Fox Body Mustang 5.0
 

Hi ive been lurking around this site for some time now...Ive done little things here and there...like weight reduction...removed A/c...tire pressures...underdrive pulleys...electric fan...shorty headers just to get better efficiency out my 91 Ford Mustang LX 5.0L

Im already looking at getting the MPGuino gauge, Vacuum gauge, more weight reduction, air tabs, grill block, advance timing, fix the cruise control..but i could basically take care of that with my foot. Possibly and electric water pump...kinda of pricey..and some 3.55 gears which after reading some it seems like those seem to get you better milage

Im shooting for a goal of 30mpg on the highway...since thats what i ussually drive.
Soon as i order my MPGuino and Vacuum gauge i will start taking note of my actual milage right now...im positive that my highway milage is around 25mpg right now...im not really to worried of not reaching that goal...i just need a way to actually keep track of my driving to keep me on check

Welcome. Sounds like your already on the right track.
Is your mustang a 5 speed or auto trans? Just looked Auto.
What gearing is in your axle?

I would only replace the water pump if you need a new 1 anyway otherwise it probably wouldn't be worth the cost.

Have you slowed down to the highway speed limit? I normally follow behind semis not tailgate because their speed limit is normally lower and their traveling slower anyways.

unfortunately its auto...Ive tried slowing down to the speed limit...but I currently need to fix my speedometer cable since its not actually hooked up so im going off engine RPM and GPS signal for speed...currently it has the stock 2.73 rear ratio I believe...or what ever stock is. I do try and keep a constant speed of 65 but at times i do creep to 70..i just gotta keep more alert...and of course there are those times when i like to do spirited driving :)

I do have some engines mods im doing soon...like an explorer intake manifold that both upper and lower have been ported...this should increase efficiency a bit

is the speedometer cable problem common my buddies stang i wanna say its 91 or 92 5.0 5 speed has the same problem.

if you have 2.73 then 3.55 would increase your rpms at highway speeds. I haven't dealt much with gearing but i believe lower is for top speed which would lower your rpms at the same speed

yes the speedo cable is very common and very easy to fix...i found one ebay for 12 bucks shipped new...just grease it up and throw it in...ive just been lazy and havent gotten around to it...lol...but one of these days ill get to...it involves pulling the instrument panel which takes like 10 mins do to and then route the cable...another 5 mins or so...and while u have the instrument panel out...might as well upgrade all the lights to LED so they wont burn out as quick...its like 18 of them i believe...the only ones that dont need changed are the battery bulb and check engine...the led does not have enough resistance to keep it off...you can find smd led lights for about 10 bucks for a 20 pack on ebay with 6smd led's per bulb...its a nice upgrade from stock. then put it all back together total time about 35-45 mins depending if u do the lights or not

yea i thought so too about the gearing being lower would increase mileage but there was an article i was reading earlier and it mentioned the 3.55 being better than the 2.73's

just looked it up 3.55 might be better for quarter miles times beings your acceleration would be better, but for fuel economy you want lower gear ratios.
Rear End Differential Gears Fuel Economy | MpgEnhance.com

And your gearing is probably 2.73

from 3.55 gear question

well in that case after reading that....i guess ill stick to 2.73 for now

I doubt any gains from electric water pump, for drag cars yes, but not for street cars. Drag cars it runs off the battery, street cars would run of alternator, so converting mechanical energy to electrical, then from electrical back to mechanical is inefficient.

Electric fans would be good since you've deleted the AC your fan is way oversized and at hwy speeds is not needed.

If you can fit some taller rear tires that will drop your HWY rpm's some, I'm sure you have plenty of torque to get them going, will throw the speedo off, but since it doesn't work anyway.

Air dam if you don't already have on.