Turbos and fuel consumption (in petrol engines)

[teatako]

hey. well my question is the following. say, if everything else was the same, a turbo engine is thirstier than an NA one, right? well, is there a graphic or a converting method to see for example how bigger an NA engine must be than a turbo one to have the same fuel consumption? I explain myself. I´m starting to see as a good idea to end with turbo lag in my smart, to remove the turbo completely, and to add a little more displacement, so it can have the kind of instantaneous response only an atmospheric can give. but i wouldn´t want to hurt consumption too much. i really dont know much about turbos, or engines at all, but to me it seems simple, you want the response of a naturally aspirated engine, then make it naturally aspirated. how crazy would the ECU go with such modification, i don´t know. im probably not taking some elements into consideration but thats out of pure ignorance. thoughts, anyone?

[KnifeEdge_2K1]

there's always a limit to how much you can increase the physical displacement, and turbo's are using waste energy from the exhaust to increase the input which is increases efficiency

you can hook up bypass valves which bypasses the turbo at low rpms giving you good fuel consumption, and close them at higher rpm so you get more power, the twin scroll turbo sorta does this and removes most of the lag and decreases backpressure at low rpms

[mmm_aapls]

How exactly are you planning on "adding more displacement"?

A turbo will increase your engine capacity depending on how much boost you run. To get the equivelent N/A displacement, you would need a larger engine (in terms of block, and cylinder capacity). So by replacing your turbo with a larger engione, you sacrifice weight.

Smart cars use turbo engines becasue you can get more effective displacement out of a tiny engine.

So to takeing your turbo off your samrt car, and replacing it with an equivelent capacity engine would be expensive and pointless.

[drakkie]

would be expensive and pointless.

So true They are so right, your car will only go lots slower in the end and probably wouldnt consume less petrol because the engine needs to be used more intense...

[lightweight]

if everything else was the same, a turbo engine is thirstier than an NA one, right?

Wrong. I will answer with an example

Lets say (for the sake of comparison) that your smart is 1000cc and it runs 0.5 bar boost. Then, roughly, the equivalent n/a petrol engine would be a 1500cc in terms of performance. BUT the smart turbo engine will consume less.

That is the reason for implementing turbochargers. They offer the benefit of downsizing, reduced fuel consumption and reduced weight and simultaneously offer identical performance compared to their n/a counerpart.

[DesmoRob]

My dad used to have a Mitsubishi when we still lived in Germany like 16 years ago, I think it was a Pajero but I'm not sure. Anyways, the thing had a Turbo, and he said that it consumed less petrol than the regular model because it used the power more efficiently or something. I found that hard to believe.

[torampettoshuji]

thought i would my 2 cents. from my experience, a turbo engine uses less gas than a larger engine, but I will say that turbos can use a lot of gas if you run high boost or stay in the boost range a lot. Mainly because even if you have a displacement of 2 liters the turbo adds to the density of the air going in the engine thus you will need more fuel to mix with the increase in O2, or the engine will run lean. For example if you drive an EVO lightly short shifting and staying out of the boost range you could get 27 MPG. But if you drive it like most people on this forum would you might get 14 MPG. Take a look at the twin charging thread I put up kind relates to this.

[NSXType-R]

Wrong. I will answer with an example

Lets say (for the sake of comparison) that your smart is 1000cc and it runs 0.5 bar boost. Then, roughly, the equivalent n/a petrol engine would be a 1500cc in terms of performance. BUT the smart turbo engine will consume less.

That is the reason for implementing turbochargers. They offer the benefit of downsizing, reduced fuel consumption and reduced weight and simultaneously offer identical performance compared to their n/a counerpart.

But then wouldn't the turboed engine ingest the same amount of air as the 1.5 L engine to produce the same power as the 1.5 L? The turbo is stuffing more air in the engine but by doing that it also stuffs more fuel. So wouldn't they end up even in the end?

[mmm_aapls]

Volumetrci Efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%. However, if the cylinder is pulling in a vacuum (N/A engines), then the engine has less than 100% volumetric efficiency. Normally aspirated engines typically run anywhere between 80% and 100% VE.

[lightweight]

But then wouldn't the turboed engine ingest the same amount of air as the 1.5 L engine to produce the same power as the 1.5 L? The turbo is stuffing more air in the engine but by doing that it also stuffs more fuel. So wouldn't they end up even in the end?

Actually no, because the cylinder of the turbo engine burns the fuel more efficiently. that is the benefit of engine downsizing. That is why many manufacturers adopt pressure charging.

[NSXType-R]

Actually no, because the cylinder of the turbo engine burns the fuel more efficiently. that is the benefit of engine downsizing. That is why many manufacturers adopt pressure charging.

You have a good point there because Honda is moving to turbos too. Hope they bring that out to more models.

[teatako]

so, in 4 words, not a good idea, right?
so far ive understood that and the following.

. i thought you could increase bore and stroke a bit, instead of replacing the engine.

the problem seems to be that yeah, turbos reroute exhaust emissions but a 700cc engine doesnt produce that much exhaust gasses, especially when it has to fill 1 bar of boost. therefore i would have to increase displacement a whole LITER to get the same amount of power? whoa.


i also thought bypass valves were oem equipment.

ill google that twin scroll turbo thing

well anyways, then how about a supercharger? you know, replacing the turbo for a supercharger, which at least is mechanical as far as i know.

[mmm_aapls]

super charges use energy from the crank to compress the air, so it is a parasitic device. I'm not sure how a super charger would go on such a small engine.

Out of interest, what sort of rev range does a smart car have?

[lightweight]

Out of interest, what sort of rev range does a smart car have?

It must rev up to 6k (probably less). It's a 3 cylinder engine, built for economy rather than performance.

Some have installed a hayabusa engine in the Smart. Maybe try that route

[NSXType-R]

super charges use energy from the crank to compress the air, so it is a parasitic device. I'm not sure how a super charger would go on such a small engine.

Out of interest, what sort of rev range does a smart car have?

The Mini Cooper S is a small displacement engine with a supercharger. It puts out about 200 HP.