6.5 Mpg!

[GrillMaster]

Is this possible? Just filled up the other day with 12.5 gallons after driving 78 miles from the last fill up. I was expecting it to be around 10 or 12.

Possibilities:

I suppose someone could have siphoned some of my gas
Or maybe I got killed from sitting in stop and go traffic.

Any ideas? Just had the carb rebuilt and I am running a 351C with 4.11 gears and a 4 speed trans electronic fuel pump and ignition.

never heard of a car getting such bad mileage! was about 50/50 stop and go city/hwy

 

[CDHUNTER]

Leak? Could be anywhere from front to back.

 

[Madgyver]

4V or 2V heads?

Carb?
cam?

The C's are known the be gas eaters, More because they produce great tq and hp numbers in the higher rpms.

Alot could be on how it was built.

 

[GrillMaster]

Think they must be the 4v heads it has a 750 DP Holley Carb and big cam, no visible leaks.

 

[Madgyver]

Think they must be the 4v heads it has a 750 DP Holley Carb, no visible leaks.

With this combo it sounds about right... Double Pumpers will do it, it explains alot.. Throw on a 650 DP and you'll notice the torque in the lower rpms.

Look at the upper corners of the heads for the number 2 or 4, it should be located right in the corner where the valve cover has a curve.. That will tell which heads you have.

 

[GrillMaster]

so you think it will run better and save fuel with the 650 Holley DP?

 

[javilamfd]

Had the 351C 2v with a edelbrock intake and holley carb. Pulled it last year due to heating issues, and the MPG was horrible. Best I could get was around 8MPG around town, hiway didnt change much. Switched back to a 302 (got the motor for free), heating issues went away and MPG around town average 10 with no change in my driving style.

 

[GrillMaster]

man that is bad too! Guess I wont be driving my EB as a daily driver as planned. Want to do the 4BT conversion once I get my other car project completed.

 

[MountainGuy]

Sounds about right to me. I'm getting about 4-5 in town. I drive a little aggressive though...

 

[73AnneBoleyn]

jeez!! 4-5?!

 

[broncnaz]

X2 on the smaller carb 600 cfm is more than enough for a daily driven 351C you may not get better than 10 but you should get better than 6.5. Also what tire size are you running toploader 4 speeds dont have quite as good of a first gear as the stock 3 sp so stop/go take offs may be a big part of your problem especailly if it is a 4V engine with a big cam.

 

[GrillMaster]

By good do you mean a lower gear? 1st is real low. sometimes start out in 2nd if I don't do a complete stop. You shift fron 1st to 2nd at 2.2k and around 4mph. 3 or 4 mph.

 

[Madgyver]

By good do you mean a lower gear? 1st is real low. sometimes start out in 2nd if I don't do a complete stop. You shift fron 1st to 2nd at 2.2k and around 4mph. 3 or 4 mph.

Sound like an NP435....

 

[GrillMaster]

tires are 33's. maybe a good excuse to go to 35's??? %) Maybe the 600 Holley is the way to go? anyone else running this combo?

 

[allenfahey]

Do you have the correct speedo gear at the transfer case for the tires your running? Your odometer will be off if you don't and your MPG will be too.

 

[broncnaz]

Yeah sounds like you have a NP435 tranny. You might be able to get away with 35in tires and 4.11s it shouldnt hurt it to much might wear clutches a little faster though. but probably wont really help your mileage except on the hiway. Speedo might be off a little but probably only off about 10% so maybe your pulling almost 8 mpg at best. I think a 600cfm carb would be your best bet at this point the smaller the carb the better the atomization of the fuel. big carbs require bigger jets to esure the fuel gets into the airstream. I'd also run a vacuum secondary carb instead of the double pumper types as the double pumper types are really jetted rich for race applications.

 

[wildbill]

You mite want to look at the plugs if a little black you mite try rejetting the carb. If you do only go down a couple # at a time like if you are running 78's try 75's till it runs right. Its best to come down slow I would think that motor would run good with about 63 to 65's. O and as I dont do keep your big right foot on it easy;D this will help good luck. Bill %) ;D

 

[bax]

My 400 got about 12 mpg before I took the AOD out. It was a good combo, high torque at low rpm in overdrive. It was not even working hard. Now with the C6 I am a bit over geared, So it is eating some gas now. But it's strong as hell.

 

[bmc69]

Strange..because my 'beast' with the Oz-400C on 39.5s gets 10 mpg highway (much to my surprise, I freely admit, but it does get that). Never bothered to check it in 'stop and go' or local driving...don't drive it very much on the road anyway. I calculated the mileage when I had to make a trip exactly 100 miles over the highway to meet up with our transport rig for atrip to Tellico. With a 15-gallon tank, I figgered no way I would make it..but had 5 gallons to spare when I arrived. ;D

I hate a DP carb myself...vacuum-secondaries only for me; the vacuum-operated secondaries know when demand for seconday opening is actually there..yr big right foot does not.

 

[bax]

Bill, What gear are you running with those 39.5 monsters. I figure I am at ten mpg. I can't fit a bigger tire but that would help my final gear.