Better mileage, 2 barrel or 4 barrel carb?

Here is what I got goin on in my head fellas. 72 Grand Safari with a 455. I have upgraded the exhaust with headers and a true 2.5 inch dual exhaust with flowmasters. I also pitched the stock point distributor and bolted in a new HEI. The carb and intake are still the stock 2 barrel units. I plan on swapping out the intake for an edelbrock performer. My question is this. Do you think my mileage would improve with a 4 barrel over the 2 barrel? I only wonder this because it seems to me this an awful lot of engine for a 2 barrel carb. I know not to expect amazing mileage out of this unit but with gas prices climbing any little bit helps. So right now I am considering rebuilding my 2 barrel and running an adaptor plate to bolt on to the edelbrock intake or going with a jet perf. quadrajet. I know quadrajets make some people cringe but I like the fact they have small primary's and large secondarys. Thoughts and suggestions appreciated.

 

A friend did the swap, with stock manifold, on a 73 monte 350 and immediatly picked up 5 MPG.
Worst thing was keeping his foot out of it!
Re-curved the distributer, too.
This was in '75, when fuel was a little better, [with lead] though.

 

It's not so much the number of air holes as it is the quality of the carb. A new Demon or Edelbrock is more precisely assembled than is an old rebuilt Carter or Motorcraft carburetor.

I had an old 1975 Motorcraft 2bbl in my wagon when I got it and it really went through the fuel till I swapped the carb and manifold for a new Edelbrock 4bbl. No working speedo yet so I can't give you numbers. But, I guarantee that I am getting vastly improved mileage simply from the fact that I have to fill it up much less now.

 

I've seen many guys switch over from a stock 2 barrel to a four barrel and the mileage actually improved.
And....I like the QJ.

 

I know on GM cars that the Quadrajet has smaller primaries than the 2 barrel Rochester carb so if you drive conservatively you'll get better mileage. Any good speadbore carb should give you better mileage than an overworked 2 barrel IMO, but I'm no expert.

I like the Quadrajet too.
The same one has been on my GTO since it rolled off the assembly line.
I had it rebuilt by a Q-Jet expert almost 20 years ago and except for fuel filter changes it hasn't been touched since.
I've seen plenty of GM guys try lots of other brand carbs but to get the car to idle and run good in all conditions they always end up going back to the Quadrajet.

 

Vote #3 for a good Quadrajet. Question for you though. Is the Edelbrock intake set up to accept a square bore or spread bore carb? If it is set up for a square bore are there any reasonably available Pontiac OEM aluminum intakes set up for a spread bore?

 

Thanks for the responses so far guys. It seems most of you are thinking along the same lines as me. KevinVarnes, I am almost positive the edlebrock performer intake has bolt patterns for square and spreadbore carbs. I looked at the performer RPM but is squarebore only. I was also a little concerned about the additional height causeing clearance issues with my hood. I havent really look into any Pontiac oem intakes, might though just to see what else is out there. I got some time though. I dont plan on doin any work till it warms up a lil here in Illinois. Who knows when I change intakes I might swap the cam out as well, seems to have a lifter ticking on cold starts but thats a whole other discussion. I never mentioned either my current MPG is a whole whoppin 11MPG. The old girl never met a gas station she didnt like!!!!

 

i have a performer RPM on mine and it takes both square or spread

 

If the goal is to get the best mileage you can, go with the Edelbrock Performer, which is engineered for maximum low end torque. Definitely use a spread bore 4 barrel. For one, because of the smaller primary bores, the throttle places are further open at cruise, so there is less restriction, which equals better mileage. The bonus is that you also gain maximum power when you need it, and that can come in handy, not to mention saving your life, should you NEED to be gone right now!

 

Well MPG is not the biggest concern with the 455! Meaning that it isnt an engine that sips.....

But remember that depending on which 2 BBL you have will push which 4 BBL. If you have a big Rochester, it might be 500CFM 2BBL. So going to a 600CFM carb will not be that big of a change.

If you want to go to the ease of a 4BBL with great throttle response and decent mileage than go with a 570 Street Avenger.

http://www.summitracing.com/parts/hly-0-80570/overview/

Smaller carbs are better for off idle and part throttle. Bigger carbs are for more top end. This is a great crab and you will enjoy the feel of the SNAPPY throttle of that big 455!!

P.S.

What rear end gears do you have? CAMSHAFT Specs?

 

I have an edelbrock performer on my 455 poncho.i am having my Q-Jet rebuilt and putting it back on.It ran better and less gas usage. The performer was great on my olds but it eats fuel like there is no tomorrow on the poncho!

 

I havent checked the #'s on the stock 2 barrel yet but would be willing to bet it is the 500cfm version. As far as rearend gears, I was lucky enough to find the build sheet and it has a 3.08 gear. The bad thing about the stock rearends in these wagons is there is no gear options available in the aftermarket. As far as the current cam specs, not really sure. Its still the stock cam that came in 455 for these big cars in 72. If I do swap cams I am not lookin at anything to rowdy. It probably should be done though seeing as the stock 40 year old timing set cant be trusted, nylon gears. Thanks again for the responses guys!

 

The smaller primaries on the q-jet give more velocity - perfect for the 455.
While driving a 75 500 CI limo, I had that thing [6000+ lbs - rear air] getting almost 18mpg, and it'd lay you back in the seat!
Had early heads, re-curve and re-jet, and leaded gas! [hollowed out cat!]

 

I have a set of 3:88's that I might be running. I also have a set of 4:10's that I won't be running until I change to an AOD transmission. Right now the car sits on a set of 3:00's.
My engine is pretty built and I was working on the math for CFM that will allow the engine to breath correctly. With the heads and valves and cam combination in the engine as it sits, I'll need a minimum of 960 CFM at WOT. I am going to down size the jets and needles in my carbs and since I have a fairly high stall (3500 RPM) in my converter, I think it'll work out just fine. Plus there is the "WOW!" factor that comes with an older car and a dual quad. Let alone a station wagon!
I can always go back to a single carb later if it isn't working out the way I want it to.
Either way I am going to do it. Mostly because I have always wanted too!
That's what this car stuff is all about. Isn't it?
Going to have to change my screen name to,.. Wait for it!
"Dual Quad Dave!" Ta Dah! (I like it!)

 

I have a Holley 4360 Economaster 450 CFM carb. Supposed to be the best 4 bbl for mileage..

$.02..

Dave