The Displacement and Specific Output Thread

[Zenith]

Is there a replacement for displacement? Are high displacement engines poorly engineered? Is forced induction an inevitability for all engines? This is where we discuss.'

In one corner we have the likes of Chevrolet who just put a 7.0L V8 into the Camaro Z/28. In the other resides the Nissan GT-R with it's twin turbo 3.8L V6.

What makes a good engine? What problems do either school of engine building present?

 

[Slash]

You're just asking for an argument, aren't you

It really depends on a lot of variables, such as technology, age, bull crapped figures, etc.

 

[Joey D]

A good engine that is properly engineered, to me, is something that's efficient and uses it's displacement to it's advantage. I also think forced induction is the way to go when wanting to get more power out of an engine since it allows for smaller engines to produce more power more effectively.

Also I'm not too keen on massive engines that make lame power numbers, if you're going to put a big engine in a car make sure it can deliver a good amount of power and torque.

 

[Harry6784]

Both?

Then again it depends what you're comparing. Performance? Dyno numbers? Production cost? Reliability? Way too many factors to simply be able to say one is better than the other...

 

[Cano]

freaking @Zenith, you want to watch the world burn

 

[Tornado]

All that ever needed to be said on the subject.

 

[Zenith]

Both?

Then again it depends what you're comparing. Performance? Dyno numbers? Production cost? Reliability? Way too many factors to simply be able to say one is better than the other...

When we discuss specific output in this thread we're referring to the engine's power output divided by it's displacement.

LS1 - 350hp/5.7L = 61hp/L for instance.

As far as the different factors? That's part of the discussion.

Does specific output matter for closely regulated race cars? You betcha. Does it matter for earth moving equipment? Probably not.

I like to judge engines on a case by case basis, unfortunately recent trends in certain recurring threads in this section constantly have half-discussions about the issue. I figured I'd nip it in the butt and have somewhere to point people to when irrelevant arguments do arise.

 

[Murcie_LP640]

You're just asking for an argument, aren't you

But if it's in here instead of within the majority of the Cool Wall threads where it's largely irrelevant...

 

[Slash]

But if it's in here instead of within the majority of the Cool Wall threads where it's largely irrelevant...

It always going to go back to the cool wall.

 

[Murcie_LP640]

Which is where this thread comes in where the conversation will kindly but forcefully be redirected to. Isn't that how the system's supposed to work?

 

[Harry6784]

When we discuss specific output in this thread we're referring to the engine's power output divided by it's displacement.

LS1 - 350hp/5.7L = 61hp/L for instance.

As far as the different factors? That's part of the discussion.

Does specific output matter for closely regulated race cars? You betcha. Does it matter for earth moving equipment? Probably not.

The only time hp/L figures are relevant are in regulated race car events and at ricer meets.

A much more useful and relevant figure to evaluate an engine's power output would be hp/kg.


LS1 - 350hp/5.7L = 61hp/L
S52B32 - 240hp/3.2L = 75hp/L

LS1 - 350hp/190kg* = 1.84hp/kg
S52B32 - 240hp/213kg* = 1.13hp/kg

*Long block weights

But these are just numbers. Then you have to tackle the issue of power distribution across the rev range. Do you want a high revving, small capacity engine or a large (not necessarily heavier) capacity, torquey motor...


We can discuss hp/L figures all day but what ultimately matters is how the motor performs when bolted to a car.

 

[Lotus Exige S]

When we discuss specific output in this thread we're referring to the engine's power output divided by it's displacement.

LS1 - 350hp/5.7L = 61hp/L for instance.

As far as the different factors? That's part of the discussion.

Does specific output matter for closely regulated race cars? You betcha. Does it matter for earth moving equipment? Probably not.

I like to judge engines on a case by case basis, unfortunately recent trends in certain recurring threads in this section constantly have half-discussions about the issue. I figured I'd nip it in the butt and have somewhere to point people to when irrelevant arguments do arise.

But how is that Figure worked out on a Calculator?

 

[Bopop4]

But how is that Figure worked out on a Calculator?

350/5.7

The majority of cars don't need anything bigger than a 2L, I'd be happy with a 1.5 for my Focus.

For a sports car though, a low hp/l can be good for reliability and wide powerband.
You obviously can't put a V8 into a Civic though, so a higher strung engine is needed to keep the weight down.

You can have a high revving engine with a flat power curve though.
My bike is only 675cc yet it makes more power than my car, the power curve is also exceptionally flat.

 

[Imari]

I'm looking for a new car to be my daily driver right now. My requirements are that it's comfortable and easy to drive, and doesn't absolutely drink fuel.

I'm starting to realise that for the same output, I'd probably rather a larger engine. A 125kw 2.5L straight 6 doesn't really use much more fuel that a 125kw 2.0L straight 4, but it's a damn sight nicer to drive. Smoother and you don't have to flog it to get that power out. Or my favourite engine, the Volkswagen VR5. Beautiful compromise of power, efficiency and weight.

In a sports car designed for handling, the weight benefits of the smaller engines start to come into their own, but for relaxed cruising there's a lot to be said for having a bigger engine. As I see it, it's not really power per litre that's important, as much as power per kg. Or in my case, how much power can I get and still do 10L/100km.

 

[OriginalCheezIt]

Oh my. This is gonna end quicker than "Free real, genuine, and fake passports", isn't it?

 

[Wolfe]

My take: Specific output completes a picture that describes more about an engine than either peak horsepower or displacement alone. For a measurement, it's no more "useless" than making note of the engine's displacement in the first place...to me, one clearly follows the other.

This isn't to say that specific output makes an engine "better" or advantageous, but I find it useful as a scale between the big-displacement-torque and high-RPM-power approaches to engine building, as already mentioned, and as a clue to a few other things.

 

[Greycap]

While I think that the engine has to be large enough to produce enough "natural" power to move the car effortlessly, that's about as much displacement as is needed. My own car is a 2.3 litre turbo and after it's been improved a bit - read: tuned to the level it should have been from the factory - it'll put out something in excess of 200 bhp and 350-400 Nm. Still pretty low specific output, yes, but it's a low revving 8V inline four so miracles won't happen.

To get similar power, or more importantly torque because that's what moves the car, figures from an NA engine the displacement would have to be around four litres and it leads to why I prefer smaller turbo engines to large NA ones. There's no need to feed fuel to keep 4000 cc of displacement running when half of it will do the job for the vast majority of the time and when the need arises, just put the foot down and the power is right there. Of course the amount of fuel injected is very low during steady cruising but still, the friction losses, compression losses, everything adds up and in the end the smaller engine makes more sense. As long as it isn't so small that it's under constant strain to keep the car moving in the first place.

 

[C-ZETA]

Ladies and gentlemen, I give you, specific output personified.

1.5 straight-4. Produced ~1400hp est. in 1986 in qualifying trim, once you turned up its bar.
If there's something you'd swap into an NA, it'd be this. (You can't have one obviously, but it'd be nice.)

I also understand it was race only. Absolutely. No one mentioned anything about it having to be road cars.

If you look today though at several hatchbacks, they're carrying engines that are around 1.0, they're turbocharged so they get a sweet amount of power. But even if you exclude the extra economy you get from it, journos are saying that they're actually an absolute ball to thrash about, as they would be with such a tiny engine screaming away at full pelt. For instance, Ford with the Focus and Fiesta - they get 125bhp out of their 1.0 straight-3.
But arguably the first example of this was Fiat with the 0.9 TwinAir straight-2 they put into the 500. That's got 84hp but the fact is, it's won many plaudits as an engine and the car itself is much loved with said engine.

 

[homeforsummer]

For instance, Ford with the Focus and Fiesta - they get 125bhp out of their 1.0 straight-3.

Up to 138 horsepower now, actually - I drove one with that output just the other week. The only two cars I could think of on sale in Europe with higher specific output are the Mercedes A45 AMG (355hp/2 litres = approx 177 hp/l) and Peugeot RCZ-R (270hp/1.6 litres = approx 168hp/l), though I may be missing a supercar here or there.

The latter two are staggering engines and the former pretty damn impressive indeed considering how tiny it is.

Realistically though, all are just numbers. It's what you do with that specific output that counts. In the Mercedes or Peugeot you're making a compact car go very quickly indeed (in the case of the A45, ever bit as quick on the road as a C63 with its V8). In the Fiesta, you're allowing a ~60mpg car to go far quicker than it has a right to.

Is specific output the be-all and end-all? Nope. The same day I drove the Fiesta I drove a Lotus Cortina, with all of 105-115 horses stock from a 1.6 depending on who you ask. Low weight means it gets within a whisker of the Fiesta performance-wise but the character of the engine itself is so much more exciting. Ditto my old MX-5 - 1.6, ~115 horses but happy to hunt for the red line all day.

Of course, to open a can of worms, if you're talking levels of performance efficiency for whatever energy you're putting into a system, there's not a road car engine out there that can match the "specific output" of an 80-90 percent efficient electric motor...

 

[C-ZETA]

The only two cars I could think of on sale in Europe with higher specific output are the Mercedes A45 AMG (355hp/2 litres = approx 177 hp/l) and Peugeot RCZ-R (270hp/1.6 litres = approx 168hp/l), though I may be missing a supercar here or there.

Well technically, if you count 'special editions' under that tagline, the latest Evo X is now up to 220hp/l. But there's only 40 of those...
The A45 certainly should be the sort of thing that causes me, most of all, to drool. But not only have I rather dismissed it (I prefer lesser hot hatches) but the Volkswagen Golf R400 shown at Beijing promises more, in a better car, although it hasn't actually been confirmed for production yet. Waah...

But yes. Fundamentally specific output is just a cool number. It can shape the feel of a car's power, for sure, but it's what else you do with it that matters. And the rest of the car in question, for that matter.

 

[homeforsummer]

but the Volkswagen Golf R400 shown at Beijing promises more, in a better car

Meh... My own view is that however much power you cram into a Golf it's still a Golf, and for me it's inherently less desirable than the Merc. And the extra power doesn't really grab me either - I've been lucky enough to drive a good few 500+ horsepower cars over the last few years and frankly, the 355hp A45 feels as quick as any of them given how compact the car is. It's utterly, utterly mental.

 

[Slash]

I feel the design of a car greatly impacts how "quick" it feels. Some cars, like the 3rd gen Camaro, weigh only 3,000lbs but feel much heavier than that.

I just don't think 115hp in a car is enough for me. I've been on a sled with about 105hp and weighing 500lbs and at full throttle it wasn't fast enough. I can't imagine how much slower that would be in a car.

 

[homeforsummer]

I feel the design of a car greatly impacts how "quick" it feels. Some cars, like the 3rd gen Camaro, weigh only 3,000lbs but feel much heavier than that.

I just don't think 115hp in a car is enough for me. I've been on a sled with about 105hp and weighing 500lbs and at full throttle it wasn't fast enough. I can't imagine how much slower that would be in a car.

That's because you're imagining things going in a perfectly straight line where your only real sensation of speed is that of being pressed into your seat on the horizontal plane.

115hp feels much better when you're say, driving on the doorhandles on a narrow country road in an old Cortina or blasting between roundabouts in the average UK city with the roof down in an MX-5. I've done both, and neither is any less exciting than the few bursts of full-throttle acceleration you can safely use in the average super saloon or similar. Context is as important, if not more so, than the numbers.

 

[White & Nerdy]

Speaking of roundabouts. Don't try to keep up with an Evo through a roundabout. It won't end well. No, I wasn't over the limit, it's a speed limit 55 road.

 

[homeforsummer]

Speaking of roundabouts. Don't try to keep up with an Evo through a roundabout. It won't end well. No, I wasn't over the limit, it's a speed limit 55 road.

I'm surprised roundabouts have even reached Alaska. Are people as confused by them there as they seem to be everywhere else in the U.S?

 

[White & Nerdy]

I'm not sure. They seem OK so far.

My guess is it was a federal thing. Maybe getting road money from D.C. required installing roundabouts wherever possible or something. I know Anchorage has had a few for a while, but we just got these a year or two ago. A twisting two-lane "semi-residential" road was getting converted into a four-lane quasi-freeway, and so roundabouts got installed at a couple of intersections. Unfortunatley much of the original twisting road is now gone. The northernmost part was closed for a while and now functions as a driveway for a farmer that lives there. The middle part was renamed and still exists. The southernmost part was sectioned off by a pavement break and a chain link fence, apparently to discourage use of the old road (seems kind of petty, though traffic patterns could have had something to do with it), but is still accessible from the southernmost part of the new road - unfortunately the south part of this part was razed to make room for the new road.

The purpose was to make it less dangerous in the winter, and I suppose it did, but still, typical Alaska. Straighten the snot out of the few roads that actually lead somewhere, put a 2 MPH speed limit on the twisiting roads that remain, most of which are dilapidated dead ends clogged with residential and/or tourist traffic. Hatcher Pass would be a great road... if it didn't have its speed limit set at 35 MPH... and didn't have a tourist attraction at the top bringing in enough traffic to justify that limit... and wasn't full of bad hops that could send you into a ditch or over a cliff if you go over them too fast... The Alaska Miata Club says Eklutna Lake Road is the best driving road in the state, but it too has a 35 MPH limit (dropping to 30 MPH when the road narrows, which isn't far from where it starts), and it's full of SUVs. And yes, the police do occasionally drop by, though that could have something to do with the water treatment plant on that road.

 

[Tornado]

In my second year, there were two traffic circles installed back to back not too far away from the college I attended. Really nicely done, with clear lines and a very nice garden planted in the center. Every 3 months or so, the bushes that lined the circumfrence had a nice car shaped hole punched through them. When it snowed, people plowed straight through the center so often I'm surprised they bothered replacing the hedges each time.






Anyway, specific output only matters to me with how it pertains to power delivery. I want a car that wants to rev; and smaller engines usually relate to that in regards to attainable cars. It doesn't even have to have a power benefit from doing so. Just the ability to do so without feeling like it is shaking itself apart or becoming completely gutless. Lardass V8 engines from the 1970s can't do that, no. Neither can crapbox 1980s V6 engines, or transplanted compact truck 4 cylinders. But it doesn't seem that the modern downsized turbo 4s necessarily like doing that either compared to the engines they replaced (having driven only one of the former, so speculation); so I'm not particularly enamored with them either no matter how impressive they are on paper.

 

[Space Dynamics]

The L67 supercharged 3.8 in many GM cars only puts out 240 HP, but the vehicles with that engine will often outrun cars with engines that put out quite a bit more power (sometimes torque too) and similar weight. A good powerband is grossly underestimated, and is much more important than many may think. More displacement is a great aid to that.

 

[Exorcet]

A good powerband is grossly underestimated, and is much more important than many may think.

Even that depends. With modern transmissions you can ignore a good part of the powerband and never really notice, at least if you're focusing more on raw performance/track use. More gears, less shift time.

I've never been concerned with specific output, it provides no benefit unless your displacement is limited for some reason. If there were numbers I'd like manufacturers to quote they would be hp/weight and some measure of engine size. If I was building a car (or buying one with many engines options) and wanted to decide on an engine, I would actually look at those numbers. Weight is everything. Less of it means more performance and more fuel economy. Size is maybe a little less important in a sporty car since long and wide tends to be type of shape they take, but height is important for lowing the CG and CD. A compact powertrain also allows doing neat things like channeling air through the car, which is what the latest supercars are doing to get that much better aero performance.

 

[homeforsummer]

But it doesn't seem that the modern downsized turbo 4s necessarily like doing that either compared to the engines they replaced

Fifty-fifty, really.

Some turbocharged fours (and threes) feel a bit flat right now. Or at least, they're quick, but they don't have the sort of turbocharged rush that makes cars exciting, nor do they have the sort of build-up that a good NA engine has as the revs creep up.

An example I've found of such engines being a bit disappointing is the 1.6 turbo used by Kia and Hyundai. Only driven it in one car, the 200-horsepower Cee'd GT. It would certainly go pretty quickly if you kept your foot in it but it was all mid-range and no top-end, a bit like a diesel really.

Others are better - Ford's 3-cyl Ecoboost is a fun little engine that's only too happy to rev to the red line and doesn't sound like it's protesting when you do so. But to an extent, it still lacks that rush - you just get a constant wave of power throughout the rev range rather than an exciting blast over the last few thousand RPM.

A Megane Renaultsport (2.0 turbo) or the aforementioned Peugeot RCZ-R (1.6 turbo) is much better, as each seems to go a bit crazy from around half-way up the rev counter and doesn't stop being crazy until you change gear. But I'm not sure whether that's because you're well into the high-200s horsepower realm with each of those, which in a car like that is fairly exciting anyway.

Again, it brings me back to my old MX-5 and the Lotus Cortina. Neither is particularly fast on paper. Each has enough low-down to move you around day-to-day. But the rewards are certainly there if you keep your foot in it - you get out of them what you put in, which is what I like the most in cars like that.