Big Block Cylinder Heads - Big-Block Cylinder Head Test

Lightweight Retainers
The problem with big-block Chevys has always been big, heavy valves and valvetrain parts. That's why all aftermarket big-block Chevy heads come with 111/432-inch valve stems instead of the stock 31/48-inch stem. Since valvetrain weight is an issue, we elected to use the Comp 933 dual springs matched with a Comp 10-degree titanium retainer to reduce weight. The difference in weight between the normal-steel 1.550-inch-diameter retainer at 35 grams and the titanium at 18 grams is almost half at 17 grams. This may not sound like much, but it's huge. Just as we completed our testing, we learned about new lightweight tool steel retainers from Comp Cams that are only slightly heavier than titanium, yet as strong as steel and, best of all, roughly half the price! We've included the part number in our parts list. By reducing valvetrain weight, we don't have to run as much valvespring pressure, which makes life easier for the entire valvetrain. How often do you get an improvement in performance while also reducing cost? Technology is a wonderful thing.

Compression Lessons
Each of the heads we tested had a slightly different combustion-chamber volume, which means static compression was another unfortunate variable in this test. The accompanying chart indicates the variation in compression. Both the Edelbrock and the Brodix (with its CNC machining) had the smallest chambers, so they benefited from the highest compression, while the Dart had the largest chamber and therefore the least compression. The difference is almost a full point of compression, and since one point is worth roughly 2 to 3 percent power, both the Edelbrock and Brodix probably received a decent horsepower bump. Had we milled the Dart heads to 110 cc, for example, that might have added another 10 hp, which would have made a significant difference throughout the entire power curve, perhaps pushing peak horsepower very close to 600. Yahoo!

We bolted in a set of coated Hedman 2-inch street headers in our '66 Chevelle chassis to see if the raised exhaust-port heads like the Dart and TFS would fit, which they did very nicely, thank you.>

Test Fit
One of the biggest headaches for big-block engines is packaging the exhaust. When we began this test, it appeared that the raised exhaust ports on the Dart and TFS heads might be a problem when it came to fitting chassis headers in a car, so we decided to put the heads to a simple test. We bolted a 454 iron-block in a '66 Chevelle along with the stock steering column and Energy Suspension motor mounts. We then bolted on the Edelbrock heads along with a set of Hedman 2-inch chassis headers. The Edelbrock heads fit with no clearance problems, so we then tried a TFS head with the same headers. One tube came very close to the steering column and probably would require a slight dimpling, but that was the only real consideration. We did not have the clutch linkage in place, but that did not appear to be an obstruction. Overall, we were pleasantly surprised that the raised exhaust-port heads still allow the headers to clear, which means we wouldn't have to do header surgery in order to make them fit.