Stock 302/2bbl/C4 est MPG?

[MustangChuck 16]

I will add that I had changed carbs from a broken Holley to a well tuned Carter when I was getting 15 mpg on the open road. I was getting 10-11 mpg with the Holley. (The car drove much better with the Carter, also.) Tuning the carb for your style of driving is very important. With carbs, though, I don't believe it is possible to get the best of both worlds -- performance and gas mileage, since the carb can't control its flow as well as EFI.

[69gmachine 15]

With carbs, though, I don't believe it is possible to get the best of both worlds -- performance and gas mileage, since the carb can't control its flow as well as EFI.

 

I can only assume you have never tried an Autolite 4100 or even a Holley with annular primaries. They do provide the best of both worlds. The front barrels on the 4100 are smaller than a typical 2 bbl, so as long as you stay out of them, you can get excellent gas mileage and throttle response. When you do choose to step on the gas, the power is there, especially for a small to mid size engine.

 

Then you need to add an OD trans, which is critical to MPG success. You end up with a final drive that's lower than the tallest gears available (2.89 or so). If you have 3.50 rear gears and a .64 OD, your final drive is only 2.24. The seat of the pants feel of leaving 1st with 3:50s is much better than grandmas 2:89 gears so it's a lot more fun to drive all around (best of both worlds). Even with 3:70s like I have, the final drive is still only 2.37. You can cruise at 60 mph at something like 2K.

 

The last major piece of the puzzle is a good electronic ignition. An inductive ignition is better for mileage and low RPM power than a CD. I'm not putting "IMO" because I can demonstrate it, and have for years. The OEMS have never used a CD ignition. When they needed to operate at higher RPMs, they added coils rather than go to a CD ignition. The only reason race cars like NASCAR use(d) them is because the rules artificially restrict(ed) them from using multiple coils. NASCAR is finally entering the electronic engine control age, so they may use coil on plug now, I don't know.

 

Last, get rid of unneccesary weight. If you insist on a rolling museum piece with heavy factory style steel wheels, heavy factory iron everything, yep it's pretty hard to get decent mileage. It takes more power to get it rolling everytime you stop with all that mass.

 

23mpg can be done if you're willing.

[Pakrat 1,043]

Wow, this is an interesting read.

 

Even more interesting is that no one seems to realize that this thread is more than 3 years old now and Relic just mysteriously resurected it. The original poster has been MIA since like this past March.

[danno 128]

I wonder a bit if some of the milage claims can be attributed to tire size and rear end ratio. I speedometer that is not correct can really have a huge effect on your mpg. It it tells you you are going further than you actually are, you get really good mpg.

 

There is probably not one of us with the original tire size (because they are no longer made). Most new tires can be purchased as very close to correct for the speedo gears, but who does that when shopping? Also think about all of you who have modified the rear end gears and not adjusted speedometer gears. Another great way for you to think you have great mpg.

[70Mach03 12]

Couple of years and a few pages ago I posted about having a new 1970 Mustang in 1970 with 302-2V, auto, and 2.79 gears. It got 15 to 19 mpg from day one. I kept that car 22 years and added several different dual exhaust system (Cherry Bomb glasspacks to finally a stock system off a 351C-4V) and drove it 186K+ miles. I always kept stock size tires (F70x14 when new, FR70 or 225/70 x14's in later years). Rebuilt the stock 2V carb twice, and finally added a Holley 500 CFM 2bbl at around the 120K mile mark. With my minor mods over the years it was getting 16 mpg city and 22 to 23 mpg on the highway at it's best. This was in the mandated 55 mph National speed limit years so I was still driving in 65/70 mph when I could.

 

If you can't get 14 to 15 mpg with a 2V and 2.79/3.00 gears there are other problems with the engine. I was always tinkering with my motor back then resetting the timing or fiddling with the carb. One thing about the older motors is the timing chain will tend to stretch over the years slightly. It will retard your timing over time if you don't continue to adjust it forward. When I finally swapped out for a new timing chain at 125K+ miles, it had stretched to the point that with the new one my timing was nearly 20 degrees advanced too far before resetting the timing. The new chain felt like it added 20 hp (LOL).

[69gmachine 15]

I've noticed a lot of really old threads have been resurected lately.

 

Anyway, I only bother to check mileage when I'm on a long trip on the open highway and I cross reference with mileage from a map and actual gas to fill the tank. I know it drops like a rock in town with my 408.

 

Since I put the car together from scratch, I used the same speedo gear (red 21 tooth) for the rear end gear (3:70) and tire size (25.5 measured dia P275/40 17) that Fox Mustangs used. When i did the math on it, it says I need 20.984 teeth to read correctly... pretty darn close.

 

When I was driving past a speed warning sign that reads out your speed on a giant digital sign, it was tracking exactly what my speedometer said in a 25 mph speed zone.

[70Mach03 12]

I've noticed a lot of really old threads have been resurected lately.

 

Anyway, I only bother to check mileage when I'm on a long trip on the open highway and I cross reference with mileage from a map and actual gas to fill the tank. I know it drops like a rock in town with my 408.

 

Since I put the car together from scratch, I used the same speedo gear (red 21 tooth) for the rear end gear (3:70) and tire size (25.5 measured dia P275/40 17) that Fox Mustangs used. When i did the math on it, it says I need 20.984 teeth to read correctly... pretty darn close.

 

When I was driving past a speed warning sign that reads out your speed on a giant digital sign, it was tracking exactly what my speedometer said in a 25 mph speed zone.

 

 

I use a dash mounted GPS as my primary speedometer in my '70 Mach when I'm cruising. I've gone to 15" rims and 235/60/15 tires so my in-dash speedo is about 10% off according to the GPS.

 

It can be a "little" optimistic at times like this: http://www.1969stang.com/gallery/Bill-Hamiltons-1970-Mustangs/IMG_0317?full=1 :scared:

[69gmachine 15]

Now that there's funny I don't care who you are.

 

That reminds me of a night when I was driving home to Dallas from College Station on I-45 at 2:00AM. Back then the national speed limit was still 55. That's a long straight stretch of road, and rather desolate at night.

 

I had a ragged looking Winter Blue M code fastback with a 5.0 liter and 5 speed I took out of a wrecked Fox body. Whenever I went over 70 MPH, the speedometer would lay over just exactly like your picture. All I knew for sure is that I was going over 70.

 

When I topped a slight hill I could see I was gaining on a couple of slower cars at an alarming rate, so I slowed down and fell in behind them. They were going exactly 55. I just couldn't take it, so I decided to pass them. A car was coming up from behind in the fast lane, so I decided I would get in behind him.

 

After going around the slower cars I pulled back into the RH lane. The car in front slowed down. Then he fell in behind me and flipped his lights and siren on. He had been chasing me for miles.

 

He clocked me doing 98. After determining I had no warrants or priors, he gave me a man's name and address and told me if I sent a money order for $200 (a lot of money in 1980) in less than 10 days, it wouldn't go on my record. I did, and he kept his word. Love those corrupt small Texas towns.

[rangerdoc 22]

Even more interesting is that no one seems to realize that this thread is more than 3 years old now and Relic just mysteriously resurected it. The original poster has been MIA since like this past March.

 

Well, dang! Call me a sucker.

[70Mach03 12]

Well, dang! Call me a sucker.

 

 

Don't worry about a 4+ year old post when we're talking about 40+ year old cars. :thumbup1:

[Pakrat 1,043]

Well, dang! Call me a sucker.

 

Is that a request for a custom title? :clown:

[rangerdoc 22]

Oh crap...I'm running away now.

[Pakrat 1,043]

LOL :lol:

[MustangChuck 16]

With carbs, though, I don't believe it is possible to get the best of both worlds -- performance and gas mileage, since the carb can't control its flow as well as EFI.

 

I can only assume you have never tried an Autolite 4100 or even a Holley with annular primaries.

 

No, I have not. I have a 4300 sitting on the shelf, but that is a larger carb than the 4100. I've had a lot of issues with broken Holleys, so I tend to shy away from them.

 

For my build, I will be putting in a T-5 and hopefully replacing the rear end with 3.27 gears. That should drop my final gear ratio to 2.22, which should put me in the 2000 rpm range at 70 mph.

 

Chuck

[MustangChuck 16]

When I was driving past a speed warning sign that reads out your speed on a giant digital sign, it was tracking exactly what my speedometer said in a 25 mph speed zone.

 

But (given the back-road Texas story you also relayed), you didn't mention how fast you were going in that 25 mph zone.... :smile:

 

Chuck