Carburetor

[MikeandCheryl]

Certainly from the current news regarding fuel prices, the 350 Chevrolet may be on it's way out, however I'm interested in knowing whether better fuel mileage is possible with a relic engine. I've a Rochester Qjet - not sure what is being used to use less of the precious juice. Ideas?
Sorry, this would be on a stock 350 rebuilt to standard specifications. no racer here.

[Steeveedee]

Holley Sniper runs about $1k, maybe more, depending on what you do with it. Maybe someone can chime in with how much their mileage improved after installation. It'd better be a lot, to make it worthwhile.

[geezer#99]

In Canada you need to double that price Steve.

The quadrajet is your best choice for mileage along with a sharp tune.
You’re basically driving a big barn door down the road.

[Palf70Step]

What rear gears is the truck? For MPG, you would probably be better off going to a 3:08 or 2.73 gear than spending that much on an EFI throttle-body. Far as carb, I have always found a quadrajet best for MPG, if they tuned right. I never quite figured them out which is why I have a holley or Edelbrock.

[Grumpy old man]

The quadra jet was one of the best carbs ever made and it really can be a gas saver with it's small primaries. But you have to keep your foot out of the huge secondaries .

[Caddylackn]

You are not going to do much better than a tuned in quadrajet for gas mileage. The small primaries make for better fuel atomization at cruise. Rebuild yours if you need to, don't buy a rebuilt one. Your factree carb is jetted and calibrated for your motor.

For gas mileage, I would swap to a factree HEI, with the mechanical advance recurved to get full advance in under 3,000 rpms, and an adjustable vacuum advance to eliminate pinging at partial throttle. Use 3.07 or 2.73 gearing.

The other tip is aerodynamics. Remove the large dumbo mirrors if you have them and replace with smaller mirrors. A bed cover will give you better mpg. Some on here have added a suburban lower front spoiler, which doesn't look bad on our trucks. High teens mpg is possible with our trucks with a stock 350. Drive sensibly.

If you have higher gearing and a turbo 350, consider swapping to a 700r4 tranny.
Tires make a big difference. Mudders and aggressive off road treads give poor mpg. If your tires are loud at highway speeds, then they are sucking mpg from the higher rolling resistance.

[GASoline71]

I hate Q-jets, but if I was building a stockish engine for MPG's only, I'd probably run one and tune it accordingly.

You don't have to have an LS and a fancy FI system to get decent mileage. A 350 and a properly tuned engine and ignition system, with an OD transmission, and butt gears to match your combo should be easy to do.

Gary

[52napco]

Send your Quadrajets to Bob Stone for restoration. My 1972 K10 with 3.73 gears and 33-10.50 BFG ATs gets in the 14 mpg range on the highway cruising 60-65..my TBI 72
K5 Blazer gets about the same..The Chinese made sniper and fitech fuel injection kits are hit or miss..some run great while others suck..I prefer GM TBI kits due to parts availability and ease of operation..trying buying a TPS sensor at AutoZone for a Fitech lol.

[chevmn]

Back in the early 80s my wife drove a 73 Chevelle, with a 400 small block. With a 450 cfm Holley spreadbore q-jet replacement, headers, 3:31 gear, TH350, the heavy car got right at 24 MPG avg, and had decent low end power. Doubt they even make that carb, or could find one today, but I was impressed with the combination. I am with others, and if a q-jet is right, it is hard to beat overall. First thing I do is check that primary throttle shaft is tight in the base, put a brass float (stock floats soak up fuel and sink), and the main well plugs are not leaking fuel, as they are famous for that. But, these trucks are not aerodynamic, and fairly heavy so don't expect too much, but the 350's are far from on the way out. Too many still out there, and they survived the supposed fuel shortages, and $4 a gallon prices from late 2000's. 350's with q-jet was probably the most popular combos to date. I have a box full of q-jets others have tossed, and once in a while find the need for a part. Most simply do not know how to repair or tune them.

[GASoline71]

Originally Posted by chevmn

Back in the early 80s my wife drove a 73 Chevelle, with a 400 small block. With a 450 cfm Holley spreadbore q-jet replacement, headers, 3:31 gear, TH350, the heavy car got right at 24 MPG avg, and had decent low end power. Doubt they even make that carb, or could find one today, but I was impressed with the combination. I am with others, and if a q-jet is right, it is hard to beat overall. First thing I do is check that primary throttle shaft is tight in the base, put a brass float (stock floats soak up fuel and sink), and the main well plugs are not leaking fuel, as they are famous for that. But, these trucks are not aerodynamic, and fairly heavy so don't expect too much, but the 350's are far from on the way out. Too many still out there, and they survived the supposed fuel shortages, and $4 a gallon prices from late 2000's. 350's with q-jet was probably the most popular combos to date. I have a box full of q-jets others have tossed, and once in a while find the need for a part. Most simply do not know how to repair or tune them.

The ol' Holley 450 "Economizer". Had one of those on a 350 with stock cast iron spread-bore intake in a '71 El Camino. I used to drive it from California and back to Washington often, and was always impressed with the mileage I got. I believe I still have that carb in a box in my rafters somewhere.

Gary

[body bolt]

Originally Posted by chevmn

Back in the early 80s my wife drove a 73 Chevelle, with a 400 small block. With a 450 cfm Holley spreadbore q-jet replacement, headers, 3:31 gear, TH350, the heavy car got right at 24 MPG avg, and had decent low end power. Doubt they even make that carb, or could find one today, but I was impressed with the combination..

I think your talking about the Holley 4360 Economaster. I have one on my truck after removing the leaky stock Quadrajet for repair. It does get better gas mileage and pulls way better at the low end. You can still find them. Look for list 7454, 7455, 7456. Those are all divorced choke.

[chevmn]

Originally Posted by body bolt

I think your talking about the Holley 4360 Economaster. I have one on my truck after removing the leaky stock Quadrajet for repair. It does get better gas mileage and pulls way better at the low end. You can still find them. Look for list 7454, 7455, 7456. Those are all divorced choke.

That jogged my memory, I could not recall details, and it went with the car when I sold it. Somewhere I have the Super Chevy magazine with the articles on the Doug Marion 70 Monte Carlo econoperformer project that he had. That was the inspiration for what I did on the Chevelle. An overdrive would likely have put the Chevelle into upper 20's MPG range, yet good low end power. I wondered how it would have done with 2:73 gearing, but I know it would have lost a ton on bottom end. In those days I was raising a family, and limited funds for toys, but ironically the whole time I had kids I never owned a 4 door vehicle. 2 door Chevelles and Chevrolet pickups (and they were not extended cab or 4 door trucks). Fast forward to my 2011 Silverado 4x4, and it is so bloated it can only average 19 with a 6 speed, and 5.3. You can tell I am not impressed (yeah, I disabled the worthless AFM -- that made zero difference in fuel mileage, and I actually believe it does slightly better with it disabled).

[MikeandCheryl]

Well i am pleased with the results of the question and the assistance from all. It's nice to know that this carb isn't another piece of the puzzle that needs to be renewed. So far lots of other things will be needed and I'm certainly not yet at the new engine/carb/running stage, but one day perhaps. My 'I can use this once i fix it' pile is pretty skinny. My 'I need a new one of these' pile is bigger. So thanks again. No idea of the gearing as yet. I haven't cut the U bolts to release either pumpkin, but it's coming.

I am trying to steer away from the higher tech advancements as well. The truck has a later model HEI installed and there are power brakes and steering, but that's about the most modern stuff i can see. It'll stay simple (like me). Just thinking of Holley, or carter, or whatever other carbs are used.

And thanks for the PM geezer#99 - I couldn't seem to reply through the message for some reason. I'll touch base with you sometime I'm sure.

[cwcarpenter98]

I've been quite pleased with the Quadrajet in my 63. It has an electric choke on it which has been real nice. Last mpg check I did was around 16 mpg on mostly interstate driving with a 283, 3.73 gears, a .7 overdrive, and 30" tires

[my67c20]

I have installed the Sniper system on my 383 stroker about a year ago and the master kit was $1420, not including all the extra bits needed for my OCD. My fuel mileage has gone down, cause now my little stroker motor is way more responsive and no I can drive it like I stole it. However, I did the upgrade cause I was tired of dealing with fuel boiling issues, leaky gaskets and other fun stuff that the desert heat will do.

[body bolt]

Originally Posted by my67c20

I did the upgrade cause I was tired of dealing with fuel boiling issues, leaky gaskets and other fun stuff that the desert heat will do.

This is my problem as well even with the Holley 4360. One of these days I intend to switch to a Sniper.

[Accelo]

I agree with Geezer "You’re basically driving a big barn door down the road".
It's easy to forget all the incremental changes that have been made over the years to increase mileage.
Things than are gone;
90W in the transmission or differentials.
Non-lock up transmissions
External radio antennas
Flat grills
Exposed undersides
Air conditioners that require 3lbs of refrigerant
Steel pumps of any kind, p/s, transmission or air conditioners
Huge rear-view mirrors
Three speed transmissions

The new directed injected motors are more efficient than any SBC every thought of being. Add displacement on demand and light weight components and you have a truck very different than the fifty year old trucks we drive. Did I forget to mention the new oils?

Yes, a good tune will help. But fewer and fewer are daily driven. However, I did see one at the gas pump today. I filled up my Silverado to the tune of $114. He must have to four gallons of fuel into his 1969 or 70 Chevy truck he was driving as it only took a minute to fill.
Many of us drive our "toy trucks" and don't care about the fuel price as they don't go much further than the next care show.
Give it your best and hopefully you can get mileage into the teens. Driving like you have a Farmers Insurance tattle-tale installed in the vehicle.
Or drive it like a rented mule and have fun.
Whichever you can afford or enjoy.
Cheers

[HO455]

The OP hinted that the engine was be rebuilt. If so then a thorough blueprinting of the assembled components will be beneficial. A thoughtful selection of parts (Like modern low tension piston rings) with the intent of maximizing engine efficiency at low RPMS will pay for itself in the long run.

We must also accept the fact that cylinder head technology installed on our trucks was not very efficient even back in the day. That being accepted then it makes sense to go to a more modern cylinder head. Vortex heads or one of the numerous aftermarket heads will have more efficient combustion.

Modifications that improve movement of air into and out of the cylinder head will help as long as port velocities are maintained in the target RPM range. The Vortex heads were engineered with this in mind. They were never expected to be a high RPM performance cylinder head.

Having a properly curved distributor with a blueprinted vacuum advance helps ensures you don't waste any fuel due to late combustion events.

Then let's not forget physics. It takes 14 parts of air to one part fuel (For arguments sake.) to have good combustion. Going to a smaller cubic inch engine will help reduce fuel consumption as long as the engine isn't asked to run too hard.

And while on the subject of physics driving at 55 instead of 60 saves fuel as the power required to push an object through the atmosphere increases exponentially as speed increases.

Thanks for startng this great thread.

[HO455]

I just came across this article and it seems to fit in with the discussion. Its descriptions and specifications are good clues to make gains in mpg.

https://www.hemmings.com/stories/201...npike-cruisers

[truckster]

Tune the engine and the Quadrajet. Keep your tires inflated and don't carry unnecessary weight. Keep your foot out of it. That's about a good as it's going to get.

[MikeandCheryl]

Thanks, HO455. A great article and an excellent post on modern improvements. While this truck will return to 'active' status, there will be limitations to it's real world duties. I like the idea of introducing at least some modern technology into the engine and will speak with my engine guy about what's possible. The engine has an HEI (I think the entire drive train came from a 78 model - al least the 4speed stuff), but i do not know yet what improvements there can be made. All interesting reads, so one has a few choices to make down the road. Original vs. stock. Improved vs archaic. Budget vs deep pockets. The 4 speed is the elephant in the room. Perhaps an entire new 4x4 drive train from a more modern vehicle is 'the way'. Still looking, reading, studying. Thanks all.

[MARKDTN]

I like EFI conversions on old cars. Here is my real-world example. I have an '83 K20. I have had it for 30 years. 350/700R4/3.42 gears. When I got it I was getting 14.5mpg with the Qjet in mixed city driving. I put over 100K miles on it that way. I had single exhaust no cats, then duals no cats, then single with factory cat, and finally dual exhaust with hi-flow cats. None of that made any difference in mileage. A cam lobe went down and I swapped in a bone stock 350 Tuned Port engine (aluminum heads) from a '90 Corvette. With no changes I now get over 17 mpg in mixed driving and have gotten over 20 with pure interstate. Driveability is much improved. It starts immediately. Towing is much better. Used to be you really had to get into the gas to maintain speed on a hill, but now you just press a little. I have done several square body TPI conversions and one in a '72 swb. For that one I used an '85 S10 Blazer tank-which was TBI fuel injected-and a in tank IROC pump. (For the square bodies I use '87 tanks with that pump, but you can't do that on a 67-72). I like TPI over anything aftermarket for a stock engine. Parts are available at any auto parts store in the country as TPI was in Corvette, Camaro, and Trans-Am. Price wise you are probably $200-250 for a nice TPI unit and distributor, $200 for a set of injectors, $250-300 for a harness, $30 for an ECM, $150 for a PROM, and $150 for a fuel tank and pump. You could use a stock fuel tank with return and use an external pump (like '88 F150) which I have done on another conversion. Anyway, another option.

[jimijam00]

There are three things you can do and expect a quick ROI. First, overinflate your tires. Second, keep the RPMs as low as possible. And third, place an egg under your gas pedal.

Other than that, just drive the hell out it and enjoy!