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Need better gas mileage...

  • Thread starter Thread starter 65fastbackresto
  • Start date Start date May 18, 2008
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65fastbackresto

Active Member
Apr 13, 2007
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May 18, 2008
#1
  • May 18, 2008
  • #1
6 mpg is what I`m getting now, there has got to be something I can do to help this. Its just a built 302, small lopey cam, and 10 to 1 comp. I`m having to run premium cause of the compresion, but what can I do to help the gas mileage? I have Edelbrock 600 with electric choke and its just like it came out of the box with only the idle and fuel-air mix screws messed with.

Smaller carb maybe?
 

jlangholzj

Mustang Master
Oct 23, 2006
248
31
93
MI
May 18, 2008
#2
  • May 18, 2008
  • #2
ha!

what exactly are you rear gears? 3-spd, 4 or a T-5 ?

I have a 289, 600 CFM holley, a mild crane cam, C-4 and 3.00 rear gears and on a GOOD day, i can get in the 12 range (of course, who's to say this isn't b/c of my driving style )


I'm geussing that if you have say 4.11's, your doing pretty darn good with 6 mpg, but if they're 3.00, you might just need to tune things up.

at an arm, leg and a left nut, running 6mpg on $4.15 gas is definately not fun! (well actually it is!!! but your wallet won't like it) but hey, its better than avgas ($5.50 per !! )
 
D

D.Hearne

New Member
Sep 29, 2000
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south louisiana
May 18, 2008
#3
  • May 18, 2008
  • #3
Refresh our memory's----What rear gears and stall are you running ?
 

70vert

New Member
Dec 31, 2004
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Bay Area, CA
May 18, 2008
#4
  • May 18, 2008
  • #4
With an OEM '70 302-2v, 2.73 rear, and a .64 final drive TKO600 5-speed, I have gotten (no joke) close to 25mpg on a 150 mile mixed freeway/country road drive. I have pretty meaty 245/275 tires too. It can get better! Do you have a manual or auto?
 
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suki243

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Dec 19, 2006
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May 18, 2008
#5
  • May 18, 2008
  • #5
25?! thats some good stuff.
 

Fast63

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Sep 20, 2007
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May 19, 2008
#6
  • May 19, 2008
  • #6
what kind of fuel pump do you have? edelbrocks can't run over 6psi of fuel pressure because it will open the needle and seats and dump gas in your engine. Also, what is your timing at? Does it advance?
 

Hack

15 Year Member
Mar 23, 2004
1,945
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May 19, 2008
#7
  • May 19, 2008
  • #7
Tune up and keep your foot out of it. Don't expect 25 though! Methinks someone's speedo is a little off, that's pretty unusual. The biggest thing you can do is to drive really easy, like you have a crappy little 4 cylinder in there. Stay at or under the speed limit on the interstate.
 

jlangholzj

Mustang Master
Oct 23, 2006
248
31
93
MI
May 19, 2008
#8
  • May 19, 2008
  • #8
Fast63 said:
what kind of fuel pump do you have? edelbrocks can't run over 6psi of fuel pressure because it will open the needle and seats and dump gas in your engine. Also, what is your timing at? Does it advance?
Click to expand...

does this go for holley's also? just curious.
 

70vert

New Member
Dec 31, 2004
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May 19, 2008
#9
  • May 19, 2008
  • #9
That's why I didn't use the speedo! I Google Mapped the drive, filled up at the beginning, and filled up at the end. Seriously, with a 2.73 rear and a .64 final drive OD, driving 55 on the freeway feels like idling. And the untouched 2v had something to do with it, I'm sure. 91 Premium gas.
 

65fastbackresto

Active Member
Apr 13, 2007
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May 19, 2008
#10
  • May 19, 2008
  • #10
I`ve got a c-4 tranny

and 355 posi track, and the speedometer says about 90 mph when I`m running 55, but I can fill the tank up and drive about 50 miles, and the gauge is under 1/4 tank.

As far as tune up, it aint had enough hours to be tuned in yet, much less wear and tear on stuff.
 

rbohm

Founding Member
Apr 12, 2002
6,698
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tucson,az
May 19, 2008
#11
  • May 19, 2008
  • #11
65fastbackresto said:
and 355 posi track, and the speedometer says about 90 mph when I`m running 55, but I can fill the tank up and drive about 50 miles, and the gauge is under 1/4 tank.

As far as tune up, it aint had enough hours to be tuned in yet, much less wear and tear on stuff.
Click to expand...

ok first we need to get your speedometer and odometer right, they are WWWAAAAAYYYYYYY to far off. depending on what tire you are using you need a 21 tooth driven gear. and that is likely part of your problem.

as for what you can do for tuning, start by swapping to a smaller jet and metering rod combination. i used a 93 jet with the corresponding metering rod in my grand marquis to reduce fuel flow.
 
C

chromedog

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worlds center for speed
May 19, 2008
#12
  • May 19, 2008
  • #12
6 mpg, thats pathetic... my 351, comp cam, 600 holley, aod with 3:00 gear got around 18 before i swapped to the 3:50 gear. now its around 15 if i keep my foot out of it. i would do a plug check, and try to jet the carb down... WAY down!
 

65fastbackresto

Active Member
Apr 13, 2007
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May 19, 2008
#13
  • May 19, 2008
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This bites....

I dont know how to change jets and metering rods, I got a buddy that can though I hope.
 

SadbutTrue

Founding Member
May 1, 2002
2,390
4
49
Granada Hills, California
May 19, 2008
#14
  • May 19, 2008
  • #14
65fastbackresto said:
I dont know how to change jets and metering rods, I got a buddy that can though I hope.
Click to expand...

it aint' hard, just read the manual on it. Jet changing takes about 10 minutes, even for the mechanically un-inclined. Don't even need to get your hands dirty.

when you say 'mild cam' do you have any idea what specs are actually on it?

If someone sold it to you saying it was just a lopey/RV cam but its actually some radical monster stuck in the body of an otherwise stock or near stock engine (trust me.. it happens... some people are really strange when it comes to cams), then that might explain why your mileage is terrible.

Other than that, cant do much except look for vacuum leaks, tune it up as far as timing and A/F ratio goes, and new plugs.
 

65fastbackresto

Active Member
Apr 13, 2007
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May 19, 2008
#15
  • May 19, 2008
  • #15
Well....its pretty freaking scary when I flog it

Not exactly sure of the cam specs, but the lift was just under 500, and the duration was I think 236, with LSA of 108.

Even in a straight line this thing will pin ya to the seat and wiggle when changing gears, I never thought a small block ford could do this, I`ve had a couple of good chevy 350 motors, but nothing I ever had ran this good. (light car too though)

The fuel pump is stock.

I think the carb came with a dvd, I`ll look into that.
 

SadbutTrue

Founding Member
May 1, 2002
2,390
4
49
Granada Hills, California
May 19, 2008
#16
  • May 19, 2008
  • #16
65fastbackresto said:
Not exactly sure of the cam specs, but the lift was just under 500, and the duration was I think 236, with LSA of 108.

Even in a straight line this thing will pin ya to the seat and wiggle when changing gears, I never thought a small block ford could do this, I`ve had a couple of good chevy 350 motors, but nothing I ever had ran this good. (light car too though)

The fuel pump is stock.

I think the carb came with a dvd, I`ll look into that.
Click to expand...

yeah, its probably just something small. that cam doesn't seem too ridiculous, though it is a bit big for an otherwise near stock motor. give it a good tune with new plugs and mileage should come up some.
 

jlangholzj

Mustang Master
Oct 23, 2006
248
31
93
MI
May 19, 2008
#17
  • May 19, 2008
  • #17
65fastbackresto said:
Not exactly sure of the cam specs, but the lift was just under 500, and the duration was I think 236, with LSA of 108.

Even in a straight line this thing will pin ya to the seat and wiggle when changing gears, I never thought a small block ford could do this, I`ve had a couple of good chevy 350 motors, but nothing I ever had ran this good. (light car too though)

The fuel pump is stock.

I think the carb came with a dvd, I`ll look into that.
Click to expand...

HA! I hear ya! it's kinda scarry how much some of the SB's can actually put out.
 

gonzothegreat

Member
May 4, 2004
421
1
16
London (uk)
May 19, 2008
#18
  • May 19, 2008
  • #18
342, with a lumpy 280 roller cam.
10Mpg in town
19Mpg combine (80% motorway, 20% town)

3.55 gears and T5 gearbox.
 
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D.Hearne

New Member
Sep 29, 2000
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May 19, 2008
#19
  • May 19, 2008
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65fastbackresto said:
and 355 posi track, and the speedometer says about 90 mph when I`m running 55, but I can fill the tank up and drive about 50 miles, and the gauge is under 1/4 tank.

As far as tune up, it aint had enough hours to be tuned in yet, much less wear and tear on stuff.
Click to expand...

Speedo gear tooth count also needs to take in account the tire size (diameter) I'm running an 18 tooth in my 77 Comet with 3.50's and 26.5" tires and it's dead on the money, untill you hit about 80, then it goes haywire. You can't really go by the reading on the fuel gauge to figure mileage, you have to get the actual miles and divide by the gallons used. The C-4 doesn't help things either, especially if it's got a radical stall converter.
 

Fast63

New Member
Sep 20, 2007
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May 19, 2008
#20
  • May 19, 2008
  • #20
jlangholzj said:
does this go for holley's also? just curious.
Click to expand...

It depends on which model holley I believe. Some can handle up to 7 psi, while others can handle 9+psi. I know the stock holley on my 85 stang runs with the stock fuel pump, which puts out 8.5 psi. I have heard people say a basic 4160 holley shouldn't run more than 7psi though. I have less experience with holleys because I just don't like them at all, so someone else could give you a more precise answer on a specific model, or you could always call holley's tech line.
 
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