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Aftermarket Parts - Are Premium Parts Worth The Price?

We Test A Pile Of Speed Parts To Discover

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Parts List
DESCRIPTION PN SOURCE PRICE
Holley 750-cfm Classic 0-4779-C Summit Racing $429.95
Holley 750-cfm Street HP 0-82751 Summit Racing 509.95
Holley 750 cfm HP 0-80528-1 Summit Racing 659.95
Holley Keith Dorton manifold 300-110 Summit Racing 239.95

Single Four-Barrel Vs. Dual-Quads
In the early days of horsepower, finding a four-barrel carburetor that flowed more than 400 or 500 cfm was the territory of exotic race-only engines. With limited cfm capability, the natural process was to bolt on multiple carburetors. That's why '50s and early '60s cars like the Hemi and the early GTOs came with multiple carburetors. Older car crafters wishing to duplicate their younger years think a pair of 500-cfm carbs is still pretty cool, as do a few car builders searching for a nostalgic theme. We thought it would be interesting to see just how well this older-style package would perform. In this case, we're testing the low-slung version rather than the tunnel-ram style, which we test elsewhere in this section. Conventional wisdom holds that a solid, high-flow, single four-barrel system is better than an older dual-quad setup, but we decided to put that theory to the test.

Edelbrock offers two different ways to play in the dual-quad scene with its original (dare we call it ancient?), low-profile manifold for a small-block Chevy, along with a brand new dual-quad Air Gap manifold that is available as a complete kit with specially calibrated 500-cfm Edelbrock Thunder Series AVS (adjustable valve secondary) carbs. Besides small-block, big-block and Gen III Chevy applications, Edelbrock offers these kits for the Chrysler 5.7L Hemi as well as 289/302 small-block Fords and even the 351W. What impressed us was the small-block Chevy kit (PN 2025 in our case), which came with an intake gasket, gasket cement, intake bolts, all the linkage pieces, and even a nice fuel line. It made the installation much smoother and easier. Edelbrock gets major style points for this effort. Just be prepared for a large deduction from your savings account, since this package sells through Summit for just under a grand.

We started our test with a single four-barrel baseline using the Edelbrock Performer RPM Air Gap configured with an Edelbrock 800-cfm EPS carburetor. This set the bar pretty high for the other two dual-planes, making this a worthy test. Our small-block 383ci was configured with its Dart 215cc Platinum heads and the smaller Comp Cams mechanical roller cam along with Westech's 131/44-inch dyno headers and open exhaust. As you can see from the test numbers, the baseline was no slouch, making 482 lb-ft of torque and 481 hp.

Our second setup was with the older C-26 manifold, to which we also added the Edelbrock finned valve covers to give it a real feel for the old days. To no one's surprise, this older casting dropped some significant torque (in excess of 26 lb-ft) over the entire power range with horsepower down by 19 hp compared to the single-quad setup. We also tried the air cleaner, but at least here we saw no further loss of power. In defense of the older manifold, bolt this package on a little 327 or 283 and the power differential would probably disappear altogether.

The Air Gap dual-quad was next up, and it fared much better. Average power was down by roughly 6 lb-ft of torque and barely 2.5 hp, which would be hard to feel in the car on the street. Also, much of the power difference we saw could have been improved with tuning since both dual-quad systems tended to run richer than we would have preferred in the midrange. So if you're searching for that vintage late '50s Henry Gregor Felson look, you've got a couple of great options that will still make great power. In fact, we've got a 0.060-over 283 that's perfect for that older C-26 manifold and those twin 500s.

Dual-Quad Test
  TEST 1 TEST 2 TEST 3 DIFFERENCE
  Edelbrock Edelbrock Edelbrock    
  Air Gap1x4 C-26 2x4 Air Gap 2x4    
RPM TQ HP TQ HP TQ HP TQ HP
2,500 409 195 394 187 407 194 - 2 - 1
2,700 399 205 391 201 392 203 - 7 - 2
2,900 398 220 392 216 404 218 + 6 - 2
3,100 419 247 403 238 416 245 - 3 - 2
3,300 441 277 418 263 437 274 - 4 - 3
3,500 457 305 435 290 452 301 - 5 - 4
3,700 465 328 449 316 465 328 0 0
3,900 475 353 458 340 468 347 - 7 - 6
4,100 482 376 463 361 470 367 -12 - 9
4,300 482 394 458 375 471 386 -11 - 8
4,500 478 410 454 389 469 402 - 9 - 8
4,700 474 424 452 404 466 417 - 8 - 7
4,900 469 438 450 419 463 432 - 6 - 6
5,100 466 453 443 430 459 446 - 7 - 7
5,300 461 466 434 438 452 456 - 9 -10
5,500 452 473 423 443 442 463 -10 -10
5,700 439 477 411 446 430 467 - 9 -10
5,900 426 479 398 447 417 468 - 9 -11
6,100 414 481 385 447 404 469 -10 -12
6,300 397 477 374 449 388 466 - 9 -11
Peak 482 481 463 449 471 469 -12 -11
Avg. 443.5 379.6 422.5 360.7 437.2 377.0
Note: Averages were taken from the entire dyno run at every 100-rpm data point. The last column is the power difference between Test 1 and Test 3.

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