How much does your vacuum advance help gas mileage?

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69B-Cuda

69B-Cuda

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Ok, I have a 69 Barracuda with a 360. Engine has a Comp cam, Weiand Stealth intake and Edelbrock 750, and newer Mopar electronic ignition(newer being mid 70's) on it, other than that, it is stock. I am getting horrible gas mileage (About 9-10) and decided to put a Holley on it to see if it ran any better and got any better mileage. (long story) anyway, I have an 800CFM Holley that I put on it and it seems to run great (did not drive it though, as I'll need to modify the throttle cable bracket)...

My issue is that this carb does not have a timed vacuum port on it. I believe leaving my vac advance unhooked on the dis till affect my gas mileage while cruising, my question is, does anyone know how much it will affect it?
 
well my first thot is for a very mild 360 800cfm seems like alot... u mite be better off getting a 650 or so vacuum 2nds. also u want ur engine vacuum as high a possible, around 16-20.

unless u are going for power i would go with a dual plane manifold and a smaller carb, it will get ur manifold vacuum up and boost ur low end!
 
There's no possible way to say how much it'll affect the fuel mileage because,

1. Every engine is different and will react differently to different combos. One engine may only loose 1-2 mpg while a similar engine may loose 5 mpg.

2. You changed the carb so that in itself may affect the fuel mileage, especially since it's really big for a mild 360. You need a much smaller carb if fuel mileage is a big concern. Nothing bigger than a 670 Avenger IMO.

Also what Crane cam is it? Mild or wild? Cams affect fuel mileage alot. And if the carb and timing curve isn't tuned to the engine combo it'll really affect the fuel mileage.

Just some things to think about.
 
I'm running a Comp cams 262H in it. I did not leave the 800 on there, I have the Edelbrock 750 on it still. Vacuum is 14-15" at an idle, that's as high as I can get it.

I probably should spend the $$ and have the carb jetted and tuned for the car. (or wait till I build the engine!!)

I would put the Holley on and drive it to check the gas mileage but, I don't want to modify linkage and brackets just to check it and then modify then to go back to the edelbrock.... The Holley I got was off a 340 but, I don't know much about how it was set up... other than jets are 72 on the primary and I think the power valve is a 3....
 
I lost 4 MPG's without a vacuum advance on a stock 360 with 2.76 gears in a B body. I also have to say that once I got the vacuum advance distributor in, it took a few more days before I did the MSD 6 box which added 3 more MPG's.
Other mods to the car added up to 20 mpg's.

It was later confirmed when the MSD took a crap. One day the OE (Junk Yard) distributor took a carp. The pick up inside failed. (Weird huh?) While it was waiting for the part to come in, and needing the car, the OE leanburn was set back in. Instant drop in MPG's.

The vacuum advance is a night and day improvment.

The Holley must have one there someplace. What model?
 
What 750 is on it? They make a couple different ones. You will more than likely find that by tuning the carb your milage will go up. Definately use the vacuum advance. I had the same basic package in a 340 years ago and it even passed CT sniffer testing. I got around 14mpg in an E body with a stick and 3.23s. You should be higher. It's probably lean and needing different step up springs.
 
Edelbrock 1411 5323 is what is on it now. (elec choke). The Holley I have has had the choke horns milled off so, the model # is gone. (at least that is where I am use to it being). It is a vacuum secondary, single pump, dual feed, dual metering block carb. The front metering block has the vacuum port where it should be for the timed vacuum but, the main body and base of the carb do not have the hole right above the throttle plate for the timed vacuum. Instead, the port goes to through the base and it is milled to get full manifold vacuum.

The car also has a 904 and 3.23 gears in the rear with 245 60-14s on it. I"d think I should be getting better mileage as well. I saw the Holley 800 on CL, it was off a 340, and I thought I'd snag it and give it a try to see what happened with mileage and performance.... I may be barking up the wrong tree though.
 
1411 is an economy carb. It's meant for stock engines and is not what you should be running. You can try to get it better butt he non-adjustable passages in the carb may be too far off for your engine package. You want the 1407 which is the same CFM but designed for performance rather than economy.
 
what is adjustable in the 1407 that is not adjustable in the 1411? I thought the difference (other than man/elec choke) was the primary jets and rods?
 
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