I like Holley DPs w/ mech. secondaries for ease of tuning and the big accelerator pump shot you get when you hit the throttle. Beyond the idling circuits all carbs function under the same basic laws of physics. Mileage is more a product of proper mixture and driving habits than of carb design. I have had many good Qjets. I just can't see spending huge sums of money to overcome characteristics that were a product of design. A good carb that was meant for passenger cars. Bought one of those Edelbrock AFBs once. What a piece of work. Invested in the Street/Strp jet and rod kit and still couldn't get that thing rich enough to run good. Pretty to look at, though.
Time to Take you to School..... I hate to step on any toes but the only benefit of staying with a Q-jet is a few extra dollars in your pocket. You can easily get a Holley to match or out mileage a Q-jet if you know what your doing. All I did was Q-Jets for years but they just don't match a Holley or Demon in any aspect. Sorry to hurt any feelings out there. The new Holleys and Demons with adjustable air bleeds allows for more fine tuning and you can do a few tricks with the power valves to reduce the main jet size to get that mileage bonus your looking for. You should at least be able to match the fuel economy your getting with your Q-Jet. Its bolt on Hp, you just have to decide if you want it.
I have stuck with the Q-Jet so I can retain my original breather on top of the Perfomer intake. You can get more power from the Holley. Never thought it could match the Q in MPG though. Still learning.
I'd love to see documented mileage increase with a Holley switch from a well-tuned qjet. It's hard to beat a qjet with the small primary venturis. I've seen weirder things though.o No:
I can pretty much guarentee that I get much worse milage with my Holley 850 DP. Although it might be more because I can't keep my foot off of the gas pedal then anything else. :grin: I have to ask the question though. Does anyone driving a hopped up 455 actually care about gas milage?? Good gas milage is what my 4 cylinder Toyota pickup is for. The feeling of getting ass ended by a bus when I drop the hammer is what my GS is for. :eek2: :3gears: :laugh:
With the vacuum secondaries on the Qjet, how can it use more fuel than you need when it is set up properly? I have run the Carter AFB type Edelbrock at 800 cfm and the stock 800 cfm Qjet. The seat of my pants says the Qjet was a better carb for a daily driven car that is driven spiritedly (read: I have to polish rubber off my rear quarters occasionally) The Edelbrock AFB type is as simple as simple gets. I love that. Easy to tune, easy to keep in tune, easy to rebuild. I still prefered the Qjet. Why? The Qjet has a center bowl, the AFB has side bowls. I get fuel slosh issues with the AFB type sometimes, and it drives me NUTS. Froma driveability standpoint which says my car must perform and it must also drive me to work, I will take the Qjet any day. I have never run a Holley of any type, but I may be able to borrow an 850 double pumper- It's way too much carb for my buddy's smog motor- late '70s Chrysler 400- and the DP is just collecting dust. Rick- I disagree on one of your points. My Edelbrock Performer 800 with an electric choke is an AFB clone, and it was much cheaper than a new or even rebuilt Qjet, by the tune of almost a hundred bucks cheaper than a rebuilt Buick 800 cfm Qjet. Maybe prices in our areas are different, but around here, no shop would sell me a rebuild for under 500 bucks- no exaggeration. I said "no way" to them, well actually I said something else to them, but then I went out and bought my carb for 400 dollars, just when the electric choke 800 was available.
Chris if you think Q-jets are easy your going to love the Holley 850 DB. Holleys are about the easiest and most tunable carb out, hence why most every racer runs one. If your looking for a fuel economy boost, you will probably be very disapointed. However I'd be willing to bet you will gain some horsepower with the DP over the Q-jet.
I don't think Qjets are easy, though. I think the AFB is easy, but I dislike the design- you misread my post I think, Mike. My mileage is no good anyway, what's losing abother mpg? It will be fun to try out the Holley, at the very least. I need to get the other things sorted out on the engine first. I am waiting on heads and a cam...
I have never seen a AFB with leaky well plugs.............by design there are no plugs on the bottom of the bowl where they could leak. (Q jet primary and secondary well plugs nearly always leak unless you are lucky.) Q jet air horns warp from overtightening rather easy compared to an AFB. Also, Q jet gas filter adapter threads strip and come out rather easily if you are not careful. But I will admit, my cars that had Q-jets did run quite well when everything was right. :bglasses:
Sorry about the misread of your post. I must have picked up the easy part from your description of the AFB. ou: I think you will be impressed with the results when you try out that Holley. :TU:
The AFB can't leak, true. But the design philosophy of the location of the fuel bowls is awful in my opinion. Fuel slosh isn't a fun problem to have. maybe I could address that with the dual fuel line kit? I only feed gas to the passenger side
I have a G-tek at my shop...somewhere amid the rubble and debris of that place. What a mess. I should find it and do some testing before I start swapping things around on the engine. Should be interesting
i had a sbc a while back in a 83 chevy pickup 4 speed and my father did some work to the quad until i could afford a holley this was with 3.73 and the edelbrock rpm heads i had performer intake with an adapter for the qjet truck dynoed 335hp 317tq at tires w/holley never dnoed with qjet holley ran 13.7/102 q jet ran 8.7 1/8 mile @ like 70-73 Holley got 300 miles to the take highway only Qjet got about 330 miles to the take highway only both on the track would get about 6 miles to the gallon ... 1/2 tank would be squashed in 4 maybe 5 runs
OK OK, I know this will stir some vittles in the pot... Years ago (like 1986), I built what I thought was a nasty BBB motor. 455 with KB (I think) 103 cam, specs were .540" lift I & E, with 320 degree duratio I & E. I wanted something special and different. I was at a mud bog and saw Big Foot there and he was running a 540 with 3 Preditors on it. I said then and there that was what I was going to run, but 2 of them. I purchased the Offy dual intake and 2 new Preditors from Summit. Say what you will, but they are about as simple as you can get for carbs. There are 3 adjustments, Idle, Idle air/fuel mixture to 3000 RPM's approx, and an internal metering cam that determines how quick the SINGLE BARRELL - VARIABLE VENTURI will open up. Yep, I was able to say that I had a 2 bbl carb setup. They flow from 600 to 930 CFM, determined by vacuum pull of your motor. That was a wicked nasty responding setup. Not the ole VAAROOOOM revving sound, but an awesome WAAAAPIITTTT sound. I had about 1500 miles on the motor and it would not rev above 3000 RPMs. I thought it was the Preditors, and went down to a single. I lost performance and problem was still there. I went to a Holley 800 double pumper, and lost power and response again, problem still there. I was told that me running Rhoads lifters was a problem becouse I was running non adjustable rocker arms, and went to hi-rev TRW lifters. That time I lost my idle-ability and all the low end torque that I actually DID have, and the revving problem was still there. To end my lengthy story about my thought of Preditor carbs, the final resolution was replacing my NEW Accel Super Coil with a stock coil. Stupid P O S super crap coil secondaries went bad. I will say that Preditors are a very usable and I think streetable carb, but I am not even sure if you can purchase them anymore. That is my $.02 , thanks for letting me pipein... Mike
I ran a 750 AFB on my 350 (1 year old carb.) I also ran a 750 Dbl.Pump Holley. I tuned both of these on a motor dyno and the Holley Gave me 30 more Horsepower. I wonder if anybody has tried a Thermoquad to see how it ran. I tried it once but it was flooding on me after the burnout but boy did it run strong. I never tried it on my new motor though I didn't like the flooding part.
Because of this thread, I went looking for auto parts stores that would sell me a rebuilt 800 cfm Qjet for my engine Imagine my surprise when Auto Palace charged me 170 bucks! Of course, the vacuum diaphragm was broken when it arrived and I refused to accept it, but it was the right carb for less than 200 bucks Qjets ARE cheap again! I have this wild idea of testing my car with the various carbs using my G-tek. I'm not sure if I'm too lazy or not.
Wow,This is a tough one. My personel choice depends on what I am doing with the car. Quadrajet for all around and more top end. The huge secondaries are hard to beat when set up right. So is dependability. Holley for more radical rides and more bottom end out of the hole. Bill
