Turbo Boost and FE
 

Hello. I was reasoning with myself last night (as any reasonable gassaver would do =P) If I had a car, with a 2.0L engine and a turbo. If I stayed out of boost, my gas consumption would be one of a 2.0L engine without a turbo correct? and only if I boosted then my FE would flush down the drain?

Thanks!

To varying degrees, yeah. And it's definately better to have a 2L Turbo than a 3L non-turbo. But just to further complicate things for you, under some circumstances a little bit of boost can increase efficiency. ;)

Yeah, I'm a relative newcomer to the FE world, but I've been a performance nut for years. One of the early arguments turbochargers was that if you drive conservatively, you should be able to get slightly better gas mileage. The idea as I remember it is that even when not under boost, the turbo is spinning and it'll just barely overcome the parasitic drag of the fuel/air charge and any pumping inefficiencies of the engine.

Folks with the 2.0t VW GTI report wildly varying MPG numbers, from 12 to 45 MPG without any hypermiling tactics. So, I'd say the answer to your question is yes.

My turbo really doesn't do much until I'm over 2300 rpm's. If I'm driving for FE I rarely get my RPM's much over that. When you have boost you must have RPM's so you will, by nature of the beast, be getting poor FE. The best part of a turbo, I have the acceleration of a small V-8 when I need it and the FE of a 4 cyl.

thats good news to hear! but now I'm wondering why do people complain about bad mileage on a gt-four. i'm planning to get one, but they run about 13L/100km mixed driving.. its a 2.0L turbo.
I'm guessing the 4wd also contributes to bad FE?

I can see where there is an advantage to having a turbo but I can pretty safely say that your turbo car will probably never see what my car is getting (35.7 average) especially when you throw all wheel drive in the mix.

a turbo diesel will get realy good mileage and I guess in theory you could get better FE out of a turbocharged gas engine if it were smaller displacement.

I remember reading about chryslers slingshot. it was a concept car kind of sporty and tremendously small (by todays standards anyway) it had a turbo charged 3-cyl. it was a concept car that died. that was before the fuel price explosion though. back in $2 days.

heck. i can't even get your mileage with my 88 camry 1.8L.
anyways. getting off topic..

so if i say i have 2 identical cars, except one has a turbo and one does not. Who'll get the better FE if driven identically?

I'm guessing at low rpm's the turbo and high rpm's the non turbo?

If the engines are identical, the non-turbo one will probably do better. The whole reason turbos are associated with fuel economy is because you can use a smaller engine.

If you have a 2.0L non turbo and a 2.0L turbo, the non will always get better fuel mileage. It comes down to compression ratio. A Turbo has a 8.5 to 8.7 to 1 compression. The NA on the other hand may have a 9.5 to 10.5 to 1 compression ratio.
More compression more HP at all throttle openings when boost isn't a factor. At any normal cruising speed the NA's throttle will be opened at a lower setting.
That 2.0L NA may make 150 peak HP where a Turbo 2.0L may make 200 peak hp. At 30 percent throttle the NA makes 90HP where the Turbo makes only 75HP. The Turbo only has an advantage in HP when boost is factored in.