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.
Last Month's Power RecapIn DM's fourth bash on the dyno last month we made some mistakes and tried a set of cylinder heads that were too big for the little Mouse to play with. DM ended the day with a maximum 379 hp and 417 lb-ft of torque. The average horsepower and torque figures were 303 and 399, respectively (see: Test 13). That was down a little from the factory iron camel hump castings we'd ran before, but the power loss was most likely due to too large of a combustion chamber and too big of valves in the heads we tried.
For DM's fifth dyno test we thought we could do a little better by installing a set of Vortec cylinder heads and trying some different-ratio COMP Cams Magnum roller-tip rocker arms. We were once again rewarded with more power, and after all testing was completed, DM clocked in at a new 416 peak hp and 440 lb-ft of torque. Average horsepower and torque also increased up to 333 and 417, respectively (see: Test 15). As usual, if you feel you've got a better idea for us to try, send it in and we'll tackle it in the upcoming months.
5th Series Of Dyno Tests
We'll number every series of tests consecutively, starting with the last number of the previous month's tests. We'll also list the last test from the previous month so you'll have something to which to compare the new tests. This month our first new test is number 14. Unless listed, no other changes were made for any test.
We used a set of Mr. Gasket's MLS (Multi-Layered-Steel) head gaskets to seal the Vortec heads. So far, we're very satisfied with their performance.
Test 13: Last test from last month. S/R Torquer cylinder heads PN 042660-2 67S (67cc chambers, 170cc intake runner volume, 2.02/1.60 valves). Edelbrock RPM Air Gap manifold, Speed Demon 750 carb, 1-inch open carb spacer, COMP Cams XE262H cam (262/270 adv duration, 218/224 duration @ .050, .462/.469 valve lift, 110 lobe separation) straight up.
Test 14: Install GM Vortec iron heads SDPC PN SD8060A (64cc chambers, 170cc intake runner volume, 1.94/1.50 valves) with COMP Cams 1.5:1 Magnum roller-tip rockers PN 1417-16, Edelbrock RPM Air Gap Vortec intake manifold PN 7516.
Test 15: Install COMP Cams 1.6:1 Magnum roller-tip rockers (PN 1418-16).