Technical Improving Fuel Mileage

Yes, open plenum, single plane. It's quite tall and the runners are a big "X" coming off of the open plenum. There is no connection of the plenum and runners to the portion of the casting that closes the lifter galley, hence the "Air Gap" name. It's absolutely intended to be used on a high RPM race motor. Why it was put on a street intended stock (to my knowledge) 305 by a previous owner is anyone's guess. I'm thinking it might have been for "male enhancement", if you get my drift.

I think rather spending a lot of time diagnosing what I have, I'm going to switch back to a stock. 305 aluminum Rochester Q-jet intake, which I happen to have, and go from there. I'm going to a swap meet this weekend and perhaps I'll come across a good looking Quadrajet. As it usually goes though when I'm looking for something I don't see it but when I'm not things seem to be on every swap meet table.

Lynn

 

Maybe someone with little knowledge coupled with a cheap price. I once bought a '63 Fairlane V8 stick car because the young kid couldn't make it run after he 'souped it up'. He thought he had a 289, so put dual fours on it, it was dead stock otherwise. Turned out it was a 221... It would start and somewhat idle, but as soon as you opened the throttle it would stumble and die. God only knows what he was thinking. Took a long time to sell that intake...

 

If it had a "slush box" [aka Fordomatic] behind it , it wouldn't pull the skin off custard.

I've had several of these last century.
The hot setup was a 4 speed trans from an English Mk4 Zephyr/Zodiac [both RHD]
The low 1st gear helped the wheezing 221 off the line.

These things were lightweight at 3000 lbs and would cruise nicely at the speed limit netting approx 25mpg [imp gal]


Later on in my younger "wheelin'n'dealin" years I realized the 221 was worth more than a 260 or 289 so I would swap them for bigger engines [plus cash my way].
In NZ we have a dirt track stock car cl*** where the engine was limited to 241 inches . A 30 over 221 with a "drop-in" 302 crank and rods came out at 235"
Chevy engines needed sleeving back or de-stroking [which cost $$] so the ford was a valuable commodity.

@lake_harley the biggest contributor to bad mileage is your right foot.
But that cannot be improved with a single plane intake. You will need to coax it past the flat spot constantly.
Throw a dual plane intake and SMALL spread bore carb on it. And get a cam that falls flat on it's face at 4500 rpm. [something around 204° duration max]
The 305 is quite a good driveable engine if you don't expect miracles from it [it has small capacity and long stroke]

 

From around 1992 and later Holley carbs had a power valve blowout protection circuit built in. Although they’re a little pricey a wideband sensor is a fantastic tuning tool. Could be an option?

 

I had the secondaries coming in a little later which helped with economy, but isn't it fun when you do get them cracked open. Quadrajets are magnificent carbs when you find someone who understands how to set them up.

 

GOOD CHOICE!

Try to find a Q-Jet from the same (or close) year 305; don't settle for just any Q-Jet.

The Q-Jet is a GREAT carburetor, but Rochester made 100's of different ones. Using the wrong Q-Jet might not give you any improvement. Using the correct original (or one that is close) Q-Jet should net some serious fuel economy gains.

IF you are running an automatic transmission, try to set up the original choke mechanism with your Q-Jet.

One of the 3 absolute DUMBEST things I have ever done in 67 years of working on carburetors was to replace a hot air choke on the wife's car with automatic transmission with an electric choke because I had one available and I was busy. I then found I was not so busy as to find time to fix the hot air choke.

Jon

 

I second the dual plane intake and SMALL spread bore carb suggested by @Kerrynzl. Saw that combo work decades ago on a late model Chevy, 305 4spd. What a wake up.

 

Do you have vacuum advance?

My OT hotrod is 2525lbs, I thought it ran great on both the street and the strip with fixed timing @ 34* (10* start retard). Engine is a low compression carbureted 355 w/ flat tops .045" in the hole, 251/261 @ .050" 114lsa solid roller, 342cfm Brodix heads, Strip Dominator single plane. Not a combo one would typically build with efficiency in mind, but this low compression 355 spins to 8600 on the track and got 20mpg on the highway with no overdrive. It also burns cheap 87 octane fuel. I had been driving this car with this style engine with a great big smile on my face since around 2008, didn't think it could get much better!

Then late last summer, I began to wonder if my 34* of total timing was leaving something on the table. Using my nitrous retard box, I started experimenting with cruise timing. The box uses plug-in chips, so flipping a switch allows instant comparisons between two fixed timing settings while driving down the highway. The seat of the pants and vacuum gauge difference between cruising at 34* vs 49* turned out to be a real eye opener for me.

In this case, coolant temp drops 5* down the highway in mid 90's weather with the extra 15* of timing. Also, you can literally be holding a steady 2400rpm in high gear @ 34*, flip the switch to add another 15*, and then have to back off the throttle a bit to maintain 2400rpm. The crankcase vacuum gauge also climbs from 16"Hg to 18"Hg @ 2400 fairly quickly, likely due to less throttle opening (no vacuum pump, a pcv valve draws the crankcase vacuum).

As a side note I found out the lowest rpm the digital tach on my shift lite can read is 390rpm, as the engine can now idle below that!

Grant