The Stovebolt Site Forums The Shop Area Engine Shop hoping for more than 6 mpg

last weekend i filled my 57 up for the 2nd time.... went 89 miles on 15 gallons of gas. 6 mpg !!!!
this is with a very mild cammed rebuilt 350 with hedders, aluminum intake and edelbrock #1405 600 cfm carb.
i knew it was smelling rich, so i called edelbrock and the guy told me the #1405's have bigger jets, metering rods and also bigger venturi boosters than the 600cfm #1406.
he recommended a .098 jet to replace the .100 jets that were in it. also said to replace the stock .047 x .070 metering rods with .073 x .052 metering rods.
i put those items in it today, along with a fuel pressure regualtor set at 5.5-6.0 psi, and retarded the timing a bit, so hopefully i will get better gas mileage now.
i gotta keep my foot out of it, but still, 6 mpg shocked me.
will let you know what happens the next time i fill up, probably in a few weeks.
leonard

At the local prices here that is 58 cents/gal just for fuel. WOW. Makes my 16mpg six banger sound wonderful.

FWIW 58 cents is almost exactly what it costs to fuel the new KW T900 crane truck demo with CAT engine coming my way and it weighs 12 tons.

I think ya mean 58¢ per mile, Dave ☺
OTOH, think how much it cost to get the truck and divide that [+license and insurance] by however many miles you'll put on it in your/its life, and 58¢ won't matter .... did you buy that thing for the fuel economy?

Bill

I was getting about 11 mpg on the highway with a similar 350, with a leaky old Holley carb. I recently switched to an Edelbrock 1406 carb, and now after the first couple of tanks I have gotten about 12 mpg in town (instead of the old 8 or 9) I haven't had a chance to take a long drive on the highway yet, but I'm hoping for 15.
At this rate, the Edelbrock will pay for itself in no time.

I've got the bottom of the line 350 from GM (I think it's 290-horse, 305 tq), Ancient Edelbrock C3B intake, Edelbrock 600 carb I haven't touched. It needs to be tuned.
HEI ignition, small cast iron ram's horn manifolds, dual exhaust and glass packs.
Manual overdrive trans with .73 final drive, and 3.55 gears with tall tires all the way around. Clutch fan behind the radiator and open element air cleaner.

I average 16mpg combined highway and around town.

I'm sure I can pick some up with dialing in the carb, and I'm also going to put 2.5-inch Ram's horn manifolds on it, and I've got a 3.42 rear gear that's going in it. I HOPE to pick up another mile or two per gallon with just those changes.

then I'm going to turn some attention to the body: Close off the un-used portion of the huge opening behind the grille to keep air from stacking up, seal the openings in the leading edge of the hood, fabricate a filler panel to go from behind the front bumper to the bottom of the cross member to keep air out from under the hood, and fab a short 2-inch tall air dam to put behind the front bumper to direct some air out from under the vehicle. These are all things that are routine on new vehicles, for aerodynamics. Again, if I can get one or two mpg, that'll help nicely.
Lowering it some more won't hurt either!
It's my daily driver, and I put between 15-20,000 miles on it in a year, so a couple extra mpg makes a big difference.
-Brad

red58, very true, didnt really buy it for economy, but would think and like to get mroe mpg. a friend has a 500hp nova and gets 6 mpg. mine aint a race car. LOL.

shoe, if i still have trouble getting mpg's, i might go with your style carb, the 1406. thats what the edelbrock guy suggested.

brad54, do you have the 1405 or 1406 edelbrock ? what trans do you have ?
also, any pics of your truck ? sounds like your gonna make a nice aerodynamic cruiser.

thanks guys.
leonard

53moneypit, i am in love with your red 57 belair. LOL.
leonard

Thanks RatRod and BTW, your welcome to come over and help me finish it, HA.

moneypit, why would retard the timing? that would usually hurt your fuel economy. I would just set it to specs and make sure the advance is working correctly

Try adjusting your valves. I was working on my wifes truck awhile back and had 1 or 2 intake valves maladjusted and the fuel economy suffered horribly. This was on a 307 with a Q-Jet from a 350. Once I readjusted them properly the mpg soared from about 6 mpg to about 14 in town. One of those things you learn by trial and error. Oh well...

Jeff

thanks rustednuts. might pull the valve covers off one weekend. since i got a mild hydraulic cam, the sheet says 0 clearance, so easy enough.
leonard

Hey Leonard;
I gotta think your truck should do better than that.

To get the best mileage advance your timing as far as it will go before pinging. Turn your dizzy about 1/16 of a turn CCW and drive it down the road a little with your foot in the throttle. If you don't hear any pinging repeat the 1/16 turn and do it agan. Eventually you'll begin to hear a little pinging sound (pre-ignition, or what we used to call "spark knock"). At that point turn the dizzy back (CW) 1/16 and lock it down.

Make sure your tires are all inflated properly.

How "mild" is that cam?

Are you running the stock rear gear? A 4:11 will really pull your mileage down on the highway.

Good luck and keep us posted.

waldo, i was getting some slight pinging on acceleration, so i backed off the timeing just a tad. seems good now, no pinging. it is running so good now.
the cam is a .450 intake, .460 exhaust lift. very mild.
tires are inflated properly.
i jacked the rear of my truck up with both rear wheels off the ground, spun the tires, and got 1 revoluton of the tire to 1.25 turns of the drive shaft. not sure what that ratio is, but that was witht he trans in neutral.
seems to be a little leaner with the carb mods i did, and witht he timing retarded the little i did, seems to have lost a little performance.
since it is not a race truck, LOL, im not too concerned about that. more interested in gaining some MPG's.
will let you all know when i go to fill it up again. hope to put 30 + miles on it tomorrow, so i might fill it up at the end of the day tomorrow.
leonard

If you have the original rear end it is more than likely a 3.90.
And if you are using a non overdrive automatic (like a 350/400)you can't expect to get much mileage out of it anyway. You can do some good by tweaking the carb & timing but it's still geared low. Put the trans in neutral, jack up one wheel, mark a location on the tire and the driveshaft, turn the wheel two complete revolutions and count the number of turns on the drive shaft. Three & 1/2 turns = about 3.55, almost 4 = 390, a little over 4 = 4.10 etc.
Fred

fred, i did that check yesterday, but with only 1 revolution. i will try it today with the 2 turn and 10 turn method. thanks.
i was told it is a motor, trans, th350, and rear out of a 1980 1/2 ton chevy truck. i gotta get someone to cruise behind me and claibrate my speedo, but if it is correct, at 50 i am pushing 1800 rpm's and at 60mph i am pushing 2200 rpm's.
thanks for the help guys, and will knwo more later today after i recheck the ratio.
leonard

To check your gear ratio buy the tire method jack up both sides mark both tires and the driveline turn both tires together one revolution counting how many times the drive shaft turns. The X2 thing is for turning one tire assuming the spider gears are .5 to 1 and that is not always so. The best way is to pull the cover and count the teeth on both the ring gear ant the pinion and divide the number from the ring by the number from the pinion.

The fact that you lost performance doesn’t sound good for your fuel mileage as a motor must be running at its best state of tune for its best mileage. The changes that you made should have boosted performance if they where going to increase mileage as the changes you made where small so you have the same motor. The good thing is you should have much better fuel mileage available from the combo that you are running. My neighbor gets almost 30 MPG with his 2004 Corvette

i did the ratio check with only 1 tire up, drivers side. 2 turns of the wheel was 2.75 turns of the driveshaft. 10 turns of the tire was 12.75 turns of the drive shaft.

before i went for a 30 mile cruise this morning, i decided to fill up again, since i had about 25 miles with the old carb settings, jets, metering rods, and timing, and with no fuel pressure regulator, and about 31 miles with the new set up.

so, 56 miles on 6. 2 gallons, so i am heading in the right direction i think.9 miless to the gallon.
i will dive it a few more weekends and fill up again and see what i am getting with this set up.
and i checked my valve adjustment, which was pretty close to good, but i tightened them up another 1/8th turn past when the pushrod stopped moving between my fingers, so they are good now also.
i am going to TRY to not put my foot in it at all for the next few weeks, trying to see what mileage i can get that way too.
but it does look like i am heading in the right direction.

also, i think i had the timing too far advanced, since it ran real good, but was getting a little pinging on aceleration, so when i retarded it a bit it SEEMS like i lost a little performance from that, seems like it.
but i dont want or have a race truck, so i am not worried about that at all.
ok guys, thanks much, and i will report back in a few weekends when i get about 100 miles on the odometer.
and i gotta calibrate my speedo also.
leonard.

Hey Leonard;
I had another thought on this. If your speedo is out of calibration then your odometer likely is too. Maybe you're going farther on a gallon than your odo is showing (?)

Drive around the block a few times, then do the same route with the family sedan and compare your odometer readings. Maybe the news isn't as bad as it seems.

thanks waldo. i am going to have my brother, drive side by side and calibrate it that way.
or, as my buddy dave suggested, take it on the turnpike for a short drive, and go a few MILE MARKERS and check it that way. and your way sounds cool also.
for some reason, i didnt think of either of these ways. LOL.
you learn something new every day.
thanks.
leonard

Ratrod,
This weekend I've put about 175 mostly highway miles on my last 12 gallon fillup, and still have a little gas left. I would say sell your 1405 Edelbrock and buy a 1406. My truck still runs very strong with it.
I used a 1" spacer under my carb, I don't know if that helped or not.

Shoe, did you have any experience with a 1405 before you went with your 1406 ?
leonard

Leonard, I bought the 1406 because it was supposed to be calibrated for fuel economy, the 1405 is calibrated for performance. Edelbrock says the 1406 is 2% leaner than the 1405, that doesn't seem like too much difference. They might be the same carb, just different calibrations.

thanks SHOE. when i did call edelbrock, the guy told me the 1406 had smaller jets, .098 comapred to .100, and different metering rods,a nd also smaller venturi boosters, (whatever they do).
so he recommended a jet and metering rod change, which i did, and a fuel regualtor.
if i dont get much better mileage, i just might go with the 1406 as you have.
thanks.
leonard