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Factory 340 carbs #992325
05/14/11 06:04 PM
05/14/11 06:04 PM
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70duster340 Offline OP
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Anyone know what carbs came from the factory on the 340? I'm interested to know all of the carbs, since I know there were several. the cfm's would be helpful, also.

TIA!!!

Re: Factory 340 carbs [Re: 70duster340] #992326
05/14/11 06:11 PM
05/14/11 06:11 PM
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340SHORTY Offline
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Thermobogs and 2300 Holleys...


I am truckless..
Re: Factory 340 carbs [Re: 340SHORTY] #992327
05/14/11 06:14 PM
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70duster340 Offline OP
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Thanks, 340Shorty. But, as far as 4 barrel carbs go, only the thermoquad was used? I thought that Carter square bore carbs were used, also.

Re: Factory 340 carbs [Re: 70duster340] #992328
05/14/11 06:20 PM
05/14/11 06:20 PM
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B5 Bee Offline
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2300 Holleys - 1350/970cfm
Carter Thermoquad - 800cfm
Carter AVS - 625cfm
Carter AFB - 625cfm

Last edited by B5 Bee; 05/14/11 06:23 PM.
Re: Factory 340 carbs [Re: B5 Bee] #992329
05/14/11 06:24 PM
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70duster340 Offline OP
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So, was the thermoquad on the later model 340's? What year for each version of carb, if that is possible? Also, what cfm rating was used?

Thanks for all the replies!!!

Re: Factory 340 carbs [Re: 70duster340] #992330
05/14/11 06:47 PM
05/14/11 06:47 PM
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ScottSmith_Harms Offline
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It would be a lot easier to answer you if we knew what year/model your car was? Also list any modifications it's had.

Re: Factory 340 carbs [Re: 70duster340] #992331
05/14/11 06:48 PM
05/14/11 06:48 PM
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autoxcuda Offline
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Quote:

So, was the thermoquad on the later model 340's? What year for each version of carb, if that is possible? Also, what cfm rating was used?

Thanks for all the replies!!!





68-70 AVS - 625 cfm
70 340-6 2300 Holleys - 1350/970cfm
71-73 Thermoquad - 800 cfm

No AFB's on 340's.

Re: Factory 340 carbs [Re: autoxcuda] #992332
05/14/11 06:54 PM
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70duster340 Offline OP
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Thanks, autox, that's what I was looking for. Now on to the next question. Why was there such a jump in cfm ratings from 68-70 to 71-73? Wasn't the 340 compression ratio dropped down a lot for emissions reasons?

Re: Factory 340 carbs [Re: autoxcuda] #992333
05/14/11 06:58 PM
05/14/11 06:58 PM
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B5 Bee Offline
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Quote:

Quote:

So, was the thermoquad on the later model 340's? What year for each version of carb, if that is possible? Also, what cfm rating was used?

Thanks for all the replies!!!





68-70 AVS - 625 cfm
70 340-6 2300 Holleys - 1350/970cfm
71-73 Thermoquad - 800 cfm

No AFB's on 340's.





Sure there was, just not automotive.
That's an AFB under the flame arrestor on this '73 340.


Re: Factory 340 carbs [Re: B5 Bee] #992334
05/14/11 07:07 PM
05/14/11 07:07 PM
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autoxcuda Offline
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Quote:

Quote:

Quote:

So, was the thermoquad on the later model 340's? What year for each version of carb, if that is possible? Also, what cfm rating was used?

Thanks for all the replies!!!





68-70 AVS - 625 cfm
70 340-6 2300 Holleys - 1350/970cfm
71-73 Thermoquad - 800 cfm

No AFB's on 340's.





Sure there was, just not automotive.
That's an AFB under the flame arrestor on this '73 340.

..




We was looking for a automotive application. But industrial, boat, etc have all kinds of different stuff.

Re: Factory 340 carbs [Re: autoxcuda] #992335
05/14/11 07:16 PM
05/14/11 07:16 PM
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B5 Bee Offline
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Well, the question was ALL the carbs that came on factory 340s.

Re: Factory 340 carbs [Re: 70duster340] #992336
05/14/11 07:20 PM
05/14/11 07:20 PM
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DEMONSIZZLER Offline
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The ThermoQuad was introduced in '71 for the 1st time as on oem carb with 800 cfm's. It had existed since '69 as an after-market performance carb avail in either 850 cfm's or 1,000 cfms and is know as the Competition Series.

The primaries on the '71-'73 340 T.Q.'s was approx 232 cfm's and a whopping 570 cfm's on the 2ndary side. The double booster design of the primaries gives the T.Q. an excellent port floor signal and exceptional fuel/air atomization. And the sophisticated metering system is very precise. And the carb was very 'change-able' to increasing EPA demands for cleaner running engines so it was easy to add smogger settings and parts that made the carb pass increasing emissions requirements.

The '71 340 T.Q. was a one year only design, derived from the 69 Competition Series carb. The carb is an air metered carb while all '72-up ThermoQuads are solid fuel metered.

CS series 850.......4846S for press in jets,
....................4846SA for screw in jets,
CS series 1,000.....4847S for press in jets,
....................4847SA for screw in jets,
'71 340 800.........4972 for 4 spd,
....................4973 for automatic,
'72 340 800.........6138 for 4 spd,
....................6139 for auto,
'73 340 800.........6318 for 4 spd,
....................6319 for auto.

These '72 carbs(oem)will suffer in performance if the correct casting # top is not used. The best 340 T.Q. is the '72 as it had the best metering system and it will make very close to the same power as the early '72-'73 big block 850 cfm carbs.

Over-all, these carbs are hard to beat in both gas mileage and performance!

Re: Factory 340 carbs [Re: B5 Bee] #992337
05/14/11 07:26 PM
05/14/11 07:26 PM
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Quote:

Well, the question was ALL the carbs that came on factory 340s.




That's true.

But without saying what the AFB's were on, some people reading it will think they came on 68-73 automotive applications and it will just confuse them.

Re: Factory 340 carbs [Re: 70duster340] #992338
05/14/11 11:56 PM
05/14/11 11:56 PM
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Lincoln Nebraska
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RapidRobert Offline
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Quote:

the cfm's would be helpful, also.


posted in a prior thread: said AFB but assuming AVS would b the same. 1&1/8 pri 1&1/4 sec is 400. 1&3/16/1&1/4 is 500 1&1/4/1&9/16 is 575 1&3/16/1&9/16 is 625 1&7/16/1&9/16 is 750


live every 24 hour block of time like it's your last day on earth
Re: Factory 340 carbs [Re: RapidRobert] #992339
05/15/11 09:14 PM
05/15/11 09:14 PM
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70duster340 Offline OP
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Don't mean to seem ignorant, but what is the difference between the AFB and the AVS?

Re: Factory 340 carbs [Re: 70duster340] #992340
05/15/11 11:31 PM
05/15/11 11:31 PM
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Spokane Washington
ScottSmith_Harms Offline
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Quote:

Don't mean to seem ignorant, but what is the difference between the AFB and the AVS?





Well assuming you are trying identify one or the other and not every single detail of what set's them appart?

These are AFB's (Aluminum Four Barrel)

There were two basic designs on Mopars, early and late. These are the early styles (with vestigial choke tube in the lid) found on early to mid 60's Mopars.

Re: Factory 340 carbs [Re: ScottSmith_Harms] #992341
05/15/11 11:32 PM
05/15/11 11:32 PM
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Spokane Washington
ScottSmith_Harms Offline
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Newer style AFB, vestigial choke is now gone from the lid casting, choke moved to the side of the carb.

6635276-70HemiAFB.jpg (105 downloads)
Re: Factory 340 carbs [Re: ScottSmith_Harms] #992342
05/15/11 11:33 PM
05/15/11 11:33 PM
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Spokane Washington
ScottSmith_Harms Offline
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AVS (Air Valve Secondary)

Has the adjustable secondary air valve and the potential for more cfm than a single AFB. The comparitively small cfm of the AFB's (most were rated at 625cfm or less) is why many were used in dual four barrel applications to provide enough fuel for larger cid engines, and as singles for smaller cube or typical lower HP passenger car V8's. The AVS was a nice middle of the road carb, very tunable and could provide more cfm (up to 850 or so) with a single four barrel carb.

Re: Factory 340 carbs [Re: ScottSmith_Harms] #992343
05/15/11 11:40 PM
05/15/11 11:40 PM
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ScottSmith_Harms Offline
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IMO the Thermo-Quad was the ultimate factory single four barrel, huge cfm potential (up to 850 in OEM applications and up to 1000cfm aftermarket) and economical because of it's stingy primary side and suberb adjustability.


Re: Factory 340 carbs [Re: ScottSmith_Harms] #992344
05/15/11 11:43 PM
05/15/11 11:43 PM
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70duster340 Offline OP
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Thank you, Scott! Very informative. You obviously know your carbs!!!

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