Carbruator for best gas mileage

[Ricos54]

I have a stock 350 crate motor 250hp with a 700R4. I'm running 300 gears posi 9" and going to put 20's all the way around tires will be 255/45/20 in my 54 Chevy 1/2 ton truck. I'm trying to decide what would be the best Carbruator to give me the best gas mileage. I got a 670 4 barrel duel feed Holley street avenger. Holley said that's to big to go with there 570 street avenger. Edelbrock said to go with there Edelbrock performer series 600. I wouldn't mine have a little power, but over all I want good MPG.
I'm not building a hot rod, I'm a nice street rod that I can drive everyday and take trips in. I don't have a heavy foot and would like to see low 20's if possible on the HWY.
Also I'm building this truck on a budget so I don't have a bunch of money to throw at it, if I did I would have bought a LS motor with EFI. With that said what would work best for what I want?

Thanks

[Highsider]

I would like to read what is suggested.

[gale]

I'll be interested to see what is suggested also. My '54 was a daily driver until recently when I took it apart for frame-up painting. It also has a 350 crate motor with Edelbrock carb. I have checked the rear end ratio but I got about 16mpg with tires that are too big for the truck.

When it is back on the road it will have 7R15 tires on 6" wide rims.

In 2004 I bought a new GMC SWB step side that was tricked out by Regency with 20" wheels. I didn't care for the look and sold them and put the GMC standard size aluminum wheels on. My gas mileage jumped from 15 to 19 even though going down in tire size makes the odometer spin faster.

So that's something to think about when you're going for the big wheel/low profile look. Another plus to the regular size tire is they cost half while they last twice as long.

[Ricos54]

Originally Posted by gale

I'll be interested to see what is suggested also. My '54 was a daily driver until recently when I took it apart for frame-up painting. It also has a 350 crate motor with Edelbrock carb. I have checked the rear end ratio but I got about 16mpg with tires that are too big for the truck.

When it is back on the road it will have 7R15 tires on 6" wide rims.

In 2004 I bought a new GMC SWB step side that was tricked out by Regency with 20" wheels. I didn't care for the look and sold them and put the GMC standard size aluminum wheels on. My gas mileage jumped from 15 to 19 even though going down in tire size makes the odometer spin faster.

So that's something to think about when you're going for the big wheel/low profile look. Another plus to the regular size tire is they cost half while they last twice as long.

I have 20's on my dodge nitro and I get 22 on the hwy and so far I have 72,000 miles in them and still going strong. I know it's a new SUV, but for me I won't go with anything smaller. I was going to put 22's on until I found out I had to put 35 series tires on and I don't want to feel everything on the road.

[jackson]

quadrajet. the end

[mr48chev]

I'd have to first ask if you have run the 670 or if it is still in the box and you can return it.
With some careful jetting and some other tuning such as picking the right accelerator pump cams to help mileage you might get reasonable mileage with it.

Any carb has to be tuned to the engine it is on and the type of driving that the car or truck it is on is going to do. Many of us put up with a box stock carb that has little more than the idle speed set and the Idle mixture screws set for the highest vacuum reading and little else and don't get too carried away with trying to get the best performance and or mileage out of the carb.

[Ricos54]

Originally Posted by mr48chev

I'd have to first ask if you have run the 670 or if it is still in the box and you can return it.
With some careful jetting and some other tuning such as picking the right accelerator pump cams to help mileage you might get reasonable mileage with it.

Any carb has to be tuned to the engine it is on and the type of driving that the car or truck it is on is going to do. Many of us put up with a box stock carb that has little more than the idle speed set and the Idle mixture screws set for the highest vacuum reading and little else and don't get too carried away with trying to get the best performance and or mileage out of the carb.

The Holley came with the engine, so I can't take it back and I'm a long ways off before driving it. My buddy wants to buy the carb so I told him to buy me the Edelbrock, but he told me he didn't know if that is my best choice. He ask if there was anyway of finding out which carb would fit my needs the best, so I told him I would post on here to see what you guy's would recommend.

[47 Fasttoys]

20 MPG on an AD series would be a stretch, the problem is that parachute in front of the hood. Add that to the wide tires and increased roll resistance you you have when running them and even with the best gearing and carb. you would be lucky to get 18. Then I had my '54 I ran a 350/700R4, 273 gear in the rear end and a 600 Holley. With 235/75/15 the best I could do was 18. Now I normally run 70 on the highway. If I would back to 65 it might help a little, but 2 MPH, no so sure.
Rob

[Denee007]

This is a good question! I only know of the Edelbrock that's on my '59 with the 350, Th350 and 3:08, and then an Edelbrock on my '67 Mustang(289), c4 and stock 2:79). I get horrible gas mileage on both, but I've never actually checked it, I just know that I'm filling them up fairly often. I'll do better about actually checking next time.

What makes the Quadrajet some much more efficient Jackson? I googled it, looks like a neat carburetor.
dne'

[Highsider]

Originally Posted by Denee007

This is a good question! I only know of the Edelbrock that's on my '59 with the 350, Th350 and 3:08, and then an Edelbrock on my '67 Mustang(289), c4 and stock 2:79). I get horrible gas mileage on both, but I've never actually checked it, I just know that I'm filling them up fairly often. I'll do better about actually checking next time.

What makes the Quadrajet some much more efficient Jackson? I googled it, looks like a neat carburetor.
dne'

Not encouraging, Denee, considering your '59 has the same set up as my '57 panel, but you have taller final gearing, which should give an advantage. I suspect mine has 3.7, or ?

[gale]

Originally Posted by Highsider

Not encouraging, Denee, considering your '59 has the same set up as my '57 panel, but you have taller final gearing, which should give an advantage. I suspect mine has 3.7, or ?

Taller gearing does not automatically equate to better gas mileage. If your engine can't efficiently pull the gearing one of the two needs to change.

[Highsider]

Originally Posted by gale

Taller gearing does not automatically equate to better gas mileage. If your engine can't efficiently pull the gearing one of the two needs to change.

Mine is wound pretty tight at 65mph.

[T-P Auto]

Denee;
I would also go with the Q-jet.
The Q-jet was the stock carb on most GM engines for a lot of years.
The Q-jet can be get from 15 to 20 mpg all depending on the trans n gears in rear end.
I have a 78 350 2bd that get 15 mpg.
The whole thing with 4bd carbs is as long as you keep your foot out of the back bds you can get fair mpg.
I just have never liked Holley for a street type engine.
Hope this will give you something more to think about.

Tim

[Ricos54]

So it looks like a Q-jet might work! What if I save my money and go with a TBI setup could that make any difference?

Thanks

[Denee007]

It's not like I drive all over the place~ it's just a classic car/truck event vehicle and on special occasions. But it does concern me if that much gas is being used, is that playing havock on the rings and cylinders? I do know the edelbrock wasn't/isn't an expensive carburetor. I do like the looks of the Q-jet after Googling it, plus it being an original carb back in the day~ that's cool! Something to put on my list of wants! I'll never get to my TR6 for restoration! lol

Originally Posted by T-P Auto

Denee;
I would also go with the Q-jet.
The Q-jet was the stock carb on most GM engines for a lot of years.
The Q-jet can be get from 15 to 20 mpg all depending on the trans n gears in rear end.
I have a 78 350 2bd that get 15 mpg.
The whole thing with 4bd carbs is as long as you keep your foot out of the back bds you can get fair mpg.
I just have never liked Holley for a street type engine.
Hope this will give you something more to think about.

Tim

[Denee007]

Just how much money would you have to save up for a TBI? I'd like to see a pic of the setup, I'd never do it, but would like to learn more, and more, but I tend to forget it soon as I learn it! lol

Originally Posted by Ricos54

So it looks like a Q-jet might work! What if I save my money and go with a TBI setup could that make any difference?

Thanks

[Ricos54]

Originally Posted by Denee007

Just how much money would you have to save up for a TBI? I'd like to see a pic of the setup, I'd never do it, but would like to learn more, and more, but I tend to forget it soon as I learn it! lol

The TBI setup is around $1100 from JEGS. Don't know if it's cheaper any where else.

[Russell Ashley]

Someone correct me if I'm wrong, but I think all Quadrajet carbs are spread bore with small primaries and large secondaries. If you are currently running an Edlebrock most likely you don't have the correct intake to use a QJ. There might be adapters available but I don't know for sure.

[Ricos54]

I just called JEGS and the TBI setup that is like a master kit which comes with everything is $2429 which is a lot of money and to improve gas mileage maybe 2 or 3 miles per gallon might not justify the cost. I ask his opinion on carbs and he said he like the Holley 600 with electric choke and vacuum secondary

[Ricos54]

I looked up the 600 cfm Holley on Summit and says not to use with overdrive transmission, so if I stuck with Holley it would be the 570 street avenger. I was also told that the Q-Jet has to be tuned about every 3-4 months. Don't know if that's true, but that's what I was told by a tech.

[Mac the Yankee]

I've been hearing lots of good things about the new Demon carbs

[OrrieG]

Over the years I have ran everything from WCFB to 780 Holleys. Currently my chevelle (355/350th 3.08) has a Qjet and I have ran it two years without any problems or adjustments. tiny primaries so mileage is pretty good. Before that I had a 500cfm Holley @bbl on it. Not as good of mileage as the Qjet because the bores are larger. Got rid of it when the idle circuit starting acting up and I could not get it to run right. Before that I had a Edlebrock 600cfm Performer, but the idle circuit in it went fubar too. Not as good of mileage as the Qjet. On other SBCs I have had Holley carbs, but always seemed to be fiddling with them. Ok for race applications where it is full throttle. Around here you can get Qjets off of running engines for less than $50 when guys upgrade. Get the early ones before they added all the electronics. IF you want to speed the cash I have heard good things about the Edlebrock FI systems but have no personal experience.

[T-P Auto]

Ricos54;

I have run the Q-jet on most every GM product. They are the best all around day after day driving carb that you can find,
Very easy to set up n adjust.
Q-jets ARE a spread bore carb.
That means they have small primaries(gas mileage) large secondaries(Performance).
They do make adapters for the Q-jets, I just dont really think they are very good.
Just find you a stock intake for the Q-jet.Q-jets hold the adjustments for a very long time once you have them adjusted to your way of driving.
When you go with the TBI system you lose some timing adjustment.
One other thing about fuel mileage with the Q-jet ,is that you can hook up to a ported vac outlet on the carb n get much better performance from the dist n carb..

Hope this helps you some more.
Good thought from (Russell n orrieG)

Tim

[Denee007]

Maybe I'd just better look around for a nicer air cleaner! This is a good thread and I'm sure many folks wonder about the question of a carburetor
dne'

[franken]

Holley made/makes a spreadbore replacement for the Qjet. A well tuned carb can rival EFI for mileage. The trick is tuning.