does this sound right.

sn95gtvert · Apr 3, 2010

when my gt was basicly stock, catback and Hpipe it got 28-26 mpg on the freeway with 2.73's

now with my cobra intake 70mm tb and 3.73's i get about 19mpg at 3k rpms does that seem right to you guys?

Rice_slayer · Apr 3, 2010

Did you correct the speedometer, if so with what? Also speed too, 3k seems a little high for 70mph, even 75mph. at 70mph I'm at around 2.4k rpms

LAFENATU · Apr 4, 2010

3.73's are a huge difference between 2.73's.

Mustangs arn't known for superior gas milage in the first place.

sn95gtvert · Apr 4, 2010

i knew it was gonna drop with the gear change but not by 10mpg.
i never changed the trans gear so it still reads speed as if i had 2.73's thats why i posted rpms and not mph. in all honesty i have no idea how fast i was going on the freeway i was at 2900-3000 rpms in 5th with 26" tall tires. my speedo was reading 110. and yeah i know i just racked up 300+ extra miles on my car doing a 540mile drive.

2.73's @ 1900-2000 rpm = 80mph @ 26-28 mpg depending on if the top was up or down
3.73's @ 2900-3000 rpm = ??mph @ 19 mpg

sn95gtvert · Apr 4, 2010

i just used the speed calc and it said at 6k in 5th (.68 od) with 3.73's and 26" tall tires i can go 183mph that just doesnt add up to me.

seems way to fast i've put 5th gear to within a few hundred rpms of redline and in no way did it feel like 180. hell it didnt much feel like 140.

i need to find a new calc

toyman · Apr 4, 2010

sn95gtvert said:
i just used the speed calc and it said at 6k in 5th (.68 od) with 3.73's and 26" tall tires i can go 183mph that just doesnt add up to me.

seems way to fast i've put 5th gear to within a few hundred rpms of redline and in no way did it feel like 180. hell it didnt much feel like 140.

i need to find a new calc

The calculation is close enough. You just aren't spinning the engine to 6K in O/D regardless of what your tach indicates. You will be hard pressed to get to 5k.

Rice_slayer · Apr 4, 2010

I don't know how your mileage changed. Stock vs 3.73s I saw no mileage change. Then again I shift below 2k all the time and generally never floor my car. I got 18mpg in the city with 2.73s and get 17/18mpg with 3.73s. Highway was unchanged, I got 31mpg stock vs. 28-30mpg with gears at 70mph. Also how do you know your mileage if your mileage without speedo corrected? Your mileage(tripometer) is connected to your speedometer for how much you have driven. The tach is is not connected to the tranny in any sense like the speedometer is.

94RockinGT306 · Apr 4, 2010

your car gets the rpms through a pick up in the distributor.

sn95gtvert · Apr 4, 2010

lol i have made the trip a total of 3 times now depending on when and where i fuel up at its 540-600 miles. i used 28 gallons durring the trip. my trip meter clocked over 820 miles.

after using that calc it looks like i was doing around 90mph at 3k rpms so 19 mpg aint to shabby on my trip home i will go speed limit and see how well it does. im guessing around 25-28mpg at 2250rpms

albany oregon to twin falls idaho.
I-5 to 205 to I-84

Rice_slayer · Apr 4, 2010

You still won't get a proper reading, just get a speedcal or a speedo gear already!

sn95gtvert · Apr 5, 2010

lol im not worried about the speedo, or the fact that it will rack up extra miles.
when i titled the car in idaho they marked mileage exempt. anything over 10 years old or over 100k miles quits getting recorded.
and now that i have it titled in oregon it stay'd exempt even tho i told the dmv desk jockie why it the title said exempt.

i will correct the speedo at some point, probly the next time i order anything from summit. im not going to spend $10 on shipping on a $12 part.

Rice_slayer · Apr 5, 2010

Thing is you cant get proper fuel mileage readings as your tripometer isn't recording your distance properly, so your readings for mileage are off.

sn95gtvert · Apr 5, 2010

Rice_slayer said:
Thing is you cant get proper fuel mileage readings as your tripometer isn't recording your distance properly, so your readings for mileage are off.

like i said before, i've made this drive a total of 3 times now. twice before with my old 2.73's and a properly working speedo and trip meter. i know how many miles the drive is.