This question I was attempting to "lure" someone from DP Tuner in to help answer, but all feel welcome.

OK, There have been several discussions on the 6.4 L diesel, of how mileage is so rough. I seem to remember someone working on a tune that was supposed to be a 7.3 extreme mileage tune, and ran lower boost.

My point on the 6.4 was, once the EGR is disabled, the boost the truck makes is too high. My thoughts were leaning towards venting exhaust past the turbocharger to achieve a lower boost down the highway, resulting in higher MPG's.

Am I wrong in thinking that too much boost can hurt mileage?

Am I right in thinking that pushing more air than the truck can burn is a waste?

I know this isn't 7.3 specific, but really it isn't 6.4 specific either, it's just "turbocharger" specific.


Thanks.

 

Could it be that the excessive boost is creating more backpressure then necessary? The EGR system is probably acting in a way that similar to the waste gate, but dumps to the intake instead of the exhaust.

I'd think that more air then necessary would keep the EGT's down, but thats just my thinking.

 

i guess that to much air could make the air fuel ratio off. there would be a lean burn and less power.

 

Diesels don't have that issue like gassers do. There is no set air to fuel ratio.

 

i know there is no set ratio but if you dont have as much fuel then it cant burn as hot and it will make less power, that is what i would think.

 

You're thinking about this all backwards. You don't bleed out boost in an attempt to lower boost and raise fuel mileage. In fact, the exact opposite would be achieved if you even tried that.

Boost levels are engine/turbocharger specific. Variable vanes, compounds, turbo size... all these different configurations will completely and totally change the spool up rate, and the amount of boost you see say at highway speed. Furthermore, the engines themselves, regarding volumetric efficiency, fueling, timing, displacement, emissions controls, etc... all play a role.

Intentionally bleeding off boost simply so your gauge reads lower is not going to help. Instead it's going to hurt. The amount of boost you see is simply a by-product of the combination of parts, engine efficiencies, how much that engine is fueling, how much power it's needing to make in order to maintain that speed, and the resulting exhaust gasses that spool the turbo. More air is never a waste.

People simply use boost as a general reference of fuel economy. It's a "poor man's" lie-o-meter. That's all it is. Nothing more. It is not always a true indicator of fuel mileage, just like the overhead display. Heck, you could run 3 psi of boost, but have 1000 degrees EGT's.... and your fuel mileage will suck.

 

But if you're cruising down the highway, using maybe 45 HP, a turbocharger is causing back pressure when the engine is in no need of positive manifold pressure.

 

Why dont you give Charles @ kem or Jeff @ Spartan a ring and find out? They along with innovative are the big dogs of 6.4 tuning... My vote would be kem because thats the tuning I run.. but jeff is very knowledgeable as well

 

I don't know much about anything, but I have been told that excessive boost causes higher backpressure so on the 7.3's causes it to call for too much fuel.

 

So in plain english, leave your wastegate plugged in...

 

What? Did I hit the nail on the head?

 

Why are you posting on the 7.3 forum? Maybe because you miss the 7.3.....lol...? After my truck dies I will probably go gas.

 

Well I know Jody from DP tuner is on here once in a while, and also remember they were working on a tune w while ago that was running very low boost on the 7.3, like almost 0.

I don't know the exact specifics of it, or if they ever managed to finish the tune for mainstream use, but I though they might have some input as to my current question.

 

This is Diane. Jody rarely has extra time to post so I would email him. I do know though just from being a 7.3 owner my old Excursion started having wacky boost issues and bad fuel mileage. The stock wastegate was adjusted as far as it would go. Jody did the banks big head and it helped the issues. As for tuning, Jody is the only one here who can answer that for you.


Diane

 

I miss my 7.3, but really the 6.4 is a way nicer truck, I just miss my 7.3 cause I was so used to it, plus imagine all the time I spent in it, just crazy. I really had to talk myself out of keeping it in the yard. I still miss it, even though it was less refined than the 6.4, I miss it.
When my 6.4 dies, I plan to buy a brand new truck, because I heard they're getting smaller, so I want to buy a brand new one the year before the downsize, so I can laugh at everyone will small superduty's.