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