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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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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.

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?

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