspensions, traction control, and tire advances greatly enhance getting the power to the road.

The old horsepower ratings were also suspect, usually delivering far less to the wheels. There were some under rated examples though, usually for insurance purposes or PR.

Well here are some numbers you can chew on for a bit.

Johnny LA’s MGB is just under 2 liters and puts out 102 HP in stock trim. 4 cylinder push rod engine, with dual carbs.
A normally aspirated 240 from the late 1980/early 1990s was 2.3 liters single overhead cam and fuel injected. 110-112 HP depending on the year.
The Volvo engine is roughly 15% larger and produces about 9% more horsepower. I would say these two cars are roughly similar in horsepower per cubic inch. The MG has bit more HP’/CI but that is only fair honest and right since it was a sports car. :cool:
My current ride is a 2005 V70 with a 2.5 liter in line 5 cylinder dual overhead cams, 4 valves per cylinder and puts out 168 HP.
So I have upped the displacement by .2 of a liter (about 9%) and increased the horsepower by about 50% When it comes to emissions, it is also way cleaner.
So within engine generations (or technology generations if you will) more cubic inches will generate more horsepower.
But when you start to compare 50 year old technology with modern technology, you will find the modern stuff kicks the shit out of the older stuff on a per cubic inch basis.
There is a reason all those hot roders are going to fuel injection systems.

  1. VW Group’s 1.4 liter TSI engines that produce from 122 to 170 hp. Consumption is ~8 liters/100km for the 140hp model.

  2. Fiat Group’s T-Jet engine series. Similar performance and consumption with the VW TSi engines.

I don’t think it’s as clear any more that a small turbo engine will get better mileage/HP than a large displacement non-turbo engine.

For one thing, some of the large displacement engines have cylinder deactivation, which turns them into a small displacement engine when the power isn’t needed. Direct injection improves fuel distribution and allows running higher compression ratios. Turbo engines have to run lower compression ratios to keep from detonating. So when you’re running without your turbo spooled up, your engine isn’t as efficient as it would have been if it had been designed to be normally aspirated.

Plus, the newer transmissions have more gears, allowing the bigger engines to maintain a more optimum RPM for fuel economy.

I just looked up the fuel economy of a few sports cars, a couple with a small engine turbo, and a couple of normally aspirated, V6 and V8

Subaru WRX (4 cyl turbo, 2.5L, 230 HP) - Mileage: 19/25
Lancer Evolution (4 cyl turbo, 2L, 300 HP) - Mileage: 16/22
Cadillac CTS-AWD (6 cyl, 3.6 L, 304 HP) - Mileage: 17/26
Chevrollet Corvette( 8 cyl, 6.2L, 425 HP) - Mileage: 16/26

The 425 HP Corvette gets better gas mileage than the high-boost, 2L, 300 HP four banger. The 304HP Cadillac gets significantly better mileage than the 300HP Evo, despite having an engine almost twice its size and no turbo.

Both the high displacement engines get better gas mileage on the highway than do the small turbo cars - probably because the turbo’s working harder at highway speeds.

To make it worse, the turbo engines both need to run on premium. The normally aspirated engines run on regular.