318 Small 4 Barrel Carb vs Original 2 Barrel Fuel Mileage

[73braved18]

  Hello!


First I would like to say I read every post on this topic I could find on here....
I have a 600cfm Edelbrock 4 barrel carburetor that I was thinking about rebuilding and putting on the 318 in my 73 Brave.
It has the stock 2 barrel Carter BBD. The Carter definitely needs a rebuild but gets decent mileage considering the Brave is as aerodynamic as a barn.

My two questions for people that have done this swap or just have knowledge on the topic:


How much loss of fuel economy did you get? Not necessarily down to the MPG but was it really noticeable? 

Did you do the swap with just an adaptor plate to the stock 2 barrel manifold or did you buy something like the Edelbrock Performer manifold?


I know a proper install of a 4 barrel is to put on a four barrel manifold because of the obvious bottle neck but...
With gas being around $1.50/litre here in Canada I would appreciate any info before I decide to go with the 4 barrel. I may go with a 12v cummins anyway in the future too so I am on the fence if I should just rebuild the Carter for now...


Thanks guys!

[LJ-TJ]

I got good news and I got bad news. You'll spend a lot of money dinking around and if you put the four barrel on you'll probably get 8 miles to the gallon varying on road an wind conditions. I you rebuild the 2 barrel you'll get 8 miles to the gallon depending on road and wind conditions. So says the great GOD of all of us Been there,done that. :)rotflmao

[Rickf1985]

If you decide to go with the 4 barrel then definitely go with the Performer manifold. Not only will it flow better but you will get more torque lower down in the power band. You tend to get less mileage at first since you have more power to play with but once the new and fun wears off and you start driving normally again you usually pick up a MPG or so. UNLESS you are like TJ and drive like a teenager all the time! W% :)rotflmao

[TerryH]

Rick - we've seen photos of your Mustang!
  Are you seriously telling us that when you strap in and start it you do not regress more than a couple of decades?   

[LJ-TJ]

 :)rotflmao :)rotflmao :)rotflmao Yeah listen to the kettle calling the pot black.

[73braved18]

Ok, so far it sounds like I probably would not notice a real difference in MPG with the Edelbrock and a performer manifold unless I really put my foot into it. But I would have improved performance...
I will give it a little longer before I press the order button on Jegs.com in case anyone else has more to add.


Thanks guys!

[LJ-TJ]

Hey we're just playing with you. Over the year's we've see lads spend hundreds of dollars on trying to get better mileage out of these old girls. They have spent hundreds to thousands of dollars on cams,carbs, etc.etc. etc. We've always come up with the same 8 to 10 usually closer to 8. Take that money you'd spend on manifolds a carbs put it into gas and go and enjoy ride. You can sit around a campfire with the rest of us and Bugger about what great gas mileage we get. NOT. D:oH!

[Rickf1985]

It boils down to physics. It takes a set amount of energy to move a set amount of weight a set distance, that is called horsepower. To boil that down into real simple terms it takes a certain amount of horsepower and torque to move that weight at a set speed. Gasoline provides a set amount of energy per gallon. SO, Regardless of the size of the engine, you will be using the same amount of gasoline (roughly) to move that set amount of weight no matter mow much power you have. IF, and only if, you drive it the same way with any of the engines or horsepowers indicated. So if you have 500 horsepower and drive it only as hard as needed to maintain a normal speed you will get 8-10 MPG. If you have 200 horsepower such as you have now and you have to push it a bit harder you are still using the same amount of the gasolines energy to produce the amount of power needed to move the vehicle at the same speed.


And Yes guys, That Mustang is very quick, 400 plus Horses at the wheels but you know what? It gets 23 MPG on the road!!! Perfect example of energy needed to move the vehicle, it only needs about 150 of those horses to move along quite well so the rest is reserve. If I use it (yes I have been known to push the envelope a bit) the mileage drops quickly.


So, Bottom line. I would definitely go with the four barrel and manifold if you plan on keeping this vehicle for a long time. It will pay of in the long run in reliability and ease of repair. The Edelbrock carburetor is the absolute best carb for adjustment without having to take the whole carburetor apart. You will probably find that the throttle shaft bores on the old two barrel are worn oblong and if they are then that carb is junk so you are looking at a lot of money for another two barrel and it is just not worth it.

[73braved18]

Makes sense! Well put!
I will go with the Edelbrock.
Thanks!

[srosa707]

FWIW, I get 6.5+ with my 2-barrel equipped Brave.  And that is driving pancake-flat Interstate 5 in California.  Thanks to Wantawinnie, I'll be doing a Cummins swap in the next year or two.