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#1 |
Registered User
Join Date: Jul 2021
Location: Nanaimo, BC CANADA
Posts: 57
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Carburetor
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. |
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#2 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,373
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Re: Carburetor
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.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#3 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,594
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Re: Carburetor
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. |
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#4 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,844
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Re: Carburetor
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.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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#5 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Carburetor
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 .
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![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#6 |
Registered User
Join Date: Jun 2016
Location: Bremerton, WA
Posts: 171
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Re: Carburetor
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.
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1969 Custom Camper C20; Factree Air, 350/TH400/Dana 70U with C30 wheel cylinders, Disk brakes, H4 conversion, headlight relay mod, 3G 135 amp alternator. 7500 GVW |
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#7 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,936
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Re: Carburetor
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
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
Quote:
Last edited by GASoline71; 06-08-2022 at 12:05 PM. |
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#8 |
Registered User
Join Date: Jun 2014
Location: upstate sc
Posts: 2,095
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Re: Carburetor
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. Last edited by 52napco; 06-09-2022 at 06:29 AM. |
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#9 |
Senior Member
![]() Join Date: Dec 2017
Location: Central MO
Posts: 894
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Re: Carburetor
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.
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#10 | |||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,936
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Re: Carburetor
Quote:
![]() Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
Quote:
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#11 | |
Registered User
Join Date: Oct 2020
Location: Albuquerque, New Mexico
Posts: 474
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Re: Carburetor
Quote:
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#12 | |
Senior Member
![]() Join Date: Dec 2017
Location: Central MO
Posts: 894
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Re: Carburetor
Quote:
Last edited by chevmn; 06-10-2022 at 02:13 PM. |
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#13 |
Registered User
Join Date: Jul 2021
Location: Nanaimo, BC CANADA
Posts: 57
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Re: Carburetor
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. Last edited by MikeandCheryl; 06-08-2022 at 09:29 PM. |
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#14 |
Senior Member
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Location: Hickory Flat, GA
Posts: 4,458
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Re: Carburetor
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
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Christian Carpenter 1963 C10 - Frankentruck 283, Muncie 3 speed with overdrive Overdrive wiring here1963-ish truck bed trailer - Half-Wit 1981 C10 - Penny 305, th350 --> Soon to be 350, Saginaw 4 speed 1995 Dodge Dakota Sport "I'll put it simple: if you're going hard enough left, you'll find yourself turning right." - Doc Hudson |
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#15 |
Registered User
Join Date: Jun 2002
Location: Tucson AZ by way of WI & CA
Posts: 509
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Re: Carburetor
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.
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#16 |
Registered User
Join Date: Oct 2020
Location: Albuquerque, New Mexico
Posts: 474
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Re: Carburetor
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#17 |
Senior Member
![]() Join Date: Mar 2015
Location: washington
Posts: 2,233
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Re: Carburetor
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 |
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#18 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,086
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Re: Carburetor
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.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#19 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,086
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Re: Carburetor
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
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#20 |
Senior Member
![]() Join Date: Jan 2001
Location: Orem, Utah
Posts: 7,901
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Re: Carburetor
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.
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I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson |
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#21 |
Registered User
Join Date: Jul 2021
Location: Nanaimo, BC CANADA
Posts: 57
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Re: Carburetor
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.
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#22 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 2,148
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Re: Carburetor
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.
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'83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project |
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#23 |
Registered User
Join Date: Apr 2009
Location: PNW
Posts: 553
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Re: Carburetor
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! |
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