CFM & MPG Carburetor myths.....

Fuel and Air Systems

  1. 318willrun

    318willrun Roadkill '80 D150

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    Thought I'd share my latest video.
     
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    • Mtrhead

      Mtrhead Ace of Spades ♠️

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      Great video and thanks for all you do !!!
       
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      • yellow rose

        yellow rose Doctor of Thinkology.

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        1. All true.
        2. That plug, from I could see, looks about bitchin'.
        3. Love the dog.

        I'd just like to remind everyone that 318WR was showing you his 100 MPG carb. That's right, the 4779 Holley 750 dual feed double pumper is a 100 MPG carb.

        All true.

        Very nice video.
         
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        • Hot Metal

          Hot Metal '69 440 Cuda

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          cool vid....explain this though.....
          my 340 with 750DP, using the formula (which I don't use)..340 x max rpm 6200=21080000 div x 3456=609cfm engine requirement
          with an 850DP still 609cfm but car ran almost 2/10nths quicker in 1/4.
          ??
           
        • 318willrun

          318willrun Roadkill '80 D150

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          If I understand you correctly, you are saying your car ran faster with a 850. Not surprising at all, and goes hand in hand with the video in the fact of letting the car decide.
           
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          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            So I guess years and years of engineering by the QJ and TQ guys are all highly educated full of shit.

            I will not dispute that "within a window" ET and performance has some "slopover" and some of that may or may not be individual carb tuning. But an 850 dbp with those great big front barrels vs a small primary anything does not fly with me. And I'm old enough "I was there."
             
          • Hot Metal

            Hot Metal '69 440 Cuda

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            Exactly, forget all the cfm formulas for anything racey...yes faster with 850 than 750 and everyone in the class I ran in said my carb was too big. Even a guy that ran a Rover 3500cc V8 put my 850 on and ran 2/10tnths faster, he couldn't believe it, were talking 215ci but it was astick car and he revved it to the moon.
             
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            • 318willrun

              318willrun Roadkill '80 D150

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              I think Hot Metal was speaking on ET only with his 850 DP. Maybe I missed your point, but nothing in the video said anything against spread bore carbs. I love spread bore carbs. Gas mileage was DP vs VS. And as far as CFM's, the TQ was advertised as 800 cfm's and was on top of 318's from the factory, which helps prove the "cfm" myth I speak of in the video.
               
            • RustyRatRod

              RustyRatRod Weenie idiot loser. FABO Gold Member

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              True, but the TQ is a totally different animal and cannot be compared to anything with mechanical secondaries, much less a double pumper. Since the TQ is a 100% vacuum secondary carburetor, that means its 850 CFM rating is only at maximum flow. If the engine doesn't need 850 CFM, it won't draw it. A better way to say it is, the TQ will flow "up to" 850 CFM as the engine demands it. If the engine demands less, then that's what it gets. I can tune (and have) an 800 TQ to run on a slant six.......and it ran QUITE good. I know I'm preachin to the choir hear, because you know all this.......but maybe some others do not. While I agree with your basic point, I disagree that the TQ comparison helps prove your CFM myth, because it is a totally different style carburetor than you are comparing it to.
               
            • 318willrun

              318willrun Roadkill '80 D150

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              LOL.. I actually put a TQ on a /6 too. Once I put a 750 DP on a /6 just to show I could get it to run as good as the 2bbl on the super six. Fun times. I'm kind of done proven things... lol
               
            • Hot Metal

              Hot Metal '69 440 Cuda

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              I'm only talking about 60 and ET, I tried an 800TQ on the 340, drove ok on the street but was soft compared to my 750DP. On the hit@the track it was rubbish compared, I know the Stocker guys get them to run ok but I didn't have a 5500stall. Any VS carb is not a start line carb, you can modify them till your blue in the face, they won't work as good as a carb with dual pump shots, I even tried a Holley 1050 3bbl, again drove ok on the street and you guessed it@the track....but we all know this.
               
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              • rumblefish360

                rumblefish360 So close, yet so far away

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                Removing the “Track” from the discussion for the moment, 318WR’s mention between the mechanical and vacuum secondary gas mileage issue was stated as zero which I agree with but his fast talking was almost a blurring blaze past the important part of the why.

                IMO, a quick mention that the vacuum secondary can be set to open sooner or later is missing with the vacuum secondary coming in slower and smoother with less fuel used vs the DP which also has squirters that add fuel in that the vacuum secondary doesn’t is just that little edge in fuel savings/consumption.

                Also the old “Your gonna drown the engine with that big carb” should also state that netting the carb properly is key. I’ve been told a zillion times I’ll drown my engine with that carb. I normally LOL & ask how long it will take to ruin the engine with my reply being, well, I’m XX years over due for that!
                LMAO

                The only time I have had trouble getting a large carb to work on a small smog engine is when there is ether no tuning jets or the rest of the system is in deep need to be adjusted.

                As far as a TQ/QJ goes, the small primary helps throttle response and mileage since it is small, only so much air can go through.
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                The formula was wrong when it was written. The formula is wrong today. It's that simple. But the math nuts will never admit to it. But it is fact.

                And the TW and QJ are emissions carbs designed to help with fuel economy.

                The spread bore design is inherently flawed.
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                The TQ is a mechanical secondary carb. Just like the AVS. Just like the Holley double pumper. The AVS is technically a VS carb but the 1850 and 3310 are the only real VS carbs out there.
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                WTH?? No one gonna call me out on my 100 MPG carb comment?

                I must be getting old or people have learned to ignore me better than I thought.
                 
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                • RustyRatRod

                  RustyRatRod Weenie idiot loser. FABO Gold Member

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                  ok.
                   
                • fishmens67

                  fishmens67 Well-Known Member

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                  I'm in the process of testing a 4479 on a Briggs and Stratton. lol
                   
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                  • 66fs

                    66fs Well-Known Member

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                    The TQ and QJ are mechanical secondary 4 barrel carbs with an infinitely adjustable vacuum air valve. Just like an AVS. No need to double pump. People who know how to tune them, can get them .2 faster than a Holley on an automatic car, but there is no difference with a 4 speed car in the quarter mile. On the street, I'd never run a Holley. I want it all! Power and mpg. I have run TQ's on everything from a 273 to a 383. I can get a good QJ to do the same as a TQ, but I prefer the TQ.
                     
                    Last edited: Dec 3, 2019
                  • 512Stroker

                    512Stroker We are all here because we are not all there.

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                    I assume that members have learned to trust your every word as the truth. LOL
                     
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                    • yellow rose

                      yellow rose Doctor of Thinkology.

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                      LOL. Then they all went nuts!!!
                       
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                      • 69conv

                        69conv error 401 FABO Gold Member

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                        Downhill with a tail wind and the engine turned off! Isn't that what you meant?
                         
                      • yellow rose

                        yellow rose Doctor of Thinkology.

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                        LOL. Pretty close.
                         
                      • RustyRatRod

                        RustyRatRod Weenie idiot loser. FABO Gold Member

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                        Actually, we're both wrong regarding the TQ. I've always called it a vacuum secondary, but that's not entirely true. It's not mechanical either. Just like the quadrajet, it's a hybrid. The base plate is mechanical, yes. But the vacuum door controls the whole show. It can be controlled by rate of opening and amount of opening. You could essentially cut the secondary side OFF with the air door adjustment. That's NOT a mechanical secondary. And true, since the secondary throttle plates are not controlled by vacuum, it's not a vacuum secondary, either, but the secondary side is certainly controlled by vacuum, but not actuated by vacuum. The vacuum of the engine itself pulls the air door open. The vacuum of the engine also slows the door through the vacuum brake/choke pulloff, so vacuum plays a huge role in how the secondaries work, UNLIKE a 100% mechanical secondary carburetor like say, a Holley double pumper. THAT is a true mechanical secondary carburetor. The TQ and Q Jet are not.
                         
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                        • yellow rose

                          yellow rose Doctor of Thinkology.

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                          I agree. Was doing some dyno work in 1999 or so with a TQ and you could close the door down so tight you could pull the secondaries all the way open and it still took a bit for the air valve to open.

                          The amazing thing is the TQ would pull the door open. If you do the same thing to a Holley (like the 3310) it won't ever open the secondaries. So if you spring the secondaries on a 3310 (or an 1850...those are the only numbers I know off the top of my head) with the stiffest spring, a 700 HP BBC would not pull the secondaries open. It would not do it.

                          That was some fun and interesting tuning.
                           
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                          • j par

                            j par Well-hung Member

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                            I won't even throw my dual quad tunnel ram on a 318 into this mix.. how did it go a half-second faster at the track...
                             
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