GM'S Iron Vortec Cylinder Heads And Some COMP 1.6 Rockers Kick It Up!
Testing engines is like running a marathon. There are some spots where you're way behind, and there are others where you're pulling ahead. However, the race is almost never done. Last month was one of the spots where we stumbled when we installed some parts that were too big for our little Mouse to handle, but now we're back into our groove and have hit a stride that'll be hard for others to keep up with.
To find cylinder heads that would make up for last month's lost power and perhaps even add a little to the total output, we turned back to Chevrolet. As we've been doing every month for the past several, we dove into the ever enlarging pile of reader's letters to Danger Mouse (DM) to find out which set of heads the readers would most like to see bolted on next. The clear winner in the iron head category was GM's Vortec, receiving more than 10 percent of the total vote. We know that the Vortec has a good head design, and it didn't take us long to make our decision.
GM has really hit the nail on the head with its iron Vortecs, but unlike so many other replacement cylinder heads on the market today, the Vortecs require some different parts to bolt them on. It would seem, at first glance, that for the power they make the Vortecs might be the best set of heads on the market for the money. However, there's a catch, and like most good things in life, the extra power isn't free. While it's true that the Vortec castings will bolt right onto your favorite old small-block, just about everything else connected to them will have to be changed to make the engine run again, and the cost of all those changes will add up quickly. Basically, if you're building a new engine and don't have any top-end components yet, then the Vortec heads and all their related components will be well worth the investment.
Starting from the top and working our way down, the Vortec heads require a different intake manifold, gaskets, and bolts; different valve covers, gaskets, and bolts, unless you already had center-bolt valve covers (then yours will work); new rocker arms, unless you were already using the self-aligning style arms; and new spark plugs, too, because chances are good that your old ones probably won't fit. The good news is that your exhaust should bolt up without a problem, and you can reuse your same distributor. If you're running a Q-jet carb, it may also have to go, depending on which intake manifold you chose to run. The Edelbrock RPM Air Gap Vortec manifold we ran is only offered in a square-flange design. Edelbrock offers its Performer Vortec intake with a Q-jet pattern, but that manifold might not produce the same power we saw in our tests.
Then there's the matter of choosing the proper set of Vortec heads for your application. GM actually offers only one set, PN 12558060 ($238.75 each from Scoggin-Dickey Performance Center or SDPC), so you'd think selecting the proper heads would be quite easy. However, GM's ready-to-run assemblies will only take a cam up to about .460 lift before you run into trouble. If you want to run a cam with more lift (as we do), you'll have to machine the spring pockets in the heads, cut down the valve guide bosses, and install larger springs. The set of heads we installed on DM came with bigger springs and all the required modifications from SDPC (PN SD8060A, $319.50 each) and can safely take cams up to .550 lift.
So, add it all up, and there's no denying the power potential of the complete package once you've bolted those Vortec heads in place.
The Vortec heads require a few different parts to bolt on, such as a special intake manifo
The combustion chamber's shape and location and the water jacket layout in the Vortec head
The Vortec heads have a heart-shaped 64cc combustion chamber that put DM's compression rat