I just bought a 1967 326 2-speed. Its fuel efficiency is worse than expected. Running around 9mpg right now. The 2-speed is not very helpfull eather but a tranny change is not what I am looking for.
The Rochester carburator, which is on it right now, is sucking air through multiple gaps so I will need to replace it.
The guy at the garage, who has been dealing with carbs for over 40 years, suggested to get an Edelbrock Performer Intake Manifold and combine it with a 600cfm Holley with vacuum secondaries. I am driving the car as a daily and the only thing to improve is the fuel efficiency.
EFI is a big step. I'd let your mechanic loose and go with the edelbrock intake and holley carb. A 326 driven modestly should get decent enough gas milage.
I just bought a 1967 326 2-speed. Its fuel efficiency is worse than expected. Running around 9mpg right now. The 2-speed is not very helpfull eather but a tranny change is not what I am looking for.
The Rochester carburator, which is on it right now, is sucking air through multiple gaps so I will need to replace it.
The guy at the garage, who has been dealing with carbs for over 40 years, suggested to get an Edelbrock Performer Intake Manifold and combine it with a 600cfm Holley with vacuum secondaries. I am driving the car as a daily and the only thing to improve is the fuel efficiency.
Any suggestions?
It's only a 326 /w 2-speed. Do you have a 4 bbl or 2 bbl Rochester carb? You don't need a Edelbrock intake. Spend your money on a mild cam, and get the correct and rebuilt QuadraJet carb for the car.
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I agree with Gus and the Dr. I was getting around 10-12 MPG with my '67 if I fully babied her. 8-9 MPH getting on her. The 326 doesn't give you a whole lot of get-up-and go like most people would expect. You could spend $thousands to maybe get one or two MPG better going down the Edelbrock path.
I used to be indecisive. Now I'm not sure. I feel like I am diagonally parked in a parallel universe. 1968 400 convertible (Scarlet) 1976 T/A - 455 LE (No Burt) 1976 T/A New baby, starting full restoration. 1968 350 - 4 speed 'vert - 400 clone (the Beast!) 1968 350 convertible - Wife's car now- 400 clone (Aleutian Blue) (Blue Angel) 2008 Durango - DD 2008 GXP - New one from NH is AWESOME! 2017 Durango Citadel - Modern is nice! HEMI is amazing! 1998 Silverado Z71 - Father-daughter project 1968 400 coupe - R/A clone (Blue Pearl) (sold) 1967 326 convertible - Sold 1980 T/A SE Bandit - Sold
I was struggling with very same thing. This is a good video to see and it helped me. I have a 67 Convertible and the weight of the car is similar to the 66 Chevelle in the video. The Chevelle has a 396 BB, so maybe a small block will get even better mileage. Mind you, in a convertible with the top down there will likely be more drag. Transmission with or without overdrive and final axle ratio will also play a huge role.
Personally, I don't think you'd have to resort to an efi or new tranny. Of course you'd most likely get better mileage with an efi, overdrive transmission and gear change but after the thousands of bucks spent on those items your car would be worth about the same. It's only a 326, probably already has a mild camshaft, and not likely to suck down gas at the rate of a 455 if it's correctly tuned. The two speed tranny is pretty bullet proof and most likely spends a lot of time in high which would be the same as any other non-overdrive tranny. You may have a steep rear gear which would not help.
Just fixing all the air leaks in your carburetor so the inlet air is going through from top to bottom will improve things. Did the 67s come with the air pump and all that smog crap? That's a sure way to get bad mileage.
I can't see replacing the manifold but the Holley 600 vacuum can be tuned to a lean idle and cruise along with a richer power setting. One would also have to tune the spark timing as well. My 428 only got 9MPG when I bought it, I tuned the Edelbrock 800 EPS for a lean idle and cruise and it went up to 14 MPG. That was with a Muncie four speed and a 373 rear gear. After I rebuilt the engine into a 464 cubic inch and installed the TKO 600 I get just under 14 MPG in fourth and between 20-22 MPG in fifth. If I can get 14 with a 428 you should be able to get that with your 326 without EFI, a tranny change, or any engine internals, if the engine components are in good condition, no worn down cam lobes, holes in pistons, burned valves etc.
I don't remember Holley ever being any kind of an economy gas miser carburetor, but they can be tuned circuit by circuit, idle, cruise and power. If you don't feel comfortable enough to rebuild yours, and you don't want to send it to a Rochester rebuilder, then maybe listen to the mechanic you're dealing with. I'd ask him if there is a fitment issue with the Holley on your existing manifold if it's a four barrel manifold.
EFI, while great & reliable, it will take a few brain cells to figure out the tuning. Best left to a professional there, And there is the cost.
Intake change is #1 item to replace. Edlebrock Performer manifold is just an aluminum version of the factory 4 BBL intake. If you can source a 68-72 year 4BBL intake that would work as well.
Holley carbs are great...for dumping lots of fuel in your engine. The Rochester Quadrajet is considered to be the perfect carb to use. Small primaries mean easy on gas, until you open up the secondary's, then your engine comes to life! Don't be scared to rebuild one, they are a very simple carb to build. Cliff Ruggles sells top shelf rebuild kits. He rebuilds them as well, but you would be waiting awhile, he is always backed up on builds.
A Turbo 350 transmission is a direct bolt in and you can convert current shifter to add detent for the extra gear!
OP never did mention if he had a 2bbl Rochester or a 4bbl. Many have assumed it was already a 4bbl (may or may-not be). So it's possible he could get an improvement there by switching types.
Myth 1: A 2bbl gets better fuel economy than a 4bbl. Truth: A properly-sized and correctly tuned 4bbl can show a fuel economy improvement over a 2bbl for the similar reason as mentioned about the Qjet "advantage." If the primaries are smaller on 4bbl than the 2bbl's bore size ,the fuel economy will improve as long as the you don't drive it aggressively. Since the 4bbl has more total flow capacity, as you exceed the power of the 2bbl, you will use more air and fuel. I've put a Holley 450cfm+Edelbrock Performer Intake on a stock Jeep 360 and saw a measurable fuel economy improvement.
Myth 2: You can directly compare carburetor flow ratings Truth: Sort of. For the most part, 2bbls are rated @ 3in-Hg and 4bbls from 1.5 in-Hg. Always be sure what the manufacturer is using as a rated pressure when comparing between brands and number of barrels. If they are different, there are formulas available to convert for direct comparison.
Myth 3: Qjets aren't performance carburetors. Truth: The performance lacking or the infamous "Quadra-bog" reputation is based on poor tuning of the transition circuits, improper carburetor sizing, or a combination. If you have the knowledge and ability to dial in the carb, it will perform well on stock, to moderately-modified engines.
Myth 4: Holley carbs are great...for dumping lots of fuel in your engine. Truth: A properly sized (and type) Holley can be economical. Again it comes back to properly sized and properly tuned. The reason why they get this reputation comes from a number of factors: -Choosing a mechanical secondary (eg. the "double-pumper") or Dominator style carburetors. These perform great on a strip car, and can be used on the street, but they are not an economy carburetor. If you want economy, use a Holley vacuum secondary version. -Picking too high an airflow for the engine. The base calibration is going to be incorrect, along with larger than necessary primaries. Make sure you size it for the correct use. -Lack of tuning or improper tuning. Holleys typically come with a base calibration slightly on the rich side out of the box. Remember, aftermarket ones are not tailored for a particular engine. So a manufacturer has to start with a "typical" high performance application, while erring on the rich side, so customers who just drop them on without tuning don't risk damaging their engine. Too much (to an extent) is safer than too little. -They're put on modified engines. If you added a camshaft, high flow heads, and other mods, of course you'll be using more fuel (to go along with more air). And even if it is the only part you changed, who can resist feeling out those new ponies? -They're often square-bore sized, and there is an advantage there. But most of the rep comes from one or a combination of the above factors.which leads us to...
Myth 5: Holleys only come in Squarebore Truth: Sadly, this is closer to truth than it used to be, but still false. Holley did carry Spreadbore versions of the street and marine models (4175 and 4011 respectively) in various flow ratings up to 850cfm. Meant to be used as a replacement for Qjets, they now only carry the 650cfm street version (Holley discontinued their marine applications all together) new. Occasionally you can find the other sizes available used or rebuilt.
Myth 6: Ignition timing adjustment is independent of carburetor adjustment Truth: Each plays a factor on the other. So be sure to do it as an iterative process, and make sure both are tailored for any hardware changes you've made to the engine (heads, cam, etc.) Get your timing close, tune the carburetor circuits, recheck optimum ignition timing settings, and final tune of the carburetor.
Bottom line: The best carburetor is the one you (or at least your mechanic) truly knows how to tune. If you don't understand the different circuits, how to adjust them, and how to tune an engine for optimum performance you won't get the best from it.
One final note. Many people tend to try setting the mixture screws with the air cleaner off. Great for access, but the air cleaner base and top contribute to preventing air turbulence and improving airflow velocity. I've seen as much as nearly a 1pt air/fuel ratio difference with it off vs. on.
Our new Swiss friend posted and never checked back in to comment on our discussion. Nice info Mike. I’m carb challenged. I buy a Holley and just plop it in and go. And they do seem to run on the rich side
I agree with the bottom line, tuning a carburetor one know and understands is an easier process than learning about and tuning an unfamiliar carb. Not everyone is ready to start drilling and tapping ports in carburetors to improve the cruise or transition phase of operation a smidge, others get right into it.
As far as timing, even which port the vacuum advance is connected to can affect fuel mileage. The vacuum advance was connected to full manifold vacuum right from when the system was developed. Right about the time our cars were being built, concerns about air pollution led to changes in the way cars were tuned. In some cars the vacuum advance was switched over to a stepped port and initial timing was lowered to the point where the fuel air charge was burning as it left the heads, which wasn't good for the cooling system. In order to keep the cars idling with the lower advance the carburetor throttle plate had to be opened more, which in turn used more air-fuel mixture at idle. Some carburetors idled with the butterfly so far opened it was getting into the transition phase of tune. Having the throttle opened so much at idle not only used more fuel but also led to dieseling, run-on, at shut down, which is why some of our cars got the idle stop solenoid. The throttle plates were set closed enough to let the engine shut off without dieseling at idle when the key is off, and the solenoid opened the throttle plate enough to get idle rpm when the key is on.
If the engine has the vacuum advance connected to stepped vacuum, there is no vacuum advance at idle and thus the butterfly has to be opened to let more fuel-air into the engine to maintain idle. Change the vacuum advance connection to a full manifold port and the butterfly can be closed more using less air-fuel at idle and improving overall daily driver gas mileage.
Everyone gave good advice. Rebuild. Keep factory intake. Think about tranny options after you see where that gets you.
BUT..
The biggest factory in gas mileage in an old car is your foot. It isn't like a modern car that changes 20 things when you hit the pedal too hard... Here you just burn lot of dead dinos. I've got a 350 with 2bbl AND A th350 with grocery getter gears. I've tuned on it relentlessly. Here is the deal. IF I drive like Grandma going to church i'll get 14-15 mpg. If I just drive like I usually do... a bit heavy on the right foot... things quickly go south to about 9-10mpg. I love to hear my engine. Even in it's sad single exhauated state. And it costs me at every stop sign. So what... I drive 500 miles a year.