[i82much]

Is it true that if I take, say, a 3310 Holley, install a billet metering block and adjustable air bleeds, go to the ends of the earth tuning it (pvcrs etc.) that it still will not get as good of fuel economy as a properly tuned quadrajet? I plan on keeping a double pumper on the car in the sig, but I am sciencing out a bbc truck as a daily driver. I am considering my carb options for the truck.


My initial intention was to run a 4150/60 style carb on the truck as well. First, I wanted to have reusable parts that fit both carbs. Second, i want to get pretty good at carb tuning, and figured why not just learn one style of carb. However, researching the finer details of holley tuning for economy keeps leading me back to folks suggesting to go with a quadrajet.

As a side note, the truck currently has a carter Afb. if anybody wants to throw out a vote for the carter as a good daily driver, fuel economy carb if tuned correctly, i am all ears.

Fwiw, I realize a bbc truck is not the best choice for fuel economy. This is really more about learning and having fun trying to put together a true all-weather daily driver, not trying to build a prius.

[shaker455]

The primary side of the Qjet is much smaller than the 3310 so it's like running on a 2bbl carb. also the booster design is more detailed & it will atomize fuel better than a straight leg Holley booster design of a standard 3310.

Holley does have much better booster in other model that are more efficient like the annular for example.

I've found once you go down the performance road a qjet will consume about the same as an equally tuned Holley.

[i82much]

Yeah i was actually thinking of a street avenger or quick fuel slayer instead of a 3310. I am wondering whether if i go down the road of optimizing pvcrs, air bleeds and ifrs whether i can approach qjet fuel economy on a stock type 400 cid driver.

[Schurkey]

Holley power valve is "on" or "off". Power enrichment therefore is "on" or "off".

Q-jet metering rods have tapers that allow full-rich, full-lean, or most anywhere in-between, within the limits of the chosen metering rods and power piston system.

The BIG deal with Holleys is that most folks use the jets to correct the full-power fuel curve, which makes the part-throttle fueling way rich.

[Sun Tuned]

I bought an 86 454 dually like that... Still got it.
Some genius pitched the qjet in lieu of a 600 egghead carb.
I pulled it and put an 800 qjet on it.
T400
4:10 axle

15 mpg solid if you drive under 60 on highway. No problem at all.

[Sun Tuned]

I've fooled around with ton trucks for 25 years. Had all of em driven all of em, can tell ya just about anything you likely wanna know bout em, gas or diesel.

Now I'm sure Jeff can get the fuel mileage out of a Holley, cliff cando a qjet, and Jon hardgrove can get ya a carter....

But I'm gonna tell ya that qjet is where it's at on that bbc.

The primary side of that carb far exceeds anything you could possibly bolt to the top of that engine.

Throw the afb clone on the ebay pile.

[Half-Inch Stud]

Originally Posted by Sun Tuned

I've fooled around with ton trucks for 25 years. Had all of em driven all of em, can tell ya just about anything you likely wanna know bout em, gas or diesel.

Now I'm sure Jeff can get the fuel mileage out of a Holley, cliff cando a qjet, and Jon hardgrove can get ya a carter....

But I'm gonna tell ya that qjet is where it's at on that bbc. The primary side of that carb far exceeds anything you could possibly bolt to the top of that engine.

Throw the afb clone on the ebay pile.

Well said. So ah what truck you recommend that will get 15 MPG while towing an RV? Curious to know if any of them can do it?

[Sun Tuned]

How heavy of an rv?

My everyday personal truck is an f450 6.0 diesel 5spd torqshift
w a 4:30 screw.

A lot of em will depending on weight of the rv.

[Sun Tuned]

Pm me his,
That way we don't hijack this thread.

[shaker455]

Originally Posted by i82much

Yeah i was actually thinking of a street avenger or quick fuel slayer instead of a 3310. I am wondering whether if i go down the road of optimizing pvcrs, air bleeds and ifrs whether i can approach qjet fuel economy on a stock type 400 cid driver.

I would try a Qjet because the as I said the primary is smaller.

And with a wideband tune both will work well...we build & tune all carbs here..no bias

[Bruce Meyer]

Originally Posted by shaker455

I would try a Qjet because the as I said the primary is smaller.

And with a wideband tune both will work well...we build & tune all carbs here..no bias

Have you ever tried a 2 stage Power valve in a Holley? Ive heard some people getting pretty good gas mileage with one by putting smaller main jets in and using a 2 stage PV.

[Cliff R]

I could literally put up 100 pages here with direct examples of how this deal really works. Instead, I'll simply say that no matter what carburetor you choose to power the BBC truck, tuning it exactly for the application will yield pretty decent results, power, fuel economy, etc.

Having a good working carburetor goes a bit further than just fuel economy, you should have a working choke, fast idle, dual plane intake, moderate compression ratio, and very well chosen cam to get the very best mile per gallon, power, and driveability from the truck. I would also have an open exhaust crossover in the intake, unless you live on or near the equator, then it really wouldn't be needed.

As far as this specific topic goes, I've actually causes the demise of quite a few TBI set-ups on Chevy/GMC BBC and SBC truck applications by swapping them over to q-jets, outrunning them at every rpm and getting considerably improved fuel economy as an end result.

I'm probably not as brand specific as most folks think. I've ran the gauntlet with Holley's, Demons, Carters, and Thermoquads. The Thermoquad and Q-jet are ALWAYS going to be more efficient at the end of any tuning efforts. It's just a better design on the primary side, and not all about having smaller primary bores. The venturi areas are super-sensitive to throttle position and pressure differential above and below the throttle plates and venturi areas. They not only pull in fuel much earlier than a large bore carburetor, they break it up into a much finer mixture, usually referred to as atomization. Later q-jets also use a fine metering system providing the user/tuner with full control of part throttle A/F without taking the carb apart or changing any parts. That deal alone will trump any other brand.

Qjets are also very reliable in long term use. No gaskets below the fuel level to leak, fuel bowl/float in the center, jets on the bottom, and excellent bowl venting.

If I were setting up a BBC truck engine it would get a q-jet, it would be a 1979 or later side inlet Chevy style with the single main airbleed design. These are very well made units, taking all the good points and upgrades from early designs and putting them into one package. They all convert and many came with electric chokes, relatively compact design, and over 800cfm airflow if/when needed. It's going to have a PCV port, power brake port, vacuum port for the distributor, and the correct location/geometry to hook up the throttle cable and return spring(s). Below is a picture of a finished unit. I've built several thousand of them since going full time here over 11 years ago. Can't even remember having an issue with one of these, or getting one back for any reason. They just flat work, while being super efficient, easy to tune, dead solid reliable in long term service, and the best choice for what you are doing....IMHO.....Cliff

[Lee]

To REALLY "tune" any of the carbs, you need to have a selection of the tunable parts.

For Q-jets you need primary jets & metering rods and secondary metering rods. It wouldn't hurt to have different hangers and pumps as well. Good luck getting a nice selection of those without spending a small fortune. APT and secondary air-door tension are freebie tuning items. [Cliff, want a new business opportunity?? Put together a Q-jet "tuning" pack with a variety of primary jets/rods and secondary rods]

Carter/Edelbrock you need primary rods, springs, and selection of jets to get started, then they have their squirters. These are easier to obtain than Q-jet, but far from cheap. I got tuning parts for these off of ebay, buying stuff from people who got tired trying to tune these things.

For Holley, you need a jet set (fairly cheap and easy to get) and an air-bleed selection (not too expensive or hard to find). A few different squirters will aid in tuning.

I've played with all 3, and have owned/daily-driven all 3, and have parts to tune all 3. Your results may vary, but here is what I've found:
- My best performances have been with a Holley, but Q's have come close
- Best MPG is with a Q, but a well tuned Holley comes close
- Carter/Edelbrock, I really don't know why anyone buys these things. The only carb I've messed with that seems to never hold a steady AFR, and the only one that gives different AFR readings on the track than on the dyno.
- If I had a Q-jet that ran really well for a motor, I'd NEVER get rid of it. I would caress it, talk sweet to it, and enjoy it. But I'd never spend money to buy a 40 year old carb and HOPE that it would work fine.
- Get a good wide-band, KEEP A LOG OF ALL YOUR CHANGES, and don't be afraid to play around.

[george kujanski]

Lee, any wideband you recommend? I'm ready.

George

[Lee]

George, I bought an Innovate about 7 years ago. It has worked great for me. I believe there are some other brands on the market now, but I haven't used them.

I like driving around and watching it, seeing what the AFR does in different situations.

[hurryinhoosier62]

Originally Posted by Half-Inch Stud

Well said. So ah what truck you recommend that will get 15 MPG while towing an RV? Curious to know if any of them can do it?

2 valve 6BT Cummins in an earlier Ram 2500.

[i82much]

So with the smaller primaries, does that make a spreadbore more susceptible to icing? Recalling some of the info posted in the previous thread, it seems like it might. Maybe not a coincidence that GM developed mechanisms like the heat passage under the carb base and the thermostatic air cleaner shortly after the quadrajet became their main carburetor?

[carbking]

Steve - the discussion about the Q-Jet and the TQ both implicitly refer to the spread-bore design, and indeed, they work well for both performance and economy on a daily driver. Holley also once made a spread-bore, but I am unfamiliar with it. As to carburetor icing: much more an issue with an inline engine that with a V-8. The heat passages under the carburetor improve initial start-up driveability. After I junked the electric choke carb on my GTO with the aluminum 455 H.O. intake and no heat crossover, I still have no icing problem at any temp from zero up here in Missouri. Current carb is an 850 CFM Carter TQ WITH MANUAL CHOKE! The use of the manual choke overcame the cold driveability issue that I had with no heat and the electric choke.

H.I.S. - I don't pull an RV, but my shop truck made by a company that rhymes with Cord and a 390 with two genuine Carter 625 AFB carbs will get 15 pulling a 16 foot trailer with two John Deere model 420 lawn and garden tractors. I will confess to spending quite a bit of time on the carbs. By the way, I use solid linkage, so both carbs are working all of the time.

Jon.

[i82much]

Originally Posted by carbking

Steve - the discussion about the Q-Jet and the TQ both implicitly refer to the spread-bore design, and indeed, they work well for both performance and economy on a daily driver. Holley also once made a spread-bore, but I am unfamiliar with it. As to carburetor icing: much more an issue with an inline engine that with a V-8. The heat passages under the carburetor improve initial start-up driveability. After I junked the electric choke carb on my GTO with the aluminum 455 H.O. intake and no heat crossover, I still have no icing problem at any temp from zero up here in Missouri. Current carb is an 850 CFM Carter TQ WITH MANUAL CHOKE! The use of the manual choke overcame the cold driveability issue that I had with no heat and the electric choke.

H.I.S. - I don't pull an RV, but my shop truck made by a company that rhymes with Cord and a 390 with two genuine Carter 625 AFB carbs will get 15 pulling a 16 foot trailer with two John Deere model 420 lawn and garden tractors. I will confess to spending quite a bit of time on the carbs. By the way, I use solid linkage, so both carbs are working all of the time.

Jon.

Thanks Jon. It is all academic at the moment since it is pretty dry in Spokane. But you would be amazed at how much moisture NE WA and north Idaho see in the fall. I really have learned a ton about carburetors and carb heat systems over the past few weeks in this thread and others.

Now i need to start thinking hard about whether my truck is going to see some steep enough terrain that I will need to be concerned about carb mods for offroading. I wouldn't have mentioned that in the street forum, but since this thread has moved I suppose it is
fair game.

[Half-Inch Stud]

Originally Posted by hurryinhoosier62

2 valve 6BT Cummins in an earlier Ram 2500.

hope sun-tuned concurs.

So, no ford F150, no GM 1500. I cannot afford SUV Excursions.