Ins and outs for MPG tunes

[LBZoom]

Hey guys,
I read some info in one of the gasser threads from a guy wanting MPG from his duramax (going into a 1500lb hot rod?) and the basic info made sense, advance timing escpecially in the cruising range, but what about boost?

If you increase boost above stock would that not create a more complete and efficienct burn? And more torque at a given RPM?

What about fuel? Would you recommend an increase in fuel at the crusing RPM to create more torque, or simply optimizing the power already being produced through timing and/or boost?

I believe that an LBZ peaks torque around 1600 RPM or so, the milage tunes I've tried making for myself have been tested for anywhere from 500-700 miles at 70 mph avg.... one had increased timing and boost as well as 5% increase in pulse....the other had no increase in pulse but the other factors were identical. The tune with the 5% increase in pulse actually got better mileage. 20.5MPG at 70mph from north central Arkansas to east Tennessee. Not bad I thought considering the speed?

[bballer182]

There are multiple threads on this with lots of info on Deiselplace.com in the EFI section.

[Brian1]

Actually lower boost would be better for mileage. non turbo 6.2 got hell of great mileage.

Brian

[LBZoom]

My dad used to have a 6.2 non turbo in a regular cab long bed that he bought new in 1990 and just sold in 2005, the best he ever got was 17mpg in the life of that truck. It seems to me that if he would've put a turbo on it, he would've increased efficiency of the burn, therefore increasing both power and MPG, at least that's what I would've thought.

What I don't get is this...boost is referenced to fuel, not the other way around. So if you increased the airflow at a given amount of fuel delivery wouldn't it increase power and make for a more efficient burn? I'm not saying like 5 psi over stock but maybe 2 psi or so...

Can anyone explain this supposed "less boost" phenomenon to me?

[DmaxHawk]

My dad used to have a 6.2 non turbo in a regular cab long bed that he bought new in 1990 and just sold in 2005, the best he ever got was 17mpg in the life of that truck. It seems to me that if he would've put a turbo on it, he would've increased efficiency of the burn, therefore increasing both power and MPG, at least that's what I would've thought.

What I don't get is this...boost is referenced to fuel, not the other way around. So if you increased the airflow at a given amount of fuel delivery wouldn't it increase power and make for a more efficient burn? I'm not saying like 5 psi over stock but maybe 2 psi or so...

Can anyone explain this supposed "less boost" phenomenon to me?

They say that less boost would create more mileage because of this...What makes the turbo spool is the expansion of hot gasses coming from the engine, not the so much the vane position. So being that HEAT not air FLOW makes the turbo spool; if the computer calls for more boost, it will add fuel to make the appropriate heat. So more fuel=less efficient.
Making a more efficient burn has a LOT to do with the right amount of timing not just air.

[LBZoom]

That makes sense in the case of mechanical turbos that rely purely on outgoing exhaust gases...don't get me wrong i'm not arguing with anyone but I am trying to learn and make sense of it all like everyone ....but in the case of an electronic turbo this is the way I'm looking at it....let's say we're working with a fixed fuel rate for a given RPM and torque value, say 70mm3. 70mm3 is only going to produce a fixed amount of exhaust gas correct? So therefore I can alter the turbo vane position to capture more or less of that exhaust gas and get more or less boost for the specific amount of fuel without even altering the amount of fuel having to be delivered?

[DmaxHawk]

IIRC, the furl rates are not completely fixed, neither are the vane positions it is more like a guide. Try this, if you have a hot tune with say 20 pounds of boost, increase the boost to 30 pounds. Only the desired boost levels, not the vane position. You will notice that the turbo has no problems making 30 pounds even thought you did not change the vane positions or fuel rate tables. If it calls for more boost, it will make the appropriate heat to make the desired boost.

[LBZoom]

I see, so the vane tables don't need to be changed to achieve higher boost then? But if I increase the vane tables I'll have to increase desired boost to allow that right? Because once when I didn't it threw a overboost code.... anyway what you're saying makes sense now, but if you manipulate the boost via the vane position rather than the desired boost, than that would produce more boost without increasing fuel delivery right? And I could probably leave the desired boost tables untouched as long as the max boost was increased so it doesn't throw a code, then it shouldn't affect fueling right?

[bballer182]

Actually....


this is actually how the boost and vanes work...

The boost tables have no effect on fueling they are completely independent. the vane tables are not a "set position" the will always be referenced and used at all times. Tables B2231 and B2232 define when the ecm uses the desired vane position tables and when the ecm determines the vanes position based on requested boost. So if you want to verify this statement set lets say from 1200 - 1600 rpm and 30 - 60 mm3 in your desired vane position table to 20% in both EGR ON and OFF and load it up and take it for a test drive with your V2 logging desired vane position and actual vane position and see what the difference in position.

The vane position table is used as a quick reference when adjusting the turbo vanes to meet requested boost based on fuel delivery. so lets say you are cruising at 35mm3 and 1400 rpm and you punch it and it down shifts so now you are at 2200 rpm and 98mm3 the ecm quickly looks up that table and adjust the turbo to that predefined (by the user or factory if it hasn't been changed) vane table and then quickly realizes that the preset value is incorrectly producing too much or not enough boost according to the desired boost tables, and then adjusts the vanes to meet it.

Now if you are worried about quickness with respect to boosting, Nick from Duramaxtuner.com has a how-to video on how to dial in your vane tables so that they actually are what the ecm i going to use to obtain requested boost for any given situation. And like i said there is a quite long thread on this very subject on the EFI section on dieselplace.

[LBZoom]

okay that makes sense, good info for working on the turbo, so you say that commanded fuel has no relation to desired boost or vane position? It's a completely seperate table, where boost is determined by fuel not the other way around....therefore simply turning up boost via vane position won't necessarily increase fuel consumption correct?