When Edelbrock introduced their Mopar small-block heads a couple of years back, they filled a sorely needed void in the Mopar performance marketplace-an affordable, bolt-on, high-flow replacement for the production passenger-car cylinder head. The head quickly became a popular choice with Mopar fans looking to build that special engine, but one question remained: When would they come out with a version for the big-block? After all, you could get the small-block with decent-flowing production iron heads, but making real power with the big-block was always a challenge with the relatively flat-flowing stock heads.
It takes a lot of airflow to feed 440-plus cubic inches, and Chrysler big-blocks needed serious improvement in cylinder-head flow. So the factory created a series of big-port high-flow heads for the Max Wedge. In 1964, the introduction of the Hemi was really an adaptation of the highest-flowing cylinder heads the engineers could conceive for the existing (but improved) RB Wedge. With the release of the Hemi, continued effort on serious high-flow wedge heads became irrelevant. The heads used on the famous 383 and 440 Magnums from the musclecar years were nothing but the very same heads used across the board on all big-block engines (except on '67 440s). That's essentially a one-size-fits-all head, from a 383 two-barrel in a four-door Polara, to the 440 Six Pack in a '69 Super Bee.
To fulfill such broad requirements, the production cylinder heads necessarily became a compromise. In the context of the time, it wasn't really a bad compromise. The biggest production cams in the 383s and 440s only lifted the valve some .450 inches, and the production head offered reasonable low- to mid-lift flow. Turn up the heat, however, and the heads become the limiting factor. Making big power with production iron heads requires porting, and competent porting at that. We thoroughly researched 440 production head mods in previous articles to get the information out there. Unless you have time, patience, and a sculptor's touch, be prepared to pay big for a set of fat-flowing old iron. We don't know any porters who work for free, and with the time involved to really get the stock heads to move air, we're talking $1000-$1500 worth of cutting. Add the cost of 16 new valves, springs, retainers and keepers, a high performance valve job, guides, machining the spring seats if a large cam is used, a set of hardened exhaust inserts, and we're talking serious dough for a really good set of iron heads.
Edelbrock has developed a line of high-flow aluminum cylinder heads for a broad range of applications, but until now the big-block Mopar version has been conspicuously absent from the lineup. The Edelbrock approach is to design the head as true to the concept of a bolt-on replacement as practical, retaining the production layout so items such as the valvetrain, intake manifold, and headers will interchange with those designed to work with production heads. This constraint makes it more difficult to design a head that offers meaningful improvement in airflow; however, it dramatically lowers the cost of making the transition from the production head to the aftermarket Edelbrock head.
Since the basic layout is similar to the production piece, the design and execution are critical to achieving high flow. With the resources of Edelbrock's high tech research and development (R&D) facilities, design engineers are able to create the basic port profiles using computer models. Through stereolithography, the electronic information is transferred to a tangible working prototype of the port. The prototype comes in the form of a laser-cut full-size plastic model, called a flowbox, that gives the design team a port that can be easily tested for flow performance. Evaluation at the flowbox stage can be incorporated into the design before any real metal castings are poured.
The goal was to show flow improvement over even a well-ported production head, allowing for strong power production out of the box in a street/strip application. When we got wind of the news that the early production prototypes were just finish-machined at the Edelbrock R&D lab, we headed out to have a look.
Starting at the combustion chamber, the familiar fully-open design of the '68-and-later production head was set aside in favor of the more efficient closed quench area-similar to the highly sought-after 915 production heads. With the correct piston clearance, the quench pad, along with a small quench area on the spark-plug side, induces turbulence to the mixture as the piston approaches TDC. The result, at least in theory, is a better burn, less tendency towards detonation, less total spark-advance requirement, and less exhaust-gas dilution of the mixture from the dead space in the production open head. The bottom line should be more power.
Another subtle change is in the spark plug location, with the more common 31/44-inch reach reduced hex rather than the production 11/42-inch. Besides having a more favorable position deeper in the chamber, the plug is angled slightly (15 degrees) towards the exhaust valve, as is the practice in most modern wedge cylinder-head designs. We like the chamber.
Filling out the chamber are a set of 2.14-inch intake, 1.81-inch exhaust valves in 21 4N stainless steel, complete with wear-reducing flash-chromed stems. The valves have an 111/432-inch stem, smaller in diameter than the production 31/48-inch, which removes material from the flowpath while reducing valve weight. The valves ride in premium heavy-wall manganese-bronze guides, which are highly wear- and seize-resistant. The top of the guide is machined to receive a small-diameter, positive-type valve seal. The seal type, in conjunction with Edelbrock machining on the spring seats, allows for the installation of dual springs without additional machining and accommodates very high lift. The heads come with a stout single spring, delivering 120-pounds seat load at the as-delivered installed height of 1.880 inches, and are able to handle up to .600-inch lift. The valves seat on ductile iron valve-seat inserts pressed into the head. The valve and seat combo has proven compatible with unleaded fuels in extended street use in other applications.
The intake and exhaust ports are in the conventional location, allowing for the retention of the stock manifolding, both on the way into and out of the heads. Though the port size is not significantly altered from production heads, the port shape is highly developed for efficient flow. The intake port widens significantly beyond the pushrod pinch, and extends to the valve via a nicely formed and finished port bowl and shortside radius. The huge, obtrusive guideboss of the production iron heads is gone. On the exhaust side, the bowl area resembles a radically ported production head, again with the flowpath lacking the production head's large guideboss, which encumbers flow. From the bowl, it's a short direct path out of the head.
Like Edelbrock's small-block Chrysler head, the big-block version does not carry an exhaust crossover-an item that has no place on a performance aluminum head. We also noted that the lower edge of the intake port face is filled in, rather than the cut-back style of the production heads. This allows the option of using a separate breast plate or valley cover, and individual composition gaskets at the manifold face. The stock one-piece valley pan/intake gasket can therefore be eliminated.
Eliminating the stock valley-pan gasket can be an advantage where heavy milling of the block or heads renders poor alignment with the stock pan. Also, the pan is simply an embossed steel gasket, questionable in its sealing ability with anything but the heavy factory iron intake on iron heads. Porting the heads reduces the available sealing area, further compromising the seal. Thin paper gaskets can be added to enhance sealing with the stock valley pan, but we think that six-piece gasket setup is garbage. Finally, to end this valley-pan tirade, the stock steel shim gasket, with its efficient thermal conductivity, adds a surprising amount of heat to the intake via the heads. Not good. We don't know if Edelbrock plans to offer an aluminum valley cover to go with their heads, but it would be simple to fabricate them at home. A valley plate combined with a composition intake face gasket seems like the way to go.
As of our visit to Edelbrock, the heads were being prepared for dyno evaluation on Edelbrock's 440 Chrysler research engine. The engine is already fitted with a nicely ported set of production iron heads, so the new Performer RPM heads have to work to prove their worth. We expect the heads to be released through Edelbrock retailers by the time this issue of Mopar Muscle hits the newsstands. We're already planning to build an engine and do our own dyno testing. At Edelbrock, we had a chance to flow the new heads, and the results showed substantial flow. Want an affordable trick aluminum head to top off that old Mopar? Edelbrock's got your engine covered.
|FLOW FIGURES |
|SUPERFLOW 600 FLOWBENCH @ 28” WATER PRESSURE DROP |
|TESTED BY STEVE DULCICH AT EDELBROCK |
|LIFT ||INT #906 ||INT EDEL ||EXH #906 ||EXH EDEL |
|.100 ||65 CFM ||79 ||61 ||70 |
|.200 ||134 ||145 ||107 ||126 |
|.300 ||194 ||209 ||142 ||160 |
|.400 ||217 ||254 ||160 ||188 |
|.500 ||231 ||278 ||167 ||206 |
|.600 ||233 ||291 ||171 ||217 |
|.700 ||232 ||290 ||N/A ||223 |
Show Me The NumbersHeading out to the Edelbrock plant to get the scoop on the new big-block Mopar heads, we took a virgin 906 casting, along with the necessary flow-testing apparatus, and tossed them into the trunk of our Edelbrock-headed small-block '69 Dart. The head, off an untouched low-mileage '69 440, still retained its production machining down to the factory valve job. The seats were in outstanding condition, at the factory height and width, with the production valve sizes of 2.08-inch intake/1.74-inch exhaust. The head and valves were just cleaned spotless, with no flow-enhancing mods or flow-robbing carbon buildup or dirt.
After surveying the new Edelbrock castings and discussing the design features with the engineers, the conversation naturally turned to flow numbers. They can vary considerably from bench to bench, and some manufacturers, and especially head porters, throw out impressive specs, but the bottom line is: How much more flow do we get for the money? We discussed how much better the Edelbrocks flowed than a production head, and mentioned that we happened to pack a stock casting; "What do you say we flow it?" The R&D crew at Edelbrock said, "There's the bench, have at it." The result is an independent and unbiased flow comparison between a pure stock 906 casting, considered by many to be the best-flowing stock regular-production big-block head, and the new Edelbrock Performer RPM-on the same bench, on the same day.
The results speak for themselves, with the Edelbrock showing a substantial gain in flow throughout the lift curve, both on the intake and exhaust. The numbers we obtained were identical to the figures given by the Edelbrock engineers, proving the integrity of Edelbrock's claims. It would take an outstanding modified production head to approach the numbers of the out-of-the-box Edelbrocks. Dollar for dollar, the amount of porting alone would likely cost more than the full price of the complete ready-to-run Edelbrocks, to say nothing of the cost of new seats and guides, valve machining, springs, valves, etc.