There is no replacement for displacement

[PanzerCommander]

currybum said:

Gooly said:

of a big unstressed engine.

If an engine is under stressed then that means its over engineered...i.e too heavy for what it does.

If you have a "lazy" V8 with a BMEP of 11bar you design it to meet those design specifications (pistons are normally peek pressure + 2 Sigma).

If you have a forced induction engine with a BMEP of 22bar you design the components accordingly. The components are only as stressed as your initial design criteria specify.

That is true however some of us simply don't like small engines, put it this way my Mustang would just be wrong with a 2.0L engine, even if the tunes and the FI meant that it had the same hp and torque curve.

There is also limited capacity for tuning when the engine is already near the limits of what it can deliver, the 4.6L engine in the 2006 Mustang I own is from what I have read good for FI boosting or N/A tuning upto 500bhp reliably - and the whole point of cars like that is the provision for aftermarket tuning.

[EvoSlayer]

V8s are for girls...

[Dr Interceptor]

EvoSlayer said:

V8s are for girls...

Have never owned a V12... If the right Jag comes along though that might change

[TameRacingDriver]

currybum said:

TameRacingDriver said:

cspan said:

Question: if I gave you a 1.0 turbocharged 3 cylinder and an NA V6, with similar outputs and dyno curves, do you think you'd have a preference for one over the other?

I would. And it would be the V6 every time for driving pleasure. However, as an every day car, I'm not so sure it would be.

What if the 1.0L delivered the exact same torque curve of the V6 and attributes of the 1.0L...does it really matter if its a V8 or a hamster wheel if the output is the same.

If the 1.0 was a 3-banger I'd probably have that, for me the ones I've heard sound almost as good as a 6-pot.

[Captain Muppet]

Happy Jim said:

You're missing the engineering point here. As the internal combustion engine is an Air Pump then the statement can only be true, any "engineering" is merely making more use of the available air, and simply increasing the size of the available air must be the easiest way to get more power (PS, as FI is "just" increasing the amount of available air, then all FI does is increase the effective displacement of the engine).

Simples

Jim

I like this bit: "simply increasing the size of the available air must be the easiest way to get more power". Yes it is, up to a point. But unless it's the only way, which it isn't, the cliche is still false.

Also you said "simples".

[SMGB]

Torque, which when multiplied by RPM gives you BHP depends only on swept volume and BMEP. so better breathing helps BMEP, thats either gas flow/cam etc or forced induction, but BMEP for BMEP the bigger engine always wins. It's the other way round at the extortion , sorry fuel , station. a smaller engine with better effective compresion ratio will always win out. So lazy V something for a laff and a tiny little turbo to cover the miles makes sense. Variable displacement lets you have almost the best of both worlds.

[ikarl]

Dr Interceptor said:

Have never owned a V12... If the right Jag comes along though that might change

I was looking at a Merc SL600 just the other day - 5.5l v12 twin turbo. I have a v8 but really want a v12 in my life.... it's the only one I really fancy (that I can afford)

also, with a little tweak to the ecu it can push 600hp (the ecu map was very conservative so it didn't compete to heavily with the SL55)

[Captain Muppet]

Just for all those who missed it in the OP and started talking about highly tuned tiny engines not being as good as huge simple engines:

Captain Muppet said:

I know that someone is going to slag off tiny engines, and probably say something entirely valid like 160bhp 1.6 Vtecs don't have the same torque curve as a 160bhp 3.5 Rover V8. But in order for the cliché to be wrong we just have to imagine a 3.4litre engine that is not worse than the 3.5 litre one, and that's easy.

[Dr Interceptor]

ikarl said:

Dr Interceptor said:

Have never owned a V12... If the right Jag comes along though that might change

I was looking at a Merc SL600 just the other day - 5.5l v12 twin turbo. I have a v8 but really want a v12 in my life.... it's the only one I really fancy (that I can afford)

also, with a little tweak to the ecu it can push 600hp (the ecu map was very conservative so it didn't compete to heavily with the SL55)

I'm down to three V8's on the driveway now the Jag has gone... I'd love a really smart XJS V12 Convertible to add to the fleet though

[kambites]

I've never really understood why anyone believes that displacement ever matters in the slightest.

In an engine: power to weight ratio matters; power to size ratio matters; throttle response matters; the shape of the torque curve matters;... the amount of volume swept by the cylinders is completely and utterly irrelevant to everything.

[Captain Muppet]

ikarl said:

like for like engine, there is no replacement for displacement

Like for like engine they are the same displacement. Unless you mean if you increase the displacement with a given level of technology you get more power, in which case yes, no one is even toying with pretending that isn't true. More is more.

ikarl said:

Easy enough saying that if you turbo this or supercharge that the engineering can replace the displacement, but if you increase the displacement and then turbo it or supercharge it, you get more

But you also get "more" if you keep the displacement the same and reduce piston skirt friction, or any one of a thousand other things. And as we only need one of these things to be true in one case just once for prove the absolute statement "There is no replacement for displacement" wrong then I think the logical part of the discussion has to be pretty much done already.

[Captain Muppet]

Gaz. said:

The cliche isn't false - I say this as someone with a pair of engines with over 100bhp/litre and owned many turbocharged cars.

More is more. Why can't you have a 7.0 litre V8 rev to 8000 rom, or supercharge it? Or the naughtiest cams you can get away with?

I could get my S2000 up to 450bhp with a supercharger, but a 6.3 litre LS3 starts at 430bhp....

What displacement increase do you need to get your S2000 to 450bhp from 240bhp?

[SuperchargedVR6]

currybum said:

Gooly said:

of a big unstressed engine.

If an engine is under stressed then that means its over engineered...i.e too heavy for what it does.

Not necessarily. Take the BMW S62 motor. All alloy 5.0 V8 making 380hp, on average. Seemingly under stressed on paper but certainly isn't over engineered or too heavy. In reality, it's not a long lasting engine and many have throw rods. Excessive big end wear, likes to drink oil and only 4mm of metal between the bores...not to mention all the VANOS and chain tensioner woes that go with it.

The LS3 V8 with all it's extra capacity is 40 odd hp shy, but it'll put in a much longer service life. That's what over engineering is. Consistency over a long period.

[300bhp/ton]

Captain Muppet said:

Hello,

I'm not a fan of clichés, but sometimes they become clichés because they are true and it's a conversational short cut.

However sometimes they become clichés because they sound right and no one can be bothered arguing despite them making no sense. See my "handles like a kart" thread.

Over in the Viper thread this happened:

PascalBuyens said:

Contigo said:

Gotta love these "Lazy" engines, I mean an 8.0 V10 with only 450bhp

It blows the old adage "There's no replacement for displacement" right out of the water lol

I'd say it would not only confirm it, but cast it in stone, rather than 'blow it out of the water'?

I'm a big fan of logic, and the only thing needed to disprove the statement "there is no replacement for displacement" is to find a replacement for displacement, right?

So if we look at this data...

Cheburator mk2 said:

Hmm, let's see... the ORECA Le Mans cars as well as the Zakspeed N-ring 24hrs were around 620bhp... nigh on 40% more... consider they had to have restrictors too...

To get 40% more power the displacement did not increase by 40%.

There is a replacement for displacement, it's called engineering.

I know that someone is going to slag off tiny engines, and probably say something entirely valid like 160bhp 1.6 Vtecs don't have the same torque curve as a 160bhp 3.5 Rover V8. But in order for the cliché to be wrong we just have to imagine a 3.4litre engine that is not worse than the 3.5 litre one, and that's easy.

And then people are going to ask if making that 3.4 litre engine a 3.5 would make it better, and chances are it would, but bigger isn't always better because the extreme end of that argument is an engine that won't fit in a car, or do more than 100rpm, or burn petrol any more.

I'm not in any way knocking how much fun huge engines are, I like that you can gets lots of reliable power/torque for not much money. I even owned a deeply lovable 4.6 V8 for a while.

However it seems the cliché is wrong.

It'd be nice if people just said "I like big reliable engines" instead, but that doesn't rhyme or imply superiority over people with smaller engines than you, which are the two things that I suspect keep that stupid cliché alive.

Let the spelling corrections begin...

Thing is, the Cliche is still right. Without the displacement you can't easily engineer in the same gains.

e.g. The Viper only had (only he says....) 400hp at launch. But if you think of the time period this was a huge amount of power. The then Corvette only recently made 300hp and even a Ferrari costing a lot more than the Viper only made 300hp too.

I think with the Viper it's also worth noting the engine hails from the Ram truck, where it was designed for low rpm use. And getting high torque at low rpms is really the preserve of large displacement.

So while 400hp isn't much per litre, it was a lot in 1992 as a total output. Had it been 600hp people wouldn't likely have known what to do or say about it. And it might even have gained negative press because of it.



The American market has always been big on modifying cars, large displacement low tune engines make this easy and appealing. Highly strung engines it's far more difficult and costly.


And lets remember, some of this engineering you talk about are just ways to artificially increase an engines displacement.

[SMGB]

kambites said:

I've never really understood why anyone believes that displacement ever matters in the slightest.

In an engine: power to weight ratio matters; power to size ratio matters; throttle response matters; the shape of the torque curve matters;... the amount of volume swept by the cylinders is completely and utterly irrelevant to everything.

Thats a different conversation, a good little un v a good big un in motorsprot isnt as clear cut as in boxing. A twisty track and enough time to cook your brakes and tyres and you can get a fun giant killing act. The instant grunt in any gear any RPM of a big engine on the road is a different thing.

[300bhp/ton]

GroundEffect said:

Increasing displacement is the easiest way to get more power. There's nothing fundamentally wrong with doing that if you can accept the package and weight penalty.

Bigger displacement doesn't mean heavier or physically bigger engine in many cases.

[kambites]

SMGB said:

kambites said:

I've never really understood why anyone believes that displacement ever matters in the slightest.

In an engine: power to weight ratio matters; power to size ratio matters; throttle response matters; the shape of the torque curve matters;... the amount of volume swept by the cylinders is completely and utterly irrelevant to everything.

Thats a different conversation, a good little un v a good big un in motorsprot isnt as clear cut as in boxing. A twisty track and enough time to cook your brakes and tyres and you can get a fun giant killing act. The instant grunt in any gear any RPM of a big engine on the road is a different thing.

I think you miss my point. I'm not advocating any particular means of designing an engine. I'm saying that displacement never, ever matters, in itself. It's no more important as a stand-alone factor than what colour the manufacturer has painted the rocker cover or what the engine designer had for tea seven weeks ago last Thursday.


It simply does. Not. Matter.

Ever.

[300bhp/ton]

cspan said:

There is a replacement for displacement - and that's forced induction, no?

And what do you think forced induction is doing? It's altering an engines dynamic displacement, i.e. forcing say 4.0 litres of capacity into a 2.0 litre engine. Thus you'll get similar power and mpg as a 4.0 n/a engine of similar design will.

cspan said:

Question: if I gave you a 1.0 turbocharged 3 cylinder and an NA V6, with similar outputs and dyno curves, do you think you'd have a preference for one over the other?

They probably wouldn't have similar torque curves.

[kambites]

300bhp/ton said:

And what do you think forced induction is doing? It's altering an engines dynamic displacement, i.e. forcing say 4.0 litres of capacity into a 2.0 litre engine. Thus you'll get similar power and mpg as a 4.0 n/a engine of similar design will.

Well quite.

The quote should be "there's no replacement for being able to shovel a lot of air into your engine very quickly"; but that doesn't have quite the same ring to it.

[300bhp/ton]

kambites said:

SMGB said:

kambites said:

I've never really understood why anyone believes that displacement ever matters in the slightest.

In an engine: power to weight ratio matters; power to size ratio matters; throttle response matters; the shape of the torque curve matters;... the amount of volume swept by the cylinders is completely and utterly irrelevant to everything.

Thats a different conversation, a good little un v a good big un in motorsprot isnt as clear cut as in boxing. A twisty track and enough time to cook your brakes and tyres and you can get a fun giant killing act. The instant grunt in any gear any RPM of a big engine on the road is a different thing.

I think you miss my point. I'm not advocating any particular means of designing an engine. I'm saying that displacement never, ever matters, in itself. It's no more important as a stand-alone factor than what colour the manufacturer has painted the rocker cover or what the engine designer had for tea seven weeks ago last Thursday.


It simply does. Not. Matter.

Ever.

I see your point, but it matters when you are talking torque

Although I do agree displacement without knowing bore/stroke doesn't always mean quite as much.


But what would you rather in a 2 tonne pickup truck that you want to use for towing a 3.5 tonne trailer.

A 250'ishhp 5.9 V8 or a 240'ish 2.0 DOHC I4

Both very similar power on paper, so they'll both perform similarly?