As everyone knows, I am a HUGE Quadrajet fan. The biggest problem most people have with them is a failure to understand how they work and to properly set them up. If all you do is go down the drag strip and your car sees no real street time, a Holley is fine. It is crude in every regard, but for dumping fuel and air into an engine at WOT it does not need sophistication. It will not hold it's tune and needs to constantly be recalibrated with every significant weather change and gets quite annoying. I was forced to drive my 1979 AMC Spirit with a AMC 360 and a Holley 3310 ( 750 vacuum) and it was a nightmare. Almost every day I had to mess with it for some reason or another. An unseen new fuel leak also got all over the intake manifold, and then a carb backfire proceeded to set the engine on fire. Quick work with a fire extinguisher (ALWAYS carry one in an old car!!!) kept the car from burning to the ground. On the other hand, I ran an Edelbrock Performer series ( Carter AFB) 600 on my 355 and it was set and forget. Reasonable fuel economy, good idle and good full throttle too. Now, a BAD Quadrajet is no fun at all, and most of the cores you find need a few repairs to work properly. Most have worn throttle shaft bores in the baseplate and for that reason will not hold a steady idle. I had one like that on my 355 and it was a pig. There is a whole story of what happened with my carb issues earlier this year that ended with me having to pull the heads due to stuff falling down the manifold, but I will spare you.
Anyhow, here's my assessment of the two carbs and their good/bad sides:
Quadrajet: Good- Holds a tune well, good fuel economy, better idle quality, air valve secondaries with adjustable spring that makes it a variable CFM carb, factory sizes of 600, 750 and 800 cfm-change size by cutting down a small stop with a Dremel, all Quadrajets use the same throttle blades, No vacuum diaphragm to blow since it is a purely mechanical system with the air valve being sucked open by the engine vacuum directly acting on it. Large number of applications allow for finite tuning much more accurately than the Holley, shorter than a Holley, vent tubes at the center and not the edges allowing for more options in air cleaners, uses stock throttle and TV cable linkages ( if you use the later carb), metering rods used in primaries allowing for both a stepped fuel curve and vacuum referenced metering, used by every one of the big 3 at some time or another( Ford used it for 1 year on the Lima V8 before switching to Motorcraft and Chrysler used it on the last of the 318 powered Diplomats, New Yorkers and Grand Fury's in the 80's)
Quadrajet: Bad- Idle feed passages must be matched to the size of the engine, so you need to find one off a similarly sized engine to yours, Throttle shaft bore wear, takes lots of time to tune and set up properly when on an engine that deviates far from stock, small float bowl capacity, limited number of tuning parts supported for purchase new, No longer available new ( Edelbrock discontinued them a few years back), air horn can warp if the carb is torqued down too tightly resulting in a minor leak, fuel filter threads on front of carb prone to stripping if you are not very careful, will not fit square flange specific manifolds
Holley: Good-widely supported in speed shops and catalogs, Simplicity- any idiot can make one run fairly well , lots of applications over the years, available anywhere from 390 cfm to 1150 cfm, Available in both square flange and spread bore designs, cheap to buy and plentiful used- can be as little as $20 for a 600cfm carb at a swap meet, large float bowl capacity
Holley: Bad- Crude part throttle and idle circuits, idle feed passages are typically sized for their original intended application and as such, may run too rich or lean in normal driving without modification ( I.E a #3310 750 vac. carb was originally intended for a 375 hp 396 and is always rich on smaller engines), Needs a large pump shot to cover up the lean spot that occurs during secondary transition, Most are square flange and have a weaker vacuum signal on the primaries than a spread bore requiring a higher idle speed to be able to run, goes out of tune quickly and is very sensitive to temperature changes, prone to fuel leaks due to side hung bowls and metering blocks. Tends to leak from gaskets and bolt holes, Power valves prone to rupture with engine backfires unless modified with a check valve, secondary operation via external diaphragm instead of air valve. Needs spring changes to tune it, but they are hard to change without a quick change kit, automatic choke is not always included, secondary metering plates on basic models are difficult to tune unless you spend more money for an upgrade or buy a selection of expensive plates, metering plates prone to warpage and will leak badly if it happens.
I will also note that there are actually 3 designs of Carburetors which were sold by Edelbrock (the Carter designs were actually manufactured by Italy's Webber for Edelbrock). The first one was the Performer series which is basically just a Carter AFB (stands for: Aluminum Four Barrel). This is an air valve carb, but the opening rate is fixed and not adjustable as it uses a counterweight instead of spring tension to modulate it. The Second was the Performer RPM carb which was a Quadrajet. It is discontinued, but the company still offers a limited number of tuning parts for it. The third is another Carter , the Carter AVS (stands for: Air Valve Secondary) which is marketed as the "Thunder Series AVS" by Edelbrock. Some consider the AVS to be better than the Quadrajet as it too is a spread bore carb with air valve secondaries and a vacuum referenced set of metering rods. Unlike the Quadrajet, however, the secondary metering is vacuum referenced with power pistons like the primaries and not mechanically determined by the air valve opening rate via a cam that rotates on the shaft. Carter also made another 4 barrel called the "Thermoquad"-so named because of the Phenolic resin "thermoplastic" main body designed to control fuel temperature. Unfortunately, the plastic warps and leaks and it was discontinued by Chrysler, the only manufacturer to adapt it. Carter's first 4 barrel was the "WCFB" (Will Carter Four Barrel) used by Chevy and Studebaker in the 50's ( maybe others too). It was the first production 4 barrel carb, but it weighed around 20 lbs! The Holley as we recognize it today saw it's first application by Ford on the "Thunderbird" 312 Y block at around the same time.
As for BG/Demon, they are based on the Holley modular concept but seem to be a nicer overall carb. The fuel metering is more accurate and the parts have a better quality feel to them. They also have variations such as removable sleeve models that can be easily re-sized, etc. I do not have any experience with them so I will withhold judgment or remarks about them.
I will also note that the best carburetor solution is probably the most difficult to tune and that is an individual runner setup with one barrel per cylinder. Companies like Webber, SU and Mikuni have all produced setups like this over the years, and some are available in the aftermarket. The only factory domestic V8 application I know of for the Webber were some Shelby cars in the 60's, and these were downdraft carbs. Ferrari, Porsche and Lamborghini also used downdraft Webbers. Webber also made side draft carbs, but for some reason I can't remember any applications right now. SU was a major supplier to British makes like Triumph, MG and Austin-Healey. Mikunis are what you will see when you open the hood of an original Datsun 240z or PL510 SSS ( Super Sport Sedan- Japan only model). The SU and Mikuni carbs were only used in side draft applications. Oddly, when British Leyland made the Rover P6 and SD1 with the old Buick 215 V8, it used dual side draft SU's feeding into an adapter on top of the manifold!
Anyhow, here's my assessment of the two carbs and their good/bad sides:
Quadrajet: Good- Holds a tune well, good fuel economy, better idle quality, air valve secondaries with adjustable spring that makes it a variable CFM carb, factory sizes of 600, 750 and 800 cfm-change size by cutting down a small stop with a Dremel, all Quadrajets use the same throttle blades, No vacuum diaphragm to blow since it is a purely mechanical system with the air valve being sucked open by the engine vacuum directly acting on it. Large number of applications allow for finite tuning much more accurately than the Holley, shorter than a Holley, vent tubes at the center and not the edges allowing for more options in air cleaners, uses stock throttle and TV cable linkages ( if you use the later carb), metering rods used in primaries allowing for both a stepped fuel curve and vacuum referenced metering, used by every one of the big 3 at some time or another( Ford used it for 1 year on the Lima V8 before switching to Motorcraft and Chrysler used it on the last of the 318 powered Diplomats, New Yorkers and Grand Fury's in the 80's)
Quadrajet: Bad- Idle feed passages must be matched to the size of the engine, so you need to find one off a similarly sized engine to yours, Throttle shaft bore wear, takes lots of time to tune and set up properly when on an engine that deviates far from stock, small float bowl capacity, limited number of tuning parts supported for purchase new, No longer available new ( Edelbrock discontinued them a few years back), air horn can warp if the carb is torqued down too tightly resulting in a minor leak, fuel filter threads on front of carb prone to stripping if you are not very careful, will not fit square flange specific manifolds
Holley: Good-widely supported in speed shops and catalogs, Simplicity- any idiot can make one run fairly well , lots of applications over the years, available anywhere from 390 cfm to 1150 cfm, Available in both square flange and spread bore designs, cheap to buy and plentiful used- can be as little as $20 for a 600cfm carb at a swap meet, large float bowl capacity
Holley: Bad- Crude part throttle and idle circuits, idle feed passages are typically sized for their original intended application and as such, may run too rich or lean in normal driving without modification ( I.E a #3310 750 vac. carb was originally intended for a 375 hp 396 and is always rich on smaller engines), Needs a large pump shot to cover up the lean spot that occurs during secondary transition, Most are square flange and have a weaker vacuum signal on the primaries than a spread bore requiring a higher idle speed to be able to run, goes out of tune quickly and is very sensitive to temperature changes, prone to fuel leaks due to side hung bowls and metering blocks. Tends to leak from gaskets and bolt holes, Power valves prone to rupture with engine backfires unless modified with a check valve, secondary operation via external diaphragm instead of air valve. Needs spring changes to tune it, but they are hard to change without a quick change kit, automatic choke is not always included, secondary metering plates on basic models are difficult to tune unless you spend more money for an upgrade or buy a selection of expensive plates, metering plates prone to warpage and will leak badly if it happens.
I will also note that there are actually 3 designs of Carburetors which were sold by Edelbrock (the Carter designs were actually manufactured by Italy's Webber for Edelbrock). The first one was the Performer series which is basically just a Carter AFB (stands for: Aluminum Four Barrel). This is an air valve carb, but the opening rate is fixed and not adjustable as it uses a counterweight instead of spring tension to modulate it. The Second was the Performer RPM carb which was a Quadrajet. It is discontinued, but the company still offers a limited number of tuning parts for it. The third is another Carter , the Carter AVS (stands for: Air Valve Secondary) which is marketed as the "Thunder Series AVS" by Edelbrock. Some consider the AVS to be better than the Quadrajet as it too is a spread bore carb with air valve secondaries and a vacuum referenced set of metering rods. Unlike the Quadrajet, however, the secondary metering is vacuum referenced with power pistons like the primaries and not mechanically determined by the air valve opening rate via a cam that rotates on the shaft. Carter also made another 4 barrel called the "Thermoquad"-so named because of the Phenolic resin "thermoplastic" main body designed to control fuel temperature. Unfortunately, the plastic warps and leaks and it was discontinued by Chrysler, the only manufacturer to adapt it. Carter's first 4 barrel was the "WCFB" (Will Carter Four Barrel) used by Chevy and Studebaker in the 50's ( maybe others too). It was the first production 4 barrel carb, but it weighed around 20 lbs! The Holley as we recognize it today saw it's first application by Ford on the "Thunderbird" 312 Y block at around the same time.
As for BG/Demon, they are based on the Holley modular concept but seem to be a nicer overall carb. The fuel metering is more accurate and the parts have a better quality feel to them. They also have variations such as removable sleeve models that can be easily re-sized, etc. I do not have any experience with them so I will withhold judgment or remarks about them.
I will also note that the best carburetor solution is probably the most difficult to tune and that is an individual runner setup with one barrel per cylinder. Companies like Webber, SU and Mikuni have all produced setups like this over the years, and some are available in the aftermarket. The only factory domestic V8 application I know of for the Webber were some Shelby cars in the 60's, and these were downdraft carbs. Ferrari, Porsche and Lamborghini also used downdraft Webbers. Webber also made side draft carbs, but for some reason I can't remember any applications right now. SU was a major supplier to British makes like Triumph, MG and Austin-Healey. Mikunis are what you will see when you open the hood of an original Datsun 240z or PL510 SSS ( Super Sport Sedan- Japan only model). The SU and Mikuni carbs were only used in side draft applications. Oddly, when British Leyland made the Rover P6 and SD1 with the old Buick 215 V8, it used dual side draft SU's feeding into an adapter on top of the manifold!
