Swaping a bad 400 with a 440 in my 73 Monaco 2dr. In 72 they used a Holley 4 barrel. In 73 its a Thermoquad. Should I go with the factory type or Holley? What issues will I come up with trying to keep the correct vacuum lines? Anything else? I don't know much about the Thermoquad.
1973 Monaco 440 swap WHICH CARB SHOULD I USE?
- Thread starter 500cubes
- Start date
The thermoquad was mostly made from plastic. It had a lot of issues with warping and cracking and good used ones are hard to find. I would not use that carb myself unless I was going for a high point restoration. The factory holly carb was undersized for the 440 engine and was primarily used to meet smog requirements. Is your engine a stock, low compression engine? If so, you can get by with the holly factory unit. If you have plans to do any performance upgrades, then I would go with an after-market AVS or holly carb that is designed for performance applications. You might have to locate a different intake manifold to use the AVS carb.
Dave
I'd look into an OEM-Replacement Holley 4175 spreadbord carb. Vac secondary. If it was me. The vacuum lines will explain themselves, but you'll need to bend some new fuel line from the filter up to the carb. Not a big deal, as I've done that before. A tubing bender and a tubing cutter (for the filter end).
With a non-spreadbore manifold, the Street Demon can be an option. Looks a lot like the TQuad, but can have either a metal float bowl or a phenolic one.
The phenolic float bowl on the TQuad can be had as a replacement part, I believe. Reman TQuads are around, but they are "one size fits most", usually, rather than a specific year and engine, which relates to the metering calibration they have.
I've rebuilt a TQuad and had no issues with it. It's a taller design than the Holleys, though, if that matters. Main issues might be wear on the throttle shaft, to me, rather than possible issues with the phenolic float bowl per se (on a used/reman one).
UNLESS you know exactly where a used carb came from, it can be best to look for a sale on the new ones. All of the speedshop vendors don't always charge the same prices, so look around. Getting a new carb with the electric choke can be good.
CBODY67
With a non-spreadbore manifold, the Street Demon can be an option. Looks a lot like the TQuad, but can have either a metal float bowl or a phenolic one.
The phenolic float bowl on the TQuad can be had as a replacement part, I believe. Reman TQuads are around, but they are "one size fits most", usually, rather than a specific year and engine, which relates to the metering calibration they have.
I've rebuilt a TQuad and had no issues with it. It's a taller design than the Holleys, though, if that matters. Main issues might be wear on the throttle shaft, to me, rather than possible issues with the phenolic float bowl per se (on a used/reman one).
UNLESS you know exactly where a used carb came from, it can be best to look for a sale on the new ones. All of the speedshop vendors don't always charge the same prices, so look around. Getting a new carb with the electric choke can be good.
CBODY67
70bigblockdodge
Old Man with a Hat
Don't use a old vintage Holley they are crap and will drive you insane with issues (they are a money pit)
Once they became all aftermarket they are much better. This is also true of Eddy's vs old AFB, AVS.
Once they became all aftermarket they are much better. This is also true of Eddy's vs old AFB, AVS.
One of probably the best Holley 4160 "deals" is the one they now/did sell under the old, orig 1971 SuperBee 383 application part number. After the OEM Replacement days, they added the race bowls, electric choke, universal throttle linkage, and a little different fuel calibration. This is a different 750cfm carb than the 3310, as it has 1.56/1.75 throttle bores, rather than the 1.690s of the 3310. If it's still available, it probably doesn't cost as much as the 3310, either.
Problem with a used carb of any brand, even a "re-man", is that the many small passages in the metering areas can have some accumulated "hard deposits" which won't be removed by "vatting" them, but can only be removed mechanically. Of a pcv passage that didn't get all the way clean. These things can throw the metering calibrations "off". Plus whether or not the throttle shafts need re-bushing. Issues which new carbs don't have.
CBODY67
Problem with a used carb of any brand, even a "re-man", is that the many small passages in the metering areas can have some accumulated "hard deposits" which won't be removed by "vatting" them, but can only be removed mechanically. Of a pcv passage that didn't get all the way clean. These things can throw the metering calibrations "off". Plus whether or not the throttle shafts need re-bushing. Issues which new carbs don't have.
CBODY67
My success rate in rebuilding factory vintage Holley 4160 carbs hovers close to zero. And I have a pretty good idea of what I am doing. My success rate with the Thermoquads is more like 80%, and I wouldn't hesitate to use one. But a new Holley equivalent with a modern design and quality materials would likely be a fine choice - but they are really expensive.
I definitely agree with the Holley comment - no doubt about it. But lately, the Eddys I have bought to replace old worn AVS or AFBs haven't been any better - like they leaned them out for some reason. 10 years ago, the Eddys would scream, but not the latest ones I have dealt with.
Thanks for all your advice. Since I want to keep it as stock as possible & have no need for performance, I'm a driver, not a racer, I'm going to take a chance on a quality built Thermoquad. Especially since that's the intake I have.
MoPar Maniac
Well-Known Member
I read it 3 times but my 72 Polara 400 had a TQ.
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