Holley or Thermoquad??

Small Block Mopar Engine

  1. AlaskaJeff

    AlaskaJeff Well-Known Member

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    Engine.jpg So on my 70 Duster, from what I've found out, has the engine and drivetrain (360/727/ 8 3/4" rear end) out of a 74 Duster. I currently have an older Holley 750 double pumper carb & LD340 Edelbrock dual plane intake on the motor. What little I was able to drive it before I put it up, the carb seemed to be doing well with no hesitation, stumbling, or any other quirks.
    I was thinking that it would be fitting to find a 74 Thermoquad to put back on it for nostalgia and overall Moparness. Truth be told I've never been a fan of Holley carbs on Mopar engines anyway. Would it be worth switching? or "If it aint broke don't fix it"
     
  2. Keven S. Clickner

    Keven S. Clickner FABO Gold Member FABO Gold Member

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    My .02ct . I'd have to go with the Holley. Based solely on Parts availability and tunability. That is if you're looking for a performance piece. I like the Thermoquads as well as the AVS , but I'm not sure what parts a disability is these days. It wasn't very good 20 years ago when I was messing around with them. I have a Thermoquad kit unopened if you happen to need one. The brand on that is Hygrade. Bought it from Mancini racing many years ago. As well as another one partly used. Cheap. AVS kit also. I don't know how the rubber Parts fair over all those years.
     
  3. Murray

    Murray FABO Gold Member FABO Gold Member

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    Just one mans opinion- your engine doesn't seem all that mopar, a carb change won't change that. Some Mopars did come with Holley carbs. The main thing is to have fun with your car, so if you don't like Holleys, why not wait until it's a problem and change to something you prefer?
     
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    • Keven S. Clickner

      Keven S. Clickner FABO Gold Member FABO Gold Member

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      Looks like you could use an improvement on that throttle linkage. The right Chrysler parts are available from Holly. Should have an adapter lever like this....

      16062530361957275789602251284172.jpg
       
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      • Keven S. Clickner

        Keven S. Clickner FABO Gold Member FABO Gold Member

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        Probably just me but I hate to see that stuff slop together that's important business right there. It's your life.
         
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        • B'cuda

          B'cuda FABO Gold Member FABO Gold Member

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          I like the sound of larger secondaries opening up, and the fact that the primaries are small enough to save gas IF you keep your foot out of it. But that's about it for me and spread bore carbs. Which brings up that you would have to open up the manifold opening ( do-able I think, on that LD340 intake, but you may ruin the value of it in the least) or use an adapter or swap to a spread bore intake. Depending on your intake valve size, the 750 is a good size and if it runs good, I'd spend my money elsewhere. Just my 2 cents.
           
        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          Im a lot in the “If it ain’t broke....” band wagon. However, if you wanna try out a TQ, I’m all for experimentation just to see how shit works.

          The first thing about a TQ is to get one that is in good to excellent shape. Also, the LD340 can be carved out to accept a TQ. No spacer needed. But you may want one anyway incase you go back to the Holley. Check hood clearance with the spacer!!!!

          Secondly, the less emissions equipment or ports on the carb, THE BETTER! Tuning kits designed for the TQ are super expensive. Find busted up fires with there rods and nets to help get it done or use AFB rods cut down 3/4 of an inch to be sized right. They are a good bit thicker than a TQ rod, so you’ll need to be a little crafty there.

          I disagree with the intake valve being a limited on carb size in a very big way.
           
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          • AlaskaJeff

            AlaskaJeff Well-Known Member

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            I appreciate all the comments and suggestions. I was leaning towards leaving the set up as is unless something starts to have issues anyway. I am always up for learning something new with the Holley. One reason I was considering the change is one of the PO of the car had put that carb/manifold combo on it while he had it, and told me IF I ever were to put a new carb on it he would be willing to buy the Holley back. I guess it has some sentimental value to him. I guess it will stay this way for now. And I will for sure look into getting the proper linkage set up.
             
          • Mike 340

            Mike 340 Well-Known Member

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            The top picture looks like a vacuum secondary Holley carb. Not that there is anything wrong with that but you need to know what you are working with in my opinion.
             
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            • rumblefish360

              rumblefish360 So close, yet so far away FABO Gold Member

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              Yea, that bracket is a helpful little thing.
              Also, get yourself a proper throttle return spring and bracket. ;)
               
            • abodyjoe

              abodyjoe Well-Known Member

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              Nothing like a thermoquad. That being said you need to know how to tune one. Parts for performance tuning aren't so readily available. Holley on the other hand are much easier to tune and parts are everywhere for them.

              Do you have a spread bore intake?



              .
               
            • A56

              A56 MoParAffliction FABO Gold Member

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              Just in case you swap carbs out and you start having problems I'll loan you this. I've used it after trying to make things better even though there was no reason.
              OIP.Ig5GK3eGWTz3hCeVnwMWiAHaEM?w=306&h=180&c=7&o=5&dpr=1.25&pid=1.jpg
               
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              • Syleng1

                Syleng1 Karma is real and Life is short... FABO Gold Member

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                I vote for fuel injection. I run a TQ on the 340 and FI tech on the 66 barracuda. Cats meow right there. Cost is the downfall.
                 
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                • PRH

                  PRH Well-Known Member

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                  Yup...... not a DP.
                   
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                  • AlaskaJeff

                    AlaskaJeff Well-Known Member

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                    That about proves how little I know about Holley carbs...… :)
                     
                  • AlaskaJeff

                    AlaskaJeff Well-Known Member

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                    carb1.jpg
                    So who can help me ID this carb to know what I'm working with? I know it's a manual choke. There was not a vacuum line plugged into the carb when I bought it. Is that bad? Where are the ID numbers on it so I can do some Googling?
                     
                  • rumblefish360

                    rumblefish360 So close, yet so far away FABO Gold Member

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                    Upper right side of the choke air horn as looking at it from the front of the car are the “List” numbers which you can google or go to Holley.com and search for.
                     
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                    • RammerJammer75

                      RammerJammer75 Well-Known Member

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                      I would honestly use what you have, but if you're dead set on getting rid of the Holley you could always resell it to recoup some cost.
                       
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                      • K.O. SWINGER

                        K.O. SWINGER Well-Known Member

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                        I ran thermal quads for over 20 years and I love that carburetor. but there's definitely a learning curve and you have to want to learn it. too many people slap one on their engine that doesn't run right and blame it on the carburetor, usually it's just poor adjustment that being said I have cleaned up 850 thermoquad big block version slapped it on a hot 340 and just tore up the street. There's a couple of things that a thermal quad does really well one is allow you to get good gas mileage if you stay out of the secondaries it's amazing. Second is it really does help keep the fuel cooler and avoid vapor locks and other problems associated with boiling fuel. As far as performance goes that will depend on your tuning ability .oh yes and one more thing the small primaries on the thermal quad make for great throttle response. Old Black magic.
                         
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                        • midnight340

                          midnight340 FABO Gold Member FABO Gold Member

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                          I’m running the big TQ o my 340 after years of playing with Edelbrock’s. I bought a box of 5 old Thermoquads for $50 and dived in. DEFINITELY a learning curve (which I enjoyed!) Not at all impossible once you round up the info. PM me if you need to know the sources or help.

                          But once I got every aspect dialed I really love this carb. I have an air/fuel meter, and the readings are much more consistent throughout RPM ranges than the Edelbrock AVS 650 or the 750! (And both were well tuned) TQ’s are great!!
                           
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                          • Nat

                            Nat Well-Known Member

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                            what about a speed demon 750 , i'm using one now and so far i like it more than the holley it replaced , better throttle response , better mpg , started right up out of the box very few adjustments to get it running 100% . parts must be easy to get as holley makes them now
                             
                          • 66fs

                            66fs FABO Gold Member FABO Gold Member

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                            Basically a square bore TQ. Even the floats are the same.
                             
                          • Tims 66 Cuda

                            Tims 66 Cuda Mopar mid life crisis

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                            Street Demon, Holley,s version of a TQ hybrid.
                             
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