storx

any enganeers out there that can explain this more to me.......my understanding is when i bought the stage 5 injectors that i would need to use up more of the fuel with more boost to get the better fuel milage........i have filled up 3 differnt times with 3 different settings for boost and im a bit boggled.......

35 PSI 17.2 MPG

48 PSI 22.1 MPG

54 PSI 20.3 MPG

these were all taken driving the same route which is a long county 2 lane road with very little traffic that i take home everyday for 34 miles........i been setting the cruise on 60 MPH and there has been a big difference in the MPG at different boost settings......im going to play with it more tomarrow after i fill up im going to adjust her down to about 40 PSI see what she shows there...... im confused on why the lowest and higher boost made such a difference in the MPG

"oh yeah these were done with a calculator based off the miles i went and how many gallons i put in during fill up.... not off the head unit"

pmtg

im confused...did you drive at a constant 54psi straight from one fuel station to the next and fill up and get that mpg? dont see how you get the correlation between boost and mpg's without using the overhead.

please enlighten...

you dont want to "use up" the fuel, you want to use what you need. the minimal amount of fuel you need would equate to best mpg's.

pmtg

are these wastegate settings?

im going to say you need to drive that road atleast 20 times per boost (wastegate) setting and get an estimate based off of more miles. this is, of course, assuming you are traveling the 34 miles each way (68 total) and filling up at the end of the day. too much variance in the amount of fuel the truck takes after only 68 miles of driving to say definitively one way or the other...

HOHN

If you're talking about wg settings, then it's probably the case that your turbo(s) are most efficient around 40psi.

jlh

lsgibb

I guess I don't understand, how are you building any boost just driving down a long country road with the cruise set for 60mph. Don't you have to give the turbo a reason to build boost such as climbing hills or WOT especially enough boost to be opening your Wastegate. I'd say the more boost you have the worse your mpg will be because you're using more fuel. Have I completely gone off the deep end?

apwatson50

It takes fuel to make boost so the higher your boost is the more fuel your using. But I don't see how you have 40, 45, or 50 psi of boost if all your doing is driving along at 60mph with the cruise set. To get the best mileage you want the turbo's to push just enough air to burn the minimal amount of fuel needed to move the truck at the desired speed.

Now if some how with the twins set up you are maybe overspeeding the small turbo, or some how you are taking more energy out of the exhaust than absolutely needed which is creating excessive back pressure. just some theories that have no real knowledge behind them, just coming up with some for you.

I don't have twins but when i'm going down the highway at 60mph no hills not towing at a constant speed I only have about 5psi 10psi tops. Is this what the rest of you have? To me the less boost you are creating the better mileage you will achieve.

duner

sounds like your driving the pistons with air pressure

storx

see i was asking this question because i didnt understand it....when im driving at 60 mph i run around 3-11 PSI.......when i turn up the boost max it runs around 10 psi if i lower it it runs around 3-5 psi..........it goes up in responce to change of the max boost on the wastegate..........

apwatson50

Are you turning the max boost up on your small turbo or you big turbo? Theres a waste gate on both right? or just the small one? I have a feeling that you may be setting the wastegate on your small turbo too high just looking for higher boost pressures and this is really hurting you. I would bet that when you have it set too high your making the small turbo do too much work, over speeding it and creating more heat. If you set the wastegate lower on the small turbo letting the large turbo get more energy from the exhaust stream than the large turbo would really do more work for you. And even though you may not see as much boost pressure you will get a larger volume of air at a lower pressure. you will also reduce the backpressure on the exhaust side.

I think that this is where some drive pressure guages and turbine inlet/outlet pressure/temperature guages would come in very handy to get everything tuned right.

storx

the small one is the only one with the wastegate.......the twins came from the factory preset to 54 PSI.....i lowered them initially because the tranny was just slipping... but since then i have rebuilt the transmission to hold it and notice that when i have it set at 48 PSI my cruise speeds are 6 PSI........"60 mph" and when i drive normal my temps run around 650 degrees and the MPG shoots up to around (22.0-22.5)....and this made no since to me so i decided to ask the crowd

lsgibb

I still don't get how adjusting your wastegate would affect your mpg just cruising at 60 since your boost pressure is nowhere near high enough to open the wastegate.

apwatson50

Storx is running twins so its a hole different ball game than with just a single.

apwatson50

I'm sorry, after all of that, it really doesn't make any sense how adjusting the wastegate is going to affect your cruise temps and pressures. I have no idea.

pmtg

storx,
how many miles of testing did you do with each wastegate setting?

Huff nPuff

Is if the wastegate is blowing open way to early anyway,and changing the adjustment stops it blowing open which affects low end boost.