Turbo newbie question - mpg and boost

[tock13]

Sports mode gives me the best mpg. The higher rpms keep the engine from lugging and it does not get into boost to maintain certain speeds. Low RPMs and higher boost numbers are what kills my mpgs.

I will have to try that. I notice that the normal mode shift points make it feel like it’s always lugging, it always feels like it’s in too high a gear. I’ve always stuck around 2k rpm’s in my Toyota trucks where throttle response was about perfect, the beauty of a manual I guess.

I’ll give the different mods a try.

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[brkdncr]

I had a buddy who had a Dodge Omni GLH turbo in the early 80s and he routinely got warnings because the turbo shut down. He beat on that thing though but I’m totally paranoid now with a turbo.

I’m an old man in a new suit.

Warnings from who? And what do you mean the turbo shut down?

 

[brkdncr]

This is my first turbo, never wanted one, still don’t but no choice if I want a bronco so thought I’d toss out the ‘dumb question of the day’ post.

I get a Bronco is a brick, I don’t drive fast and furious, and I’d like to do what I can to maximize mileage.

I keep reading to maximize MPG, “keep out of boost”. I get what it means but exactly what boost range fits that comment?

I usually see 0 psi but on winding rolling country roads I see between 3 to 5 PSI coming back up out of the dips and then it’s back to 0 PSI.

Is 5psi dipping into the “keep out of the boost” range or is that range a lot higher?

I have owned a number of turbos. This is the first with an auto.

For best mpg, keep your foot out of it, use cruise control often. Keep your tires inflated.

my v6 2-door SAS is getting 19.1mpg.

the thing about turbos is that when you floor it, the engine is getting a lot of air forces into the chamber, and the engine is adding fuel to compensate. A non turbo operates in a similar fashion but not nearly as much air is going in since it’s relying on suction from the pistons moving down.

I wouldn’t worry about trying to chase 0psi with the throttle. Just go the speed limit, use cruise control, tire pressure, and don’t accel hard from stoplights.

also, turn off the a/c if you don’t need it.

in my sports cars I’d suggest emptying out the cargo areas to save on weight, but i honestly have not noticed any change in mpg when fully loaded with camp gear in the bronco.

 

[AZ_Liberty]

Put it in Eco Mode

That just makes things worse.

He needs to downshift to 5th from 6th so the engine doesn't lug.

 

[AZ_Liberty]

Good explanation, thank you. so the last paragraph is a good one, I’m only seeing up to 5psi for just split seconds at a time so should be close to getting the best MPG I can get. Last I manually checked mpg it was 20mpg. 4 dr BB SAS 2.3 auto.

I was going to say you need to downshift when going up the hills but since you have an auto you will do better in sport mode.

Sport mode will downshift more aggressively, therefore using less boost to maintain torque.

 

[Dmorty217]

I mean you bought a brick and you acknowledge that so you don’t actually care about gas mileage that much. I drive mine like I stole it and get 16.7 mpg in normal, 14 or less in sport.

 

[SHANUT]

This is my first turbo, never wanted one, still don’t but no choice if I want a bronco so thought I’d toss out the ‘dumb question of the day’ post.

I get a Bronco is a brick, I don’t drive fast and furious, and I’d like to do what I can to maximize mileage.

I keep reading to maximize MPG, “keep out of boost”. I get what it means but exactly what boost range fits that comment?

I usually see 0 psi but on winding rolling country roads I see between 3 to 5 PSI coming back up out of the dips and then it’s back to 0 PSI.

Is 5psi dipping into the “keep out of the boost” range or is that range a lot higher?

If your goal is good mpgs, 0 boost is your goal.

 

[Brian_B]

Sports mode gives me the best mpg. The higher rpms keep the engine from lugging and it does not get into boost to maintain certain speeds. Low RPMs and higher boost numbers are what kills my mpgs.

Yup. Kinda like on my 7MT 5th gear is better than 6th - sits a bit higher in RPM : torque band and doesn’t have to sit at a constant 2-3 psi boost

 

[JohnnyBronco]

This might help put it in perspective.. let's see how good I am at explaining things today lol..


Producing a certain amount of HP requires a certain amount of fuel.. no way around it. N/A.. turbo.. blower.. really doesn't matter.. it's mathematical/scientific rule. 300hp from a 250cc motor would need just as much fuel as 300hp from a 632ci bigm block chebby.


Boost, as we know, increases the amount of power a motor makes by forcing it full of more air (and subsequently more fuel) than it could draw in under vacuum.

14.7 PSI from a turbo/blower will double the power output of a motor compared to if it were naturally aspirated. Simple enough. 300hp naturally aspirated motor will make (close enough to) 600hp if one were to put a turbo on it and let er rip at 14.7 psi.


So.... running at 5psi reduces efficiency by about 33%.. around 7mpg in my case.

I will try to only poke small holes in your math. Power curves are not straight line 45 degree angle, which would be indicative of simply doubling air and fuel.

And doubling the amount of air does not necessitate an equal doubling of fuel consumption.

Where charging the air really comes into play is the higher one gets from sea level and away from nominal 14.7 psi. At mile high Denver and beyond atmospheric pressure can be half or less. Without boost to achieve full combustion requires half the fuel mass and certainly burning half as much fuel will produce reduced power. In a carbureted engine A/F ratio will be too rich and extra umburned fuel will exit tailpipe. Solution? Smaller carb jets or more air.

More efficient combustion due to boost compared to no boost does not always decrease mpg. I had several supercharged GM V6 vehicles that routinely returned 30+ highway mpg at 70+ mph. With SC boost is usually available quicker and power produced compensates for more moving parts at idle. But that's why most modern performance turbos are twin turbos

 

[swamp2]

don’t accel hard from stoplights.

I've heard the opposite from some hypermiling types...

The idea is to always get in to it hard off the line for good fuel economy. Why? Maintaining a speed is only fighting various forms of drag, whereas accelerating is fighting the mass/inertia of the vehicle and this is what really takes the power and fuel. One needs to minimize the time spent accelerating. So get up to cruising speed as quickly as possible and then even throttle or cruise control.

I've not seen data to back the claim nor do I practice this myself. I'd like to know the answer though.

 

[Brian_B]

I've heard the opposite from some hypermiling types...

The idea is to always get in to it hard off the line for good fuel economy. Why? Maintaining a speed is only fighting various forms of drag, whereas accelerating is fighting the mass/inertia of the vehicle and this is what really takes the power and fuel. One needs to minimize the time spent accelerating. So get up to cruising speed as quickly as possible and then even throttle or cruise control.

I've not seen data to back the claim nor do I practice this myself. I'd like to know the answer though.

What I've always heard, and like @swamp2 , I don't have any justification for it other than it makes sense to me

For acceleration:
You want to get to the toe point of the torque curve as quick as you can and move through the gears - that point is going to be your most efficient fuel-wise, going beyond that has diminishing returns, and before that your just extending the time out you spend accelerating, which is a huge fuel burn. So don't hammer it to the red line, but don't baby it along either.

For the 2.7 that's right around 3k RPM, for the 2.3 that's 3500. If you are mashing the pedal hard enough that the auto is going past that on shift points you are accelerating too hard, if you aren't hitting those RPMS your spending too much time getting to cruising speed and should be a bit more aggressive. That should give you the least amount of time in "boost" and get you up to speed in an efficient manner where you can cruise.

Once you hit your speed, you want to be in the gear with the the lowest boost / lowest rpm you can sustain without bogging down - roughly in that order. An Auto is going to do that for you with it's electric mapping.

 

[JohnnyBronco]

First rule of mpg on these vehicles....get rid of the sasquatch setups and run highway tread 33s. Inflate back to the as delivered to the dealer 50 psi (not really recommended but higher psi is better to reduce rolling resistance.)

And with the factory Bridgestones OBX 2.7 auto advanced after 40,000 miles I still get 19.6 mpg average

 

[HPNQ420]

This might help put it in perspective.. let's see how good I am at explaining things today lol..


Producing a certain amount of HP requires a certain amount of fuel.. no way around it. N/A.. turbo.. blower.. really doesn't matter.. it's mathematical/scientific rule. 300hp from a 250cc motor would need just as much fuel as 300hp from a 632ci bigm block chebby.


Boost, as we know, increases the amount of power a motor makes by forcing it full of more air (and subsequently more fuel) than it could draw in under vacuum.

14.7 PSI from a turbo/blower will double the power output of a motor compared to if it were naturally aspirated. Simple enough. 300hp naturally aspirated motor will make (close enough to) 600hp if one were to put a turbo on it and let er rip at 14.7 psi.


So.... running at 5psi reduces efficiency by about 33%.. around 7mpg in my case.

Pretty good explanation, but, running boost might increase efficiency as measured by lbs/hp-hr or whatever the metric equivalent is. Mileage drops because you are throwing the power into the wind, but, technically, the engine itself might be working more efficiently.

 

[Fly by Nite]

.....
to maximize mileage.

I keep reading to maximize MPG, “keep out of boost”. I get what it means but exactly what boost range fits that comment?

I usually see 0 psi but on winding rolling country roads I see between 3 to 5 PSI coming back up out of the dips and then it’s back to 0 PSI.
.....

Use the mpg gauge in your dash display. You'll quickly learn the techniques to maximize mpg.

I drive in mostly rural areas with rolling hills. I average mid 19's mpg with a 2.7 2 dr BaseSquatch.
Accelerating up hills kills mpg, try to anticipate by going faster downhill to gain some momentum to go up hills. Stop n go traffic hurts mpg too.
If I can maintain 45-55 mph while minimizing stops and rolling up/sown hills, I can see over 20 mpg on a typical 30 min drive. A short 10 minute drive to the store, I may get 17-18 ish.
I love the turbos! It's tough to not use them more, I enjoy the rush!

 

[3People1Body]

Tons of opinions and science here... if you bought it for MPG, it might be the wrong vehicle for you. Also, turbos got a bad wrap in the 70's/80's, modern turbos have better lubrication and cooling, all lessons learned from years of turbo applications.

If you're constantly worrying about MPG, how can it be pleasurable to drive? I play the game too on trips trying to get the best MPG, but in the end I averaged around 17 (before 37's).

Headwind is a killer! Driving through Idaho with a headwind slightly downhill going 80, I was running 12-14PSI just to maintain speed... at the end of the 6-7k (x2) trip, ~17MPG was what I got. Lot of folks ask me about my MPG, I just say 17 (stock Sasquatch).

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