Cylinder Head Test - Get Your Heads Right

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.

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.

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

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.

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.