'73 340 carb & intake thoughts

[73LemonTwist]

I have a stock '73 340 RR automatic with factory intake and 6319SA Thermoquad. The wells on the TQ are leaking, so I epoxied them and re-assembled the carb - however who knows how long it will last. So, am now beginning to think its time to make some changes to let the engine breath better.

I have been wondering about carb size to use. I have seen CFM numbers from 650-800 for the stock TQ (small primary bore version) - don't know what the real number is. The online calculators suggest that I need less than 600 CFM if I stay under 6,000 RPM (and assume 83% VE). The car has a 3.55 rear end, so am turning 3500+ rpm on the highway at 70 mph. The car will not see any track time - strictly street fun.

Have been considering Street Demon 625 and RPM Air Gap manifold. However a bit concerned that with the 625 I could be opening the secondaries while highway cruising, and hence thinking maybe 750 a better choice.

Thoughts, experiences, recommendations? Tnx all

 

[PurpleBeeper]

Well......I'm pretty sure this isn't the response you're looking for, but I think you'll get your best performance/mileage/drivability with the stock carburetor + stock intake manifold....seriously. The spreadbore Thermoquads are really good carburetors in my opinion. With small primaries (good mileage/drivability) and secondaries the size of sewer lids (good performance) you get the best of both worlds with a Thermoquad.

If by "plastic wells" you mean the main body, I think I've seen those available online. As for epoxy....as long as you remove ALL the oil/dirt, rough up what your epoxying with sandpaper & use an epoxy designed for plastic (halogenated resin, usually have a mercaptan-smell like natural gas & cure very, quickly...usually 1min. or 5min. cure times) your repair will last for many, many years. Epoxy is not affected by gasoline at all. Non-halogentated resin epoxies (like JB Weld) won't stick to plastic.

 

[73LemonTwist]

You have captured the quandary perfectly. The TQ is a decent carb for sure. Those monster secondaries have lots of capacity. My current mileage is acceptable, even on the highway. So changing up something that is known to work, raises questions.

Yes, I was referring to the two pieces epoxied into the phenolic bowl under the main jets. I had read to use JB weld, so that is what I have tried this time around. After my rebuild the accelerator pump quit squirting when the engine was warm (cold it was fine), so I changed to a leather cup accelerator pump, and so far that has been working well too.

If you know of a halogenated epoxy resin to use on the bowl (brand or source), I would be most interested. As you noted by chosen repair may not last.

 

[idrivemopar]

Interesting comment by Purplebeeper, I am running a 6322TQ, and I had the problem with the plastic well caps on the center section, and I cleaned sanded and used JB quick weld to reset and seal them, so it will be interesting to see how they hold up, so far, no issues. By the way, the center sections that were reproduced a few years ago are no longer available, I think I got the last one for my 6319 TQ about 3 yeas ago. I wish someone would start making them again, as I have a few spares that I would like to complete, but center sections are bad on them, cracked.

Just read this comment about JB weld with use with gasoline,
Is J-B Weld resistant to water and/or gasoline?
When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical. For wet-surface or submerged water or gasoline repairs, try our SteelStik or WaterWeld.

 

[polywideblock]

I've got the performer rpm and a Holley street avenger 670 vac secondary ,no complaints so far but its a 4 speed

 

[73runner]

All stock and going strong.