using turbo for fuel economy

[Sleepingsquirrel]

What say you all about this claim?


"Maximum fuel economy is realized when the engine is operating in Stage 1 at low boost levels. The theory behind turbo charging for economy was that by keeping the intake manifold pressure as close to 0 psi as possible (no vacuum), volumetric efficiency would peak because no work would done by the crankshaft during the intake stroke (no work required to pull vacuum). I was able to average 68 MPG this past summer in Arizona, but the all time running average for the car is 54 MPG. The fuel economy largely depends on driving technique and habits. Here are a couple links to some more info on the engine:

D15B 1.5l SOHC VTEC
3-stage VTEC - Wikipedia, the free encyclopedia

Although the car was not designed to be fast, it does make 228 HP at 12 PSI of boost. The car was professionally tuned by Locash racing in Phoenix, and it has been my daily driver for over 9 months. Everything works fine (cruise control, pwr windows/mirrors, sunroof, ect...) and the car does have VERY COLD A/C! I am only selling to free up some garage space for a new project."

Thanks for your thoughtful replies!

 

[Maciej]

What say you all about this claim?


"Maximum fuel economy is realized when the engine is operating in Stage 1 at low boost levels. The theory behind turbo charging for economy was that by keeping the intake manifold pressure as close to 0 psi as possible (no vacuum), volumetric efficiency would peak because no work would done by the crankshaft during the intake stroke (no work required to pull vacuum). I was able to average 68 MPG this past summer in Arizona, but the all time running average for the car is 54 MPG. The fuel economy largely depends on driving technique and habits. Here are a couple links to some more info on the engine:

D15B 1.5l SOHC VTEC
3-stage VTEC - Wikipedia, the free encyclopedia

Although the car was not designed to be fast, it does make 228 HP at 12 PSI of boost. The car was professionally tuned by Locash racing in Phoenix, and it has been my daily driver for over 9 months. Everything works fine (cruise control, pwr windows/mirrors, sunroof, ect...) and the car does have VERY COLD A/C! I am only selling to free up some garage space for a new project."

Thanks for your thoughtful replies!

Stay away, no one is turbo'ing a '92-'95 Civic for fuel economy.

 

[Capt. Geoffrey Thorpe]

" by keeping the intake manifold pressure as close to 0 psi as possible (no vacuum), volumetric efficiency would peak because no work would done by the crankshaft during the intake stroke (no work required to pull vacuum)."

That much is true, more or less. But how do you do that and drive at 45 mph?
This also ignores the fact that the turbo increases back pressure which results in pumping work on the exhaust stroke. And it appears that the VTEC is using valve lift / disabling to limit power which results in pumping work across the intake valve. But it also runs lean (per wiki) which helps for a couple reasons - less pumping work and small increase in thermal efficiency.

"The fuel economy largely depends on driving technique and habits." Bingo.

 

[bnt83]

The engine in an air pump right? Unless the throttle is wide open there will always be a vacuum behind it, yes/no?

When you are driving down a city street the throttle is what? 15% open? That means it is restricting air into the cylinders....


Also, what other have said...

 

[docmirror]

There are no ultra hi BSFC Otto cycle spark ignition engines with turbos. They are all NA engines in the field. Toyota, Nissan, Hyundai etc all use a form of Atkinson cycle to improve BSFC, but no turbos.

Having said that, if one does put a turbo on a non-diesel engine, there is some sweet-spot of MP which yields the best BSFC, but it's highly dependent on a bunch of factors, not just the MP of 0(actually 29.92"Hg) PSI(atm). There's so many things at work that will alter the BSCF of the engine it's a fools game to try pegging one thing. Chances are, he found the sweet spot by trial and error, and viola! it came at 0PSI MP for that car, under those conditions, with that engine, on that fuel, etc.

 

[N801BH]

There are no ultra hi BSFC Otto cycle spark ignition engines with turbos. They are all NA engines in the field. Toyota, Nissan, Hyundai etc all use a form of Atkinson cycle to improve BSFC, but no turbos.

Having said that, if one does put a turbo on a non-diesel engine, there is some sweet-spot of MP which yields the best BSFC, but it's highly dependent on a bunch of factors, not just the MP of 0(actually 29.92"Hg) PSI(atm). There's so many things at work that will alter the BSCF of the engine it's a fools game to try pegging one thing. Chances are, he found the sweet spot by trial and error, and viola! it came at 0PSI MP for that car, under those conditions, with that engine, on that fuel, etc.

Agreed...

And the more air forced into the motor , the better the VE.... so that claim in the OP's post is invalid...