what kind of gas mileage do you get?

Hey Guys, I was wondering what kind of gas mileage most of us get with engine mods? I know my 302 in my Mustang got 25 on the highway on a great day with a tail wind but all it had was dual exhaust and a four barrel intake and carb. Then I put the Crane Fireball cam (294 dur.-465 lift guessing but close) in and it went right down the drain! But that cam sure was great before a stupid valve broke! I'm wanting to put a cam in my 66 with a 289 but I don't need that big of cam. Anyone know what kind of gas mileage a 289 hi-po got on the highway? Cams have changed so much it's so cool to look at all the grinds out there.

I'm getting a tad over 19.5 mpg with a single plane intake, 600 cfm carb, 493 lift cam, big valves, 3.25 / 9” gear, 25” tires at 65 mph/3000 rpm with two people in the car.

My 427 powered 1967 Fairlane used to get about 14 MPG.

The 390 one got about 12 MPG.

Wm.

1bad6T, was that with a 289? My Mustang had the 302 with a dual plane high rise, 600 holley, C4/stall coverter, headers and that Fireball cam with .464 lift. I only got 12 in town but never took it out on the highway much since it turned high rpms at even 55. Sounds like you have a nice set up 6T! Could you tell a difference with the 3.25 gears when you put them in? I was thinking of putting that gear in my fairlane...good compromise for all around.

If your not using the Vacuum advance, it could be the reason why your not getting good milage. Or when you changed your cam, you did not re-curve your distributor.

The vacuum advance not being connected, or not set up correctly can easily cost you 30 - 40% of your gas mileage at highway speeds.

I got best of 22 MPG on two road trips I did last year. I usually get about 18 MPG, and a lot less if I lean into the throttle.

Originally Posted by RickRacer

1bad6T, was that with a 289? My Mustang had the 302 with a dual plane high rise, 600 holley, C4/stall coverter, headers and that Fireball cam with .464 lift. I only got 12 in town but never took it out on the highway much since it turned high rpms at even 55. Sounds like you have a nice set up 6T! Could you tell a difference with the 3.25 gears when you put them in? I was thinking of putting that gear in my fairlane...good compromise for all around.

Yes it's a 289 with mechanical advance distributor sat at 10*. I never checked mpg in town. My guess is 15 or 16 if I act like my age driving. I did have a 3.70 gear and it was fun but 4000 rpm trying to keep up with 65 mph traffic on expressway. The 3.25 is more practical on a daily driver. I though it wouldn't be enough gear when I was changing it out but I thought wrong. This is a 4-speed not automatic. Rick DeVito just swapped to a 3.00 from a 4.11 in his wife's car (automatic) and is happy. I tried to talk him into a 3.25 but he found a deal to good to pass up. A lot of people will be surprised how much difference a gear ratio changes things unless you been there done that. My 60 Falcon Engine

I get 14 on the highway with my 489,and got about 13 when it was a 427, but have recently gained a ton of low/mid efficiency with an ignition box (with the butt dyno)

Planning a good run in about 10 days will see

The vacuum advance was one thing I didn't have on my Mallory Unilite distriibutor back then. It really makes that big of a difference?! This is so cool, I can have my cam and gas mileage too! I would love anything above 18 mpg on the highway but 20 would be fantastic....

Yes, Timing is very important for milage. If your running mechanical only, there is your issue. Easy 30% mileage gain.

The trick is, first before doing anything, find where your timing is at 3000 RPM's with the mechanical only advance.

It should be between 34 - 37 degrees.

When you add the vacuum advance, make sure your "no-vacuum" timing at 3000 is the same as you started with.

Then attach to the vacuum port. At 3000 RPM's your timing should now be near 45 degrees. The vacuum can adds 10 degrees when vacuum is over 10 HG.

Do not have timing over 50 degrees. If you do, something is wrong.

You may need to put timing tape on your engine dampner to see up to 45 degrees.

If you do not understand anything that is written here, ask, cause you can get into trouble.

63 w/ 221 and 3sp O/D.....30mpg or better. :-D (if I keep my foot out of the carb)