The Stovebolt Site Forums The Shop Area General Truck Talk Gas Milage?

howdy,
I have a '48 chevy 1/2 ton- with a 235/3 speed syncro trans/and 2.73 rear axle(chevy blazer-6 bolt)
I just got back from a 500 trip and only got 16 mpg...the points seem right, the timing seems right ...the exhaust is black with a "rich" smell when idling...
I was hoping to get 20 mpg or better...what do you thinK????

thanks
Jimmy

i would guess your rear gear is too high, putting the engine to low in the powerband. I got 16-17 consistently w/230-3psd/3.73, best was 18.5, but that was all under 60mph. Truck was all stock except HEI. brian

so... if I go faster I would get better milage?
the truck will run 70- just as soon as I get the tires balanced again...it's a long story...I averaged 55-60 in the rain on the previous trip

My 235 w/ granny 4spd and low rear axle ratio gets about 16 when i am going 60. if i keep it down in the fifties then it is better. I am going to put in a t-5 and a new rear end ratio to get me into the 20's hopefully.

faster doesn't make better mileage, but running at the 'optimum' RPM and loading does make a diff, w/ the 2.73's at 50-60 [about stock tire height of 30"], you'll only be turnin 1500-1800RPM - don't know where the best mileage will be, but if you're not on dead flat road, it'll be luging on every slight rise - and only 70? should be able to do 85 and be turnin about 2600RPM

runnin too rich for starters w/ the black pipes [check the plugs] - carb adjustment might help, and make sure the choke isn't stickin part on, or rejetting might be needed - hotter plugs too

Bill

I kept my 292 around 23-2500 rpm on the highway which was like 53-56 mph on 59 1 ton with sm420 and 4.10 gears and it got 17 mpg on a 600 mile trip. I had expected worse.

what kind of adjustments can you make on a one barrel carb? there is the screw on the lower outside that can be adjusted but what else can be done?
and will a rebuild kit be the way to go?
thanks

Make sure the vacuum port between the carb base and manifold spacer is not blocked by a gasket or spacer installed wrong. This will richen up your carb to the tune of about 5 MPH by keeping the high power jet open all the time. Don't ask how I know this.

Powerband, I've noticed the same problem. I'm usually driving short trips, but if this truck were my daily driver, I'd be riding the bus due to gas costs. I have a 235 with a 4 speed and single barrel carb. It doesn't seem overly rich. I'd be interested in learning how to correct this as well.

Clean out the carb & put a kit in it. It.s a real simple carb. Make shure the power piston is working. It should go up & down & kick the ball off it,s seat. Make shure no gas is in the float & set the float level. Like Grant posted make shure vacuum is geting to the port to the power valve. Check the timing & make shure the vacuum advance works.

I didn't think 16 mpg sounded to bad for a '48. It's not fuel injected, has a standard ignition, and is probably not very aerodynamic. Not to mention, that it is a pretty heavy vehicle.

It's a fact that burning a little rich could definitely affect the mileage, but I still think that 16 isn't bad.

I would never dream of 20 mpg or better, am I way off on this one?

has anyone tried platnim plugs or bosch quatros? made a difference in my newer truck,,,more go and better fuel milage..do they sellthem...i don't know?....look into it tommorrow

There's several other threads on this topic, from which I've gathered that you can average about 20-25 with a tuned truck having dual carbs, headers, t-5, appropriately geared rear differential, electronic ignition and PCV valve.

The theory is with the dual carbs you are getting the fuel to the cylinders more efficiently (less waste), that combined with headers, electronic ignition and PCV valve you are maximizing the engine's efficiency. The tranny with overdrive and rear differential with higher gearing (3.73:1, 3:42:1, 3.06:1... in stead of stock 4.11:1) you are able to get operating speeds without having to rev the engine real high and burn more gas. In otherwords, maximizing the efficiency of putting the engine's power into the tires.

Tuning and engine performance are only gonna get you so far in terms of gas savings if you have to keep the engine in the 3k range to maintain 55-75 mph or do lots of stop and start driving.

I have a serious rodder buddy that swears a 4 barrel gets him better mileage than the old style one barrel carb(s). Insists that crusing down the highway, the four barrel is running on two relativly small primaries vs one large throttle plate. His theory makes since to me and should hold true with the Holley-Weber type progressive carb.

Many other factors though as mentioned above.

I belive my truck runs much better, not as rich and plugs not as sooty after going with the HEI.

My pipe is black and my plugs are sooty. Combined with the fact that I average about 12 mpg with a Rochester 1bbl on a 250/3-spd/3.73:1, gas is eating up my checking account. I know that the Roch isn't the greatest carb around, but is there a way to tune it out to get better gas mileage. I do a bunch of stop-and-go driving combined with long stints at 55-75 mph on the highway. Any help is much appreciated.

Drew

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'66 C-10 stepside

One of the really interesting things is that the float level can affect how rich the mixture is. I always thought that if it doesn't flood or starve, the float level doesn't affect much, but that view is wrong.

well, i was thinking of putting an overdrive and a taller gearbehind my 250/3speed, hoping i would get better milage. should i start worrying abt the carb on it before i do all that stuff?

andre;
I run Bosch platinums in ALL my stuff. I've found that,on average,they've given me about 2 more miles per gallon over AC plugs,and the damned things seem to last forever. Well worth their cost!
This is just MY observation-I'm sure someone will have proof to the contrary...
Speed

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