Cylinder Head Test - Mopar Muscle Magazine

It wasn't long ago that the Mopar enthusiast running a big-block had very few choices when it came to cylinder heads. Most of us would refresh our steel heads and do a little port work ourselves or pay a professional to try to make more power. The only economical upgrade we had was to go to a 452 casting with hardened valve seats compatible with the crappy fuel we could get at the local station. Those with deep pockets could upgrade to an aftermarket cylinder head, but unless you were a serious racer the cost kept most of us out of the market. What we longed for was a quality aluminum head that made good power and would perform well in street and race applications, while not blowing our automotive budget.

Several years ago when Edelbrock produced their Performer RPM heads, we felt a great void had been filled in the Mopar aftermarket. While we have run the heads with great success on street/strip engines, we have always wondered how the Edelbrocks compare to a set of fully ported steel heads. We figured that a trip to the dyno was the only way to know for sure, so we packed up a worked iron head 440 and a set of 84cc Edelbrocks and headed over to Autoshop Racing Engines in Orlando for a little dyno thrashing.

Our test mule is a steel crank 440 that sees track duty in our friend Garret Struck's '72 Duster bracket racer. We felt this motor would be a great test of the Edelbrock heads as it is a solid combination that the average racer can build . . . not stock, but nothing exotic either, just a stout 440. The basic combination includes an older Torker intake manifold with an equally old Holley 1050 Dominator, 12.5 to 1 dome pistons, aftermarket steel rods, a .590 lift solid flat-tappet cam, and a set of fully ported and polished 452 casting steel heads. Fully ported and polished is actually an understatement as these heads have received extensive port, bowl, and seat work, as well as 2.20 intake and 1.81 exhaust valves. We figure these heads flow about as well as a set of 452 castings can, so we were a little skeptical that the out-of-the-box Edelbrocks would outperform them . . . boy, were we wrong.

Our initial dyno pull was to establish a base line for the combination. We also needed to address a detonation issue since the car seemed to run better at the track with C16 (116 octane) fuel than it did with the C12 (112 octane). Our first pull was with C12 and 42 degrees of total timing and slight spot detonation was evident. Our second pull with the C16 cleared up the problem and netted 5 additional peak horsepower, as well as 14 lb-ft of peak torque! All subsequent dyno pulls were performed using the C16 fuel. Remember that fuel requirements are based on many variables, not just the compression ratio of your engine. Our detonation issue was related more to the open combustion chamber design of the 452 casting cylinder head than the compression ratio of the engine.

With our baseline established, we felt the 1050 Holley may be a little much for our .030 over 440, so we changed carburetors to a Holley 950hp unit to check for over-carburetion. The engine fired immediately and seemed crisp with the 950, but we actually lost substantial horsepower and torque, and our air/fuel ratio went to a rich 12.2 at peak rpm, indicating that our engine was now under-carbureted. The Holley 950HP is a nice piece, just a little small for our combination. With the carburetion issue settled, we switched back to the 1050 Dominator, and it was time to swap heads.

Edelbrock claims their heads will work with up to .600 lift camshafts, and we found that to be true. This combination utilizes 1.6 ratio rocker with the .590 lift cam for a net valve lift of .629; we knew we were exceeding the advertised limits of springs, but by checking the open and seat pressures of the springs we determined they were compatible with our camshaft. We also checked for coil-bind and keeper-to-guide clearance at maximum lift, and discovered we had plenty of room to spare before either would be an issue. Since the springs passed the test, we checked piston-to-valve and piston-to-head clearances and found them to be adequate as well. The only issue we encountered was that Edelbrock relocated the spark plug toward the exhaust valve in their heads and slightly away from the stock location. While the relocated plug does promote more efficient combustion, it also places the spark plugs out of the plug reliefs cut in our piston domes. The solution to this problem was to either index the plugs or allow them to be smashed by the pistons; we chose to index the plugs.

A nice feature of the Edelbrock heads is they utilize stock hardware, so our stock length head studs, as well as manifold hardware and rocker arm assemblies, could be reused. The only items that were not interchangeable were the spark plugs, so we installed a set of Champion C59CX plugs. Another great feature is the exhaust mounting bolt holes don't invade the water jackets, so no more sealant mess or coolant seeping from around the header bolts, a definite advantage. A comparison of the 452 casting to the Edelbrock revealed that the out-of-the-box port size was very similar to our ported 452s, so we didn't expect much gain by flow alone. We did notice a difference in the combustion-chamber design with Edelbrock's heads having a somewhat closed-chamber design offering more quench than the openchamber steel heads. The combustion-chamber design, along with the relocated plug, should offer a power increase over the 452s, but how much? Read on and find out.

With our checking complete, we installed the heads with new gaskets and torqued our head studs to 70 lb-ft. After setting valve lash and reinstalling our intake and headers, we were ready to warm up the engine and make another pull on the dyno. So that the results of the test were accurate, we left everything else the same as our baseline pull with the steel heads. We re-installed the Torker intake and the 1050 Dominator, and left the carb jetting, timing, and valve lash unchanged for a valid comparison. The following results speak for themselves. we not only saw a power increase, but also a broadening of the torque and horsepower curve. We also found the Edelbrock heads responded well to a change in intake manifolds, further optimizing our combination. Check out the dyno results, and we're sure you'll agree that Edelbrock's heads are definitely a worthwhile investment.

Speed TQE power BSFC1 Fuel1 Water Oil Oil Fuel_P C.A.T. RPM LB-FT HP   F F psi PSI F 4,000 545 415.4 0.36 24.7 154 162 63.9 5.8 84 4,{{{100}}} 556 434.3 0.375 25.6 154 162 64 5.9 84 4,{{{200}}} 560 447.4 0.37 26.3 154 162 64 5.9 84 4,{{{300}}} 561 459.5 0.367 26.9 154 162 64.1 5.9 84 4,400 561 469.8 0.365 27.5 154 162 64.1 5.9 84 4,500 560 479.7 0.366 28.2 154 162 64.1 5.9 84 4,{{{600}}} 556 487.4 0.37 29.1 154 162 64.2 5.9 84 4,700 552 494.2 0.374 29.9 154 162 64.4 5.9 84 4,800 548 501 0.377 30.5 154 163 64.6 5.9 84 4,{{{900}}} 545 509 0.383 31.4 154 162 64.9 5.9 84 5,000 542 516 0.389 32.4 154 163 65.1 5.9 84 5,100 540 524 0.394 33.3 154 163 65.3 5.9 84 5,200 537 532 0.4 34.4 154 163 65.4 5.9 84 5,300 532 536 0.407 35.5 154 163 65.4 5.9 84 5,400 525 540 0.417 36.7 154 163 65.5 5.9 84 5,500 518 542 0.44 37.5 154 163 65.6 5.9 84 5,600 509 543 0.428 38 155 163 65.7 5.9 84 5,700 498.9 541 0.431 38.3 156 163 65.6 5.9 84 5,800 489.6 541 0.431 38.3 156 163 65.4 5.9 85 5,{{{900}}} 478.7 538 0.431 38.1 156 163 65.3 5.9 85 6,000 462.4 528 0.431 37.9 156 163 65.1 5.8 84 6,{{{100}}} 445.2 517 0.439 38 156 163 64.8 5.8 84 6,{{{200}}} 430.6 508 0.456 38.7 156 163 64.4 5.8 84 6,{{{300}}} 416.8 500 0.468 39 156 163 64.1 5.8 84 6,400 406 494.7 0.479 39.3 156 163 63.9 5.8 84 6,500 395.6 489.6 0.489 39.7 156 {{{164}}} 63.6 5.8 84 Average Data 5,250 510 503 0.408 33.66 154.7 162.7 64.7 5.87 84.1 Inertia Factor 1.32     Time 6.9 Secs

These are the results of our best pull with the ported 452 casting steel heads. Note that peak power came at a leisurely 5,600 rpm, then dropped off dramatically after 6,000 rpm. This combination should like a fairly low shift point, which will substantially increase the life of the engine.

Speed TQE power BSFC1 Fuel1 Water Oil Oil Fuel_P C.A.T. RPM LB-FT HP     F F PSI PSI F 4,000 540 411.4 0.412 27.5 156 181 60.3 5.9 82 4,{{{100}}} 547 427.1 0.419 27.8 156 181 60.3 5.9 82 4,{{{200}}} 551 440.8 0.409 28.2 156 181 60.3 5.9 82 4,{{{300}}} 554 453.6 0.402 28.6 156 181 60.3 5.9 82 4,400 556 465.8 0.395 28.9 156 181 60.4 5.9 82 4,500 558 478.5 0.39 29.3 156 181 60.4 5.9 82 4,{{{600}}} 561 491.3 0.387 29.9 156 182 60.4 5.9 82 4,700 563 504 0.387 30.7 157 183 60.5 5.9 82 4,800 564 515 0.39 31.7 158 183 60.5 5.9 82 4,{{{900}}} 565 527 0.393 32.7 158 183 60.6 5.9 82 5,000 564 536 0.394 33.5 158 183 60.8 5.9 82 5,100 560 544 0.401 34.7 158 183 60.9 5.9 82 5,200 555 550 0.409 35.9 158 183 60.9 5.9 82 5,300 549 554 0.423 37.5 158 183 60.9 5.9 82 5,400 540 556 0.438 39.2 158 183 60.9 5.9 82 5,500 530 555 0.457 41 158 183 60.9 5.9 82 5,{{{600}}} 520 554 0.477 42.7 158 184 60.8 5.9 82 5,700 507 551 0.483 43.2 158 185 60.7 5.9 82 5,800 497.4 549 0.482 42.8 158 185 60.6 5.9 82 5,{{{900}}} 486.7 547 0.475 42.1 159 185 60.5 5.9 82 6,000 477.4 545 0.475 41.9 160 185 60.4 5.8 82 6,{{{100}}} 466.4 542 0.476 41.9 160 185 60.2 5.9 82 6,{{{200}}} 456.5 539 0.48 42 160 185 60 5.9 82 6,{{{300}}} 445.9 535 0.485 42.2 160 185 59.7 5.8 82 6,400 434.3 529 0.484 41.8 160 185 59.5 5.9 82 6,500 423.8 525 0.487 41.6 160 185 59.5 5.9 82 Average Data             5,250 522 516 0.435 36.1 157.9 183.9 60.4 5.89 82 Inertia Factor 1.32     Time 6.8 Secs

Two back-to-back pulls were made with the Edelbrcok heads, and, as this dyno sheet shows, horsepower was up to 556-an increase of 13 hp over the best the steel heads could do. Even more interesting was the fact that the horsepower didn't drop off as suddenly as it had with the steel heads. Also noteworthy was the fact that while peak torque only increased by 4 lb-ft, the torque curve was substantially broader than with the steel heads and at a higher rpm. This means more usable power at the track and more consistency with shift points being less critical. Backing up our dyno numbers was the fact that the pull time was reduced by one-tenth of a second, which means the engine accelerated quicker, a function of the additional torque and horsepower.

Get Your Heads Right

GET YOUR HEADS RIGHT Speed TQE Power BSFC1 Fuel1 Water Oil Oil Fuel_P C.A.T. RPM LB-FT HP F F PSI PSI F 4,000 513 390.5 0.415 26.2 165 162 63.1 6.2 83 4,100 526 411 0.421 26.4 165 162 63 6.1 83 4,200 537 429.8 0.407 26.9 165 162 62.9 6.2 83 4,300 545 446 0.397 27.4 165 162 62.9 6.1 83 4,400 550 460.4 0.395 28.3 165 162 62.9 6.2 83 4,500 551 472.3 0.393 29.1 165 162 63 6.2 83 4,600 553 484.2 0.396 30.1 165 162 63.1 6.2 83 4,700 554 495.6 0.398 31 165 162 63.1 6.2 83 4,800 553 506 0.404 32.2 165 162 63.3 6.2 83 4,900 553 516 0.405 32.9 166 162 63.5 6.1 83 5,000 551 525 0.411 34.1 167 162 63.6 6.2 83 5,100 550 534 0.409 34.5 167 162 63.7 6.1 83 5,200 546 541 0.416 35.7 167 163 63.8 6.3 83 5,300 543 548 0.42 36.5 167 163 63.8 6.1 83 5,400 539 554 0.421 37.1 167 163 63.8 6.2 83 5,500 533 558 0.424 37.8 167 163 63.7 6.2 83 5,600 528 563 0.432 38.8 167 163 63.6 6.2 83

5,700 523 568 0.435 39.4 167 163 63.4 6.2 83 5,800 517 571 0.442 40.3 167 {{{164}}} 63.4 6.2 83 5,{{{900}}} 511 574 0.449 41.2 167 165 63.3 6.2 83 6,000 502 574 0.455 41.9 167 165 63.1 6.2 83 6,{{{100}}} 494.1 574 0.461 42.5 167 165 63 6.2 83 6,{{{200}}} 484.9 572 0.476 43.9 167 165 {{{62}}}.9 6.2 83 6,{{{300}}} 475.2 570 0.484 44.5 168 165 62.7 6.1 83 6,400 465.6 567 0.487 44.6 169 165 62.5 6.2 83 6,500 454.2 562 0.486 44.3 169 166 62.5 6.2 83 Average Data 5,250 525 522 0.429 35.7 166.5 163.2 63.2 6.18 83 Inertia Factor 1.32   Time 6.6 Secs

Not wanting to leave well enough alone, we felt our Torker intake manifold was not properly matched to the rpm range that the engine was making its power, so we decided to try a Mopar M-1 with our combination. As you can see, our engine benefited from the swap to the tune of 18 additional horsepower! Although we lost some midrange torque, look at the horsepower numbers at the higher rpm-up to 574 hp.

Speed TQE Power BSFC1 Fuel1 Water Oil Oil Fuel_P C.A.T. RPM LB-FT HP     F F PSI PSI F 4,000 512 389.6 0.421 26.7 167 162 63.3 6.1 83 4,{{{100}}} 526 410.5 0.428 26.9 167 162 63.2 6 83 4,{{{200}}} 537 429.5 0.415 27.5 167 162 63.1 6.1 83 4,{{{300}}} 544 445.8 0.{{{405}}} 28.1 167 162 63.1 6.1 83 4,400 549 460.1 0.402 28.9 167 162 63.2 6.1 83 4,500 552 473 0.401 29.8 167 162 63.2 6.1 83 4,{{{600}}} 553 484.3 0.401 30.6 167 163 63.3 6.1 83 4,700 554 496.2 0.4 31.3 167 163 63.3 6.1 83 4,800 556 508 0.406 32.5 167 163 63.5 6.1 83 4,{{{900}}} 556 518 0.41 33.6 168 163 63.7 6.1 83 5,000 556 529 0.416 34.8 169 163 63.8 6.1 84 5,100 555 539 0.422 36 169 163 63.9 6.1 84 5,200 553 547 0.429 37.2 169 163 64 6.1 84 5,300 549 554 0.436 38.4 169 163 63.9 6.1 84 5,400 544 559 0.44 39.2 169 163 63.9 6.1 84 5,500 540 565 0.443 39.9 169 163 63.8 6.1 84 5,600 534 570 0.448 40.8 169 163 63.7 6.1 84 5,700 528 573 0.455 41.8 169 163 63.6 6.1 84, 5,800 520 575 0.466 43 169 165 63.4 6.1 84 5,{{{900}}} 511 574 0.475 44 169 165 63.3 6.1 84 6,000 503 574 0.479 44.3 169 165 63.2 6.1 84 6,{{{100}}} 494.1 574 0.484 44.8 169 166 {{{62}}}.9 6 84 6,{{{200}}} 484.3 572 0.493 45.6 170 165 62.5 6.1 84 6,{{{300}}} 474.7 569 0.499 46 170 165 62.2 6 84 6,400 464.8 566 0.502 46.1 170 166 61.9 6.1 84 6,500 454.9 563 0.{{{505}}} 46.1 170 167 61.7 6 84 Average Data 5,250 527 524 0.442 37.1 168.4 16.6 63.3 6.08 83.6 Inertia Factor 1.32   Time 6.7 Secs

Our last tuning mod was to retire our antique Holley and switch to a newer Holley 1050 Dominator carburetor. While this only added one peak horsepower, our average torque and horsepower through the pull each increased by two. Our end results were pleasing-our peak horsepower increased from 543 with the steel heads to 575 with our best Edelbrock combination. With 32 more horsepower to play with and a much broader torque and horsepower curve, we should definitely see some results at the track.