The Stovebolt Site Forums The Shop Area Engine Shop eating gas

so right now ive got a 283 with a 4 barrel holley carb thats eating gas and im thinking about switching to a 2 barrel to save a little. any recomendations?

if yer 4 barrel is tuned properly, and you quit pokin yer foot in it, it should get as good mileage as a 2 barrel - 283's ain't designed for mileage

Bill

well thanks but id still like to know if anyone has any recomendations

Keep askin'...I'm sure someone will give you the answer you want to hear

sarcasm?? btw i found that i have a rochester 2 jet on my 64 that i havent looked at in a few years (been sittin in the backyard).

oh and im also in the market for a new air cleaner, but i cant seem to find one for a 2 bbl carb..

I would pitch that "race only" Holley and put a Quadrajet on it. The primaries are a lot smaller than the 2 barrel carb but you'll have secondaries when you need it. A Quad, when driven nice, will get better MPG's than a 2 barrel. You can also adjust the opening point of the secondaries to prevent the use of excess fuel while driving modestly,
Scott

which cfm? can you give me a link if you like one better than the others? thanks.

Just get one off of a simular size engine. Preferably an older one like the 283 or 327 era that would be rather simple to install and adjust. May want to go to a salvage yard and get one and have it rebuilt. That way you can get everything you'll need (bolts, choke parts, linkages, etc.)
Scott

Holley carbs and fuel economy are not normally mentioned in the same sentence!

What would be better??? Not necessarily a two barrel.

Before doing anything, do the math. If your proposed new carburetor does 25 percent better than the Holley (and that generally is probable!); how long will it take the increased mileage to pay for the carburetor, and associated extras. Lets say your Holley gets 8 MPG, and you increase that to 10 MPG (25 percent). If you drive 100 miles per week, you go from using 12 and 1/2 gallons to 10 gallons; or a savings of 2 1/2 gallons per week. At $3.50 per gallon, you save $8.75 per week. A quality rebuilt 4-barrel is probably going to cost at least $250. Then you will have a new fuel line, possibly an air cleaner, possibly an intake manifold, etc.

If you decide to make the switch, what you install (or how much it costs) may depend on your current intake manifold. DO NOT attempt to put a quadrajet on a square-bore manifold using an adapter; as this is the best method of causing a Q-Jet to perform as poorly as the Holley! Match the carburetor to the intake (and the engine) with NO adapter. Brand is pretty much up to you, but an original 283 Rochester 4GC (if you have an original intake) is going to outperform ANY new carburetor on a stock 283, both in economy and power; and still doesn't carry the costs of the more popular Carter WCFB. Probably the very best carburetor ever built for the stock 283 was the Carter AFB 9400 (but these are no longer available new, and the demand has driven the price of rebuilts through the roof).

Oh, since you did ask about the two-barrel, expect maybe a 10~15 percent mileage increase over the Holley, provided that you have a stock 283, and replace the intake with a stock 283 2-barrel intake, and use a stock 283 Rochester carb. Trying to install the two-barrel on the four-barrel manifold with the adapter would result in worse fuel economy than the Holley.

Jon.

If you haven't already changed your rear axle ratio that would get better mpg than anything else.
Larry

If your Holley seems to be running rich & loading up you probably need a new power valve. They frequintly go bad & are easy to replace.

63Custom...not sarcasm...a weak attempt at humor

carbking - thanks for all the info. ill look to see what the intake is and see if i can use a quadrajet on it.

lgriffin - i havent yet, but have thought about it. how much does it cost to do that?

wrenchbender - thanks ill check that out.

To formalize what Jon said about payback :

Thinking about a {your swap here} swap to save on gasoline? How long will it take to break even? I ciphered out a formula.
Let C = Cost of the conversion in dollars
G = Price of gas per gallon in dollars
P = Present Miles Per Gallon
N = New Miles per Gallon
and
M = Miles driven to break even
Then
M=C/[G*(1/P - 1/N)]
For instance if I spend $1000 (C) to boost my mileage from 17MPG(P) to 20MPG(N) and gas is $2.95 per gallon (G)
1000/[2.95*(1/17-1/20)] = 38418 miles to payback.

If I went from 8MPG to 11MPG (same 3MPG difference)
1000/[2.95*(1/8-1/11)] = 8994 miles to payback.

Too much like math? I put the formula into an Excel spreadsheet so you can just plug in the numbers.
http://www.chuckthetruck.com/payback.xls

Chuck - does "C" represent the estimated cost of conversion or the actual cost (after one buys all the things one didn't think about in the planning stage )?

Actually, glad to see you did the equation. I was too lazy to do one. Your examples point out very distinctly that a finite increase at a higher initial point is requires a much longer payback period.

Would like to throw one other issue in this discussion. Most would assume that the Q-Jet (spread-bore) will always do better on fuel economy than a square-bore; but this is NOT ALWAYS true.

Many years ago, I converted a motor home with a 454 from a Q-Jet to a custom Carter AFB due to lack of low-end torque with the small primary bores of the Q-Jet. Both the Q-Jet and the AFB were 750 CFM. After the conversion, the power difference was astounding. The difference was measurable in that we dropped driving time from our residence to Hershey, PA from 20 to 18 hours (with the cruise set at the same speed). The difference was maintaining that speed in the mountains. However, when we figured fuel economy, we were very pleasantly surprised to see that our MPG climbed from 6.3 to 7.2. I would have been happy to break even. The key here is the mass (weight) of the vehicle. The small primary of the Q-Jet simply was not large enough.

Every application is different; which is why there is never a single "right" answer.

Jon.

If "C" represents the estimated cost of the conversion, then "3C" would represent the actual cost!

Hello 63 I am with griffin,sure a two barrell will help but not as much as the diff.Try going to a couple of rear end shops and see what they say about a gear swap.Right now you've probably got a 410 or 456 ratio and should go to at least a 373 or lower.Gotta keep the four barrel, they just sound to cool when your trying to really get somwhere

Sorry to jump in guys. The relationship between fuel economy and operating cost is linear. A 3 MPG savings will pay back a $1000 investment in the same amount of miles... no matter where you start from. Using "chuckthetruck"'s notation, the actual mileage calculation is:

M = (N - P) * 1/G * C

example:

(11 - 8)MILES/GALLON * GALLON/$2.95 * $1000 = 1017 miles

(20 - 17)MILES/GALLON * GALLON/$2.95 * $1000 = 1017 miles

The law of diminishing returns comes in when you consider how much it COSTS to increase fuel economy. The first MPG increases are relatively inexpensive compared to what it takes to eek out further savings.

Thanks for the helpful carburetion info "carbking".

P.S. This is my first post to the site. I have learned a lot here and hope to contribute where I can.

I was going to write up an equation to explain Bent's post but I was too lazy. :p

Zigler,
I think I disagree - it's been a long time since I've done math - but this is what I'm thinking:

If I spend C to increase my mileage and my efforts fail, then N and P are equal. My delta mpg goes to zero and by your formula it takes zero miles for payback, when it should go infinite. It will never payback, as my formula correctly predicts.


Looking at it another way (and this is how I derived my formula):
I travel 12000 miles at 17 miles per gallon and gas is 2.95 per gallon, I ‘ve used 706 gallons that cost $2082
(M/P*G in my notation)
I travel 12000 miles at 20 miles per gallon and gas is 2.95 per gallon, I ‘ve used 600 gallons that cost $1770
(M/N*G)
I will have saved $312 at the higher mileage (M/P – M/N)*G= c the cost savings.

When the cost savings (c) and the cost spent (C) are equal that’s my payback mileage. If I spent $312 to go from 17 to 20 mpg, then I break even at 12000 miles.

Shuffling those terms around leads to my equation (I’m sure “shuffling” isn’t allowed in a formal proof but this all for fun.)

Using the lower numbers
I travel 12000 miles at 8 miles per gallon and gas is 2.95 per gallon, I ‘ve used 1500 gallons that cost $4425
I travel 12000 miles at 11 miles per gallon and gas is 2.95 per gallon, I ‘ve used 1091 gallons that cost $3218
I will have saved $1206 at the higher mileage.

The starting point does matter. With these old trucks, many aren’t driven enough to justify an upgrade strictly for mileage. Do the upgrade for fun and this is all moot. Please don’t take offense and feel free to correct me if I’m again wrong.
Thanks,
Chuck

Carbking you are right on. The Q-Jet is best for light throttle cruising. GM put square bore carbs on there larger trucks. All that math is too much for me.

i hate math. well it looks like i wont be doing any of this engine work anytime soon, i got rear ended today on the way to get my haircut. luckily it was the other guys fault. the bed needed replacing anyway haha, but it looks like the frame is ok. im praying its just the body but im bringing it to get an estimate on monday. its still driveable though. anyway, sorry this was off topic haha thanks everyone for the replys.

63Custom, Before you take Bent and my advice on the rear axle do some home work. Assuming from your handle that your truck is custom decide what tires you are going to run, find out what their diameter is. What engine are going to have. Will the tranny have an overdrive. When you have a fair idea of where your going, then find RPM calculator on the web. The RPM calculator will allow to input Tire dia., rear axle ratio, mph and get RPM or switch RPM for mph and get rear axle ratio. may of not got tha quite right. I don't have one bookmarked at the moment or I'd add it. The object is to find rpms in the bottom half of your torque curve. Then you tell the rear end shop and tell, them what you think you want and why. They may have a few suggestion and prices. The other option would be to look for used rear axle. Do a search in the archives rear axles should come up quite often. Swapping rear axles can get messy, rear axle width, coil springs or leaf springs, shock mounts. panhard bar, get the right width and swap mounts. Lots to think about. An overdrive will let you compromise a bit for street and highway performance. That's a start. I changed the rear axle in my 68 C20 from 4:56 to 3:73 out of a 73 C20 or 30 with a BB and automatic. It was almost a direct swap till I got to the shocks. GM went from both shocks going forward in 68 to one going back and one forward in 73. My mpg increased by about 20%
Larry

Sorry to hear about your misfortune. Hopefully you can work it out in your favor.
Larry

yea im hoping they dont call it totaled because it might cost less to do that, but because theres work done to it im hoping they'll take that into consideration. it still makes me want to vomit when i see it haha

You can buy it back from the insurance company if they total it, at least I did several years ago in California.