funny these cars get such bad mpg while in boost, makes no sense, free power = low mpg wtf, kind of defeats the purpose of a turbo imo

i run a 16 psi tune and get 21/35 mpg in my 335i around 1.5~2k rpms

I think the tune on my STi is 23 or 25 pounds, can't recall from the top of my head. On E85, I get about 15 city/17.5 highway.

Gas prices just dropped greatly, so I'll probably switch to 91 at the end of this tank and maybe the numbers will climb a couple.

small turbo? what rpm does it spool at?

im amazed at how little mpg you get, i feel like if your turbo spools at 1.5k you should be getting like 20-22 mpg going 50mph at 1.5k-1.8k rpm

i always assumed that the free power would lower your mpg

is your tune a professional dyno tune?

maybe its just all the boost you are running, you have to spend so much fuel to match the air flow

must be a crackly little motor, probably sounds nice


then again, im more used to working on old 350's and 400's, my bimmer is the first car ive owned that has a computer lol

This post was edited by t9x on Dec 5 2014 10:21am

^I just bumped the thread for the car. Has stock VF48 turbo, so it's a tiny guy.

TBH, I'm not quite sure when the turbo spools. It's definitely at low RPM though, because if I drive in Sport Mode, I honestly have to baby the gas to help prevent boost. My back pressure usually sits at -2.225 or so.

I generally drive in Intelligent Mode and that's when it does require a good push to spool, and when it does spool, it's pretty slow (luckily). I do 90% of my driving in I-Mode, haven't really gone nuts due to poor weather in CO.

see thats how my turbos are, tiny little guys, i have to be at about 15% throttle or more for them to spool though, but they spool instantly

i always get better gas mileage in boost though

seems odd you only have 305hp with that much boost though, my car has 300hp stock, i removed the air box for 2 cones, got a new charge pipe, intercooler, and a 16psi tune put me at 440hp

Elevation plays a huge factor, there's very thin air up here. But the tune shop told me 305 awhp was the best they've ever seen on a stock turbo.

Colorado is full of Subarus, especially all of the military that drop the big bucks when they get back from tours in Iraq/Afghan. So having that said about my car raised an eyebrow in the "Interesting Department."

And you do have two turbos, a bigger motor, etc. Definitely makes up the difference of 100 hp

I always wanted the 2005 sti :\

was my dream car for a long time



these things just look so nice

we have a lot of the newer ones down here in florida, but not really any older ones

He is getting bad mileage because he is running E-85. It has less available energy per gallon than gasoline but higher octane. When he switches back to gas his mileage will go up considerably. It still won't be great though.


These cars get bad mileage because of the AWD system causing parasitic loss and performance oriented valve events and tuning. The drivers aren't exactly the miserly type either. I don't know who told you turbos are free power but they fed you a lie. There is no such thing as free power. Turbos have far less parasitic loss than a mechanically driven supercharger but it isn't free. When you start making boost the ECU starts adding more fuel at the same time. Power increases, fuel usage increases. The benefit of a turbo engine toward fuel economy is being able to make the desired power (in boost) from an engine that is smaller/more efficient (out of boost.) When you cruise on the highway at low load you should be making very little boost. That keeps the backpressure to a minimum and essentially lets you cruise like you have a 200hp engine from a civic in your 350hp car.

This post was edited by FMX_89 on Dec 5 2014 10:53am

^^

THANK you.

I read so much misinformation I didn't even bother to start.

Thanks for saving me some writing time.

Isn't e85 supposed to get a lot better mileage than 91+ octane?