Carbs: AFB/AVS or Thermoquad

[tparker]

Saw the other post on Thermoquad and thought I'd ask this question. A long time ago I read an article that was talking about how good the thermoquad was. It was over 30 years ago so I don't remember the details. And me not knowing any different went to a junk yard and got a later thermoquad after I replaced my 2 barrel 318. It worked fine and I don't have any complaints. I currently and going with an Eddlebrock that is known to work when I break in the engine, but then thinking about switching to an actual AVS or perhaps an AFB. But I still have that thermoquad and I am curious what others think about that carb. Is there advantages to the AVS/AFB carbs? Are there better years or models of that carb? Just currious. My car is a 70 Challenger so it isn't stock, but that isn't an issue. Heck I don't even have the right air cleaner for a 340. LOL.

Thoughts?

[Mr Cuda]

AVS if stock engine,  or  performance Holley.

That's my rule.

[Bullitt-]

  If you have a good Thermoquad I doubt you will see any advantage with any out of the box reasonably priced carb... Tuning a T/Q for a more or less stock engine is not that difficult if it's otherwise in good shape and properly set up.
  I would definitely prefer an AVS to the AFB but from all I understand for ultimate adjustability there is a lot more that can be done with a Holley style unit. 

[tparker]

@Bullitt- Huh, i was thinking the AFB would be better since it has the three step needle instead of the two step. I am assuming the vacuum secondaries are preferred over the mechanical? Or is there something else? Can't wait to play with all these options. LOL.

The only problem with my Thermoquad is it is a late model off of a van. Not sure how much they varied and if this one is good or not. I'll finish rebuilding it and test it against my Edlebrock and carter once I get them all in shape. 

[Bullitt-]

@Bullitt- Huh, i was thinking the AFB would be better since it has the three step needle instead of the two step. I am assuming the vacuum secondaries are preferred over the mechanical? Or is there something else? Can't wait to play with all these options. LOL.

The only problem with my Thermoquad is it is a late model off of a van. Not sure how much they varied and if this one is good or not. I'll finish rebuilding it and test it against my Edlebrock and carter once I get them all in shape. 

  The current Edelbrock AVS & AFB use the same 2-step metering rods, it's the T/Q that has the 3-step.   AFB secondary uses a counterweight air valve to control airflow (adjustment achieved by removing material from the counterweights https://youtu.be/6Cv6PLW-9Wg?t=297 ), the AVS uses an adjustable spring similar to the T/Q... read here https://www.motortrend.com/how-to/mopp-0309-edelbrock-avs-carburetors/
  Later model Thermoquads are not the preferred units as they were set up from the factory to run much leaner and have extra gizmos not found on the more sought after mid '70s pieces. I once had a NOS early '80s T/Q on my '73-340 & it performed well with the gizmos not connected.

[Chryco Psycho]

In order the best is the TQ
second is the AVS
& last is the AFB
the TQ is by far the most tunable & the AFB is almost impossible to tune , the AFB were built for a specific engine & cam & don't work well when things are changed .

[tparker]

Aweseome, thanks for the info. I'll have to recheck the year of the TQ. I believe it is a later one and is probably quite lean. I think if was from a Van or RV or something similar.