What Carb

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If you are looking for good economy, shop for something with a small primary.

If you want good throttle response, tune your carb, no matter what it is.
 
Per Carroll Shelby: gas mileage, who gives a damn about that! Go get yourself a six pack - stat!
 
JGC403 said:
I already have the Holley 80457 with an electric choke. So why buy something for the 1850?
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Our bad. I'll speak for the three of us who said that. Somehow we had the impression that the other two carbs were not already owned.

According Holley's Carb List, the 1850 comes from the factory with a lighter secondary spring (plain) and the early ones came with smaller accelerator pump nozzles (aka shooters).

For economy with performance, I'd go with a choke. Frankly, If I had that choice, the only reason I would not go with the 1406 is that I already have a stash of Holley parts, jets and micro-drill set. Even so, I might take the Eddy first.

The 1850 will need to be modified to 4150 model with a secondary rear block to change secondary jets. And if I recall, the 1850s are mostly or all single feed with a transfer tube. The 'easy' Holley set up is dual feed - especially if you set it up so the blowls can come off without messing with the feed tubes. The fuel inlet requires a 1" open end wrench to keep it from spinning while the fuel line is tightened or loosened. There's several workarounds because this becomes annoying after a while.

So, in your case, I'd take the 1406. If you really want to compare power you can put it on the dyno after running the current Holley. There was a chassis dyno in Pottstown I used a few years ago. More recently I've been using the one in Pheonixville. Once tuned in, my bet is the power is going to be very similar. But the if some tweaking of the low speed circuits is needed, the Eddy should be easier - and this is where the economy will come.

If you've never felt like you understood how all the carb circuits work, see if you can find a copy of HP Book's Urich and Fisher's Holley Carburators and Manifolds. There's several versions, it doesn't matter which one, an old one is fine unless you aintereted in Holley's FI.

There's a few of us in the area that could probably help on tuning, feel free tp PM or e-mail
 
Or should I sell all 3 carbs and get a street demon? What is so great about Demon carbs? I have heard they are good carbs but why?
 
JGC403 said:
Or should I sell all 3 carbs and get a street demon? What is so great about Demon carbs? I have heard they are good carbs but why?
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Honestly, it sounds like you're a bit lost. There's a couple of threads going in the fuel section discussing the new 'street demon'. But you really need to get some direction or their not going to help you much. This is because the 'whys' mostly discussed in carb forums are the details. Everyone is different, but when I was starting out, I wrote out on paper the major differences between carbs. Then I grouped the carbs that were similar. So if you want to try that., maybe that will help you.
Get them organized by which models are sqare bore and which are spread bores, Which models use direct linkage between the primary and secondary throttles, which ones only use fixed jets and bleeds an which ones use moving rods, etc.

Certain intakes are better matched to spread bores and others to square bore. Also you have a 4 speed car and a slightly hot cam. So then within your budget, see if there is any reason to look beyond what you own. As Dave posted, the biggest factor will be tuning. So you'll need money for the parts and and track or dyno time.

If this is for the Barracuda in your sig, you'll also have to watch stack hieght of the intake, spacers if any and carb. A taller intake and carb will put the air cleaner in to the hood.
 
A lot of good posts here. Reason I picked the 80457 in post #5 is, it was the easiest swap, and gave you the electric choke.

OldmanRick said:
#2......I prefer Holley's anyway, and since you are already running one, it's just a swap, tune & go.
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From a strictly performance standpoint, could you use more cfm....yes.

From a economy standpoint, it's about carb metering. Too many think that the smallest primary will give better mileage. In some cases yes, in some not so much difference. Just remember, a givin' engine, at a givin' rpm, requires a certain air flow. As a example....all things being equal, it might take a 1/4 throttle on a T/Q to get the same as a 1/8th throttle on a AVS/Holley with larger primaries.

I'll just stick with my original thought, and if properly tuned and you use the image below properly, It will give you what you want and will cost the least.
 

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Mattax said:
Honestly, it sounds like you're a bit lost. There's a couple of threads going in the fuel section discussing the new 'street demon'. But you really need to get some direction or their not going to help you much.
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When I was born, Carbs weren't on production cars any more. TBI took over. The first engine that I built was for my fuel injected Jeep. So when it comes to Carbs, I never had a car with one, so I know very little about them. But what better way to learn than to start monkeying with them.

What do you mean direction?
 
So when it comes to Carbs, I never had a car with one, so I know very little about them
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For years people had cars with carbs, and 99% of those people knew very little about carbs. So you didn't miss anything.

To get some direction you need to do two things:
One is to understand the big differences in carb types.
The other is to look at your particular package and decide what type will work best.

In the post above for example, Rick was describing an operational difference between two broad categories of carbs. "....all things being equal, it might take a 1/4 throttle on a T/Q to get the same as a 1/8th throttle on a AVS/Holley with larger primaries." He assumes you know that T/Q is a spreadbore and the AVS and Holley is squarebores. (Holley makes spreadbores too, but if someone says Holley they generally mean a model 4150/60 unless they say otherwise).

That's where the suggestion came to teach yourself to recognize the physical differences in the carbs "Get them organized by which models are sqare bore and which are spread bores, Which models use direct linkage between the primary and secondary throttles, which ones only use fixed jets and bleeds an which ones use moving rods, etc." Other big differences are how the fuel bowls are attached, where the jets are located, and the material(s) that the carb is made of.

As some of the others have posted, they're all different ways to skin the cat, but the final result is pretty similar once they are tuned in. That said, some types of carbs work better both in fit and operation with certain setups.

So go back to your package and see what intake and exhaust is going with that engine and tranny you told us about. Also how much gear in the diff. The intake will have a lot to do with determining whether a spreadbore or squarebore is best. Some are tapped and drilled for both patterns, some don't even physically fit both without adapters. Adapters add hieght - which could be an issue - and often hurt perfomance.
 
JGC403 said:
Or should I sell all 3 carbs and get a street demon? What is so great about Demon carbs? I have heard they are good carbs but why?
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The appeal behind the Street Demon is nearly the same as a Carter ThermoQuad. They have the same design principals, set up for street use performance. The design principal behind a Carter Thermo Quad, Street Demon are based on keeping fuel temp regulated at a lower temp with the plastic body, to prevent boiling/ vapor locking, while providing a lot of atomization from using multiple boosters in the primaries, coupled high velocity throughout the entire range of the primay openning, to help atomization.

The more atomization you get out of a carburetor, the more efficiently it will burn.

Holley makes these, there are some videos and other info about them on their website -

http://www.demoncarbs.com

You could do the same thing with a Carter Thermo-Quad, but sometimes finding jets to tune your carburetor for them, as well as finding one that isn't warped can be tricky. You can get new bodies for them for around $100 if needed, to get proper sealing.

The reason a lot of people stray away from them or love them is because they have a sophisticated idle and cruise circuit, meaning different throttle positions feed the carburetor through different metering systems, so if the throttle position is off from idle, it hinders tuning the cruise and give false fuel metering.

If a ThermoQuad is tuned properly, they run great for street use. They are not the greatest race carb, in my opinion, because of how much the running conditions change in them between idle, cruise and secondary systems. You won't get very consistant runs in rounds, if you are drag racing one, but for street use, they do the right thing. You will need a spread bore intake manifold, preferably a dual plane, in order to run one of them, because they are a spread bore carburetor.

Some of the reasons I went with the Street Demon is because parts are new, I don't have to go through it myself and chase problems out of the one I have (including replacing it's body on the particular one I have) and they fit on a square bore intake.

I think the principal behind a square bore gives more even distribution within the manifold, than a spread bore. The Demon also has a really nice idle feature that helps stabilize it, with an air bleed at the base of the carb, right in front of the primary throttle plates that helps move the air that comes in at the front openning of the throttle plate, back toward the center of the carb.

I also like what they did with the goggle valve secondary, because it helps equalize a dual plane manifold up at higher RPM/throttle, similar to an open passage in a dual plane divider, to get a bit more balancing and power out of the top end of the RPM range. It also helps gain more CFM in a smaller bore pattern, which again, helps fuel mapping, over a spread bore design.

There are sources that do a great job with rebuilding Carter Thermo Quad carbs and do a good baseline tune, but they are about the same price as a Demon. You could learn, yourself, but it does take extensive jetting/ metering, idle mixture, timing and parts that you may not have access to right away.

The best way to go about rebuilding a Thermo Quad is to accumulate all of the parts that you will need for your altitude and tune it. Anything you can use, like a tach, vacuum gauge, timing light, 02 sensors and reader to give you a visualization of how it is running at idle, cruising rpms and wide open throttle are going to give you the best results. That is a good way to gain a baseline, then as stated above, do some passes with it to tune it even further, to get an idea of what it is doing under different acceleration loads.

Basically, by going with the Demon, I just decided to skip the rebuilding aspect of doing my Thermo Quad and started at tuning. They baseline tune these carbs at sea level and are adjusted pretty close to what you will see, with the exception of some minor parts changing and adjustments within small incriments to perfect it on your engine.

If you want high RPM performance, go with a Holley. If you want economy and something more friendly on fuel, go with a Carter Thermo Quad or Street Demon.
 
You might think me crazy but I bought the composite body Street Demon a year ago to put on my magnum crate 360/320 with a 2 plane M1. Yep, call me crazy. Replaced a Holley 750dp that was running ok after a rebuild but it's a 727 car and wanted to put vacuum secondary's back on it, so I took the chance. I took the chance after reading all I could about it and looking for all the intell that was out there. Heck, I didn't want to spend nearly $400 smacks on a carb that didn't give me what I wanted, especially a first year unproven model. What really sold me was that even for a flow of 625cfm, the carb had enough flow to dyno out a big block at 425hp which told me it would have plenty of flow potential for my unmassaged cast iron magnum heads with long tube headers.
I'm not a big fan of Edelbrock Carbs, mostly because the few I've been associated with in the past just didn't have the greatest response when you mashed the pedal and lord knows we love to mash the pedal. Nonetheless I was also concerned that the Demon was just another Eddy and I'd be stuck with a paperweight when I was done. Holy cow did I make a great choice. I absolutely love it. Easy tunability, idle control, smooth quick throttle response and "ohhh my God" pedal mashing kickdown launch.
I'm going to try an Eddy RPM air gap next just for fun. Happen to have one on the shelf here.

http://www.demoncarbs.com/Categories.asp?#Carburetors

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Totally agree with DaveBonds. Check it out on their website too and research all you can. It def did exactly what I wanted and looks like your in the same ballpark as me.
Good luck. :D
 
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