Is a turbo more fuel efficient?

[Lurker27]

The problem here is the type of efficiency we're discussing. Volumetric efficiency of the engine increases greatly with the turbo, and things like the intake geometry have less of an effect on airflow since air is being rammed down their throats (This manifests as a pressure drop in boost rather than the engine not being able to pull ambient or slightly above ambient pressure into the cylinder - it changes spool and max power but from the engine's standpoint it doesn't really matter.

I'd expect turbos to have a cleaner combustion and better carnot efficiency when compared to low compression engines - although an equivalent combustion under NA conditions will do just as well. (7.5:1 CR engine @ 14.7psi boost = 15:1 engine @ twice the displacement from a carnot standpoint)

[xLibelle]

well..... i'm not sure hot much further to drive the topic. lurker has made a good point. It would be nice if we could get some more elaboration on the subject, to drive the point home, but i think the I4-T could somehow take it.

I've been tossing around a few other ideas like on the NA engine, shut off 2 or 3 cylinders to essentially lower it's displacement, thus drop fuel consumption. some current diesel pickups are doing it now.

[Collin]

Would the time it takes the turbo to spool during acceleration affect economy? I mean if you're making 15 lbs of boost, the engine has to create 15 pounds of pressure on the exhaust side of the turbo, naturally taking power and energy from the engine.
The fuel economy of any vehicle under acceleration will be for shit, but does a turbo make it worse?

[Danny]

The fuel economy of any vehicle under acceleration will be for shit, but does a turbo make it worse?

With good tuning it shoudn't be too bad.

[moatilliatta]

Like top gear said, Its not what you drive, its how you drive it..

[xLibelle]

sorry radiocambodia but dont speak any more about the subject of boost.
you need to get Corky Bell's book and read the entire thing.

youre exactly right moatilla. it helps tho, to have the EXACT engine for the job.

[Pinepig]

sorry radiocambodia but dont speak any more about the subject of boost.
you need to get Corky Bell's book and read the entire thing.

In the last couple of forced induction topics I've been in, I've wanted to put my foot through the monitor hoping it might hit some of these posters.

[xLibelle]

its all good, no need to string them up. dont want to scare off those that make points with the wrong perspective. Just gotta correct them and get on with it. :)

[Tbolt]

engines like 1.8ts seem to be fuel-efficient power

[StereoInstaller1]

So think of it this way: turbos turn waste heat into power, basically.

Turbos are more efficient, if properly tuned.

If a N/A engine and a turbo engine are making 100HP each, the turbo motor will get better fuel economy.

Read: http://www.allpar.com/fix/holler/slant-six-turbo.html

http://www.sae.org/technical/papers/2004-01-0988

http://www.acarplace.com/cars/turbochargers.html

[gstuning]

A little explanation.

A scenario of two engines
200hp/200lbs torque..

One is a 2.5 multivalve engine
One is a 1.6 turbo (opel astra 1.6 turbo for instance)

Now to explain why the little engine gets more mileage just cruising is that it´s manifold pressure will be higher (closer to ambient) , while the 2.5 engine will have lower manifold pressure.

Difference is pumping losses are higher in the NA engine for a given HP output. No matter what that output is 0-200hp is the range.

One of the reason a NA Diesel engines are very efficient as they run ambient manifold pressure constantly and only vary load with fuel, not the other way around like petrol engines vary load by AIR and the compensate with fuel.

Also to note.
6cyl engines have less frictional loss over a 4cyl engine given the same engine capacity.

Expect to see 50-80psi diesel engines coming on the market in the next 5-7years.
engine sizes ranging from 500cc and upwards. Maximing the fact that a small engine has less pumping losses at cruise then a bigger one while still maintaining the specific HP output of a bigger engine.

[xLibelle]

Man, thanks for the links luke... looks like i could have resorted to google instead of bothering you guys. ;)

gunni, i forgot about the 6cyl having a better crank design than the 4 cyl. i believe that to be an huge factor here!

and i'm still trying to wrap my head around the conceptual differences with gas and diesel. i understand how it works, its just that i must keep reminding myself of the aspects of properly tuning it since its reverse of what tuning a gas engine is about.

[gstuning]

It´s not the crank design it´s frictional losses based on equal engine size.
so a 12cyl 2liter engine will have less frictional losses over a 4cyl one. Sounds crazy but that´s how it is.

Diesel engines run on mixture control not air control, in a simple term.
so at idle the AFR are about 80:1 , and as you give it more diesel , the mixture goes up and the engine revs.

Imagine a steady state dyno run, maximum torque = maximum fuel injected per cycle.
Give it more, and it will just be more powerfull until your in the black smoke AFR´s.

[WlknGenius]

A turbo is inherently more fuel efficient by design. Regardless of car, engine, etc.

[WlknGenius]

Man, thanks for the links luke... looks like i could have resorted to google instead of bothering you guys. ;)

gunni, i forgot about the 6cyl having a better crank design than the 4 cyl. i believe that to be an huge factor here!

and i'm still trying to wrap my head around the conceptual differences with gas and diesel. i understand how it works, its just that i must keep reminding myself of the aspects of properly tuning it since its reverse of what tuning a gas engine is about.

A large part of the increase in efficiency you get from a diesel is due to the higher compression ratio diesel engines can achieve. You can write a motors efficiency in terms of the compression ratio w/o too much trouble.