Theories abound as to what we saw with this test, and the numbers deserve some explanation. Conventional wisdom holds that the smaller cross-sectional area of the small-block heads create a much higher inlet velocity, which is the main reason that the small-block made more torque throughout the entire rpm band compared to the Rat. The similar cam timing numbers created very similar torque and horsepower peak rpm points, even though the Rat had a valve lift advantage given its 1.7:1 rocker ratio compared to the small-block's 1.6:1 rockers.
The Rat's stronger airflow numbers might lead you to believe that it should have an advantage. While it's entirely possible that the camshaft may be optimized more for the small-block's smaller heads, another possibility is that the huge inlet ports never achieve sufficient airspeed to truly fill the cylinders. This can be backed up with evidence from older dyno tests that the late John Lingenfelter performed more than 10 years ago, making over 650 hp with a 496ci Rat using ported oval port heads with cross-sectional port areas closer to the small-block area numbers.
Despite the huge difference in head dimensions, the peak horsepower differential is a mere 7 hp and the greatest horsepower difference over the entire curve was only 12 hp. So we're not talking about monster differences here, but its worth mentioning that calculating bearing speed differences between the two engines could also be significant since the Rat motor's larger rod bearings spin 4 percent faster while the mains spin 5 percent faster than the small-block's bearings. This is simple frictional horsepower robbing the Rat, especially at higher engine speeds.
Another nail in the Rat motor's coffin is weight. Not only is the Rat motor crank heavier (perhaps as much as 15 pounds) due to the engine's greater length and girth, but everything about the big-block is, well ... big! Even on the conservative side, an aluminum-headed Rat motor weighs about 75 to 80 pounds more than a typical aluminum-head small-block. In our case, our Rat motor was equipped with anchor-like iron heads that add an easy 75 more pounds to the overall Rat weight penalty. However, these same iron heads should offer a slight improvement in power since iron heads tend to increase power slightly over aluminum, all other variables being equal.
Ironically, the Rat motor would appear to be less expensive than the $10,495 price tag that World Products currently has assigned to the 454ci small-block. Our Rat motor would run slightly less expensive at around $9,000 depending upon where you bought the parts, assuming you start with the GM Performance Parts 454 H.O. short-block.
ConclusionDespite some significant differences in port flow area, valve sizes, and rotating weight, to discover a difference of less than 10 peak horsepower and a average torque difference of 7.4 lb-ft, it doesn't take much to see that the small-block will out-perform the big-block down the quarter-mile, all other variables being equal. This may come as a bit of a shock to the Rat motor true-believers, but when it comes to the 454ci Mouse motor, it appears good things do come in small packages.
Cylinder Head Tech ChartThe following chart is port-flow cfm numbers tested on Westech's Superflow bench at a test pressure of 28 inches of water. The numbers for the big-block heads are actually from a different set of World Products heads fitted with smaller 2.250-inch intake valves. The heads used on the test 454 employed larger 2.300-inch valves that would increase flow slightly at every data point. The small-block head flow numbers are also from smaller 2.08-inch intake valves.