Fuel psi newbie question...

[Matt Weiser]

I recently installed an AFPR and trying to get comfortable tuning with it. What I'm wondering is, how does fuel pressure affect mpg?

I'm assuming that as fuel pressure increases, mpg will drop because you're injecting more fuel per piston stroke, all else being equal. Is that right, or am I way off base?

In either case, somebody set me straight, eh?

Right now I'm running 42 psi fuel pressure, 14# boost, on 89 octane gas, JL 93 octane chip. I have no knock at WOT but just a bit of KR during the transition to boost (say, while cruising). I realize I might be stretching things a bit with this chip and the octane I'm running, but the car is a daily driver and I'm looking for a good power/mpg compromise while using gas that's a bit more affordable. So call me crazy.

Any and all feedback appreciated.

 

[TurboShane]

Well running 89 octane is a bit crazy considering how much a replacement enging is. But I don't think fuel pressure will really affect gas milage because the computer controls how much fuel it put's in. It would affect it at WOT but that's a tuning thing and if it does't have enough you will blow a headgasket in shortorder.

 

[U1ARUNIT]

You would need to run the FP at like 50# vac line off to notice a difference. It does eat more fuel with it turned up.

 

[JToups386]

89 octane??? Did you read the text under your speedo. "Premium Fuel Only"!
I wouldn't run 89 octane in my weed eater! Well, okay, that's a bit extreme, but, why would you take chances with that watered down stuff on a performance, boosted engine?

And yes, raising FP will affect gas mileage, by default, due to the fact that you're going to be putting your foot into it from time-to-time, and therefore the added pressure will accentuate more fuel usage, even if only a little bit.

It sounds to me that you're too concerned about fuel economy though, having confessed to running the cheap gas too. Maybe you should buy a Honda for transportation, and just use the Buick for fun...?

 

[JToups386]

Ahhhh, but now I correct myself, after noticing you've put the LC2 in an old Malibeast wagon, therefore you wouldn't see the "Premium Fuel Only" listing.

So, we'll tell you first hand ---- "Stop running the cheap stuff!" Your car will like you much more if you do!

 

[Matt Weiser]

Thanks for the feedback, guys. Actually, I do know about the "premium only" advice since I also swapped in a TR dash. Anyway, I'll take all your advice into account.

 

[BLACK6PACK]

If you're lucky you'll save about $500 in gas this year by running 89 octane. The bad thing is once the year is up you'll need to spend $3500 for a new motor, that's if you're lucky and don't do any damage to the block.