W-2 Offset-Rocker Heads Configuration - Pump-Gas Punisher 360
537 Streetable Horsepower From Your Flat-Top 360
From the August, 2004 issue of Mopar Muscle
By Steve Dulcich
The starting point for our...
The starting point for our little project was this used dyno-mule 360 short-block. The bottom end package consisted of basic fare, a factory crank and rods with .030-over SpeedPro hypereutectic pistons at zero deck. We spun in a set of head studs from Milodon to receive the W-2s. W-2 heads use two of the extra-long bolts or studs per bank, in contrast to just one long bolt per side attaching production heads.
Ever wonder what kind of power can be coaxed from a garden-variety street 360 short-block? You know, a basic bottom end, nicely built, with popular flat-top pistons at zero deck. We have always considered the production-style cylinder heads to be a limitation here. Sure 400 to 450 hp can be achieved easily these days, but even back in the day, Chrysler knew that getting the pushrods out of the way and really opening up the ports was the prescription for serious power. Want evidence? The precedent goes all the way back to 1970 and the Trans Am program. Mopar engineers knew that to reach the power levels required in their racing engines, something had to be done about the port constriction between the parallel pushrods. To homologate a package for the racing effort, production T/A engines had special cylinder heads with offset intake rocker arms, and intake pushrods tilted at an angle away from the port runners. The relocated valvetrain was the only change made to the street Trans Am castings. The casting and ports remained the same. Although the pushrod bulge still protruded into the port, as with any "X" head of the time, the bulge wasn't providing for pushrod clearance in the offset-valvetrain T/A heads. In fact, with the pushrod drilling angled to meet the offset rockers, the bulge was just a solid chunk of iron that could be cut away completely in the porting process.
The camshaft is a custom Comp...
The camshaft is a custom Comp Cams solid, just the compliment to our high flowing W-2s. This camshaft has aggressive ramp rates, but relatively short total duration. With our plans calling for a high-flowing top end feeding the short-block, we chose to be conservative with the camshaft duration to limit the peak power rpm to a survivable level of under 7,000 rpm.
All serious small-block heads were built upon the concept of the T/A heads because they worked. The most famous of these special offset-rocker heads has to be the W-2. Officially introduced in 1976 as part of Chrysler's Direct Connection parts program, the W-2 has earned a reputation of making the already strong running small-block invincible. The pinnacle of the W-2's fame was reached in 1979, when Bob Glidden destroyed the Pro Stock field with his W-2 small-block Plymouth Arrow to win the Pro Stock championship. The W-2 has seen continuous production ever since, and has been offered in many versions with the same basic port configuration. While the W-2 was a dramatic success as a race head, its performance characteristics were such that it also made a phenomenal street piece. The ports could support tremendous airflow; the port size was not excessive, and W-2 engines exhibited broad power curves. A well setup W-2 engine will make great torque lower in the rpm band, but just keep pulling as the revs fly, making seemingly endless power upstairs. W-2 small-blocks have long been feared on the streets.
Taking The Plunge
To drive the camshaft, a Milodon...
To drive the camshaft, a Milodon roller chain (PN 15011) was installed, putting the intake centerline at 106 degrees. The Milodon chain features a three-position crank keyway, which allows adjustments in 4-degree increments. Finer adjustment will require the use of MP offset keys (PN P4286500) at the camshaft.
Switching to W-2 heads takes a little more than simply bolting on a pair of heads. offset W-2 rockers are needed, and with any of the long-valve heads, corresponding pushrods are needed to match the increased distance to the rockers. Since the intake port is much wider than a production casting, the intake manifold bolt pattern is spread. This, along with the W-2's unique oval port shape, requires a dedicated W-2 intake manifold. On the exit side of the head, the ports are substantially relocated requiring a wider bolt pattern to give acceptable header tube clearance; so dedicated W-2 headers are required, as well. all things considered, the changes required aren't prohibitively complex, just headers, intake rockers, and maybe pushrods. The question remains-what kind of power can be expected?
Our W-2s are the long-valve...
Our W-2s are the long-valve econo versions that carry the longer valves of the race W-2s, but have cast-in rocker pedestals. The valve size is 2.02-inch intake and 1.600-inch exhaust, and the heads are fully ported. Comp titanium retainers (PN 721) and stiff dual springs (PN 939) installed at 1.950 inches were used, a combination that has proven to provide excellent valve control with these aggressive-rate solid profiles.
The Milodon pan required removing...
The Milodon pan required removing the oil pump to install the matching Milodon pick-up for their pan (PN 18345).
More good stuff from Milodon...
More good stuff from Milodon to aid reliability, a windage tray (PN 32230) secured with a set of Milodon main studs. Main stud kit (PN 81186) includes special studs to mount the tray.
A small-block problem area...
A small-block problem area is at the front two pan bolts, where the timing case seal retainers interfere with socket access. A switch here to Allen-head cap screws solves that problem.
The Milodon pan is much wider...
The Milodon pan is much wider than the stocker. This allows for greater capacity without making the pan excessively deep. This helps preserve reasonable ground clearance. when installing the engine check carefully for adequate clearance, particularly at the front of the pan near the K-member. It gets quite close in some chassis, sometimes requiring minor clearancing of the K-member lip.
We switched from a replacement...
We switched from a replacement chrome oil pan to a Milodon deep sump (PN 30940). A non-baffled replacement pan will allow the oil to flow back,under a hard dragstrip launch and uncover the pick-up, with a resultant loss of oil pressure just when it is needed most. We've seen destroyed bearings as a result of this deficiency before, so the baffled Milodon pan is cheap insurance.
There are two types of oil...
There are two types of oil filter adapters used on small-block Mopars: the common plate-type (shown here) and the cast 90-degree style. Some headers require the 90-degree type, but the tti pipes we planned to use will clear either setup. typically, the adapter plates have four 91/432-inch holes through which all oil must flow to reach the engine. It's a good idea to drill four additional holes (as shown on this plate) to help reduce the flow restriction.
To find out, we decided to configure a 360 short-block representative of a typical high-performance street engine. We had the ideal combination in one of our dyno mules. The basic block was a production '79 casting, bored .030-over and fitted with SpeedPro C116CP pistons-a flat-top hypereutectic piece that has proven very reliable. The block had been decked and squared to let the pistons sit flush at zero deck. The rods were resized stockers fitted with Milodon bolts, and the crank was the production piece, ground 10/10 in typical rebuild fashion. Nothing truly special here, although the block was fitted with main studs for an added measure of bottom-end durability. The bottom end is not unlike thousands of hot 360s powering street machines everywhere.
To operate the valves, we...
To operate the valves, we measured the required pushrod length and ordered custom, high-strength, 51/416-inch pushrods from Smith Brothers. Note the wide and cavernous ports possible with the offset W-2 heads.
We anticipated the heads would like high rpm, and since our 360 was already fitted with a small solid grind, we elected to leave the cam previously used with this short-block. The duration was relatively tame (see cam specs, Table 1) considering it is a solid grind. That suited us well, since a lot of duration with our high-flowing heads would easily push the limits on the rpm capabilities of the stock-based bottom end. The W-2 specific items to complete the assembly included an Indy intake manifold, Crane Gold 1.6:1 rockers, tti 171/48-inch headers, a Milodon head-stud kit, and a custom set of Smith Brother's 51/416-inch pushrods. We also upgraded the oiling system with a Milodon pan to ensure adequate lubrication under dragstrip launching conditions. The cylinder heads (the subject of a previous Mopar Muscle article), are a set of fully ported, long-valve, open-chamber, econo castings (PN P4529995). These long-valve econo heads are essentially the race heads with cast-in rocker pedestals. The familiar 2.02-inch and 1.60-inch valve diameters were retained, and the finished product offered more than adequate flow (see Port Flow, Table 2). All in all, the swap was very simple.
A set of Crane's reliable...
A set of Crane's reliable Gold rockers work the valves. We went with 1.6:1 ratio rockers on both the intake and exhaust that boosted lift to a theoretical .578/.586-inch on the intake and exhaust, respectively. Lash was set to .018 intake and .020-inch exhaust.
Did the W-2s deliver? We brought the assembly to Johnson's Machine Service (JMS) in Monrovia, California, to test the combo on their DTS dyno. The engine crackled to life, and we set the total timing on the locked out MSD distributor to a conservative 34 degrees. With the temperature up from a little running time, the engine was shut down for a hot lash adjustment, and we were ready to run for the numbers. A partial pull revealed a somewhat lean mixture, so the jetting on our Holley 950 HP was bumped up a couple of sizes, and it was time to make some real power pulls. The 360 sounded very healthy up the range, as we pulled it over a broad range from 3,000-7,000 rpm. The result: 537 hp at 6,500 rpm and 467 lb-ft of torque at 5,100 rpm. The engine willingly pulled to 7,000 rpm; dropping only 8 hp over the range from peak power to the top of our test at 7-grand. Yes, it just wanted to keep pulling, and certainly would have stretched the rpm range too high for this short-block if we had gone with a longer duration cam. Torque production was stout over a broad range, showing over 390 lb-ft at 3,000 rpm and never looking back. No wonder the W-2 has a reputation that kills.
An Indy 360-3 single four-barrel...
An Indy 360-3 single four-barrel intake was the perfect match to our W-2 heads. We have found the Indy intake to be among the best available in single four-barrel manifolds for the W-2.
The perfect complement to...
The perfect complement to our induction package was a Holley 950 HP carb (PN 0-80496-1).
A MSD billet distributor was...
A MSD billet distributor was our choice for ignition. We based our selection on components that experience has shown to work. The distributor is very tunable with the quantity of mechanical advance adjusted with interchangeable bushings, while the advance rate can be altered quickly by exchanging the top-mounted springs. The advance mechanism can also be easily locked out, which we did for this application
These 171/48-inch W-2 chassis...
These 171/48-inch W-2 chassis headers are made by tti for most performance Mopar applications. The sizing is perfect for the power potential of the W-2 package. We didn't have a set of secondary wires made up for the test, and initially collected the rag-tag assortment of wires seen here to run the engine. It proved to be a mistake, leading to a high rpm misfire.
After the engine was run to...
After the engine was run to operating temperature, JMS dyno-operator Robert Hendrix reset the valve lash to the same .018/.020-inch spec we had set them to cold. It is important to set the lash hot and after run-in with a performance solid-lifter engine.
With everything in order and...
With everything in order and total timing set to 33 degrees, the W-2 360 was producing 537 hp at 6,500 rpm and a peak of 467 lb-ft. of torque at 5,100. Stout numbers for a pump gas 360 that's streetable enough to get in and drive anywhere.
The jetting proved to be a...
The jetting proved to be a little lean for our liking, so the carb was opened for a jet change. We found number 76 jets inside and swapped them at all four corners for 78s, which are the factory-supplied jets for this carb.
To remedy the problem, a fresh...
To remedy the problem, a fresh set of Mallory wires were cut and crimped, and we were ready to run.
|Custom Comp Solid||Intake||Exhaust|
|Advertised Duration (@.020")||272||276|
|Duration @ .050"||243||247|
|Duration @ .200"||157||161|
|Theoretical lift @ 1.5:1 rr||542"||549"|
|Theoretical lift @ 1.6:1 rr||578"||586"|
|Lobe Separation Angle||108°|
|Installed intake centerline||106°|
Note: This camshaft is based upon the FL-Series .875-inch tappet lobe profiles. Comps quicker equivalent MM-Series .904-inch lobe profiles offer more velocity andarea under the curve, typically further enhancing performance. Contact Competition Cams for info.
|Port Flow Summary|
Flow Tested by Steve Dulcich
Westech's Superflow 600 Flowbench (with FlowCom)
All tests at 28" water depressionsion
|Peak flow with pipe||230*|
Tested at JMS