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Ask Anything - July 2014

If by chance you are using a dished piston, then a 64cc combustion chamber is a better way to go since that will keep the compression in the neighborhood of 9.5:1 to 9.8:1 with a 13cc dish. If that's the case, then the Chevy iron Vortec head is a great selection. This is the best-flowing production iron head for the small-block Chevy, developed for truck engines from 1996 through 2000. It has good port flow for a small production head, but the exhaust port is its Achilles' heel. But it will still make excellent torque and decent horsepower on a 383. Back in the Dec. '04 issue (“Torque Tales”), we built a 383 with Vortec heads and an Isky 221/232 cam with 0.496-/0.517-inch lift. We used a set of conical Pioneer springs to allow that much lift (the stock heads are limited to a maximum of 0.450 inch lift), but the engine responded with 444 lb-ft of torque at 3,600 and 375 hp at 5,400 using a 1.6:1 rocker to help the lift. This was with headers, an Edelbrock Performer RPM Air Gap Vortec manifold, and a 750-cfm carburetor. Remember that the Vortec requires its own specific intake manifold bolt pattern. A stock Chevy bolt-pattern intake will not fit the Vortec heads. The Vortec head means added expense for a Vortec-style manifold.

If you have a little bit more money to spend on a set of aluminum cylinder heads, we tested the Speedway Motors aluminum heads as part of Car Craft's budget cylinder head test in the Sept. '12 issue—you can find that complete story on Car Craft's website. The Speedway heads made 381 hp on our Saturday Night Slayer test 355. We also tested the iron Vortecs on that engine, and they made 378 hp and 408 lb-ft of torque. The aluminum Speedway heads got the nod for average horsepower per dollar, where we took the price of the heads and divided it by our test engine's average horsepower. When we tested these heads, they sold for $739.98 for the pair and were the least expensive heads that still made decent power. This, however, is also a 64cc chamber head. Looking at larger chamber heads, we found a set of 70cc chamber Edelbrock E-Street aluminum heads on Scoggin-Dickey's website that we also tested in our head comparison. These heads made 395 hp on our 355 Slayer engine and offer the virtue of being cast and machined in America. Our original price as tested in the story was $909, but our latest search found the price actually lower at Scoggin-Dickey at $854, which was a nice surprise. This is an outstanding price for a quality head.

We alluded to cam timing in the Vortec head previous test example, and the cam we employed in our cylinder-head test is also relevant. The cam we chose was a Summit brand hydraulic flat-tappet cam measuring 224/234 degrees at 0.050 with 0.465/0.485 lift, but we enhanced it with a set of 1.6 roller rockers to bump the lift up to 0.496 and 0.517. This cam has a lobe-separation angle (LSA) of 114 degrees that reduces the overlap and calms the idle characteristics. Since you are young and probably want a little bit more lump to the idle, you might look for a cam with a tighter LSA angle. What this refers to is the amount of time (in degrees of duration) the closing exhaust valve and the opening intake valve are simultaneously open. A tighter LSA angle of 110 degrees means the exhaust valve closes a little bit later and the intake valve opens a little bit earlier, which increases the overlap. This directly impacts idle quality by decreasing intake manifold vacuum. This makes the idle a little lumpier. This also tends to bleed off a little cylinder pressure at low engine speeds, which can make the engine a little less sensitive to changes in ignition timing. This allows you to run a little more timing at low speeds to improve throttle response and low-speed torque.

Note that the cam we chose was what's called a dual-pattern cam. This means the cam includes more duration on the exhaust lobe than on the intake lobe. This is important, especially when using stock or stock-type cylinder heads. The small-block Chevy generally has a somewhat weak exhaust port relative to intake port flow. Even below 6,000 rpm, that peak horsepower is affected by the exhaust port's inability to scavenge the cylinder of most of the combusted material. This leaves some exhaust gas remaining in the cylinder, which does a great job of reducing net power in the next four-stroke cycle. By increasing the duration on the exhaust side, this gives the exhaust port a little more time (degrees of duration) to vent more of the remaining exhaust gas out of the cylinder. This usually results in making a little more peak horsepower. So look for a cam with around 220–226 degrees of duration at 0.050 with a little more duration (230–236 degrees) on the exhaust side. This will be a good cam timing package for a mild street engine with compression around 9.5:1. Be sure to use high-quality break-in oil when you start the engine for the first time. We did a specific camshaft break-in story that you can find online at that goes into specific recommendations that will help you with the initial fire-up so that you don't lose a cam lobe due to improper lubrication.

More Info

Edelbrock; 310/781-2222;
Scat Enterprises; 310/370-5501;
Scoggin-Dickey Parts Center; 800/456-0211;
Speedway Motors; 800/979-0122;
Summit Racing; 800/230-3030;

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El Segundo, CA 90245

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