modaddict

It doesn't work like that. If you put 120# injectors on your car and set the fuel for as low as you could go in the tune at idle, you would still flood and foul the plugs within seconds at idle. You would need to set the idle for 3 grand just to keep it at idle and you'd still foul the plugs within seconds under 1200-1300 rwhp.

Think of it in terms of straws... A #39 injector is like pouring the gas in through a coffee straw and the #60 is now pouring it in with a regular soda straw. Fuel pressure being close to equal - you are going to tune according the a/f but more fuel is going to be delivered and your mpg is going to go down. It's not a matter of 'pulsed' - it's a matter of volume delivery.

No offense - but if you are so worried about fuel economy - why did you buy a mustang and frequent a modding forum?

I always tell people who are consumed with mpg to get a prius. I just don't get why someone would buy a muscle car, want to mod it - and give any concern for gas mileage at all.

Again, nothing personal - and I'm not directing this at you personally - just in general about MPG cause it bugs me when people interested in modding their cars for more power want to talk about mpg...it's an oxymoron and confusing. HP takes fuel - good fuel - and lot's of it...

Like I said, my car gets about 6 mpg and costs $6.00 a gallon but who cares - it's freakin' fast...lol

Vapour Trails

I did a 200 mile cruise @ 70 mph with the Whipple and returned 22 mpg, a drop of about 2 mpg over N/A (and that's with 4.10 gears). That's not bad considering how fast it is.

In the city though, it's much worse, but I can live with it...I live close to work and my friends. Everytime I drive to work I have to get in boost a least once .

shanec

MPG...don't want to waste there if I don't have to, that's all.

Haven't calculated anything yet but by the car's behavior on week 1 of the supercharger mod, I think the mpg is pretty close to what it was before....unless I got around boosting all the time.

On one outing, I spend a lot of time in boost and I could about watch the needle to down. LOL

I don't care how bad it sucks gas when I'm hot rodding it. But I'd like to be able to baby it if I want to and get not sucky mpg if possible.

mac10chap

lol, i am having the same issue....wouldnt call it a problem persay. Before the procharger, i was getting around 22mpg just driving too and from work. Since then, my car sees about 12-13mpg. That could have something to do with me not upshifting to 5th gear much. something about keeping it around 3 grand and being able to touch the throttle and get thrown back. I'm sure it will wear off one of these days though.

mygt500

I am at 11.3-11.5 and that is thru 6500 RPMs......I was at 10.9 at WOT and had start and idle issues and since had that corrected and the new A/F ratio is what was stated above!

mygt500

I agree and totally understand where Chevykiller (Mark) is going with his explanations on inj size etc.

I also have to include that I run 60# inj for only 465 RWHP....my tuner likes the spray pattern and more importantly for him its in the way he tunes the car and its personal preference. Not overkill IMO but others may not agree.

I would get about 23 MPG in the city before FI and now I get 16 MPG in the city when I am not beating on her .

Car dyno'd at 270 RWHP with CAI and no tune before FI and 465 RWHP after FI. I like to think my stock motor from Ford was a better made one....or I ran her in the right way -etc....

shanec

After my dyno runs yesterday, my wideband gauge is spot on. The 10.9-11.3 I see from it matches what a mustang dyno gave me when it measured A/F in front of the cat.

A later run on a dynojet measured A/F behind the cat at 11.4-12.3.

Haven't calculated MPG yet, but just from looking at the fuel gauge - my highway mpg appears to be about equal to what me 50-50 city/highway mpg used to be.

mygt500

your A/F ratio is great and not sure if you knew but the reading before the CAT is more accurate.....anyway I am sure you did as you did your homework on this one!

08GT4U

let me get this straight.when they dyno your car with sniffers on the tail pipe the reading is actually leaner than what the car really is?im asking cause when i had my car dyno for the nitrous i was running the stock h pipe with cats and my a/f was at 11.1 to 11.3 through the power band with sniffers on the tail pipe.does this mean my car is actually running reacher than 11.1 if i was to read before the cats.

Doogie65

That sounds right. When mine was being dyno tuned, the AFs were monitored post cat with sniffers... and according to the tuner, that reading is always about .5 leaner than when monitored pre-cat. Mine was set for about 12.0 throughout the boost RPM range with a snifer, which keeps me right at 11.5.