first mpg, from the locked thread. i thought the topic was interesting and i want to address some points.

more air more fuel right?
and the question was asked about whether there is any reason you couldn't just drive it easy and save your gas mileage.

answer: SC has a rolling mass which must be turned, wasting engine work and therefore less efficient. it allows more air to flow at open throttle conditions, but it's just extra friction to overcome and weight to move when you're trying to drive nice.

TC creates a less than optimum back-pressure condition when not on the boost, also friction in TC bearings.

Also compressing air makes it hotter. Hotter air is less dense and therefore less explosive potential.


So there's a couple reasons why an FI car could never be as fuel efficient as NA.

Also you could say that it's harder to modulate your pedal since your potential air movement is increased and therefore harder to fine tune the total amount of air with your right foot.


I'd be interested in hearing more ACTUAL mpg reports, since that's the only number of consequence.

 

I had planned on starting a thread with my MPG for my car since 4 miles up to today first oil change at 4783 miles. (oil was changed when sc put on so I didnt really go that long with out a change).

I track all my milage including prices and all. I will post up later today.

 

with the supercharger they reccomend 3000. and to not mess with the warranty and to keep reslae up I want documented regular oil changes at the recomended times. Thats the only reason I will do it at 3000 miles. Plus I have a bunch of free changes.

 

I feel that the more power you have, the less throttle you need to get up to and keep at a certain speed. The amount that the drag created by a SC ot TC is minimal compared to the power they provide. I think if you don't hammer it everytime you drive, the fuel mileage should be the same if not a little better. With proper tuning of course!!!

PS...about the hot air...Yes, not as much power can be produced, but the engines are more eficeient when hot air is used rather than cold. Less power, but more efficient.

 

What you are suggesting is not so much a more efficient engine as it is a change in driving habits.

If you use 100% throttle before SC, you can go 0-60 in X seconds and with Y fuel mixed into Z air.
If you use 100% throttle after SC, you can go 0-60 in <X seconds and with >Y fuel mixed into >Z air.

Remember it's an air pump, and the more air you send through the engine the more fuel needs to be mixed in.


What you seem to be suggesting is that you can get the same 0-60 time but by using less throttle and therefore less fuel.
Not true. You can use less throttle to get the same acceleration, but the gearing is the limiting factor here and you will find that a 0-60 time of X will require the same Y and the same Z regardless of the position of the gas pedal.

Add in the factors I tossed out in the first post and you will see that your reduced throttle 0-60 actually DOES require more fuel due to the factors I mentioned in first post.

In fairness, higher pressure air CAN get proper detonation with less fuel used, but the difference created for this application is very small and grossly overshadowed by the added friction/backpressure/rotating mass.



If on the other hand you overcompensate for your car by driving less aggresively, you certainly might see better fuel mileage.
Just don't make the mistake of thinking that your engine is using less fuel to do the same work. It's using less fuel to do less work.

 

I see where you are coming from. I was just thinking that if you drove the same after FI, you shouldn't see a big drop in MPG...it may even be better because the effort to get there would be less. But I'm the type that would hammer down whenever possible and get worse mileage. I mean...you don't put a turbo on to get better mileage...LOL

 

A gallon of gasoline has a fixed amount of energy that can be extracted from it. Other than minor efficiency improvements in the combustion process, more power = more gasoline used. You can't make a gallon of gasoline produce more power than is inherantly in it.

 

^^^BUT, don't you think that if before, you had to floor it to hit 60 in 10 seconds, to reach 60 after boosting, you wouldn't need to 'floor it' to get there in 10 secs. Of course it would do it quicker after boosting, but if it were done in the 10 second timeframe....I'm getting myself confused now.

I see what you are saying, but it is like taking weight off in a way. The more power you add is kind of the same as removing weight....and the less 'pedal' you would need to use to get around. I am just talking normal everyday driving though, not performance or speed or quickness....Ahhh, but we are getting off topic here...LOL.

I guess what I mean is IF I had a turbo, and drove like I normally do without a turbo (stay at or under speed limits, no fast starts) it may get the same or better mileage. I know my mustang got better mileage than 4 and 6 cylinder models and mine had a v-8. Almost the same weight, more power and more torque. Is this an accurate comparison? Probably not, but it is the example I am using...hehehe

 

Also, although gas has a fixed amount of energy, the engine is what decides how that energy is used, no matter if it is turbo'ed or N/A. If, by using the turbo, you use more fuel, the torque and power increase will probably outweigh the fuel consumption. If you have 50% more power and torque, do you need to flow as much fuel as before just normal driving to keep a steady speed?

I know sometimes I NEED to floor my car to get going or get out of someone's way...if I were running a turbo, would I NEED to floor it to do the same? I wouldn't think so, and that means less fuel so to say (because of it not being WOT), but I could be wrong.

 

A 'charger simply allows you to get more air into the engine so that it can burn more fuel to produce more power. The ratio of air to fuel needs to be in the 14.7:1 area for the engine to work efficiently, so if you are pushing in 20% more air you need to add 20% more fuel to keep the proper mix. The result is more power - because you can burn more fuel.
(Yes, that's over simplified, but it is essentially the short version of the story. :D )

If just pushing in more air was all it took to get more power, and not putting in more fuel to match, can you even imagine some of the massive blowers people would have on their intakes?

Free Power, Just Add Air! :D

I can see it now, a 'built' Briggs and Stratton one lunger with a GM '71 supercharger bolted on getting 100 MPG while pushing an Escalade to 5 second quarters...

Nope, the energy comes from the fuel, and energy use boils down to how much time are you taking to accelerate a given mass to a given velocity ('delta V'), and how much mass and friction losses are you overcoming in a steady state. That will tell you how much energy you need, and that energy comes from burning gasoline.

 

thanks for helpin Tomas. I was about at the end of my knowledge....


maybe we could talk about things that DO improve mileage. Better ignition systems can get you a more complete fuel burn, for example.

 

I see what you guys are saying...more air in needs more fuel. I didn't mean to upset or confuse anyone...I just thought that the more power, the less throttle was needed. Very good points are made by you guys and I understand where you are coming from.

 

I don't know all the tech stuff involved, but I have kept track of my mileage along the way with all my mods.

Started off with stock xb and got 30-32 mpg most of the time.

Added the AEM cai and DC Sport headers and got much better performance, but mpg dropped to 27-29 mpg.

Added the Borla daul exhaust and mpg did not change any.

Added the Blits Sc and performance was way up there and mpg is back up the 28-30 mpg?

The SC is great for that extra punch when you need it, but didn't appear to affect the mpg thing at all. More air in, not more gas.

 

Of course you use more gas.

Like Tom was saying you need to keep a certain air/gas ratio in order for the engine to run correctly. By SC'ing you throw the ratio off by adding way more air, so more gas is added to even out the ratio.

 

So is the stock ECU settings going to compensate for a SC? I didn't think that anything would change unless you had someone adjust the setting?

 

On straight highway miles I have lost nothing. And daily driving I have lost 3-4 mpg. But that could be attributed to maybe I drive it alittle harder. here are ny numbers cut from another post I made: https://www.scionlife.com/forums/vie...800&highlight=

Date-------gallon--- Total Miles -- price/gal--- total price--- Tank Avg--- total Avg

17 oct 05---14.1 ------ 0 ------ 2.25 ------ 31.00
27 oct 05---12.344 ---285 ----- 2.34 ------ 29.00 --- 23.08 --- 23.08
01 nov05---7.940 -----482 ---- 2.39------ 18.25 ---- 24.81--- 23.76
07 nov05---10.533 ---736 ---- 2.27 ------ 24.00 ---- 24.11--- 23.88
10 nov05---6.75 ------883 --- 2.22 ------ 15.05 ----- 21.77--- 23.50
11 nov05---11.165--- 1190 --- 2.23 ------ 25.00 ---- 27.49--- 24.41
17 nov05---12.177 --- 1511 --- 2.19 ------ 27.00 --- 26.36--- 24.80
19 nov05---12.28 ----- 1847 --- 2.19 ------ 27.00 --- 27.36
28 nov05---12.319 --- 2124 --- 2.02 ------ 25.00 --- 22.48
15 dec05---11.84 ----- 2385 --- 2.37 ------ 27.00 --- 22.04
21 dec05---21.344 --- 2630 --- 2.34 ------ 29.00 --- 19.84
01 jan06---12.074 --- 2884 --- 2.31 ------ 28.00 --- 21.03
08 jan06---12.192 --- 3139 --- 2.39 ------ 29.25 --- 20.91
16 jan06---12.504 --- 3406 --- 2.39 ------ 30.00 --- 21.35
20 jan06---6.856 ----- 3544 --- 2.47 ------ 17.00 --- 20.12
21 jan06 ---11.471 --- 3860 --- 2.65 ------ 30.50 --- 27.54
22 jan06 ---12.707 --- 4182 --- 2.47 ------ 31.50 --- 25.34
07 feb06 ---13.029--- 4448 --- 2.37 ------ 31.00 --- 20.41
15 feb06 ---12.618 --- 4716 --- 2.21 ------ 28.00 --- 21.23

 

"answer: SC has a rolling mass which must be turned, wasting engine work and therefore less efficient. it allows more air to flow at open throttle conditions, but it's just extra friction to overcome and weight to move when you're trying to drive nice. "


That is not an accurate blanket statement, many MANY more variables enter here than you have accounted for.

 

I have top agree with hip_2b_sqr. Just filled up today, 215.1 miles and 7.684 gallons
equals 27.99 mpg. I'm driving normal, at least for me. I'm not nursing it. I like to play.
I drive about 70 miles a day in Atlanta traffic with speeds from dead slow to 75 mph.
I can't explain it, but the reality seems to contradict the theory. Perhaps the difference
would be greater if we where at a much higher boost. My gauge is showing a max of
nearly 8 psi. That's not very much boost and I only get that high when I really stand
on it.