ORIGINAL: USMCrebel

just cant afford 5-8 mpg,

Well an engine that makes more torque at a lower RPM will get better mileage than one that makes less torque at the same RPM. If the engine doesnt have to
work very hard to get to speed and maintain that speed, assuming its correctly tuned, it will get better mileage than one that is working harder to maintain
speed. Also gearing and vehicle weight play a part in addition to tuning and power production. If you build a 351W to make peak torque around 2800-3000 rpm
it will have plenty down low and be able to maintain cruise speed easier than a 302 with a torque peak of 3500-4000 rpm. With older vehicles with carbs think
of it this way. You want to cover more distance for each revolution of the engine, so that equals either lower numberically gears or adding an overdrive.
Using a car I used to drive long distances and daily as an example. It had a 403 ci engine with 2.73 gears and 28" tall tires. It would get 21 mpg on long
trips and around 10-15 in town. How did it do that with a big engine? Well it was set up efficiently, with a mild aftermarket cam, headers, and the gears
allowed it to cruise at a low rpm and have more than enough torque to maintain speed with a slight throttle opening. Another car with a 350ci 2 barrrel
engine and 3.08 gears was quite a bit slower, made considerably less power and was lucky to get 10mpg even when tuned quite well. It just didnt make enough
power to move the car and no amount of tuning would change that. A cam swap, a 4 barrel Qjet intake, headers, and dual exhuast allowed it to make more
useable power where it needed it most. Once I did that it was getting around 14-16mpg on highway and was alot more fun to drive. If you can make torque in
the right rpm range with a 302 you can get great mileage with sensible driving. An overdrive helps, but you can also get decent mileage with a 351ci engine
if its set up right. After 5.0L it seems more like where and how much power it makes than what size it is.
If you have 2.5-3.23 gears and arent getting over 15mpg then you need to make some changes inside the engine or under your foot..lol


Its true about leaning the carb, finding power and improving mileage. Even a large V8 can get decent mileage if it is geared, cammed, and has the right
intake and exhaust on it, then driven decently. 22mpg from a 7.5L with a carb in a 4000lb vehicle can be done. The stock 60s era cams arent so great for
mileage, technology has come a long way in the last 30-40 years, same with intakes, and exhaust. If you want better mileage make the engine not work so hard.
Get the right cam so it makes torque down low, use a tall gear like a 3.00 or 2.79 to keep the revs low. Covering more distance for each revolution is the
idea, if it burns the same fuel at 2500 rpm as it does at 1700 rpm then gear it so it is at cruise speed between those points. A single plane intake on a
small engine isnt going to get good mileage, at low rpm the fuel will puddle in the intake the puddle will grow untill it runs into a cylinder creating a
rich condition in that one. Dual planes dont do that, the velocity stays up in the intake and the fuel wont fall out of the airstream. Carb size is up for
debate, it will only flow as much air as is needed and you just need to jet it so the air/fuel ratio is right. Going with jets that are too small will hurt
power, economy, and overheat the engine, while causing severe driveability issues. Lean is power, but too lean hurts parts. Power means efficiency. Get the
max power from your combination and gear it so it runs in the torque rich part of the curve, and you will get good mileage. More power down low means the
car moves easier taking less throttle to get to the desired speed. When building an engine there are things you can do to improve mileage. Shorter pistons
skirts can reduce drag and weight, lighter pins also decrease drag, getting the engine balanced will make a difference. Roller cams and full roller rockers
will also benefit reducing parasitic drag. Add in thermal barrier and friction reduction coatings and you can see marked improvements. Making the car lighter
and more aerodynamic has a large impact as well. Cant do much about your 67 Mustangs aero qualities? Sure you can. Keeping air from under the car helps,
lowering can make an improvement in aero, so does keeping air out of dead spaces like behind the headlights. Waxing the car helps a little, if you have
decent paint keep it clean and waxed.

Alignments, tire pressures, wheel bearings, and brakes all have to be right, check your tires. Go to the max pressure they are rated for. the 17" Goodyears
on my daily driver are rated at 45psi, so they are at 45psi. When I run them at 32 like the tire shop had them I cant get over 25mpg, when they are maxed I
get 28-31mpg.
Repack your wheel bearings yearly. Pull the front rotor or hub off and repack them bearings. Make sure the rear bearings arent dragging either. While you
are there check the brakes, if they are draging you are fighting them as well as rolling resistance, wind resistance, and the natural tendencey of a body
at rest to stay at rest. If you can push the car easily up a slight hill by yourself, you arent wasting much in the suspension and drivetrain.
Every little bit helps.

ORIGINAL: USMCrebel

new shocks/springs, and my air pressure is good too timing is at 10*