Stock-Block 535HP Screamer - D.S.S. Engine Build

In addition to flow, we also measured the swirl. The fact that this proved to be very good (uncharacteristic for a conventional style Ford head) is a strong indicator as to why these heads have historically produced such a wide power curve. Based on what we found on our bench, it's hardly surprising these heads work as well as they do.

The Valvetrain
It should go without saying that we'll use roller rockers for this engine. Although the Comp Cams items selected are far from exotic, the combination used did take some care during assembly to ensure it would all work right. With the springs being used, the forces are such that we are moving into 3/8-inch-diameter pushrod territory. However, there are some space constraints that make this a doable but less-than-easy move. What saves the day here is that the short 5.0 block height also means a shorter-than-usual pushrod. This being the case, we can just about get away with 5/16-inch pushrods. To get the rockers to align over the valve tips, it's essential that the guideplates be positioned to allow this before having the rocker studs tightened down, as alignment only occurs over a small range.

Once all the rockers have been installed and aligned, it's time to fit the stud girdle. The obvious intent of the stud girdle is to add rigidity to the rocker system. We can safely suppose it does that, but the best part of having a stud girdle is that it allows the rocker adjusting nuts (polylocs) to be clamped in place rather than relying on the socket locking screw normally used for this purpose. By employing the stud girdle to clamp the adjusting nuts in place, a more accurate lash setting can be achieved. Lash for our valvetrain was set to 0.018 inch and 0.020 inch for the intake and exhaust, respectively.

Intake Manifold
Our first move here is to check the amount of space for the valley end seals to fill. With some head/intake combos, this can be a larger gap than the thickness of the regular cork seal. This was the situation for our heads and intake combo, so the cork gaskets from the Fel-Pro set were used together with a bead of sealer to make up the small difference.

Those of you who have explored a number of cylinder-head/intake combinations have more than likely come up against the problem of such a combination achieving a respectable port match. It's not uncommon to burn up four hours or more to match an intake to the heads because this is so often a necessary move. With our build, things were fortunately a little different. Our Edelbrock Victor Jr. was a near perfect match for the ports in the AFR heads. The only place a mismatch occurred was in the corners. Here the heads had a larger corner radius than the runners in the intake manifold, but the difference was small. This being the case, it was left as is.

Ignition And Carburetion
Ignition on our 331 was to be handled by an MSD system from distributor to spark box. To make wiring up the plugs a neater deal, it helps to install the distributor first, then the carb, followed by the headers.

The carb used here was a 750 Mighty Demon from Barry Grant. It's not often appreciated, but these Demon carbs' flow rating is with wet air, not dry, as is the case with most other carbs. The 750-cfm wet works out to about 810-820 cfm dry, so that's the size you need to relate to here. This may seem like a lot of carburetion capacity for an engine of only 331 inches, but there is justification. The higher-than-average booster gain on these carbs means they are not overly sensitive to dropping low-speed output if the carb is sized more for top end power. We also have some deep-breathing heads and a valvetrain with enough lift to access the heads' high lift flow. Our thoughts were that although BG might recommend a 650 for this application, we felt a 750 was worth trying. If it didn't work, the dyno would show it, and the fix would take only five minutes at most.