Choosing a carburetor

Revision as of 13:09, 26 January 2012 (edit)

Revision as of 14:34, 26 January 2012 (edit) (undo)

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The vacuum secondary Holley uses a different approach where the throttle blades are what is controlled by engine demand, but the vacuum secondary Holley is also self-regulating. And because of that, the Edelbrock/Carter and Holley vac. secondary carbs are somewhat more forgiving.

−

I say somewhat more forgiving because even though a 750 Holley w/vacuum secondaries will self-regulate the secondaries, the primaries- what you drive on 99% of the time- are also larger on a 750 than a 600 Holley. And what that can mean is the 750 won't give as crisp of a throttle response and possibly less MPG because of the bigger throttle bore and venturi. This is not an issue w/the Q-jet; its primaries are small and have primary booster rings to provide a strong vacuum signal. The 800 cfm Q-jet castings are used on 4.3L truck engines to give you an idea of the flexibility of a Q-jet.

+

I say somewhat more forgiving because even though a 750 Holley w/vacuum secondaries will self-regulate the secondaries, the primaries- what you drive on 99% of the time- are also larger on a 750 than a 600 Holley. And what that can mean is on a mild or smaller displacement engine, the 750 won't give as crisp of a throttle response and possibly less MPG because of the bigger throttle bore and venturi. This is not an issue w/the Q-jet; its primaries are small and have primary booster rings to provide a strong vacuum signal. The 800 cfm Q-jet castings are used on 4.3L truck engines to give you an idea of the flexibility of a Q-jet.

−

So all in all, I would have to say there's definitely something to be said in favor of sizing the carb as close as you can to what the engine actually needs. The Q-jet is damn hard to beat but if it has a downside it's that you have to learn how to tune it. The secondary side is easy as pie to tune- everything needed is external. It's the primary side that you have to open the carb up to tune almost anything except the APT (as long as you've got a removable APT plug) and the idle mixture. And there's a little more to taking the top off a Q-jet than the front bowl off a Holley.

+

So all in all, I would have to say there's definitely something to be said in favor of sizing the carb as close as you can to what the engine ''actually'' needs. The Q-jet is damn hard to beat but if it has a downside it's that you have to learn how to tune it. The secondary side is easy as pie to tune- everything needed is external. It's the primary side that you have to open the carb up to tune almost anything except the APT (as long as you've got a removable APT plug) and the idle mixture. And there's a little more to taking the top off a Q-jet than the front bowl off a Holley.

Regardless of what carb is used, if using a GM OD automatic tranny the trans TV cable adjustment is super critical. It has to be right or the trans will fail.

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Holley carburetors have been around for a long time, and their quality is fairly good. They manufactured carburetors for GM in the 60's, and have been a favorite among hot rodders through the years. Holley has several different models for different applications.

−

Ford used Holley carbs basically from their beginning. GM began using Holley carbs in the '60's on select high performance engines, including 3x2 bbl on BBC Corvette engines.

+

Ford used Holley carbs basically from their beginning. GM began using Holley carbs in the '60's on select high performance engines, including 3x2 bbl on BBC Corvette engines.

Here are just a few:

Line 55:

-Holley 80457S - Decent 4 BBL carburetor that flows 600 CFM. It uses mechanical secondaries, so economy takes more of a "backseat" on this one. Would probably be ideal for your daily driver/mild build. This is about the average 4 BBL sized carburetor.

−

The 0-80457 is a vacuum secondary carb with electric choke, and is in the 4160 family. ~~All 4160 carbs are vacuum secondary.~~ I would use the 0-1850 as an example a basic 600 CFM carb, and the 0-3310 as a 750 CFM example. And I'd start by describing the various carb families, like 4150, 4160, 4175, etc. Newer and more popular carbs are Street Avenger series of 4150 carbs. By the way, the S or C after the carb list number designates the finish. S = shiny, C = zinc chromate. I can do a complete write-up here, or you can simply go to Holley's website for the facts.

+

The 0-80457 is a vacuum secondary carb with electric choke, and is in the 4160 family. I would use the 0-1850 as an example a basic 600 CFM carb, and the 0-3310 as a 750 CFM example. And I'd start by describing the various carb families, like 4150, 4160, 4175, etc. Newer and more popular carbs are Street Avenger series of 4150 carbs. By the way, the S or C after the carb list number designates the finish. S = shiny, C = zinc chromate. I can do a complete write-up here, or you can simply go to Holley's website for the facts.

−

-Holley 80531 - This carburetor is 850 CFM. There is little to no economy with this bad boy; this is for use on race/high RPM or strong street/strip type engines.

+

-Holley 80531 - This carburetor flows 850 CFM and is a model 1850. There is little to no economy with this bad boy; this is for use on race/high RPM or strong street/strip type engines.

+

4776, 4777, 4778, 4779, 4780, 4781 - These are the traditional "double pumpers". Ranging from 600 cfm to 850 cfm, they are a mainstay of racing and hot street engines. If matched correctly to their application they can be used on the street but economy will not be as good as a vacuum secondary carb similarly chosen. These are 1850 type carbs, having both a primary and secondary metering block and accelerator pumps on both the primary and secondary sides of the carb.

+

BTW, the 4160 is a vacuum secondary carb- w/one exception, and that is the 660 cfm "center squirter" carb, originally designed to fit on a dual four barrel intake end-to-end. The 4150 can be either a vacuum secondary or a double pumper carb.

+

4604 - This is one of the Holley 3-barrel carbs rated at 1050 cfm. The 3 barrel Holley was originally designed for NASCAR stock car racing and was used on the 426 Hemi in 1964. It preceded the Dominator and offered in several versions. It never really hit its stride, suffering from issues below WOT because of the less-than-ideal secondary venturi shape (and booster style in the 1050 cfm version). It was made basically from a Holley 850 w/the center taken out of the secondaries. It used an oversize secondary vacuum diaphragm housing (which the diaphragms are no longer available for) and an early version of the "cathedral" center hung float bowls made famous later, on the Dominator. A carb kit for a 850 can be used w/some modification to rebuild them. Today it has a following among collectors and some actually still use them. They can fetch high prices for good examples.

+

0-80532-1 - This represents the Dominator series of Holley carbs, this one is 1250 cfm. The Dominator first was used on the high banks of NASCAR to feed the biggest engines ever used in that form of motorsports. They became just as popular for drag racing and today are available as small as 750 cfm (Holley 0-80186-1) for the "look" w/o the huge flow so it can be used on the street. Because the bolt pattern and footprint is considerably larger than the traditional Holley "squarebore" pattern, a Dominator requires a dedicated intake manifold. Adaptors are available, but should only be used in special circumstances if at all.

[http://www.usmotors.cz/old/tech_tips/HolleyCarbList.pdf Holley Carb Numerical Listing]

Choosing a carburetor

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@@ Line 34: / Line 34: @@
 The vacuum secondary Holley uses a different approach where the throttle blades are what is controlled by engine demand, but the vacuum secondary Holley is also self-regulating. And because of that, the Edelbrock/Carter and Holley vac. secondary carbs are somewhat more forgiving.
-I say somewhat more forgiving because even though a 750 Holley w/vacuum secondaries will self-regulate the secondaries, the primaries- what you drive on 99% of the time- are also larger on a 750 than a 600 Holley. And what that can mean is the 750 won't give as crisp of a throttle response and possibly less MPG because of the bigger throttle bore and venturi. This is not an issue w/the Q-jet; its primaries are small and have primary booster rings to provide a strong vacuum signal. The 800 cfm Q-jet castings are used on 4.3L truck engines to give you an idea of the flexibility of a Q-jet.
+I say somewhat more forgiving because even though a 750 Holley w/vacuum secondaries will self-regulate the secondaries, the primaries- what you drive on 99% of the time- are also larger on a 750 than a 600 Holley. And what that can mean is on a mild or smaller displacement engine, the 750 won't give as crisp of a throttle response and possibly less MPG because of the bigger throttle bore and venturi. This is not an issue w/the Q-jet; its primaries are small and have primary booster rings to provide a strong vacuum signal. The 800 cfm Q-jet castings are used on 4.3L truck engines to give you an idea of the flexibility of a Q-jet.
-So all in all, I would have to say there's definitely something to be said in favor of sizing the carb as close as you can to what the engine actually needs. The Q-jet is damn hard to beat but if it has a downside it's that you have to learn how to tune it. The secondary side is easy as pie to tune- everything needed is external. It's the primary side that you have to open the carb up to tune almost anything except the APT (as long as you've got a removable APT plug) and the idle mixture. And there's a little more to taking the top off a Q-jet than the front bowl off a Holley.
+So all in all, I would have to say there's definitely something to be said in favor of sizing the carb as close as you can to what the engine ''actually'' needs. The Q-jet is damn hard to beat but if it has a downside it's that you have to learn how to tune it. The secondary side is easy as pie to tune- everything needed is external. It's the primary side that you have to open the carb up to tune almost anything except the APT (as long as you've got a removable APT plug) and the idle mixture. And there's a little more to taking the top off a Q-jet than the front bowl off a Holley.
 Regardless of what carb is used, if using a GM OD automatic tranny the trans TV cable adjustment is super critical. It has to be right or the trans will fail.
@@ Line 47: / Line 47: @@
   Holley carburetors have been around for a long time, and their quality is fairly good. They manufactured carburetors for GM in the 60's, and have been a favorite among hot rodders through the years. Holley has several different models for different applications.
-Ford used Holley carbs basically from their beginning.  GM began using Holley carbs in the '60's on select high performance engines, including 3x2 bbl on BBC Corvette engines.
+Ford used Holley carbs basically from their beginning. GM began using Holley carbs in the '60's on select high performance engines, including 3x2 bbl on BBC Corvette engines.
 Here are just a few:
@@ Line 55: / Line 55: @@
 -Holley 80457S - Decent 4 BBL carburetor that flows 600 CFM. It uses mechanical secondaries, so economy takes more of a "backseat" on this one. Would probably be ideal for your daily driver/mild build. This is about the average 4 BBL sized carburetor.
-The 0-80457 is a vacuum secondary carb with electric choke, and is in the 4160 family.  All 4160 carbs are vacuum secondary.  I would use the 0-1850 as an example a basic 600 CFM carb, and the 0-3310 as a 750 CFM example.  And I'd start by describing the various carb families, like 4150, 4160, 4175, etc.  Newer and more popular carbs are Street Avenger series of 4150 carbs.  By the way, the S or C after the carb list number designates the finish.  S = shiny, C = zinc chromate.  I can do a complete write-up here, or you can simply go to Holley's website for the facts.
+The 0-80457 is a vacuum secondary carb with electric choke, and is in the 4160 family. I would use the 0-1850 as an example a basic 600 CFM carb, and the 0-3310 as a 750 CFM example.  And I'd start by describing the various carb families, like 4150, 4160, 4175, etc.  Newer and more popular carbs are Street Avenger series of 4150 carbs.  By the way, the S or C after the carb list number designates the finish.  S = shiny, C = zinc chromate.  I can do a complete write-up here, or you can simply go to Holley's website for the facts.
--Holley 80531 - This carburetor is 850 CFM. There is little to no economy with this bad boy; this is for use on race/high RPM or strong street/strip type engines.
+-Holley 80531 - This carburetor flows 850 CFM and is a model 1850. There is little to no economy with this bad boy; this is for use on race/high RPM or strong street/strip type engines.
+, 4777, 4778, 4779, 4780, 4781 - These are the traditional "double pumpers". Ranging from 600 cfm to 850 cfm, they are a mainstay of racing and hot street engines. If matched correctly to their application they can be used on the street but economy will not be as good as a vacuum secondary carb similarly chosen. These are 1850 type carbs, having both a primary and secondary metering block and accelerator pumps on both the primary and secondary sides of the carb.
+BTW, the 4160 is a vacuum secondary carb- w/one exception, and that is the 660 cfm "center squirter" carb, originally designed to fit on a dual four barrel intake end-to-end. The 4150 can be either a vacuum secondary or a double pumper carb.
+- This is one of the Holley 3-barrel carbs rated at 1050 cfm. The 3 barrel Holley was originally designed for NASCAR stock car racing and was used on the 426 Hemi in 1964. It preceded the Dominator and offered in several versions. It never really hit its stride, suffering from issues below WOT because of the less-than-ideal secondary venturi shape (and booster style in the 1050 cfm version). It was made basically from a Holley 850 w/the center taken out of the secondaries. It used an oversize secondary vacuum diaphragm housing (which the diaphragms are no longer available for) and an early version of the "cathedral" center hung float bowls made famous later, on the Dominator. A carb kit for a 850 can be used w/some modification to rebuild them. Today it has a following among collectors and some actually still use them. They  can fetch high prices for good examples.
+-80532-1 - This represents the Dominator series of Holley carbs, this one is 1250 cfm. The Dominator first was used on the high banks of NASCAR to feed the biggest engines ever used in that form of motorsports. They became just as popular for drag racing and today are available as small as 750 cfm (Holley 0-80186-1) for the "look" w/o the huge flow so it can be used on the street. Because the bolt pattern and footprint is considerably larger than the traditional Holley "squarebore" pattern, a Dominator requires a dedicated intake manifold. Adaptors are available, but should only be used in special circumstances if at all.
 [http://www.usmotors.cz/old/tech_tips/HolleyCarbList.pdf Holley Carb Numerical Listing]