There is no replacement for displacement

[quiraing]

American drag-racing cars use big V8s, artic trucks use large-displcement engines, they don't really go for tuned-up 2-litre engines. Or even 2.5 24V turbos.

More swept area and fuel converted into energy = power. More fuel used but, hey, it's required for whatever reason.

Edited by quiraing on Thursday 21st February 15:20

[kambites]

300bhp/ton said:

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

As I said, the shape of the torque curve, and the responsiveness of the throttle matters; the capacity only matters in how it effects these things and how it effects the weight of the engine.

[jimbob82]

IMO the statement is both correct AND incorrect. It should read:

Depending on application and perspective, there is no replacement for displacement.

Job done. No one else need post anymore

[300bhp/ton]

Captain Muppet said:

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?

I would guess something like 14psi of boost or more, so effectively forcing twice the amount of air into the engine making it when running under boost a 4.0 litre engine.

This is no different to filling a dive tank with O2 by compressing it thus allowing you to carry more for a given physical displacement.

[kambites]

jimbob82 said:

IMO the statement is both correct AND incorrect. It should read:

Depending on application and perspective, there is no replacement for displacement.

Job done. No one else need post anymore

It should read "there is no replacement for making your engine's energy conversion characteristics as good for the application as possible". But that wouldn't create so many arguments, so wouldn't be as interesting.

[jimbob82]

kambites said:

It should read "there is no replacement for making your engine's energy conversion characteristics as good for the application as possible". But that wouldn't create so many arguments, so wouldn't be as interesting.

True.

[300bhp/ton]

kambites said:

As I said, the shape of the torque curve, and the responsiveness of the throttle matters; the capacity only matters in how it effects these things and how it effects the weight of the engine.

But how do you significantly affect the torque curve, especially at low rpms without doing something to displacement?

[DJRC]

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 rpm, 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....

You can Gaz...its called an Maclaren M8F. Unless you have the skills of Denny Hulme though...

[Captain Muppet]

300bhp/ton said:

Captain Muppet said:

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?

I would guess something like 14psi of boost or more, so effectively forcing twice the amount of air into the engine making it when running under boost a 4.0 litre engine.

This is no different to filling a dive tank with O2 by compressing it thus allowing you to carry more for a given physical displacement.

So using a device to make it seem like it's more capacity is the same as giving it more capacity? Yet somehow not a substitute for more capacity.

Lets assume I have no problem with that. I do, but getting agreement will never happen.

So moving on: What if you add a low friction coating to your pistons, machine away the side of the cam bearings that don't see any load and replace your hydraulic tappets with shim and bucket. What you've done is reduce frictional losses. For the same capacity, and even the same air going in to the engine, you are getting more out of it. It's not as cheap, or simple, as just making the engine a tiny bit bigger, but it has the same effect (apart from it also reduces your fuel use, which we can ignore because no one cares).

[kambites]

300bhp/ton said:

kambites said:

As I said, the shape of the torque curve, and the responsiveness of the throttle matters; the capacity only matters in how it effects these things and how it effects the weight of the engine.

But how do you significantly affect the torque curve, especially at low rpms without doing something to displacement?

Supercharging? Electric motors? Steam power?...

[Captain Muppet]

300bhp/ton said:

kambites said:

As I said, the shape of the torque curve, and the responsiveness of the throttle matters; the capacity only matters in how it effects these things and how it effects the weight of the engine.

But how do you significantly affect the torque curve, especially at low rpms without doing something to displacement?

I'll try to ignore your use of "rpms" and just say "variable inlet manifold".

[300bhp/ton]

Captain Muppet said:

So moving on: What if you add a low friction coating to your pistons, machine away the side of the cam bearings that don't see any load and replace your hydraulic tappets with shim and bucket. What you've done is reduce frictional losses. For the same capacity, and even the same air going in to the engine, you are getting more out of it. It's not as cheap, or simple, as just making the engine a tiny bit bigger, but it has the same effect (apart from it also reduces your fuel use, which we can ignore because no one cares).

I don't think anyone would deny this. But as your thread title says there is no replacement for displacement[/b].

Doing as you describe is an alternative, not a replacement. And in terms of cost, vs effort vs actual performance gains it has to rank a lot lower than simply upping the displacement of an engine.


I mean, if I took two Rover 3.9 V8's and did the above to one of them and stoked the other to 4.8 litres. Which would produce the most gain? It's it's the latter then there was no replacement for displacement.

[300bhp/ton]

doogz said:

Add electricity.

But you don't like that either!

Nope not against it at all. Although I was thinking along more conventional lines. Such as if you have a 2.0 litre engine in your car now (na) how would you make it produce significantly more low end torque without adding physical or dynamic displacement. I know how you can extend the torque curve to higher rpms and how to produce slightly more torque as a PEAK figure, but nothing that would dramatically change the engines low rpm ability.

[300bhp/ton]

Captain Muppet said:

I'll try to ignore your use of "rpms" and just say "variable inlet manifold".

But surely a variable inlet manifold isn't allowing more low rpm/revs torque, it just means you don't strangle it once you have it spinning quicker.


Simple scenario, two 2.0 engines. Once you want 240hp from, the other you want 240ft lb or torque below 2000rpm.

Getting the power is easy as proven by variable control systems like Honda's iVTEC and others.

But getting the torque is a tough one, even turbocharged you are unlikely to achieve this.

[quiraing]

Across the same rev-range you could never achieve the same torque from a small hi-spec stressed 1.6 or 3-litre, (or whatever), against maybe a lazy 7.2 V8.

[300bhp/ton]

doogz said:

300bhp/ton said:

But surely a variable inlet manifold isn't allowing more low rpm/revs torque, it just means you don't strangle it once you have it spinning quicker.

No, the clue is in the name.

http://en.wikipedia.org/wiki/Variable_length_intak...

Ta. But all it's doing is allowing you to optimise it for different rpm ranges. You could have a static intake manifold optimised for max low rpm torque and it'd be just as effective at that rpm range.

[Captain Muppet]

quiraing said:

Across the same rev-range you could never achieve the same torque from a small hi-spec stressed 1.6 or 3-litre, (or whatever), against maybe a lazy 7.2 V8.

But could you make a 7.1 V8 better than a lazy 7.2 V8? Yes. Thus cliche is wrong.

[300bhp/ton]

Captain Muppet said:

quiraing said:

Across the same rev-range you could never achieve the same torque from a small hi-spec stressed 1.6 or 3-litre, (or whatever), against maybe a lazy 7.2 V8.

But could you make a 7.1 V8 better than a lazy 7.2 V8? Yes. Thus cliche is wrong.

But could you make a 7.2 V8 better than a lazy 7.1 V8? Yes. Thus cliche is right.

[Captain Muppet]

300bhp/ton said:

doogz said:

300bhp/ton said:

But surely a variable inlet manifold isn't allowing more low rpm/revs torque, it just means you don't strangle it once you have it spinning quicker.

No, the clue is in the name.

http://en.wikipedia.org/wiki/Variable_length_intak...

Ta. But all it's doing is allowing you to optimise it for different rpm ranges. You could have a static intake manifold optimised for max low rpm torque and it'd be just as effective at that rpm range.

But without a VIM your won't also meet your power target. So you'd need a bigger engine to make the same torque and power, unless you had a VIM.

[300bhp/ton]

Captain Muppet said:

300bhp/ton said:

kambites said:

As I said, the shape of the torque curve, and the responsiveness of the throttle matters; the capacity only matters in how it effects these things and how it effects the weight of the engine.

But how do you significantly affect the torque curve, especially at low rpms without doing something to displacement?

I'll try to ignore your use of "rpms" and just say "variable inlet manifold".

What if it already has an intake manifold design to make the most torque at low rpms it just doesn't perform so well at higher ones. How then do you make more torque at low revs?