Thoughts on fuel pressure and timing for a mileage tune

[gmduramax]

What is the difference between adding fuel pressure or timing for a mileage tune? If you were to bump fuel pressure 20% in the cruising areas you would need to take alot of timing out to reduce rattle. So wouldnt you be able to just add timing instead of fuel pressure to increase fuel mileage? Or does adding fuel pressure increase atomization which gives you better mileage, and better atomization allows the fuel to burn sooner so you're reducing timing to put the ignition point back to where it was before.

Now if you were to increase fuel pressure 20% in the cruising areas, would that effect how long the injectors and CP3 last?

 

[McRat]

Fuel pressure is tied into the rate the fuel is injected at. You can't shoot fuel in faster than it will vaporize, or it will knock, make smoke, ruin economy.

Timing can do the same thing but for a different reason. Timing is tied into how hot the air in the cylinder is. As the piston comes up, the air gets hotter and hotter. If you shoot the fuel in before it's hot enough to vaporize it, is does the same thing as too much fuel.

 

[gmduramax]

So if you were to run low timing that would create more heat in the cylinder and you would be able to run higher fuel pressure because it will vaporize in the higher heat?

 

[Chevy1925]

Ive got a question to go along with this. So me running bigger tips (45% overs), i and steve have been continually tweeking my DD tune for better mileage.

based on Pats explination, something occured to me.

as i was increasing timing to the point to get the truck to rattle, i had gone well beyond the typical 60-70% before TDC in the timing area to accomplish rattle. i am spraying all 100% of the injection cycle prior to TDC.

question is, is this typical or should i be playing with fuel pressure/something else to bring injection timing back into 60% or so?

i feel that is where im missing mpg

 

[gmduramax]

Is your fuel pressure table stock?
Also what method are you using to get your BTDC %?

 

[Chevy1925]

Is your fuel pressure table stock?
Also what method are you using to get your BTDC %?

fuel pressure is stock other than my cruise area where i bumped it up ~10mpa. right now im using joshs calc to tell me where im at BTDC wise.

 

[McRat]

The real solution would be to have variable flow nozzles, which is not possible with today's tech. So to "fake" it, they use pilot shots.

If you could pulse the injector at a high frequency, you could make the perfect fueling curve for economy and emissions. A little at first, then more and more, then shut off.

 

[Chevy1925]

But since we cant really play with that given what we currently have at hand, are we strictly limited to rail pressure and timing in a LB7? i just wanna make sure having the injection cycle end before im at TDC is not goin to kill something.

to me, since i can be at 100% and have the motor just as quite as it would be at 50%, im assuming the fuel burn is so slow that its not causing a fight with the piston yet, hence no rattle.

or am i off base here?

seems like anthony and i are the only ones on the quest for MPG on oversized injectors lol

 

[gmduramax]

But since we cant really play with that given what we currently have at hand, are we strictly limited to rail pressure and timing in a LB7? i just wanna make sure having the injection cycle end before im at TDC is not goin to kill something.

to me, since i can be at 100% and have the motor just as quite as it would be at 50%, im assuming the fuel burn is so slow that its not causing a fight with the piston yet, hence no rattle.

or am i off base here?

seems like anthony and i are the only ones on the quest for MPG on oversized injectors lol

Few people with big injectors actually drive their trucks

 

[Chevy1925]

Few people with big injectors actually drive their trucks

Thats what it seems like. or the mpg they get is no issue to them. my current MPG isnt hindering me from going anywhere due to fuel cost but i do like to squeeze every mile i can out of her on road trips.

 

[gmduramax]

Thats what it seems like. or the mpg they get is no issue to them. my current MPG isnt hindering me from going anywhere due to fuel cost but i do like to squeeze every mile i can out of her on road trips.

I just hate having to fill up every 300 miles. Maybe I should just put in a bigger tank. :rofl:

 

[Chevy1925]

lol i got 500 out of the last tank. that extra 8 gallons over the sb trucks is nice sometimes .

 

[SSchmi5519]

Not about the miles per gallon, its about the smiles per gallon

 

[Chevy1925]

Not about the miles per gallon, its about the smiles per gallon

gotta have best of both worlds! :angel:

i want my damn cake and i wanna f***king eat it too!! Now go get me some cake steve:woott:

 

[Dirtymaxx03]

James is your truck your daily driver? As on every single day?

 

[McRat]

I'd try lower the pressure in the economy areas. To be honest, "I like stock sticks and I cannot lie" ...

 

[Chevy1925]

James is your truck your daily driver? As on every single day?

being my zuk has no a/c, it sure is currently! when fall starts coming around, i usually park the truck for the week and only drive it on weekends or if i need to pick up things or when i head out for camping with the trailer.

i use her jsut as she was intended for and then some .

i wasnt kidding in my motor build thread long ago about this build seeing high miles

 

[Dirtymaxx03]

Nice man. You never hear of guys putting serious miles on a built motor.

 

[Ne-max]

I have been wondering if bumping up rail pressure a with lower pulse width would create more heat in the fuel temp aspect.

 

[sweetdiesel]

To this day I've seen best results from the old mc105 tune slighty modded. I've tuned tuned and retuned my lly for milage and from what I've read in diesel economy paper onSAE and othe internetz don't work in real world! I read a paper saying that iirc 1000* egt produce best burn. This did not work! Low boost also did not work! I talked to zach and a few others while doing this and they noticed the same.

After that I didn't care about my milage and just mild race tunes in my lly