400ci Engine Blueprinted

Testing Day

We also experimented with a set of Comp red aluminum guided roller rockers that bumped the rocker ratio from 1.5:1 to 1.6:1. This adds another 0.032 inch of valve lift and reduces friction over the stock stamped rockers. This one change was worth an extra 20 hp, so clearly these heads want more valve lift. End

We also experimented with a set of Comp red aluminum guided roller rockers that bumped the

With an increase of two full points of compression and good ring seal, we expected some serious power improvements over the stock baseline, and we weren’t disappointed. Right at the first pull on the dyno with 36 degrees of timing (versus 44 degrees with the old engine), the 406 grunted out 486 lb-ft of torque compared with the previous 458 and produced between 20 and 30 lb-ft of torque increase across the board with similar gains in horsepower with the peak of 436 hp at 5,200 rpm. The biggest problem now seemed to be that we needed some way to make the engine breathe better at higher engine speeds to make more horsepower. The limitation seemed to be valve lift, so we thought the simple addition of a set of 1.6:1 rocker arms might help.

Generally, an increase from 1.5:1 to 1.6:1 rockers is usually worth about 0.030 inch of valve lift, and since our cam barely made 0.490-inch lift, that seemed like a good solution. We also tried a 1-inch-tall Wilson tapered spacer that was worth roughly 3 hp at the peak with no loss of torque down low. We also drained the 10W-30 break-in oil and tried some thinner-viscosity Lucas 0W-20 race oil, hoping to push over the 500-lb-ft plateau. All these little efforts really paid off. The rockers alone were worth almost 20 hp, which helped us excel to 501 lb-ft of torque and upped peak power to 466 hp at 6,000 rpm, and the engine responded positively to nearly all the changes. All this really proves that quality machine work and proper engine assembly techniques really do pay off with big rewards. We are already thinking about how to make even more power with this 406ci, and we might have to start calling it the BFH because it brings down the big freakin’ hammer on torque.

Power Curves

This graph illustrates the big differences in torque between the previous combo and our latest version. Note how the shape of the curves remains basically the same, since we did not change the cam, heads, intake, or exhaust. But look carefully at how the horsepower curve dips slightly between 5,300 and 5,900 on Tests 2 and 3. The dip is more pronounced in Test 3, which is where we added the rocker ratio. Our theory is that the valvesprings are right on the ragged edge and became “fussy” in this rpm range. The fix is a different (not necessarily higher load) valvespring that would probably take care of this. The big news is the huge gain in torque between Test 1 and Test 3. This would make an excellent street engine.

Dyno Numbers

Test 1 is the best power we pulled from the original test of the engine from the May ’11 issue. Test 2 is with the same Bow Tie Vortec heads, Comp cam, Weiand intake, Holley carb, and dyno exhaust with no mufflers. Test 3 added a Wilson-tapered carb spacer and a set of Comp 1.6:1 roller rockers and performance pushrods.

Power Curve

*Average power numbers were calculated between 3,200 and 6,000 rpm to ensure a fair comparison.

Parts List

Machine Work

*These separate part numbers and prices for the pistons and rods are for reference.