Hp displacement ratio

[derekthetree]

Which pretty much means nothing in the read world, with gears, and cars and all.

I thought we were talking generally??

Please would you explain to me how, for example, a 5.7 LSD putting out 330bhp say would match the economy a 3.2 BMW straight six putting out same power?

[henk4]

I thought we were talking generally??

Please would you explain to me how, for example, a 5.7 LSD putting out 330bhp say would match the economy a 3.2 BMW straight six putting out same power?

because they use that power to potter on at 60 mph, doing 1200 revs....

[derekthetree]

because they use that power to potter on at 60 mph, doing 1200 revs....

aah, now I am enlightened, I realise the folly of my argument and of course rescind to the greater knowledge of my learned cousin (metaphorically)

[Ferrer]

Ever noticed that the engines in all performance cars are continuously getting MORE dispalcement?

Because it's a cheap and easy way to increase power? But anyway the Koenigsegg CCX produces 806bhp with "only" 4.7-litres...

[hightower99]

A higher HP/L rating leads to more fuel being wasted per HP made...

A simple example:

You have two cylinders, both have 1:1 bore:stroke ratio. However one cylinder is 150cc and the other is 875cc.

150cc cylinder:
12.5:1 compression ratio
12.5:1 air:fuel ratio
Valve timing set for large amount of overlap.
206:HP/L (31hp)
Amount of energy lost: 65hp (includes wasted energy from excess fuel compared to 14.7:1 A:F ratio)

875cc cylinder:
10:1 compression ratio
14:1 air:fuel ratio
Valve timing set for small amount of overlap
72:HP/L (63hp)
Amount of energy lost: 113hp (includes wasted energy from excess fuel compared to 14.7:1 A:F ratio)

Now hopefully we all know that the amount of heat transferred per unit time is effected by the temperature difference. So my first question is which cylinder has hotter air in it? and therefore loses more to the surrounding enviroment? Next look at the air:fuel ratios the bigger cylinder can aford to use 10% less fuel per unit air there alone. Notice that the little cylinder throws away 2.1hp for every useful 1hp it makes whereas the big one only throws away 1.8hp.

get my point?

[Slicks]

I thought we were talking generally??

Please would you explain to me how, for example, a 5.7 LSD putting out 330bhp say would match the economy a 3.2 BMW straight six putting out same power?

Generally, IRL?
The 3.2L I6 will most likley get worse gas milage in everyday driving, probably at WOT too, being that it has to rev much higher to make the same amount of power.

[hightower99]

BMW I6s are magic anyways...

Biased

[derekthetree]

Generally, IRL?
The 3.2L I6 will most likley get worse gas milage in everyday driving, probably at WOT too, being that it has to rev much higher to make the same amount of power.

but on each stroke the v8 will be using that much more fuel...

BMW I6s are magic anyways...

something we can agree on

[Slicks]

Because it's a cheap and easy way to increase power?

If hp/l matters so much though, why would they increase displacement? Why are there no cars powered by the 1 cylinder RC car engines, with their amazing hp/l?

But anyway the Koenigsegg CCX produces 806bhp with "only" 4.7-litres...

And "only" twin superchargers running over 17psi of boost. Id love to know how much one of those engines costs.

[Slicks]

but on each stroke the v8 will be using that much more fuel...

While the I6 is revving much higher, consuming fuel.

[derekthetree]

While the I6 is revving much higher, consuming fuel.

yes. but others and i are saying that a large engine, revving slower will consume more fuel than a smaller engine revving higher.

If hp/l matters so much though, why would they increase displacement? Why are there no cars powered by the 1 cylinder RC car engines, with their amazing hp/l?

because their overall power and torque are poor

[hightower99]

Slicks you need to relax everyone here KNOWS that HP/L ratings doesn't mean anything and that it doesn't make one engine better than another...

But some people think that you think that FI sucks because in you POV it increases HP/L (It doesn't FI increase the "true" displacement of an engine without a physically larger block)

I know you aren't against high HP/L engines you are against the dumb guys who think that there S2000 with it's 120HP/L can take anything...

I for one agree with you!

[SIMPLETON]

1 kW is a set standard

it is 1kW anywhere...

If you are referring to a set test method than no they don't but thats because they use simple formulas that everybody in the ICE industry knows...

as in it doesn't need to be a set standard.

I was reffering to nota's post about RC engines. Each one of those manufacturers use a different dyno test so their numbers are basically meaningless. The only thing that maters with those tiny engines is their real world performance. Most RC car engines have a true amount of power that is about 60-80% less than the manufacturers claim

[hightower99]

yes. but others and i are saying that a large engine, revving slower will consume more fuel than a smaller engine revving higher

I hope you realise that forces tend to increase linearly with increases in weight and porportionaly with increases in speed...

The higher you rev the less air you tend to keep in the cylinder for combustion while the amount of fuel injected increases.

The lower your revs the easier it is to keep a full cylinder's worth of air in for combustion and the fuel injected is decreased

higher revs = lower effeciency, more power
Lower revs = higher effeciency, less power.

[SIMPLETON]

Have you ever seen one of thoose things go? or even driven one? Mine is a measly 2.5cc and the thing sometimes looks likes it's going to run up the walls!

Yes. I have one with the same amount of displacement and I will agree that they are very fast. But they are helpded out alot with their somewhat unconventional fuel (mixture of nitromethane,methane, and oil) and the fact that they only weigh a few pounds.