Announcer: Brought to you by JEGS.
Male: There is no such thing as a one size fits all carburetor.
Purchasing a carb that's best suited for what you will actually be doing with your car versus
what you wish you'll be doing with it can make a large difference in your satisfaction
level.
Do you have a street car that goes to the drag strip once or twice a year?
Are you bracket racing every weekend, or just attending cruise in's once a month?
In this short video, we'll explain the things you need to know, why you need to know them,
and what you'll need to determine the proper type and size carburetor for your application
before you call JEGS.
There are four different types of common carburetor flanges which are determined by the intake
manifold you're using.
The most common style is a square bore, which is what typical Holley 4150 or equivalent
carburetor will use.
Older G.M.
factory quadra jet and some older OE 40 intake manifolds will use what's called a spread
bore.
A dominator or 4500 series flange is wider than a square bore flange and is typically
used on serious race engines.
Then there's the two barrel flange which will require you to check the center to center
measurements of the mounting holes before ordering.
Like your lawn mower or leaf blower, an automotive carburetor can also have a choke.
There are two styles; electric or manual.
An electric choke will operate automatically when the engine is cold.
It needs to be powered by an ignition on circuit, and will require adjustment seasonally to
promote optimal performance in all conditions.
A manual choke uses a cable, and will require proper installation in operation.
The cable will need to be pulled out every time the engine is started when cold, and
then pushed back in to open the choke plates once the engine is warm.
Lastly, race carburetors typically don't use a choke at all.
There are also two different types of secondaries.
The throttle passages the carburetor uses during high load operation, mechanical and
vacuum.
Vacuum secondaries are typically used for street cars as they have the ability to modulate
fuel supply at different input speeds based on the vacuum signal the carburetor sees from
the engine.
Conversely, mechanical secondaries are optimal for use with wide open throttle race applications.
The formula we're using here will help you to determine the proper carburetor size for
your engine.
You're solving for the engines airflow capability and cubic feet per minute.
The RPM number should be the highest RPM the engine achieves before shifting gears.
And you'll need to estimate the volume metric efficiency of the engine.
A naturally aspirated stock engine's VE is around 70%.
Well, tuned performance engines are around 85 to 90% efficient.
And a professionally built race engine will be 95% efficient at its peak or more.
For example, let's calculate the right CFM for a 350 cubic inch engine with a 6,500 RPM
red-line and an estimated 75% VE.
For this example engine, a 500 CFM carburetor would be a good choice for drivability and
fuel economy.
At this point, you should have a greater understanding of what's require to know when you're selecting
a carburetor.
You can check out the JEGS website or call us to pick out the carburetor that best suits
your needs from Holley, Quick Fuel, Demon, Pro-form, Edelbrock, and others.
Each of the brands has different features and benefits, and now that you know how big
your carburetor needs to be, you can decide what's best for you.
Keep in mind that proper carb selection is just the starting point.
The manufacturers do a good job setting up carburetors to run straight out of the box
for typical engines.
But you can expect to do a bit of tuning for best performance and drivability.
Stay tuned for more useful information from JEGS on getting your new carb dialed in.
Announcer: Brought to you by JEGS.