Manifold Comparison
The baseline used a Weiand Stealth Air Strike dual-plane and 750-cfm Street HP carburetor. The middle test is the same engine with the addition of the Holley-Dorton single-plane intake using the same 750 Street HP carb. The third test converted to the Summit-Weiand tunnel-ram system using a pair of Holley 600-cfm vacuum-secondary carburetors.
| TEST 1 | TEST 2 | TEST 3 | | DIFFERENCE |
| | Weiand | | Holley-Dorton | | | | |
| | Air Strike 1x4 | | Holley 1x4 | | Weiand 2x4 | | | |
| RPM | TQ | HP | Fuel | TQ | HP | Fuel | TQ | HP | Fuel | TQ | HP |
| 2,500 | 403 | 192 | 101 | 395 | 188 | 80 | -- -- | -- | -- | -- | |
| 2,700 | 386 | 198 | 108 | 384 | 197 | 85 | -- | -- | -- | -- | -- |
| 2,900 | 375 | 207 | 107 | 384 | 212 | 97 | -- | -- | -- | -- | -- |
| 3,100 | 400 | 236 | 110 | 400 | 236 | 98 | -- | -- | -- | -- | -- |
| 3,300 | 441 | 277 | 122 | 419 | 263 | 96 | -- | -- | -- | -- | -- |
| 3,500 | 459 | 306 | 134 | 428 | 285 | 104 | -- | -- | -- | -- | -- |
| 3,700 | 471 | 332 | 146 | 435 | 307 | 118 | 397 | 279 | 155 | -74 | -53 |
| 3,900 | 481 | 357 | 154 | 439 | 326 | 126 | 404 | 300 | 148 | -77 | -57 |
| 4,100 | 483 | 377 | 164 | 448 | 350 | 133 | 420 | 328 | 151 | -63 | -49 |
| 4,300 | 480 | 393 | 174 | 456 | 373 | 144 | 441 | 361 | 155 | -39 | -32 |
| 4,500 | 478 | 409 | 182 | 456 | 391 | 155 | 450 | 386 | 161 | 28 | -23 |
| 4,700 | 473 | 423 | 188 | 456 | 408 | 164 | 456 | 408 | 164 | 17 | -15 |
| 4,900 | 467 | 436 | 194 | 457 | 426 | 172 | 462 | 431 | 169 | -5 | -5 |
| 5,100 | 459 | 446 | 199 | 460 | 447 | 180 | 462 | 449 | 179 | +3 | +3 |
| 5,300 | 456 | 460 | 206 | 456 | 460 | 184 | 456 | 460 | 194 | 0 | 0 |
| 5,500 | 448 | 469 | 215 | 448 | 470 | 189 | 449 | 470 | 206 | +1 | +1 |
| 5,700 | 437 | 474 | 222 | 438 | 476 | 196 | 440 | 477 | 217 | +3 | +3 |
| 5,900 | 425 | 477 | 226 | 427 | 479 | 201 | 427 | 480 | 225 | +2 | +3 |
| 6,100 | 412 | 479 | 228 | 416 | 483 | 205 | 411 | 477 | 228 | -1 | -2 |
| 6,300 | 400 | 480 | 238 | 404 | 485 | 210 | 394 | 473 | 238 | -6 | -3 |
| 6,500 | 387 | 478 | 250 | 387 | 479 | 222 | 378 | 468 | 251 | -9 | -10 |
| Peak | 483 | 480 | 250 | 460 | 485 | 222 | 462 | 480 | 251 |
| Avg. | 440.4 | 377.8 | 174.7 | 429.4 | 369.7 | 150.4 | --- | --- | --- | | |
Note: Averages were calculated on the entire power curve every 100 rpm. Averages were not calculated for the tunnel-ram due to an incomplete pull from 2,500 rpm, making any average invalid.The Difference column compares Test 1 and Test 3.
280 VS. 292 Cams, 215CC VS. 227CC Heads
Up until now, we've been testing with a set of Dart 215 Pro 1 Platinum heads that have performed very well. These are as-cast heads, and everybody knows that a CNC-ported heads will bring some serious ponies to the party. The computer-ported star in the Dart lineup is the 227cc CNC head, which not only has increased port volume, but also adds a bunch to the flow curve along the way. If you've been paying attention to our tech diatribes throughout the years, then you may know about midlift flow. Our contention is that ignoring big head flow numbers at high valve lifts in favor of strong midlift flow numbers will always deliver a stronger overall power package for a street engine. In testament to that, the Dart CNC 227 bumps the 0.400-inch lift flow numbers up over the 215 Platinum on the intake side by a staggering 28 cfm, a 13 percent increase. The 0.300-inch lift numbers are equally as impressive, gaining 26 cfm, a 15 percent bump. Combined, this makes for an impressive midlift one-two punch, and when blended with excellent exhaust flow numbers it's an outstanding opportunity to make power.
Even with a strong roller cam, Dart 215 aluminum heads, and making 480 hp, the Weiand Stealth Air Strike dual-plane made the best overall power of the three intakes we tested. And it was only down 5 hp at the peak against a very good single four-barrel Holley Keith Dorton manifold.
To test that theory, we baselined the engine with the Dart 215 heads, the Holley-Dorton single-plane and 750-cfm Street HP carburetor, and the Comp Cams Xtreme Energy mechanical XR-280 Street Roller cam. For the second test we switched to the bigger XR 292 mechanical roller cam, and then for the final mondo-combo, we bolted on the Dart CNC 227 heads.
As you can see from the dyno chart, this motor loved the combination of lift, duration, and more cylinder head. The addition of the bigger cam in tests 2 and 3 illustrates how more duration trades torque in the low- to midrange portion of the rpm curve for more power above peak torque. But what's interesting is that the peak torque rpm point didn't move up as we expected. Note that in all three tests the peak torque hovered between 4,900 and 5,100 rpm. Of course what everyone will latch onto is the stellar power increase. When you can make almost 70 more horsepower from a cam and cylinder head swap, you know the parts are working. This doesn't come at a discount price, though. The bill for the larger cam and a pair of assembled Dart 227 CNC heads will top $2,800, and that's assuming the engine is already equipped with a mechanical roller cam. If you have to purchase all the mechanical roller pieces, expect that price tag to exceed $3,400. But we're also looking at a 383ci small-block Chevy that makes just shy of 550 hp. That, friends, is a solid 1.43 hp per cubic inch. Plug this power and torque into a 3,500-pound street car, and if you can hook it up it will run high 11s all day long. Sounds like fun, doesn't it?
We chose the twin 600-cfm carburetor package for this test, but even for a strong 383 it appears that the smaller 450-cfm Holley carbs would have been a better choice. Unless your engine is making over 550 hp, we'd go with the 450 cfm carbs. | 
The latest (-9) version of the 0-1850S now comes with no external float adjustment and no sight plug screw to externally check the float level. Holley did this to reduce the number of returns on its carburetors from under- educated carb tuners. |
Holley Manifold Test | |