Charging for mpg: turbo vs. sc
05-08-2011, 01:38 PM
#1
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Thread Starter
Join Date: Apr 2011
Posts: 100
Charging for mpg: turbo vs. sc
I am trying to put together a setup in my head for a near future install. I want to use either a small turbo or sc to increase my mpg as well as performance. From what I've gathered so far I would want a small turbo/sc for minimal lag. What I'm wondering is what effect a turbo vs. a sc will have on mpg.
Oh, and I have an auto and want to keep it. Another reason to go small with no lag.
Oh, and I have an auto and want to keep it. Another reason to go small with no lag.
05-08-2011, 02:26 PM
#2
SC will drop mpg while turbo will remain the same or possibly slightly increase with a turbo. SC being belt driven is an extra load on the motor. Think how much more gas the car takes with the ac on all the time to somewhat give you an idea. Turbo doesnt require power to make power.
05-08-2011, 04:22 PM
#3
1. TC and SC help force more air into the motor.
2. When you force more air into the motor, you naturally need more fuel to compensate for the increased flow of air.
3. More fuel = a drop in mpg.
4. Make sure your car is up to date on normal maintenance to get the optimal gas mileage for your car.
5. Try to keep the rpm under 2.5k when you drive.
2. When you force more air into the motor, you naturally need more fuel to compensate for the increased flow of air.
3. More fuel = a drop in mpg.
4. Make sure your car is up to date on normal maintenance to get the optimal gas mileage for your car.
5. Try to keep the rpm under 2.5k when you drive.
Essential
05-08-2011, 07:30 PM
#5
not to mention youll probably end up going with larger injectors, stronger fuel pump, etc. aaaand tune it to run a little richer under boost. idk, to me theres just so many things going against mpgs than going for it.
05-08-2011, 09:13 PM
#6
You can always tune it a little leaner. A turbo setup will yield same or better results and a proper tune can only help. BTW just because you have bigger injectors and a more capable fuel pump doesn't mean you will be spraying more while cruising, that's why we tune.
05-09-2011, 05:18 AM
#8
I don't think this is accurate. The energy to compress the air into the cylinder has to come from somewhere, unless you have discovered a perpetual energy machine. Google "Law of Conservation of Energy".
I think the MPG benefit from using turbos comes from smaller displacement. So if you drop in a VQ20 and turbo it, you could have VQ30 power with better MPG.
The Maxima is a pretty efficient car. With the automatic its not hard to get 30+ mpg on the highway. If you are interested in fuel economy, I agree with the above post concerning preventative maintenance. Also, if you don't drive as fast, it will be beneficial as well. Air resistance increases exponentially with speed. In other words, the air resistance at 60 mph is more than twice as high as the air resistance at 30 mph. I'm not saying avoid highways, because the constant speed has benefits as well, but instead of 75 on the highway, driving 65 will save gas.
I think the MPG benefit from using turbos comes from smaller displacement. So if you drop in a VQ20 and turbo it, you could have VQ30 power with better MPG.
The Maxima is a pretty efficient car. With the automatic its not hard to get 30+ mpg on the highway. If you are interested in fuel economy, I agree with the above post concerning preventative maintenance. Also, if you don't drive as fast, it will be beneficial as well. Air resistance increases exponentially with speed. In other words, the air resistance at 60 mph is more than twice as high as the air resistance at 30 mph. I'm not saying avoid highways, because the constant speed has benefits as well, but instead of 75 on the highway, driving 65 will save gas.
05-09-2011, 06:50 AM
#9
I don't think this is accurate. The energy to compress the air into the cylinder has to come from somewhere, unless you have discovered a perpetual energy machine. Google "Law of Conservation of Energy".
I think the MPG benefit from using turbos comes from smaller displacement. So if you drop in a VQ20 and turbo it, you could have VQ30 power with better MPG.
The Maxima is a pretty efficient car. With the automatic its not hard to get 30+ mpg on the highway. If you are interested in fuel economy, I agree with the above post concerning preventative maintenance. Also, if you don't drive as fast, it will be beneficial as well. Air resistance increases exponentially with speed. In other words, the air resistance at 60 mph is more than twice as high as the air resistance at 30 mph. I'm not saying avoid highways, because the constant speed has benefits as well, but instead of 75 on the highway, driving 65 will save gas.
I think the MPG benefit from using turbos comes from smaller displacement. So if you drop in a VQ20 and turbo it, you could have VQ30 power with better MPG.
The Maxima is a pretty efficient car. With the automatic its not hard to get 30+ mpg on the highway. If you are interested in fuel economy, I agree with the above post concerning preventative maintenance. Also, if you don't drive as fast, it will be beneficial as well. Air resistance increases exponentially with speed. In other words, the air resistance at 60 mph is more than twice as high as the air resistance at 30 mph. I'm not saying avoid highways, because the constant speed has benefits as well, but instead of 75 on the highway, driving 65 will save gas.
05-09-2011, 07:17 AM
#10
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Join Date: Jul 2009
Location: Richmond, VA
Posts: 191
That being said, everyone's basically right. Proper maintenance is key, but assuming that's all up to date, a small turbo might help (depending on your driving style). A turbo is better for MPG than a supercharger because it creates far less parasitic drag by being exhaust driven, and there's a sort of natural correction in mileage when you restrict exhaust.
It's kind of tricky though. I don't know if you'll be able to get better mileage with a turbo or not. Most of the gains in gas mileage from restricted exhaust come from improving the efficiency of EGR, both by allowing more air to remain in the cylinder after the exhaust stroke and by making the actual EGR system more efficient. Having more pressure in the intake manifold (from the turbo) would likely undo all of this, but maybe not if you stay out of boost.
Another thought is that, since you'd have more power, you could run taller gearing to save gas. Still try to stay out of boost, but you'd have it available if you needed it. I don't hear about many people altering their gearing on Maximas, especially automatics, but if you're serious enough to build a turbo setup to maybe save 1-2MPG, I guess it's possible that you're serious enough to pursue this too. Good luck, I'm looking forward to seeing the results.
05-09-2011, 07:40 AM
#11
Just because you don't understand it doesn't mean that it's not relevant.
That being said, everyone's basically right. Proper maintenance is key, but assuming that's all up to date, a small turbo might help (depending on your driving style). A turbo is better for MPG than a supercharger because it creates far less parasitic drag by being exhaust driven, and there's a sort of natural correction in mileage when you restrict exhaust.
It's kind of tricky though. I don't know if you'll be able to get better mileage with a turbo or not. Most of the gains in gas mileage from restricted exhaust come from improving the efficiency of EGR, both by allowing more air to remain in the cylinder after the exhaust stroke and by making the actual EGR system more efficient. Having more pressure in the intake manifold (from the turbo) would likely undo all of this, but maybe not if you stay out of boost.
Another thought is that, since you'd have more power, you could run taller gearing to save gas. Still try to stay out of boost, but you'd have it available if you needed it. I don't hear about many people altering their gearing on Maximas, especially automatics, but if you're serious enough to build a turbo setup to maybe save 1-2MPG, I guess it's possible that you're serious enough to pursue this too. Good luck, I'm looking forward to seeing the results.
That being said, everyone's basically right. Proper maintenance is key, but assuming that's all up to date, a small turbo might help (depending on your driving style). A turbo is better for MPG than a supercharger because it creates far less parasitic drag by being exhaust driven, and there's a sort of natural correction in mileage when you restrict exhaust.
It's kind of tricky though. I don't know if you'll be able to get better mileage with a turbo or not. Most of the gains in gas mileage from restricted exhaust come from improving the efficiency of EGR, both by allowing more air to remain in the cylinder after the exhaust stroke and by making the actual EGR system more efficient. Having more pressure in the intake manifold (from the turbo) would likely undo all of this, but maybe not if you stay out of boost.
Another thought is that, since you'd have more power, you could run taller gearing to save gas. Still try to stay out of boost, but you'd have it available if you needed it. I don't hear about many people altering their gearing on Maximas, especially automatics, but if you're serious enough to build a turbo setup to maybe save 1-2MPG, I guess it's possible that you're serious enough to pursue this too. Good luck, I'm looking forward to seeing the results.
05-09-2011, 07:54 AM
#12
Every time work is done (compression of intake charge) energy is used. Because energy can neither be created nor destroyed (law of conservation of energy), this energy must come from somewhere. This is textbook conservation of energy. It's physics son!
EDIT:
You can also consider Newton's third law: every action has an equal and opposite reaction. The force the compressor exerts on the intake charge is equal to the force that must be exerted on the turbine blades by the exhaust (neglecting friction and turbo efficiency). That force comes from the combustion of the gasoline through the expansion of the exhaust gasses and the reciprication of the piston on the exhaust stroke, both of which are feed by chemical energy in the gasoline.
While it may be more efficient than a super charger, the point is a turbo does use power to make power.
Last edited by ajm8127; 05-09-2011 at 08:21 AM.
05-09-2011, 10:00 AM
#13
I still get 30mpg with my RMT.
With a turbo, mpg should not change much since under cruising conditions since you do not hit boost thus the AFR staying in the 14.7 range. It doesn't matter if you have 1000cc injectors, you are still hitting the same air fuel ratio.
With a turbo, mpg should not change much since under cruising conditions since you do not hit boost thus the AFR staying in the 14.7 range. It doesn't matter if you have 1000cc injectors, you are still hitting the same air fuel ratio.
05-09-2011, 02:57 PM
#14
The exhaust pressure that spins the turbine is created by the engine through the combustion of gasoline. So the chemical energy of the gasline gets changed to mechaical energy to spin the turbine.
Every time work is done (compression of intake charge) energy is used. Because energy can neither be created nor destroyed (law of conservation of energy), this energy must come from somewhere. This is textbook conservation of energy. It's physics son!
EDIT:
You can also consider Newton's third law: every action has an equal and opposite reaction. The force the compressor exerts on the intake charge is equal to the force that must be exerted on the turbine blades by the exhaust (neglecting friction and turbo efficiency). That force comes from the combustion of the gasoline through the expansion of the exhaust gasses and the reciprication of the piston on the exhaust stroke, both of which are feed by chemical energy in the gasoline.
While it may be more efficient than a super charger, the point is a turbo does use power to make power.
Every time work is done (compression of intake charge) energy is used. Because energy can neither be created nor destroyed (law of conservation of energy), this energy must come from somewhere. This is textbook conservation of energy. It's physics son!
EDIT:
You can also consider Newton's third law: every action has an equal and opposite reaction. The force the compressor exerts on the intake charge is equal to the force that must be exerted on the turbine blades by the exhaust (neglecting friction and turbo efficiency). That force comes from the combustion of the gasoline through the expansion of the exhaust gasses and the reciprication of the piston on the exhaust stroke, both of which are feed by chemical energy in the gasoline.
While it may be more efficient than a super charger, the point is a turbo does use power to make power.
05-09-2011, 05:55 PM
#15
SC will drop mpg while turbo will remain the same or possibly slightly increase with a turbo. SC being belt driven is an extra load on the motor. Think how much more gas the car takes with the ac on all the time to somewhat give you an idea. Turbo doesnt require power to make power.
As for your second comment, ajm8127 already touched on the subject matter. I'll just add that that the exhaust/air that runs through the turbo is restricted by the relatively small orifices/channels and thus is a restriction on the system...ie takes some power to make power.
If you want some really good reading, pick up the Supercharging! and Turbo books by Corky Bell.
http://www.amazon.com/Supercharged-T...4988426&sr=8-1
http://www.amazon.com/Maximum-Boost-...4988486&sr=1-2
05-09-2011, 08:52 PM
#16
Also I think my MPG stayed the same city and my Highway MPG went up once SC-ing. But then again, I drive like a grandma. I stay 1.5 - 3k rpm.
05-09-2011, 09:39 PM
#17
My MPG's have stayed the same since I installed my turbo.
I do not see any boost until at least 2500 RPM even under WOT.
But I have noticed that if I do a couple of WOT runs, I burn a **** ton of gas. This is because I am using much more fuel because I am running richer as well as making more power.
Highway cruising is the same.
I do not see any boost until at least 2500 RPM even under WOT.
But I have noticed that if I do a couple of WOT runs, I burn a **** ton of gas. This is because I am using much more fuel because I am running richer as well as making more power.
Highway cruising is the same.
05-09-2011, 10:58 PM
#18
It does not surprise me that those like kevlo, uncklejoe and homermac see the same mpg figures with and without turbos. As long as you stay out of boost, no more air is feed into the engine than it can draw in naturally. This means that no more fuel is added because there is a direct relationship between fuel and air. That's how companies like Ford are getting v6 mpg and v8 power. If the engine/turbo system was designed so that it does not begin producing boost until 3000rpm (totally arbitrary figure, for the sake of argument), you could easily keep your revs down and enjoy v6 fuel economy. But crank it up to 6k and you have v8 power from the turbo. So to the OP, you can get a Maxima that get better gas mileage and has the same or better power than stock. Stick the VQ20 (or another engine with less displacement than stock) in there and put a turbo on it. You get 2.0 liter mpg when you want, and 3.0 power when you don't.
As for the supercharger being less efficient, it probably has a lot to do with the belt. Each time you change its shape, like as it wraps and unwraps around pulleys, that takes additional energy. Energy that is not requires in turbo setup. There could also be more friction if you consider that the belt tension puts load on the bearings of the super charger. This frictional force would not be present in a turbocharged engine system either. All this added friction comes from energy that could be used to propel the vehicle. That power come directly from the crank, as was mentioned. More power used by the front of the engine means less makes it out of the rear.
EDIT: But in no way is the power to compress the intake charge free using a turbo. It also comes from energy that could be used to move the car, but the added benefit of a more dense charge in any FI vehicle greatly eclipses any drawback from the additional energy required to compress the charge (while the turbo is operating with reasonable efficiency). That was my main point from the get go. Your parents probably told you once that nothing in life is free, and your physics professor would agree.
As for the supercharger being less efficient, it probably has a lot to do with the belt. Each time you change its shape, like as it wraps and unwraps around pulleys, that takes additional energy. Energy that is not requires in turbo setup. There could also be more friction if you consider that the belt tension puts load on the bearings of the super charger. This frictional force would not be present in a turbocharged engine system either. All this added friction comes from energy that could be used to propel the vehicle. That power come directly from the crank, as was mentioned. More power used by the front of the engine means less makes it out of the rear.
EDIT: But in no way is the power to compress the intake charge free using a turbo. It also comes from energy that could be used to move the car, but the added benefit of a more dense charge in any FI vehicle greatly eclipses any drawback from the additional energy required to compress the charge (while the turbo is operating with reasonable efficiency). That was my main point from the get go. Your parents probably told you once that nothing in life is free, and your physics professor would agree.
Last edited by ajm8127; 05-09-2011 at 11:04 PM.
05-09-2011, 11:09 PM
#19
Yup. FWIW, my gas mileage has stayed exactly the same as well if I drive "normal".
OP. Totally off tangent here, but depending on where you live, the Supercharger is 50 state legal and you'll pass the visual/sniffer test, a custom turbo kit not so much. Just figured I throw that out there as some food for thought when deciding between the two.
OP. Totally off tangent here, but depending on where you live, the Supercharger is 50 state legal and you'll pass the visual/sniffer test, a custom turbo kit not so much. Just figured I throw that out there as some food for thought when deciding between the two.
05-09-2011, 11:16 PM
#20
i get 22 mpg now on the highway after the s/c. lol. but its ok, mpgs was my last concern when i decided to do this, and it still is. ive just accepted it. imo, boosting your car for a mpg increase just doesnt sound right. youre willing to spend $2k plus to gain a mile per gallon or two...just use that $2k towards gas if its like that.
also, maybe im the only one who just doesnt look too far into that whole S/Cers using power to make power comment, a net gain everywhere sounds ok to me.
also, maybe im the only one who just doesnt look too far into that whole S/Cers using power to make power comment, a net gain everywhere sounds ok to me.
05-10-2011, 02:16 AM
#24
10 second street turbo GNs still get 24-26 mpg with a lockup converter, bc under normal driving the car drives with a good mixture.. something i look at is car manufacturers who have smart engineers working for them, how many cars bring a centrifugal blower out the box? vs turbo? just some food for thought..
05-10-2011, 06:57 AM
#25
I think you get teh general idea. I think what you missed was that the SC takes power(parasitic) directly from the crank where as Turd does it through the exhaust setup.
Also I think my MPG stayed the same city and my Highway MPG went up once SC-ing. But then again, I drive like a grandma. I stay 1.5 - 3k rpm.
Also I think my MPG stayed the same city and my Highway MPG went up once SC-ing. But then again, I drive like a grandma. I stay 1.5 - 3k rpm.
My MPG's have stayed the same since I installed my turbo.
I do not see any boost until at least 2500 RPM even under WOT.
But I have noticed that if I do a couple of WOT runs, I burn a **** ton of gas. This is because I am using much more fuel because I am running richer as well as making more power.
Highway cruising is the same.
I do not see any boost until at least 2500 RPM even under WOT.
But I have noticed that if I do a couple of WOT runs, I burn a **** ton of gas. This is because I am using much more fuel because I am running richer as well as making more power.
Highway cruising is the same.
i get 22 mpg now on the highway after the s/c. lol. but its ok, mpgs was my last concern when i decided to do this, and it still is. ive just accepted it. imo, boosting your car for a mpg increase just doesnt sound right. youre willing to spend $2k plus to gain a mile per gallon or two...just use that $2k towards gas if its like that.
also, maybe im the only one who just doesnt look too far into that whole S/Cers using power to make power comment, a net gain everywhere sounds ok to me.
also, maybe im the only one who just doesnt look too far into that whole S/Cers using power to make power comment, a net gain everywhere sounds ok to me.
And I applaud you F/I guys for keeping your foot off the gas and getting good mpg figures. Even with the high prices of gas, I dont think i'd be able to hold back. lol.
05-10-2011, 10:28 AM
#26
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Thread Starter
Join Date: Apr 2011
Posts: 100
Damn! I've never had so many responses to a thread in such a short amount of time! Thanks for all the input, positive and negative.
I realize that to some people, F/I with mpg in mind seems, shall we say, totally stupid. However, there are a lot of turbos out there stock that get extremely decent gas mileage. I've also talked to a few people who have done custom setups and seen a slight increase in gas mileage without trying for it. Like many of you have said, its all in how you drive it.
I didn't really explain myself fully in first post. I definitely am interested in a turbo because of extra power. My auto transmission (which I want to keep) seems to make it more practical to have a smaller turbo for no lag (since for most of my driving I am not over 3000rpms). Might as well aim for better fuel economy as well, no? Especially with fuel prices around $4.50 and rapid rising around here. If I have more power on tap down low, I won't need to get into the throttle as much or for as long=better fuel economy? Then when I want to beer bong my gas into my motor, I just floor it.
I like the idea of putting a smaller engine in and turboing that, but the extra time/money doesn't seem practical. (I realize some of you will have fun with that statement )
I realize that to some people, F/I with mpg in mind seems, shall we say, totally stupid. However, there are a lot of turbos out there stock that get extremely decent gas mileage. I've also talked to a few people who have done custom setups and seen a slight increase in gas mileage without trying for it. Like many of you have said, its all in how you drive it.
I didn't really explain myself fully in first post. I definitely am interested in a turbo because of extra power. My auto transmission (which I want to keep) seems to make it more practical to have a smaller turbo for no lag (since for most of my driving I am not over 3000rpms). Might as well aim for better fuel economy as well, no? Especially with fuel prices around $4.50 and rapid rising around here. If I have more power on tap down low, I won't need to get into the throttle as much or for as long=better fuel economy? Then when I want to beer bong my gas into my motor, I just floor it.
I like the idea of putting a smaller engine in and turboing that, but the extra time/money doesn't seem practical. (I realize some of you will have fun with that statement
)
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