How To Choose A Carburetor

today we're gonna talk about selecting a proper carburetor main focus is we're gonna speak about today are gonna be the overall size and type of the carburetor that you're going to choose so we're gonna start by talking about selecting the proper carburetor size carburetor sizing is a very important aspect of selecting the correct carburetor for your overall combination one thing you want to avoid doing is selecting a carburetor that is too large for your overall combination it's kind of what we referred to as more's Law lot of people think that more is better when it comes to carburetor selection it's anything but the case it's very important to make sure you select the proper carburetor to give you overall drivability, throttle response, and the characteristics that somebody's looking for on a daily driver or even a race application so your selections gonna depend if it's a race application or a streetcar there are some differences in between when we talk about carburetor size were initially talking about selecting one for a street application we talk about selecting a carburetor for a Street application or even a race application one of the tools that Holley's provided for you to make it easy and to take a little bit of the guesswork out of it is the Holley carburetor selection tool you can view that tool and utilized by going to www.Holley.com it will allow you to put in some specific information relative to your combination and it will give you a directional guide as to available carburetors that Holley has available at Holley as well as the demon carburetor line that will figure specific needs when your dealing with carburetors there's also a generalized formula that you can use a common example would be to take a 406 cubic inch small block Chevrolet at 6,500 rpm you take the engine displacement times maximum RPM it would give you a total of two million six hundred and thirty nine thousand you can then take that total and divided by three four five six it's an easy for me to remember it's engine displacement times maximum RPM divided by three four five six in this case it would give us a total of around seven hundred and sixty-four CFM which if you rounded down a little bit brings in about 750 CFM now its based at a hundred percent volumetric efficiency that formula would be good for a performance application we are really focus more on mid to upper rpm performance potential if you stay a little bit smaller on the carburetor its gonna give you better low to mid end characteristics as far as throttle response and general low to mid rpm drivability if you look at that engine at approximately eight what we refer to as a 85% volumetric efficiency which you normally have in an Street Stock to mild application that will put you in it about a 650 cfm carburetor that general difference of a hundred CFM can really make a broad difference when it comes to the overall characteristics and drivability of the vehicle so next we're going to talk about carburetor types we've talked about size now let's talk about the overall types of carburetors that are available what we see before me are 2 commonly refered to as a modular Holley design carburetor which most people refer to as a model 4150 or 4160 carburetor the carburetor down here on the bottom is a single feed vacuum secondary side hung bull carburetor this style of carburetor has been on for years and is a excellent type of carburetor choice for a average street application the second carburetor looking at is a Holley double pumper everybody knows a Holley double pumper it's been really the staple for performance applications for several decades now and it's still one of the most popular carburetors we produce today some of the differences that kind of go on to play with what we're talking about with carburetor sizing when we talk about a vacuum secondary carburetor we talked about more's Law the Holley vacuum secondary carburetor will actually self regulate itself based on engine demand if you were to look underneath the carburetor if i open the throttle wide open you'll see the primary throttle blades open all the way but the secondaries don't as engine demand increases the demand for a additional air flow well increases for additional performance in rpm and the carburetor when properly tuned will have a vacuum control diaphragm that will open up the secondaries where this is really key is if you do select a carburetor that's a little bit oversized for your application it will do everything within its power to regulate and reduce that overall amount of airflow to maintain optimal air velocity and efficiency through the carburetor and when you get into a double pumper carburetor what you will find is when you go to wide-open throttle the primary and secondary is automatically open that's gonna give you the application that requires a rapid increase in rpm that has the actual need and ability to handle that rapid increase and airflow some of the common differences that you would run into as far as uses if you have a vehicle thats heavier weight low to mid rpm Street drivability automatic transmission a vacuum secondary car bridge can give you much better throttle response and overall drivability and characteristics when when you deal with the double pump Holley carburetor it's really key to have this match to the requirements a double pumper carburetor is generally good properly suited for a lightweight vehicle generally with a manual transmission with a lot of gear or an automatic with a loose performance converted that's going to allow it to build rpm rapidly without getting too technical one of the things to kind of think about carburetor functionality it's a lot like an aircraft if you think of a wing of an airplane you need a certain amount of air speed the generate lift and sustained flight otherwise the wings stall the plane crashes a carburetor works really in the same way the air speed through the venturi creates a pressure drop that gives you a fuel signal the higher the air velocitiy is through the venturi of the carburetor the stronger that signal is in the better the overall performance in response is going to be the characteristics of that carburetor so you really want to make sure that you match the carburetor based on your specific requirements one of the other carburetors that we've released through the demon line is the Street demon this kind of brakes conventional a little bit compared to a modular single feed 4160 and a double pump 4150 carburetor and the design character if you look at the bottom of the carburetor when we open the throttle you'll see that they physically open like a double pumper but when we look at the top you see that the only section what's up with the choke is the primary they have an adjustable air valve that's at the back that based on physical demand will open very similar to a vacuum secondary Holley so their characteristics are kind of a blend between the two we offer the street demon in a 625 as well as a 750 CFM application version these carburetors are ideally suited to a stock too mild performance street application to give you X on throttle response instead of a conventional moduel on Holly this is a two piece design there are no actual exposed fuel services below the top gasket level and these are really nice addition that we've created through the Holley product line so we've talked about the size of carburetor and we've talked about from general types of carburetors one of the things we want to speak about as well as the choke some carburetors are equipped with a choke some carburetors are equipped without a choke and are different types of chokes depending on the area that you live in especially relative to climate may dictate whether or not you need a choke or you may want to have a choke and there are some pros and cons to having a carburetor with or without a choke and different types first type of carburetor choke we can talk about is going to be an electric choke alot of Holley carburetors are designed with an automatic electric choke it makes for a simple operation all the end user has to do with the install the carburetor is wire a switch 12 volt wire to the choke housing to the cap and when the key is on the engines running it will basically power up the choke as its powered up it heats up and as it heats up it rotates and opens up the choke when a vehicle cools off it allows it to close for comfort and automatic electric choke another type of choke we have is a manual choke a manual choke requires a actual physical connection of a control cable that is run into the passenger compartment of the vehicle were can be controlled by the operator of course it requires manual intervention for it to function one of the benefits you can run into with an electric choke is it kind of takes the guesswork and the need to manually operate a cable out of the mix when you deal with a manual choke it gives you full control one of things a lot of the times you see is when you start getting into more hiring performance carburetor for street and strip use you start getting into a carbureted generally is going to either have a manual choke or we'll talk about the moment are ultra XP style carburetor some of our street HP's that do not have a choke at all one of the benefits to having a manual choke for performance applications is a lot of the times because of the design of the intake manifold the camshaft you may or may not need much choke or you may need to give it a lot of initial choke and then take it off rapidly and you have that overall control whereas with an automatic choke it sorted limits you a little bit you can adjust how hard the joke is on how fast it comes off but you just don't have that finite control me personally if I'm gonna run a choke I prefer mechanical choke maybe just cause I want to have that control over it but it's generally for me personally what I would prefer another option that you can have would be more of a race Pacific Harbour that has no choke at all where this can be a little bit problematic as if it is a street vehicle you live in a cold climate the vehicle can be a little harder to start it can be more temperamental at cold Operation those of you that have run a vehicle without a choke you know the deal you get in there it's cold you gotta pump the throttle you've got trying to find the sweet spot you get the engine the start you got a feather the throttle and you basically have to babysit your engine until it comes up to temperature where as if you're utilizing a physical choke you don't have to do as much babysitting automatic choke will work automatically manual choke is the engine warms up you physically just push the choke off you will find that depending on your climates we've discussed it's more critical so if you have somebody that for example I got some friends that live in North Pole Alaska they're gonna want to have a choke i've also got some friends that live in South Florida chances are they won't need a choke when it comes to choke selection and they need for what it really boils down to personal preference you just need to understand that if you do not have a vehicle with the choke that it can be hard to cold start until engine gives up the operating temperature can tend to be a little bit temperamental and may want to hesitate could potentially backfire so you need to understand the difference of having a choke and not and some of the overall characteristics when you're selecting a carburetor we've talked about size we've talked about type and we've talked about chokes let's talk about finish this particular double pumper has our classic dichromate finish this is a finish has been around for decades characterized by the overall gold type of appearance to the carburetor this type of finish is really popular with older muscle car owners people doing restorations want to keep that nostalgic year and period correct apperence for their vehicle this finish will commonly be found on our classic double pumper series of carburetors times have changed a little bit and people want something that's a little bit more fancy or little bit of bling for lack of a better term one of the features that we have a lot of a carburetors now is the shiny finish that's featured on a lot of our aluminum as well as ours zinc based Street HP carburetors and it's a tumble polished finish that gives you a nice shiny appearance one of the other finishes we have is the hardcore gray you'll find this featured on some of our new ultra Street Avengers the ultra double pumpers as well as the ultra XP series of carburetors the hardcore gray finish is not only there for a apperence and grant it can't deny that it looks fantastic it gives you that rugged strong aggressive look i always talk about black being the new chrome but it goes beyond overall appearance this particular hardcore gray finish is a mil-spec hard coat anodizing and anodized both externally as well as internally what that does is as well as giving you good looks it gives you corrosion protection a lot of your newer race fuels are pretty exotic with some of the chemical combinations in them well as the ethanol chasm pump gas that can lead to corrosion problem and this not only gives you aggressive looks it also gives you protection against those corrosive properties of a lot of your modern pump fuels next carburetor brings them and turn around so you can see it a little bit better and angle it up is a combination of a shiny finish as well as a bright dip anodized metering block and baseplate combination this particular ultra Street Avenger is featured with silver and red this style of carburetor is also available in silver and blue as well as silver and black we do have the multi color combinations available in the ultra street avengers the ultra double pumpers the ultra XPs as well as some of the gen 3 dominators we have available last finish i want to talk about as we see here on our 625 as well as the 750 CFM Street demons it's also a black finish you will see that the overall appearance is slightly different this particular finish it's offered on the street demon is a black ceramic coating gives you that rugged look as well as being some kind of gives you a lot of durability the street demon is also available in 2 other finishes its available in the shiny tumble polished finish we talked about on the modular Holley's as well as a basically hand polished mere type of finish that's available on that carburetor as well some of the other things to keep in mind when you are dealing with the carburetor they really should be talked about on types I just want to cover really quick is fuel inlet types in this particular soft carpet is a single filament which simply requires a single fuel line from your fuel pump and regulator and supply to feed the carburetor when you get into our classic modular 4160 type of street Holley it also is available with a single feed its got a single feed their primary fuel bonus or transferred to that feeds fuel to the secondary the other application and style of carburetor you have you see on the ultra XP is what's commonly referred to as dual feed the dual feed is generally can also be characteristic associated with a center hunger cathedral type of fuel bowl when you select your cartridges really keep that in mind that if you are selecting carburetor that's a dual feed that when you're looking things up you need to remember to hook up a fuel line to both fuel bowls every once in a while we will get a call on a tech line we get a customer that went from a single feed carburetor to a dual feed carburetor they weren't thinking about it they just look up a single fuel line and when they open up that secondary there's no fuel there well we're talking about that stumble situation in so just make sure that you really plan out your installation matchup your size your type your choke and your overall finish that really that really compliments your combination and gives you a nice rounded out balance for good looks as well as drivability performance and cold start reliability

Channel: Holley

Views: 296,780

Keywords: carburetor, Holley, Performance, Products, How To

Id: pKG8-NnS9OI

Length: 15min 49sec (949 seconds)

Published: Wed Dec 16 2015