Forced induction and fuel economy..

[Scothew]

I know that sounds like an oxymoron, but I wanted to post what I heard the other day that is now the beliefs of a friend of mine.

He said he wanted to supercharge his 04 mazda 6 (v6 automatic) and states that it will help his MPG. When I heard him say this I laughed. My first question was "is this what the manufacturer claims". Of course his answer was yes. But then followed with, I also had a guy at work give me a great physics explanation of how it would make sense and work the way he is hoping. I didnt the explanation and quite frankly it probably would have made my head hurt.

I explained that physics really wouldnt have much to do with it, as he would be forcing more air into the motor, therefore requiring more fuel from the car to support the air. Also that the blower is belt driven, therefore requiring power to operate and when not under a load in theory would create enough drag to possible rob him of power. I also said that with a good tune, the best I think he could hope for would be gas mileage equal to what he has now, but I know he wouldnt be able to keep his foot off the throttle so its a pointless arguement anyways.

Wasnt sure where to post this, but this was the funniest thing that happened to me lately.

[QWKSNKE]

Actually it is possible. But it does depend on a lot of variables. Type of supercharger, power output, power range, etc.

Actually when Dave supercharged his 97 GT several years ago, he actually did improve his fuel economy.

[96GTS]

Originally Posted by QWKSNKE

Actually when Dave supercharged his 97 GT several years ago, he actually did improve his fuel economy.

Thats cuz you have to bury your foot in the floor to get a stock 97 2V up to highway speeds

[Wicked]

Originally Posted by Scothew

Wasnt sure where to post this, but this was the funniest thing that happened to me lately.

Wow, that is funny. :insert batard sarcasm meter here:


I agree with your point though, parasitic loss alone will decrease some MPG.
And your right again by saying anyone with a S/C will not get better gas mileage simply because of the heavy foot syndrome.

[Italian LX]

Originally Posted by QWKSNKE

Actually it is possible. But it does depend on a lot of variables. Type of supercharger, power output, power range, etc.

I just can't bring myself to believe that you could improve fuel economy by adding a supercharger. To me, it sounds like you would be going against the law of physics. How can you use available power (the crakshaft) to produce more power and heat and consume less fuel at the same time?

A turbo can get away with it because it utilizes "waste" to create it's power; the engine was never going to benefit from the exhaust gases anyway... however, the supercharger is robbing power that would have otherwise been used to turn the driveshaft.

Originally Posted by QWKSNKE

Actually when Dave supercharged his 97 GT several years ago, he actually did improve his fuel economy.

As far as Dave's improvement, how was this measured? Did he drive the exact same way before and after the blower when he measured the fuel consuption (highway and city)? Did he measure it by topping off his tank and then topping it off again a record the amount of fuel between fill-ups... if he did it this way, did he use the exact same pump both times? How many tanks of gas did he use to measure.

My point is that there are a lot of variables that could throw the test way off.

[QWKSNKE]

Originally Posted by Italian LX

As far as Dave's improvement, how was this measured? Did he drive the exact same way before and after the blower when he measured the fuel consuption (highway and city)? Did he measure it by topping off his tank and then topping it off again a record the amount of fuel between fill-ups... if he did it this way, did he use the exact same pump both times? How many tanks of gas did he use to measure.

My point is that there are a lot of variables that could throw the test way off.

WTF???

You fill up the tank. Drive from point A to B. Highway or city (whatever your normal drive is) Fill the tank up and calculate the average consumption based off what your miles driven are. Isn't this how everyone calculates mileage?

I don't see what so hard to understand about potentially getting better mileage. Hell, even Wicked made a post awhile back (on the mafia I believe) about getting 25 mpg in his vert when going to the beach. (which is way better than Shelly's has ever gotten)

Wall mentioned when his supercharger was put on that he didn't see a economy difference vs when it was n/a.

Depends on the blower and how much drag it has on the motor. It is quite possible on the smaller blowers to help the car become more efficient enough to help its economy.

[Wicked]

Originally Posted by QWKSNKE

I don't see what so hard to understand about potentially getting better mileage. Hell, even Wicked made a post awhile back (on the mafia I believe) about getting 25 mpg in his vert when going to the beach. (which is way better than Shelly's has ever gotten)

Yeah, but that was not my normal driving style. Max RPM was probably 2000rpm. Most of the trip was at 50 mph in 5th.

[Italian LX]

Originally Posted by QWKSNKE

You fill up the tank. Drive from point A to B. Highway or city (whatever your normal drive is) Fill the tank up and calculate the average consumption based off what your miles driven are. Isn't this how everyone calculates mileage?

Well, there are a lot factors involved. Was he doing the same type of driving (same ratio of highway vs. city) when he measured fuel consuption with both set-ups? Was one possibly during a time that he may have been using the A/C more? Did he merely measure one tank of gas with each set-up? Did he fill up at the exact same pump that he first filled up at in order to measure the consumption.

That last point may sound crazy, but I found that there is big difference in when pumps shut off when the tank is full. I filled up one morning in Anniston and drove 50 miles to work. During lunch, I filled up and it took over 3 gallons to fill it back up. When I got back to Anniston, I filled back up at the same pump and it took just over 1 gallon.

My conclusion is that my coupe must get better gas milage when traveling east-bound for some reason.

[93Cobra#2771]

A slight downhill grade can cause a difference in mpg between two points coming and going, as well as a nice headwind.

Best way to do mpg is to fill up at the same station, same pump, with car pointing the same direction.

With that being said, I'm running tailgate down this week to see if it really makes a difference in mileage or not...

[Italian LX]

Originally Posted by 93Cobra#2771

A slight downhill grade can cause a difference in mpg between two points coming and going, as well as a nice headwind.

I agree, but not as much as I recorded. There is no way my coupe got 40mpg on my way home and only 16mpg on the way to work.

I will admit that my BMW gets slightly better milage on my way home; it has a milage computer and I watch it a lot. I usually get around 25mpg on the way to work and around 26mpg on the way home.