I've got a midly built 390 with an Edelbrock 1406 4 barrel carb. I'm getting about 8 to 9 mpg. I've taken a look at adjusting the Edelbrock and have pretty much come to the conclusion that it's running about as lean as it can.

What are suggestions for a good 2 barrel that I might be able to find on ePay. I have an Edelbrock Performer RPM intake.

Peter

 

A 2 bbl wont help your gas milage... keeping your foot out of the gas with the 4 bbl will get you the best gas milage.

 

Get rid of the Edlebrock...Not trying to start anything, just not a fan of them...But atleast try a smaller CFM Holley or a Motorcraft carb...Like a stock carb.. But the advice above is good... A vacuum secondary 4bbl when runing on just the primiaries with give you better MPG then a 2bbl!!!

 

If you want mileage, find a guy that knows what he's doing and have him set up a quadrajet for it. either that or a thermoquad off of a dodge, but the Q-jet has a better aftermarket.

The Q-jet will give you the best throttle response, mileage, and power if setup correctly.

OR just to go an auto supply house and buy one already setup for a roughly equivalent GM. Since you say it's mildy built I'd guess a Q-jet setup for a 325HP 396 from a '68 Camaro would be a good place to start.

Justin

 

Great, but where do you get a spreadbore manifold? Or does the Performer have an open plenum?

 

Spread-bore carbs will not work w/o an adapter. Of course neither will a 2bbl!

http://www.edelbrock.com/automotive/man_ford_332.html

 

I don't see how this would help, as the q-jet on my chevy 350 1/2 ton only got about 10 mpg after a professional rebuild. Although I have never taken apart a q-jet that was made up of the same parts as the last one/dozen twice, so YMMV.

 

a mildly built 390 with a performer RPM intake isn't going to do much better than 10 MPG with a 1 or 2 MPG cushion either way... you didn't say if you had headers or not, that'll help. the vacuum secondary's will help too... higher gears?

 

Isn't his Edelbrock carb already a Q-jet design???

 

The only thing that will help is a smaller carb!! Less air/fuel= more MPG!!

As I already said, a small vac. sec. 4bbl will get better mpg than a 2bbl when running on the primary side..

 

Let the truth be told, regardless of 2bbl or 4bbl, it's the price we get to pay for being an FE owner......

 

But I've heard people on this forum talk about getting 12 to even 15 mpg. How are they doing that? 8 to 12 mpg may not seem like a big difference, but it is 33% more miles per gallon.

Peter

 

This is where you run into efficiency limits. A mildly built motor with a properly jetted carburetor will almost always get better mileage than a stock motor of the same design. The built motor will tend to have a higher compression ratio and such, which in turn increases the thermal efficiency of the motor. Alot of times the motor will use the same amount of fuel to return more power, less fuel for the same power, or slightly less fuel for slightly more power.

It isn't uncommon for properly tuned (jetted, recurved, dyno tuned, whole nine yards) medium displacement motors (300-400 cubes) to return 20 mpg while their stock counterparts barely eeked out 10. Now mind you, having an engine properly dyno tuned is by no means cheap but it is about the only way to actually get mileage out of one of these motors.

And as for the question about the Edelbrock being of a q-jet design, the answer is no. The Edelbrock Performer series uses metering rods like a quadrajet but is a squarebore design (according to the company itself). UNLESS you buy an Edelbrock q-jet (they bought the rights to the design from Rochester). Then you have a q-jet with Edelbrock stamped on it, but they're $$$$. However, i don't even know if they still make those. For what they cost, most people were turned off.

Justin

 

my point exactly.. as for the 2 barrel getting better than a 4 barrel, i agree that a smaller carb will help some. i'm pretty sure i posted that vacuum secondaries would help. i changed from a 2 barrel to a holley 600 vacuum secondary carb and not only got more power, but better fuel mileage- so in my experience i don't buy the 2 barrel= better mileage all the time. driving habits play a major part in it.. i realize that my 30 year old truck was not designed for fuel efficiency in any way, aerodynamic shape, or form...
a vacuum secondary holley is cheap, so are headers. get the distributor curved to the motor, i think that cost me $25 for a guy locally to do it, and let it be... anything much more than that won't be a major improvement, and not worth the cash output IMO. custom carbs are spendy as is dyno tuning time. takes a long time to recur expenses at an extra 2 MPG...
thats only 36 miles extra a tank, or 3 'free' gallons, which is about 10 bucks. unless you rack the miles on, it'll be a while. if you do rack the miles on, you can afford the gas so why worry?

 

Alot of these higher mpgs come from higher rear axle ratios (3.50 and up), so the motor doesn't run as many rpm. Also, even though a lot of them won't admit it, their odometers are off and their mileage numbers reflect that error.