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Carb shopping
340, larger than stock cam (no specs), RPM Air gap, stock bottom end, headers
Looking for a Holley 750 double pumper
I think I have it narrowed down to the 4150 Street HP,
anyone run this carb on a mostly street driven car??
Opinions
Posted By: johnmilner
Re: Carb shopping - 01/11/15 01:17 AM
650 double pumper.
IMO: I agree with above. Sounds like a street car, I'd go with a 650 street HP. The 750 might ultimately give a better ET at the drag strip with open headers, but the 650 will be better at everything else on 340 cubes. I think it would offer better throttle response and a crisper feel.
Posted By: RobX4406
Re: Carb shopping - 01/11/15 02:10 AM
Auto with some converter or 4 speed?
If you can tune a carb, go with the 750.
I run my 340's with nothing smaller than a 750.
Posted By: MR_P_BODY
Re: Carb shopping - 01/11/15 02:13 AM
Its more about your conv and rear gear as to what carb
you need to use... a 750 was on a stock 340
Posted By: Cuda367
Re: Carb shopping - 01/11/15 02:46 AM
You won't listen but 750 street demon. More throtle reponse than you will know what to do with and the air to feed it upstairs
automatic, gears are 323,
eventually I may stroke it
Posted By: YO7_A66
Re: Carb shopping - 01/11/15 04:57 AM
Stock stroke 340/auto (unknown conv)/3:23 gears= vacuum secondary with tunable circuits (jets/air bleeds). 650-700cfm
Posted By: Rob C
Re: Carb shopping - 01/14/15 01:25 AM
When was a 750 stock on a 340?
The square ore Carters were 600/630
Both size TQ's came on the 340 IIRC. You call them what for cfm size?
Normally I hear them called 800/850.
They had over 1000 cfm on the T/A's
Posted By: Rob C
Re: Carb shopping - 01/14/15 01:39 AM
Yes, the race TQ. I own one. Haven't had the chance to run it yet.
I wonder about the true cfm dry vs. wet.
Sorry, fat fingers and home distractions left this post...... Unfinished.
And yes, as stated below, the 6pack induction was a street strip champ.
See below for cfm ratings between 4 & 2 bbl. carbs.
Posted By: dogdays
Re: Carb shopping - 01/14/15 01:39 AM
Not that again! Two-barrel carbs are rated differently, you need to divide the two barrel rating by the square root of two (1.4142) to convert to a four barrel reading. For 1350 two barrel cfm that equates to 955 four barrel cfm. BUT, the carb setup opened the end carbs only as much as the engine needed so I don't think any stock 340 ever used all of the 6-pack capacity.
R.
Right but if you look at it this way. A motor will only draw in so much cfm of the carburetor. It doesn't matter what carb, style, or model if motor only can take in 500 cfm and you use a 650 then what? Is it to big now? You can run any carb you want but if it's a street set up then who gives a turkey about size really lol. As long as motor is getting fuel and is working like it's supposed to.
Posted By: DaveRS23
Re: Carb shopping - 01/14/15 01:59 AM
Quote:
You won't listen but 750 street demon. More throttle response than you will know what to do with and the air to feed it upstairs
(except for the 750 part) The Double Pumpers are awful rich when used on a street car unless lots of time is spent tuning them. They are good carbs, but are more geared toward acceleration competitions than cruising.
The Demons start much more street friendly on their tune. If adjustments are needed, they are fewer and typically take fewer steps.
And besides the tune, the Demons also have some street friendly design features that the Holleys don't. Which will also help throttle response and driveability.
If you are choosing for the strip, then I would probably choose the 750 DP. But for the street, the 625 Street Demon should get the nod.
Posted By: Mopar Bob
Re: Carb shopping - 01/16/15 04:40 AM
Street car, mild 340. You might consider a 650 vacuum secondary. Is it an automatic? I didn't see that noted.
Posted By: VincentVega
Re: Carb shopping - 01/16/15 07:28 AM
I'd love to own the competition series TQ (1000 cfm), but those are like hen's teeth
Posted By: ademon
Re: Carb shopping - 01/16/15 09:30 AM
I used this 750 Holley choke less race carb with good results in my 400hp 360.
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Posted By: ademon
Re: Carb shopping - 01/16/15 09:37 AM
But this mechanical 6 pack setup replaced the 4bbl and single plane. The engine seems slightly stronger with the 6 pack even with the 1,150cfms and no jetting!
.jpg "8398020-6pack023(1280x960).jpg")
Posted By: ademon
Re: Carb shopping - 01/16/15 09:38 AM
Posted By: RobX4406
Re: Carb shopping - 01/16/15 09:42 AM
Quote:
But this mechanical 6 pack setup replaced the 4bbl and single plane. The engine seems slightly stronger with the 6 pack even with the 1,150cfms and no jetting!
~813 cfm in 4 bbl terms.
Posted By: Mattax
Re: Carb shopping - 01/16/15 03:41 PM
Still scratching your head on this?
If you're really set on a double pumper for street, then a Holley 600 or 650 rated 4150 is your best choice. Especially true with stock or stockish converter and those gears.
A higher rated carb has potential for better 1/4 mile performance with the right converter, tires, gearing.
Since you have unknowns, I agree with those recommending a vacuum secondary carb. Only dings against the T-quads is that you will have to buy used, and the rear bores may not clear the Eddy RPM. My suggestion is to try the new Speed Demon instead as its a more square bore interface with the intake. It's also a lot cheaper than that shiny "street HP".
Posted By: Thumperdart
Re: Carb shopping - 01/16/15 04:41 PM
Quote:
340, larger than stock cam (no specs), RPM Air gap, stock bottom end, headers
Looking for a Holley 750 double pumper
I think I have it narrowed down to the 4150 Street HP,
anyone run this carb on a mostly street driven car??
Opinions
I had an 850 on a mild 450 hp 360 which ran hi-11`s at L.A.C.R. and bigger than "Suggested" cam in the same motor. Now that I`m finally getting a handle on these things a 750 in NOT too big and I can and have recently dialed a couple in that are working great including a 750 Speed Demon on a 4-speed truck that went from 13.30`s to 13.10`s and went from 15 mpg`s to 17............MILD smallblock Ferd......... 
Posted By: ademon
Re: Carb shopping - 01/16/15 05:07 PM
Quote:
Quote:
But this mechanical 6 pack setup replaced the 4bbl and single plane. The engine seems slightly stronger with the 6 pack even with the 1,150cfms and no jetting!
~813 cfm in 4 bbl terms.
No .. this is the mechanical setup sold in the late 70's early 80 through DC. The end carbs are a 850dp cut in half with slabbed throttle shafts and all. The middle is a 355cfm which I removed the choke plate and shaft.
Mike,
I ran a 4150 750 HP on my old 340 back when the dart went 12.50's. I probably put 10,000 street miles on it without issue. It would get 14mpg if I kept my foot out of it.
Posted By: OUTLAWD
Re: Carb shopping - 01/16/15 05:41 PM
I would go with a 750 vac sec. maybe get an aftermarket main body with adjustable air bleeds and secondary metering block.
My experience with the HP carbs (950...not sure if the 750 HP is the same or not) is that they use different metering block, with idle restrictions, power valve restrictions and emulsion tuning that are tailored for the track, not the street. Great at WOT, but pig rich at part throttle out of the box.
Also with 3.23's I imagine tuning transitions would be a bit easier with a vacuum secondary
Posted By: Rob C
Re: Carb shopping - 01/16/15 10:09 PM
Quote:
Right but if you look at it this way. A motor will only draw in so much cfm of the carburetor. It doesn't matter what carb, style, or model if motor only can take in 500 cfm and you use a 650 then what? Is it to big now? You can run any carb you want but if it's a street set up then who gives a turkey about size really lol. As long as motor is getting fuel and is working like it's supposed to.
I understand what your saying. The thing here is that it is not to big or oversized, the carb will work. In the case of a VC carb, it will only open up so much. In a DP carb, if the carb is to big, you'll probably have a slower car and or a soft bottom end and or middle.... The list carries on...
If it is a 850 cdm carb on a 273, getting it even near right at idle will probably be... inventive on new cuss words. LOL
Posted By: Rob C
Re: Carb shopping - 01/16/15 10:10 PM
Quote:
I'd love to own the competition series TQ (1000 cfm), but those are like hen's teeth
Keep your eyes open. Look to FABO's for sale section. One popped up not to long ago. Happy (carb) hunting!
Posted By: Rob C
Re: Carb shopping - 01/16/15 10:16 PM
And Dog Days says this--->
Quote:
Not that again! Two-barrel carbs are rated differently, you need to divide the two barrel rating by the square root of two (1.4142) to convert to a four barrel reading. For 1350 two barrel cfm that equates to 955 four barrel cfm. BUT, the carb setup opened the end carbs only as much as the engine needed so I don't think any stock 340 ever used all of the 6-pack capacity.
Not to start in and make a mess of things, but what is the conversion for the stock 6pack equal to in 4bbl. terms/cfm??
And the mechanical MP unit cfm rating in 4 bbl. terms?
Posted By: ademon
Re: Carb shopping - 01/17/15 01:15 AM
Quote:
And Dog Days says this---> Quote:
Not that again! Two-barrel carbs are rated differently, you need to divide the two barrel rating by the square root of two (1.4142) to convert to a four barrel reading. For 1350 two barrel cfm that equates to 955 four barrel cfm. BUT, the carb setup opened the end carbs only as much as the engine needed so I don't think any stock 340 ever used all of the 6-pack capacity.
Not to start in and make a mess of things, but what is the conversion for the stock 6pack equal to in 4bbl. terms/cfm??
And the mechanical MP unit cfm rating in 4 bbl. terms?
Stock 6 pack I've always read and heard about 950cfm
DC carbs have slabbed throttle shafts and thinner blades plus I'm pretty sure the Venturi is bigger on the end carbs. About 1,100cfm
Posted By: DaveRS23
Re: Carb shopping - 01/17/15 03:00 AM
Quote:
340, larger than stock cam (no specs), RPM Air gap, stock bottom end, headers
Looking for a Holley 750 double pumper
I think I have it narrowed down to the 4150 Street HP,
anyone run this carb on a mostly street driven car??
Opinions
Opinions are all over the place, aren't they? One important piece of information that carb questions should include is the OP's desire and/or ability to properly tune the carb. And also, what's more important to you; maximum performance or maximum drive-ability?
Most guys are not carb tuners and don't have the wide band, drill bits, jets, bleeds or knowledge of the carb's circuits to get the most out of their choice of carb. For them, the carb that comes out of the box closest to the design and tune that their combination likes, is usually the best choice. Or at least the best starting point.
There are a lot of different configurations of 750 cfm carbs. All of them will run your car, but some will do a better job ON YOUR COMBO than others. But that doesn't necessarily mean one is actually better than the others, just maybe that it is closer to the tune that you combo likes.
A good tuner with the proper tools and experience can start with most any 750 and get it to rock. But the farther away from the combo's preferred tune the carb is, the more changes the tuner has to do to get it right. So whether an experienced tuner or not, it is best to start with the carb that is closest to the tune that your combo wants.
And irregardless of the tune, some carb configurations are designed to do one job better than another. Like spread bore or square bore, mech secondaries or vacuum, annular or down leg boosters and on and on.
Sorry for the long response. But carb selection is as complicated as cam selection. Most guys turn to a cam grinder for recommendations. And any cam guy worthy of your money will want A LOT of info on the engine, drive train and the customer's desires before he makes a recommendation.
In order to get the optimum carb, the same approach should be taken. How about asking Thumper to set one up for you? Tell him what you want and what your combo is and let him pick the platform and through his tune in it. That would likely get you a better carb than the one ordered by a catalog number.
Posted By: Thumperdart
Re: Carb shopping - 01/17/15 04:28 AM
I would love to hook you up...............
Holley 650 ultra double pumper...best carb OOTB for your application.
Posted By: DaveRS23
Re: Carb shopping - 01/17/15 03:57 PM
Quote:
Holley 650 ultra double pumper...best carb OOTB for your application.
Absolutely NOT the best choice for the OP's mostly street driven car with an automatic and 3.23s. Unless he enjoys a tuning challenge. Every circuit would need a good amount of tuning to keep it from loading up the combustion chambers, washing down the cyl walls, diluting the oil, and wasting a lot of fuel.
Posted By: Thumperdart
Re: Carb shopping - 01/17/15 05:03 PM
Quote:
Quote:
Holley 650 ultra double pumper...best carb OOTB for your application.
Absolutely NOT the best choice for the OP's mostly street driven car with an automatic and 3.23s. Unless he enjoys a tuning challenge. Every circuit would need a good amount of tuning to keep it from loading up the combustion chambers, washing down the cyl walls, diluting the oil, and wasting a lot of fuel.
Yep.........the BEST one is a modified one because of the different tunes each carb series has and even though close, not perfect...........kinda like guys buy Afco shocks then send em in to be "Fine tuned" to suit YOUR needs. You want to talk best "Bang for the buck"? Get a 750 MODERN carb not some wore out one that needs EVERYTHING anyhow, and have it worked cos trust me, EVERY carb needs something and as we speak I re-did two "Modified" carbs by two well known shops and although close each had issues..........the same ones I see in every carb. Too rich here, stumbles when I do this goes lean here. You get the picture............ 
.jpg "8398021-6pack027(1280x960).jpg")