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Carburetors: Holley 750 vs Edelbrock 750 vs Quick Fuel Slayer

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Quadrajet Remanufactured

GM originally built the Q-jet for use on its mid-level and high-performance engines from the mid ’60s well into the ’80s. Edelbrock offered a high-performance version of this carburetor for a while and still offers rebuild and tuning parts. We found this remanufactured Q-jet on Summit Racing’s website squeezing in just under our $299 ceiling. While somewhat complex on the surface, the Q-jet offers excellent street manners with its small primaries aided with very active boosters. Once you get acclimated to this carb’s idiosyncrasies, it offers excellent tuning options. While it’s incredibly easy to tune the secondary side with metering rods and hangers, it’s likely to frustrate rookie tuners on the primary side due to the somewhat complex procedure required to remove the lid. One note on our test, we had to use an adapter since the spread-bore Q-jet design did not allow us to bolt it directly to a Performer RPM intake. The Q-jet placed third in our out-of-the-box horsepower test but ran very rich in the cruise A/F evaluation and also tended to use more fuel in the BSFC test. Tuning helped, but this carb would require some significant changes to reveal its true potential. Despite these setbacks, we still heartily recommend a Q-jet for mild street engines, especially if you are willing to invest time in tuning.

Testing, Testing… Bolt-On Horsepower

The first test for each carb was simply measuring peak horsepower right out of the box with only an idle mixture adjustment. This test should not be used as the sole indicator of performance for several reasons. First, this test is really only valid for this engine. A big-block Ford, for example, could and probably would produce different rankings. More importantly, the top three carbs are separated by a mere 4 hp, which is literally 1 percent. It would be nearly impossible to feel that in the car. We did, however, simulate the difference in quarter-mile times using the power difference between the Slayer and the Holley 3310C, which was worth about 0.25-second and 2.5 mph. Nearly all of the e.t. difference is not in the peak power but rather in the Slayer’s significant torque improvements in the midrange over all the other carburetors. Again, these were out-of-the-box comparisons. Later tests show average power numbers after tuning. Note that the swap meet carb performed poorly and placed last in this test because the secondaries barely opened, causing the 40-plus-horsepower difference between it and the Quick Fuel Slayer carburetor.

Carburetor HP
Quick Fuel Slayer 401
Q-jet 397
Edelbrock 397
Holley 3310 Reman. 392
Summit 386
Holley 3310C 382
Swap Meet 3310 Holley 358

Cruise A/F Ratio

This test is intended to show how each carburetor would operate in a typical highway cruise situation right out of the box. Part-throttle operation is directly affected by the idle air-fuel (A/F) ratio, so each carb was set to 13.5:1 (A/F) ratio at idle. The cruise test consisted of loading the engine to 50 lb-ft of torque with engine speed at 2,400 rpm. On our test engine, this resulted in 18 inches of manifold vacuum, but that number is subject to change, depending upon your vehicle and engine. We evaluated each carburetor with leanest results rated highest as long as the A/F did not exceed 16:1. All new cars with EFI operate at 14.7:1 at part throttle, but an A/F well in the 15:1 range is not necessarily too lean. We should point out, however, that while the Slayer was the leanest, a too-lean A/F could generate a surge in certain situations. Ideally, a lean A/F will always generate better fuel mileage and will generally also produce crisp throttle response. While the richer A/F numbers at cruise are not necessarily bad, they will certainly reduce fuel mileage. Note the spread of almost four A/F ratios between the leanest and richest. It would be safe to say that most street engines would be very happy at around 13.5:1 to 14.5:1 A/F at cruise.

Carburetor A/F Ratio
Quick Fuel Slayer 15.2:1
Swap Meet 3310 14.2:1
Summit 13.5:1
Holley 3310C 13.3:1
Holley 3310 Reman. 12.8:1
Edelbrock 11.7:1
Q-jet 11.5:1

Average Tuned Power

If you had to pick a single evaluation for a carburetor, this is the test that tells the best power story. We tested each combination twice for best tuned peak power, then averaged all the horsepower readings into one overall number. Average power is the best evaluation and indicates which carb would produce the quickest elapsed time in a dragstrip test. What demands to be pointed out is that less than two percent (roughly 5 hp) covers the entire spread of all the carburetors. This means once all these carbs were tuned, there was only a minor power difference between all seven carburetors. We aimed for a 12.5:1 A/F at peak torque, but noticed that this particular engine preferred a slightly richer A/F ratio all the way through. The swap meet 3310 tended to run into the high 11:1 A/F at the top of the power curve compared to the other carburetors. This feature of early Holley carburetors contributed heavily to the average power final number because the other carburetors tended to create a more stable A/F ratio across the entire rpm band. We simulated dragstrip passes for both the swap meet and Holley 3310 and the difference was only 0.19-second and less than 1 mph. Further, richer tuning on all the carburetors would have negated the differences and minimized the average power spread to less than 2 hp. This means the spread in average power would have been even tighter. The bottom line is that all these carburetors performed virtually the same at wide open throttle over the entire curve.

Carburetor Avg. HP
Swap Meet 3310 306.2
Holley 3310 Reman. 306.0
Summit 305.1
Quick Fuel Slayer 303.6
Q-jet 303.5
Edelbrock 301.2
Holley 3310C 301.0

Peak and Average BSFC

Here’s where we get into specifics on how efficiently (or inefficiently) engines make power. One way to evaluate an engine and a carburetor is to look at how well the engine converts fuel into heat and pressure by measuring the amount of fuel used to make horsepower. This is done by dividing the observed horsepower by the amount of fuel used in pounds per hour (measured with a flow meter). This produces results in pounds of fuel used per horsepower per hour (lbs/hp-hr). This number is referred to as brake specific fuel consumption (BSFC). This number (for gasoline) is usually around 0.500, which represents a half-pound of fuel used per horsepower per hour. The smaller the number, the less fuel the engine uses to make power, which makes it more efficient. Peak (lowest) BSFC numbers generally occur around peak torque since that is where the engine generates its best volumetric efficiency. The average numbers were compiled over the entire rpm curve. A portion of any BSFC number is related to jetting and air-fuel ratio, but a larger portion is how efficiently the carburetor mixes and delivers the fuel to the engine. This is not necessarily a function of leanness or richness. As you can see, the Holley 3310C excelled in this category, taking both the peak and average BSFC positions. One surprise result was the Summit carb’s average BSFC number of 0.527. Annular boosters pull more fuel at both the very bottom and top of the rpm curve, which may have negatively affected its average.

Carburetor Peak BSFC Carburetor Avg. BSFC
Holley 3310C 0.432 Holley 3310C 0.447
Swap Meet 3310 0.446 Holley 3310 Reman. 0.461
Edelbrock 0.450 Swap Meet 3310 0.464
Quick Fuel Slayer 0.478 Edelbrock 0.467
Summit 0.493 Q-jet 0.489
Holley 3310 Reman. 0.493 Quick Fuel Slayer 0.489
Q-jet 0.519 Summit 0.527

Final Evaluations

Each carburetor has something that will recommend it for use on a normal street car. The author admits to a fondness for adjustability because I can’t leave a good carburetor alone. That’s why the Q-jet is not intimidating, but like other complex pieces, it’s an acquired taste. For the entry-level car crafter with limited tuning knowledge, the Edelbrock has much going for it as it works very well right out of the box. Frankly, all of these units worked well (except the swap meet survivor) and ran rich enough that they would exhibit good street manners in most applications, so you really can’t make a bad decision. We rated the Quick Fuel at the top for lean air-fuel, but if this carb were mated to an engine with a big single-plane intake and a large overlap camshaft, it might exhibit some part-throttle hesitation. On the surface, the carb that might appear to be the most attractive is the swap meet 3310. But that carb also required more work than all the other carbs combined just to make it run correctly. So consider yourself warned. If your engine has a bigger camshaft than our mild small-block, the Summit carb’s very active annular discharge boosters would offer superior part-throttle operation. End

Parts List

Description PN Source Price
Edelbrock Performer 750 1407 Summit Racing 284.73
Edelbrock Remanufactured 750 9907 Summit Racing 259.95
Holley New 750 0-3310C Summit Racing 279.95
Holley Remanufactured 750 0-3310S Summit Racing 249.95
Quadrajet Reman. 750 SUM-210216 Summit Racing 299.95
Quick Fuel Slayer 750 SL-750-VS Summit Racing 299.95
Summit 750 SUM-M08750VS Summit Racing 279.95
Swap Meet Holley 750 N/A Swap Meet 85.00
Edelbrock tune kit, Performer 750 1480 Summit Racing 50.95
Edelbrock Q-jet second hanger, B 1960 Summit Racing 4.39
Edelbrock Q-jet sec. rods, AY 1953 Summit Racing 9.99

Sources

Edelbrock; 310/781-2222; Edelbrock.com

Holley Performance Products; 270/781-9741; Holley.com

Quick Fuel Technology; 270/793-0900; QuickFuelTechnology.com

Sean Murphy Induction; 714/843-9169; SMICarburetor.com

Summit Racing; 800/230-3030; SummitRacing.com

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